Skip to content
Frontiers
Search

Original Research

Frontiers in Amphibian and Reptile Science ·

Volume 4 - 2026 | https://doi.org/10.3389/famrs.2026.1733610

Urbanization is associated with alterations in immunity, stress physiology, morphology and reproduction in western fence lizards

  • Amanda M. Sparkman1*corresponding author
  • Corban A. Muthiah1
  • Eric Reyes1
  • Alexander J. Rurik1,2
  • Noah Hareb1
  1. 1Biology Department, Westmont College, Santa Barbara, CA, United States
  2. 2Department of Biology, Middle Tennessee State University, Murfreesboro, TN, United States
Article metrics0 viewsView details
PDFCiteMetrics

Abstract

Urbanization presents both opportunities and challenges for wildlife that have implications for behavior, physiology, morphology, and overall fitness. Responses to urbanization can vary widely among urban adaptors, yet studies integrating multiple measures of immunological, endocrinological, and fitness-related traits remain limited, especially in non-avian reptiles. We tested for alterations in innate immunity, stress physiology, morphology and reproduction in western fence lizards, Sceloporus occidentalis, across an urban-rural gradient in Santa Barbara, California, USA. We found that agglutination via natural antibodies differed across the urban gradient in a sex-specific manner, with females showing an increase with urbanization and males a decrease. Complement-mediated lysis, baseline blood glucose in spring and summer, and summer baseline corticosterone did not differ across the urban gradient. However, there was a significant positive correlation between urbanization and spring corticosterone. There were also notable alterations in life-history traits with respect to urbanization, with urban lizards exhibiting smaller body sizes, lower egg volume, and lower clutch volume, though body condition and clutch size were unaffected. Additionally, lizards in more urban environments had lower prevalence of both ticks and mites. We evaluate our findings within the context of current research on urbanization emphasizing the influence of parasite prevalence, anthropogenic stressors, and pace-of-life, and evaluate their utility for a deeper understanding of the manner in which western fence lizards have adjusted to anthropogenic landscape change.

Keywords

1 Introduction

Contemporary landscapes have been intensively altered by anthropogenic activities, creating both opportunities and challenges for wildlife (Miller and Hobbs, 2002; Destefano et al., 2005). Urbanization, interacting with anthropogenic climate change, poses a significant threat to biodiversity (Urban et al., 2024). While some taxa struggle to adjust, others species have found ways to successfully colonize urban habitats through alterations in genetics, behavior, morphology, physiology, and/or life-history (French et al., 2018; Lapiedra, 2018; Bonier, 2023; Deviche et al., 2023). Empirical evidence over the last couple of decades has in some cases pointed to compelling evidence for a functional role of immunological and/or endocrinological factors in the transition to urban life, but numerous recent papers and reviews also suggest that the causes, mechanisms, and effects of urbanization on wildlife are highly complex (e.g., Møller, 2009; Sepp et al., 2018; Ouyang et al., 2018; French et al., 2018; Murray et al., 2019; Doherty et al., 2020; Iglesias-Carrasco et al., 2020; Injaian et al., 2020; Putman and Tippie, 2020; Bonier, 2023; Chen et al., 2023; Deviche et al., 2023). Thus, additional studies across diverse taxa and urban contexts that incorporate many more genetic and phenotypic measures are needed to elucidate the impacts of urbanization on specific populations, and discern any general trends across taxa (French et al., 2018).

Studies of non-avian reptiles represent a small but growing body of research in urban ecology focused on issues ranging from changes in occupancy, to alterations in physiology, morphology, behavior, and life-history strategy (e.g., Winchell et al., 2016; French et al., 2018; Sparkman et al., 2018; Winchell et al., 2018; Doherty et al., 2020; Putman et al., 2021; Brum et al., 2023; Rurik et al., 2022; Winchell et al., 2023; Virgin et al., 2023). Reptiles are particularly of interest, given unique aspects of their immune system that differentiate them from birds and mammals, their ectothermic thermoregulatory strategy, and their extraordinary variability in life-history strategy, reproductive mode, and sex determination (Zimmerman, 2020; Field et al., 2022). Studies of Anolis lizards form a particularly large and valuable contribution in this field, but studies across other reptilian taxa remain scarce (Putman and Tippie, 2020), and there is a notable dearth of studies investigating immunological endpoints, in particular (French et al., 2018; Putman and Tippie, 2020). One of the limiting factors for study of immunological and endocrinological dynamics in free-living reptiles, particularly lizards, can be small body size and challenges of obtaining blood samples of a volume that can be utilized for a wide range of physiological endpoints. Nevertheless, the studies that have been done have shown evidence of change in immune function, hormone levels, parasite load, body condition, oxidative stress, and life-history traits with urbanization in reptiles—however, as for birds, the direction of these differences across the urban-rural gradient varies wildly, and changes may or may not be evident (Injaian et al., 2020; Iglesias-Carrasco et al., 2020; French et al., 2018; Putman and Tippie, 2020). This does not necessarily mean there are no general trends to be discovered with regard to complex, multi-faceted physiological systems in the context of diverse urban rewards and challenges (Iglesias-Carrasco et al., 2020). However, at this stage, the number of studies in reptiles are far too limited to draw any firm conclusions. Furthermore, the diversity in organismal responses to urban environments suggests that more intensive study of multiple urban populations of the same species—focusing on specific environmental factors and physiological endpoints—may be more informative than attempting to deduce general patterns of urbanization effects across taxa.

A notably widespread species of the western United States, the western fence lizard, Sceloporus occidentalis, has increasingly become the focus of a range of studies of the effects of urbanization on reptiles (e.g., Delaney et al., 2010; Putman et al., 2017; Sparkman et al., 2018; Putman et al., 2019; Rurik et al., 2022; Álvarez-Ruiz et al., 2023; Putman et al., 2024, Putman et al., 2025). While largely absent from the most heavily urbanized centers, this species can be abundant in parks and yards across the suburban-urban gradient. In many regards, it appears to be thriving in a variety of anthropogenically-altered environments—its very presence in areas of regular human activity, artificial light, noise, and altered structural landscape indicates a reasonable degree of tolerance, provided basic requirements for thermoregulation and refuge are met (Rurik et al., 2022). However, as with most reptile species, there has been limited investigation of the immunological, endocrinological, and life-history effects of urban life on this species, leaving substantial potential to investigate these physiological and life-history responses across its range.

Several interacting frameworks emphasizing different aspects of the selective environment, and different physiological and life-history metrics have been used to generate predictions and interpret findings regarding wildlife responses to urbanization. Hypotheses related to parasite prevalence suggest that if urban animals experience lower levels of parasitic infection, they might be able to divert less energy into immune function, and more energy into growth and reproduction (Sheldon and Verhulst, 1996). Hypotheses related to anthropogenic stressors—such as human activity and noise, artificial light at night (ALAN), pollutants, habitat fragmentation, reduced resource availability, and/or urban heat island effects—might predict detrimental effects on wildlife health, that may include maladaptive elevation of glucocorticoids in urban areas, depressed immune function, and depressed reproduction (Birnie-Gauvin et al., 2016; Murray et al., 2019). More general hypotheses such as those based on pace-of-life (ranging from slow to fast life-history strategies) and the role of immunological and endocrinological mechanisms in mediating trade-offs, predict that greater exposure to anthropogenic stressors–or reduced exposure to predators–might alter investment priorities to optimize fitness (e.g., Lucas and French, 2012; Sepp et al., 2018). However, even within these frameworks (which can be both distinct and complementary in different regards), predictions may not be straightforward, given that prior work suggests that altered levels of immunological and/or endocrinological variables can be both a sign of stress or a sign of successful coping (Romero and Beattie, 2022). Furthermore, the key selective variables in urban environments may be unclear, and the actual target(s) of selection, should it occur, may not be the variables measured. Thus, our primary goal in this study was to test for alterations in immunology, endocrinology, body condition, and reproduction across the urban gradient, and to evaluate our findings in light of current theory and empirical research.

We tested for changes in innate immunity across the urban gradient using a hemolysis-agglutination assay to measure natural antibody activity and complement-mediated lysis. Natural antibodies are constitutive, non-specific defenses that recognize a broad array of pathogens and promote their opsonization and phagocytosis (Ochsenbein and Zinkernagel, 2000). In addition, natural antibodies can activate the complement system, resulting in the lysis of invading pathogens (Ochsenbein and Zinkernagel, 2000). We also assessed differences in baseline corticosterone (CORT) and baseline blood glucose, given their important roles in stress response and energy availability—though it is well known that glucocorticoids affect a host of physiological systems, including electrolyte balance, immunology, cardiology, growth and reproduction (Timmermans et al., 2019). While CORT has been explored extensively with respect to urbanization–and it is widely recognized that urbanization may or may not alter glucocorticoid physiology (Injaian et al., 2020; Iglesias-Carrasco et al., 2020)–less has been done with the simple measure of blood glucose. Studies in birds have shown increases in glucose with urbanization (e.g., Ahmad et al., 2025; Kaliński et al., 2014, Kaliński et al., 2015), and there is some evidence it may be responding to resource availability (e.g., Alonso‐Alvarez and Ferrer, 2001; Sparkman et al., 2018—but see Basile et al., 2022), thermal environment (Gangloff et al., 2016; Telemeco et al., 2017) and/or acute stress (Neuman-Lee et al., 2020)–all factors relevant in urban environments. Finally, we tested for differences in body size, body condition, and clutch size, egg volume, and clutch volume to assess whether and how life-history variables change across the urban gradient (generated from satellite measures of imperviousness and nighttime light levels), and how they relate to immunological and endocrinological patterns in this population of fence lizards.

2 Materials and methods

2.1 Study area

We captured the western fence lizard, Sceloporus occidentalis, via lasso across an urban-wild gradient in Santa Barbara, California, USA. Santa Barbara is located on a narrow coastal plain that runs east-west, parallel between the Pacific Ocean and the Santa Ynez Mountains. The study area was historically covered with chaparral, oak woodland, and sycamore riparian communities though, with the exception of remnant oak woodlands, riparian corridors, and restored parks, most of the original vegetation has been cleared due to rapid urbanization since the 1920s. To quantify urbanization levels, we derived imperviousness and anthropogenic light levels at each site from publicly available geospatial data. We obtained urban imperviousness from a raster dataset providing the mean percentage of anthropogenic impervious surfaces (such as asphalt or concrete) for each pixel at a resolution of 30 meters (Dewitz, 2011). We quantified anthropogenic light according to Global Nighttime Light levels for each site obtained from the VI Annual Composite of the Visible and Infrared Imaging Suite (VIIRS) Day Night Band (DNB) from the Earth Observation Group (Elvidge et al., 2017). As artificial light and urban imperviousness were strongly positively correlated (r = 0.87), we combined them into a single urbanization index, defined as the first principal component from a principal components analysis (PCA) of these two variables. This component explained 93% of the total variance and was used as a continuous predictor of urbanization in subsequent analyses.

2.2 Sampling methods

For physiological sampling across a continuous urban gradient, we captured 31 (11 females, 20 males) lizards in spring (March 10–April 7, 2022) after emergence from hibernation, and 107 (51 females, 56 males) in summer (May 31–June 28, 2022) when egg-bearing was at its peak (Figure 1). We captured 51 (Urban: n = 17; Rural: n = 34) female lizards for our analyses of reproduction in May and June in 2018 (n = 12), 2019 (n = 20), 2021 (n = 11), 2022 (n = 2) and 2024 (n = 6). We captured reproductive females from a single suburban site, Westmont College, (34˚ 26’56.33”N, 119˚39’39.71”W) and compared them to lizards from the Los Padres National Forest (Santa Barbara district) that begins <2 km from the Westmont campus. Previous work has shown that lizards from Westmont, along with conspecifics from Cal Poly San Luis Obispo, have diverged morphologically and behaviorally from nearby undeveloped land (Sparkman et al., 2018).

Lizard sampling locations with respect to imperviousness (bluescale) across the urban gradient in Santa Barbara. White circles represent lizards sampled in spring 2022, and black circles represent lizards sampled in summer 2022. The orange circle indicates the location of Westmont College, from which the suburban sample of reproductive lizards was derived.
Figure 1. Lizard sampling locations with respect to imperviousness (bluescale) across the urban gradient in Santa Barbara. White circles represent lizards sampled in spring 2022, and black circles represent lizards sampled in summer 2022. The orange circle indicates the location of Westmont College, from which the suburban sample of reproductive lizards was derived.

We took body temperature immediately after capture via cloacal thermometer (DeltaTrak 11063), so that we could control for any physiological variation primarily due to body temperature differences. We then bled each individual from the caudal vein within 1–10 min of capture, with the number of minutes elapsed recorded for inclusion as a covariate in analysis of physiological variables. We took baseline blood glucose readings of a small drop of blood using a handheld glucometer (FreeStyle Lite by Abbott). We centrifuged the remaining blood, and plasma was separated from the blood pellet and stored at −80 °C until analysis. Note that limitations on blood volume limited our ability to conduct both CORT and immune assays on all individuals. We recorded weight (g) (measured with Pesola scale Micro-Line 20030), snout-vent length (SVL, mm), and the presence or absence of ectoparasites (ticks and mites). We determined sex via presence of enlarged postanal scales present in males but not females (Stebbins, 2003). We examined females for presence, developmental stage, number, and size of eggs via field-portable ultrasound as described below. We released all animals at the point of capture following processing.

We followed all applicable international, national, and/or institutional guidelines for the care and use of animals. We captured lizards with permission from the California Department of Fish and Wildlife. All methods were approved under by the Institutional Review Board (IRB) at Westmont College (protocol #855).

2.3 Ultrasonography

We scanned females with a field-portable Sonosite M-Turbo Ultrasound (Fujifulm SonoSite, Inc.) with a 15 MHz transducer. We conducted ultrasounds with a water bath, where each female was gently but firmly restrained with her head above water and her abdomen submerged. When present, we counted eggs and classified them as pre- or postovulatory (Figure 2). Vitellogenic, preovulatory follicles were identified as spherical and exhibited varying degrees of echogenicity, whereas post-ovulatory eggs were identified as elliptical in shape and highly echogenic (Martínez-Torres et al., 2006; Gilman and Wolf, 2007) (Figure 2). Ultrasonography in lizards has been shown to have high accuracy for clutch size (Gilman and Wolf, 2007; Sacchi et al., 2012), and reasonable accuracy for egg volume and clutch volume (Gilman and Wolf, 2007). Because the greatest variability in volume through development occurs during vitellogenesis, we excluded preovulatory eggs from our analysis of egg volume and clutch volume, and focused exclusively on females with postovulatory eggs (Urban: n = 11; Rural: n = 18) for those analyses.

Ultrasonographic images of **(A)** a transverse scan of spherical preovulatory eggs, **(B)** a transverse scan of elliptical postovulatory eggs, and **(C)** a longitudinal scan of elliptical postovulatory eggs with digital calipers measuring length **(A)** and width **(B)**.
Figure 2. Ultrasonographic images of (A) a transverse scan of spherical preovulatory eggs, (B) a transverse scan of elliptical postovulatory eggs, and (C) a longitudinal scan of elliptical postovulatory eggs with digital calipers measuring length (A) and width (B).

Given the small size of our study species, we found the most effective way to determine clutch size was to do a transverse scan with the transducer, moving slowly from the pelvis up through the abdomen and back (Figures 2A, B). Longitudinal scans were then used to confirm numbers. We found longitudinal scans to be most suited to making egg measurements, and adjusted the transducer until we reached the maximum length and width of a clearly visible egg (Figure 2C). We measured length and width of one egg per female, and calculated egg volume of postovulatory eggs with the volumetric equation for a scalene ellipsoid V = (3/4) πlwh (Stahlschmidt et al., 2011), with the assumption that width was equal to height. Clutch volume was estimated as the product of clutch size and egg volume. Relative clutch size, egg volume, and clutch volume were calculated by adjusting for SVL.

2.4 Physiological assays

Agglutination of natural antibodies and complement-mediated lysis were measured using a hemolysis–hemagglutation assay (Matson et al., 2005) with modifications for squamate reptiles (Sparkman and Palacios, 2009). Briefly, 10 µL of plasma was serially diluted 1:2 with phosphate-buffered saline (PBS). Each well then received 10 µl of a 1% sheep red blood cell suspension. Plates were incubated for 60 minutes at 28 °C and then scored for agglutination and lysis. Intermediate titers were assigned half scores. We ran all samples in duplicate, and ran wells containing only PBS and red blood cells on each plate as a negative control.

We conducted baseline CORT assays conducted using an enzyme immune assay kit (Arbor Assays K014-H1) previously validated for Sceloporus (Trompeter and Langkilde, 2011) and optimized for S. occidentalis by testing for the optimal dilution of plasma that produced values within the standard curve. Briefly, plasma samples were thawed and diluted by adding 6µl of plasma individually with 6µl of the dissociation reagent and 93µl of the assay buffer. We ran all samples in duplicate. We assayed spring samples on a single plate on one date with an intra-assay CV of 2.8%. We assayed summer samples on two plates on another date, with an inter-assay CV of 13.8% and an intra-assay CV of 9.6%.

2.5 Statistical analyses

All analyses were conducted in R 4.4.1. Using the function glm we conducted logistic regression, simple linear regression and generalized linear model analyses. CORT, egg volume, clutch volume, and relative clutch volume were log-transformed to achieve normality. Body condition was calculated as the residuals of log SVL on log weight.

We first used logistic regression to test for a relationship between ectoparasite presence/absence and urbanization, season, and their interaction. For physiological (agglutination, complement-mediated lysis, blood glucose, CORT), and morphological (SVL, body condition) response variables, we conducted an initial screening to identify potential covariates. Covariates included body temperature at capture, minutes elapsed between capture and blood sampling, body condition, and SVL; only those with P ≤ 0.1 when fit individually were retained for subsequent models.

To test the effects of urbanization while accounting for sex and relevant covariates, we constructed the following sets of models: (1) urbanization index + sex + retained covariates; (2) as in (1) but including the interaction between urbanization index and sex; (3) as in (1) but including interactions between covariates and sex; (4) as in (1) including all interactions with sex; (5) covariates only; and (6) null (intercept-only) models. Table 1 shows the resulting top models. We also tested for correlations among physiological response variables using simple linear regression. For reproductive variables (clutch size, relative clutch size, log egg volume, log relative egg volume, log clutch volume, log relative clutch volume) we compared models containing only urbanization category (urban/rural) and year. We compared models using Akaike’s Information Criterion (AIC), with models having ΔAIC < 2 considered top models. Significance of model effects was presented for the top model with the highest number of parameters.

Table 1. AIC values, change in AIC, and weights (w) of top models for physiological, morphological, and behavioral variables in western fence lizards across the urban gradient.

ResponseModelAICΔAICw
Agglutinationurbanization + sex + urbanization*sex + condition87.350.000.60
urbanization + sex + urbanizationsex + condition + conditionsex88.901.550.28
condition91.634.280.07
intercept-only94.176.820.02
urbanization + sex + condition94.266.910.02
urbanization + sex + condition + condition*sex95.438.080.01
Complement-mediated Lysisintercept-only84.290.000.68
urbanization + sex86.432.140.23
urbanization + sex + urbanization*sex88.434.140.09
temperature189.140.000.50
Log CORT (Spring)urbanization + sex + condition + condition*sex21.520.000.70
urbanization + sex + urbanizationsex + condition + conditionsex23.501.970.26
condition28.677.140.02
urbanization + sex + condition29.327.800.01
urbanization + sex + urbanization*sex + condition31.099.570.01
intercept-only32.0410.520.00
Log CORT (Summer)urbanization + sex + temperature191.260.000.35
urbanization + sex + urbanization*sex + temperature191.550.290.30
urbanization + sex + temperature + temperature *sex193.021.760.15
urbanization + sex + urbanizationsex + temperature + temperaturesex193.402.140.12
intercept-only194.152.890.08
Glucose (Spring)intercept-only312.630.000.79
urbanization + sex315.923.290.15
urbanization + sex + urbanization*sex317.925.290.06
Glucose (Summer)intercept-only1003.600.000.58
urbanization + sex1004.901.300.30
urbanization + sex + urbanization*sex1006.803.200.12
SVL (Spring)intercept-only204.330.000.59
urbanization + sex205.831.500.28
urbanization + sex + urbanization*sex207.433.100.13
SVL (Summer)urbanization + sex + urbanization*sex614.370.000.51
urbanization + sex614.440.070.49
intercept-only645.6631.290.00
Body Condition (Spring)intercept-only118.930.000.34
urbanization + sex119.000.070.33
urbanization + sex + urbanization*sex119.040.110.33
Body Condition (Summer)urbanization + sex356.420.000.53
urbanization + sex + urbanization*sex356.720.300.45
intercept-only363.196.770.02

3 Results

3.1 Ectoparasites and physiology

Across both spring and summer, lizards from more urban sites were significantly less likely to host mites (z = -2.092, df =136, P = 0.036) and ticks (z = -2.897, df = 136, P = 0.0038). Additionally, all lizards were significantly more likely to have ticks in summer than in spring (z = -3.001, df = 136, P = 0.0027), but there was no seasonal difference in presence of mites (z = 0.644, df = 136, P = 0.519).

For lizards captured in summer, there was a significant positive relationship between agglutination and lysis titers (t = 4.855, df = 47, P < 0.0001). There was no significant relationship between baseline CORT and either agglutination (t =-0.853, df = 34, P = 0.400) or complement-mediated lysis (t = 0.826, df = 36, P = 0.414), and blood glucose was unrelated to agglutination (t = 0.435, df = 45, P = 0.6659) or complement-mediated lysis (t =1.401, df = 47, P = 0.168). Similarly, there was no relationship between baseline CORT and blood glucose in either spring (t = 1.616, df = 23, P = 0.120) or summer (t = 0.673, df = 79, P = 0.503).

Our initial effect screening indicated that agglutination was not significantly related to SVL, body temperature, time to bleed, but was significantly negatively correlated to body condition (t = -2.137, df = 47, P = 0.0379). Body condition was therefore included in subsequent models testing for a relationship between agglutination and urbanization. The top model included body condition, urbanization index, sex, and the interaction between urbanization and sex (Table 1). The only other model with ΔAIC < 2 relative to the top model also included the interaction between body condition and sex. Agglutination declined with body condition in both sexes, indicating those in higher condition had lower natural antibodies (Table 1; Figure 1). There was no significant interaction between body condition and sex. Notably, there was a significant interaction between urbanization and sex, with females having higher agglutination with increasing urbanization, and males having lower agglutination with increasing urbanization (Table 2; Figure 3A).

Relationship between urbanization index and **(A)** summer agglutination, **(B)**, summer complement-mediated lysis, **(C)** spring baseline blood glucose, **(D)** summer baseline blood glucose, **(E)** spring baseline CORT, and **(F)** summer baseline CORT in male (grey) and female (black) fence lizards. Agglutination was significantly higher for females and lower for males with increasing urbanization, and baseline spring CORT was significantly higher with urbanization for both sexes.
Figure 3. Relationship between urbanization index and (A) summer agglutination, (B), summer complement-mediated lysis, (C) spring baseline blood glucose, (D) summer baseline blood glucose, (E) spring baseline CORT, and (F) summer baseline CORT in male (grey) and female (black) fence lizards. Agglutination was significantly higher for females and lower for males with increasing urbanization, and baseline spring CORT was significantly higher with urbanization for both sexes.

Complement-mediated lysis was not significantly related to SVL, body temperature, time to bleed, or body condition. Models with urbanization and sex were not superior to the intercept-only model (Table 1), and there was no significant relationship between lysis and urbanization, with or without interactions with sex (Table 2). This indicates that complement-mediated lysis did not vary across the urbanization gradient in either sex (Figure 3B).

Table 2. Results of top models for physiological, behavioral, and reproductive variables across the urban gradient in western fence lizards.

ResponseEffectEstimateSEdfFP
Agglutinationurbanization0.4330.1851,432.3380.024
sex0.4520.1961,432.3050.026
urbanization*sex-0.7210.2521,43-2.8590.007
condition-0.2340.0941,43-2.4840.017
condition*sex-0.0820.1301,430.6310.532
Complement-mediated Lysisurbanization-0.0340.1151,48-0.2980.767
sex0.1950.1521,481.2890.204
Log CORT (Summer)urbanization-0.2040.1741,77-1.1780.242
sex-0.3491.9501,77-1.7870.078
urbanization*sex-0.2930.0321,772.7740.007
temperature0.0880.2301,771.2740.207
Log CORT (Spring)urbanization0.7020.4031,181.7410.099
sex0.1430.1891,180.7580.458
urbanization*sex-0.0760.5341,18-0.1420.889
condition-0.3080.0881,18-3.5160.002
condition*sex0.3020.1021,182.9740.008
Blood Glucose (Summer)urbanization2.3574.2061, 1010.5600.576
sex-9.1445.8311, 101-1.5680.120
Blood Glucose (Spring)urbanization-17.43020.1801,33-0.8630.394
sex-15.24013.2701,33-1.1490.259
Log Egg Volumeurbanization-0.4390.1661,26-2.5940.015
year-0.0670.0491,26-1.3720.182
Log Relative Egg Volumeurbanization-0.0070.0041,26-2.7330.011
year-0.0010.0011,26-1.4120.170
Clutch Sizeurbanization0.5650.6171,480.9160.364
year-0.0450.1541,48-0.2910.773
Relative Clutch Sizeurbanization0.0110.0011,461.2340.224
year0.9990.0021,46442.356< 0.0001
Log Clutch Volumeurbanization-0.5230.1961,26-2.6740.013
year-0.1350.0581,26-2.3420.027
Log Relative Clutch Volumeurbanization-0.4800.1901,26-2.5240.018
year-0.1310.0551,26-2.3470.027
SVL (Reprod. Females)urbanization-2.3510.9851,45-2.3860.012
SVL (Summer)urbanization-2.7160.8801, 105-3.0880.003
sex2.7180.9961, 1052.7310.007
urbanization*sex-1.7051.2011, 105-1.4190.159
Body Condition (Summer)urbanization0.0010.2721, 1030.0030.998
sex1.0060.3081, 1033.2660.001
urbanization*sex-0.4770.3711, 103-1.2850.202
SVL (Spring)urbanization-3.7994.2961,27-0.8840.384
sex2.6922.6921,271.0000.326
Body Condition (Spring)urbanization0.0431.7761,260.0240.981
sex-0.7330.8311,260.8830.385
urbanization*sex-2.8402.1461,26-1.3240.197

Significant effects are indicated in bold.

Neither spring nor summer blood glucose was significantly related to SVL, body temperature, time to bleed, or body condition. Models including urbanization and sex were not superior to the intercept-only model for glucose at either time point (Table 2), and there was no significant relationship between glucose and urbanization, with or without interactions with sex (Table 2). This indicates that neither spring nor summer blood glucose varied across the urbanization gradient in our sample in either sex (Figures 3C, D).

Our initial effect screening indicated that spring CORT was not significantly related to SVL, body temperature, or time to bleed, but was significantly negatively correlated to body condition (t = -2.332, df = 26, P = 0.0283). The top model contained urbanization, sex, body condition, and the interaction between body condition and sex (Table 2). There was a trend for increasing spring CORT with higher urbanization; this effect was significant in the top model (P = 0.0193), and only became non-significant (P = 0.0987) with the inclusion of the interaction between urbanization and sex (itself highly non-significant) that was present in the second-best model. Spring CORT was also negatively correlated with body condition in females but not males (Table 2).

Our initial effect screening indicated that summer CORT was not significantly related to SVL, body condition, or time to bleed, but was significantly positively correlated to body temperature (t = 2.673, df = 80, P = 0.009). The top model contained only body temperature with urbanization and sex, and addition of interactions between sex and urbanization, and temperature and sex had similar model fit (Table 1). Males had marginally significantly higher summer CORT than females, and individuals with higher body temperature at capture had significantly higher CORT levels (Table 2). Summer CORT did not vary significantly across the urbanization gradient in our sample in either sex (Table 2; Figure 3F).

3.2 Morphology and reproduction

For both spring SVL and spring body condition, the models with urbanization and sex were not superior to intercept-only models (Table 1), and there were no significant effects of urbanization or sex (Table 2). For summer SVL, the model with urbanization and sex and their interaction had a similar AIC value to the model with urbanization and sex without the interaction (Table 1), but the interaction between urbanization and sex was not significant (Table 2). Males were significantly larger than females, and size significantly decreased with greater urbanization. For summer body condition, the model with urbanization and sex and their interaction had a similar AIC value to the model with urbanization and sex without the interaction (Table 1), but the interaction between urbanization and sex was not significant (Table 2). Furthermore, there was no significant relationship between body condition and urbanization, but males had significantly higher body condition than females.

The SVL of reproductive females was significantly lower at the urban site. Log egg volume was weakly positively correlated with clutch size (r = 0.35; t = 1.986; df = 27; P = 0.0572). There was no difference in clutch size or relative clutch size between urban and rural sites (Table 2; Figure 4A). However, log egg volume, log relative egg volume, log clutch volume, and log relative clutch volume were all significantly lower at the urban site (Figures 4B, C). There was significant heterogeneity among years for relative clutch size, log clutch volume, and log relative clutch volume (Table 1). There was a marginally significant positive correlation between baseline blood glucose and log egg volume (t = 1.835; df = 27; P = 0.0780), but there was no significant relationship between blood glucose and clutch size or clutch volume (P > 0.1).

4 Discussion

We found evidence for physiological, morphological, and reproductive changes with urbanization on western fence lizards across the urban-wild gradient in Santa Barbara, California (Figure 5). One index of innate immunity, agglutination via natural antibodies, was significantly associated with urbanization. However, the relationship was sex-specific, with agglutination increasing with urbanization for females, and decreasing with urbanization for males (Figure 3A). Summer (though not spring) body sizes were lower on average in more urban lizards. There was also a positive correlation between spring baseline CORT and urbanization for both sexes (Figure 3E), and urban females had lower egg volume, resulting in a trend towards lower clutch volume overall, even when adjusting for body size (Figures 4B, C). However, there was no relationship between urbanization and complement-mediated lysis, summer baseline CORT, blood glucose, clutch size, or body condition (Figures 3B–D, F, 4A).

Boxplots comparing **(A)** clutch size, **(B)** log egg volume, and **(C)** log clutch volume for female fence lizards between one urban site—Westmont College—and the adjacent Los Padres National Forest. Both egg volume and clutch volume differed significantly between urban and rural lizards.
Figure 4. Boxplots comparing (A) clutch size, (B) log egg volume, and (C) log clutch volume for female fence lizards between one urban site—Westmont College—and the adjacent Los Padres National Forest. Both egg volume and clutch volume differed significantly between urban and rural lizards.
Summary of findings regarding patterns in physiological, morphological, and reproductive variables across the urban-rural gradient in western fence lizards. Illustrations by Henry Sparkman Zylstra.
Figure 5. Summary of findings regarding patterns in physiological, morphological, and reproductive variables across the urban-rural gradient in western fence lizards. Illustrations by Henry Sparkman Zylstra.

Within prior studies across diverse taxa, including reptiles, there exist nearly every combination of patterns among physiological, morphological, behavioral and life-history variables across the urban gradient (French et al., 2018; Iglesias-Carrasco et al., 2020; Injaian et al., 2020; Putman and Tippie, 2020). Thus some of our findings are consistent with prior studies, and others not. To aid in interpretation of the patterns we observed in this population of fence lizards, we explore our findings within interpretive frameworks focused on parasite prevalence, anthropogenic stressors, and pace-of-life.

4.1 Parasite prevalence

It has been proposed that urban birds may have fewer macroparasites (e.g., ectoparasites and helminths) because complex parasitic life cycles are less likely to be maintained in urban areas (Sepp et al., 2018). However, there appears to be a great deal of variability across taxa in patterns of infection among city, host, and parasite type (Delgado & French, 2012). Prior studies have found lower (e.g., Sepp et al., 2018), higher (e.g., Lazić et al., 2017; Murray et al., 2019; Her and Slade, 2025), or no difference (e.g., French et al., 2008; Amdekar et al., 2018) in parasite prevalence in wildlife across the urban gradient. In our study, more urban fence lizards in Santa Barbara, like populations of their conspecifics in San Bernardino and Claremont (Putman et al., 2025), were less likely to have either ticks or mites. Thus there is some basis for evaluating changes in physiology/morphology of western fence lizards across the urban gradient as a function of reduced ectoparasite prevalence. This could potentially cause a general reduction in investment in immune function (especially if lower ectoparasite prevalence is mirrored by lower viral, bacterial, and other blood-borne pathogens, which remains to be determined). Furthermore, it could potentially result in more resources being allocated to traits such as body size and reproduction.

Whether or not there are other aspects of immune function that are affected by reduction in ectoparasites, the two indices of innate immunity that we measured performed differently across the urban gradient, indicating no monolithic change in immunological investment. In fact, while we did find alterations in agglutination, the sex difference in the direction of this change makes it difficult to interpret simply in light of changes in parasite prevalence. And while release from parasite pressure in the context of energetic limitations might suggest the possibility of larger body sizes and increased reproductive investment, we observed the opposite. Furthermore, we found no change in body condition with urbanization, and those with lower body condition generally had higher agglutination. Thus, while we did find differences in parasite prevalence with urbanization, it offers little interpretive power for understanding the physiological, morphological, and reproductive patterns we observed in this study.

4.2 Anthropogenic stressors

Environmental stress has been proposed as a major factor both in reducing indices of health and condition, as well as mediating life-history trade-offs (Wingfield et al., 1998; Ricklefs and Wikelski, 2002; Wingfield and Sapolsky, 2003; Hau et al., 2010; Palacios et al., 2012). Evidence that stressors associated with urbanization—such as increased anthropogenic activity and noise, artificial light at night (ALAN), pollutants, habitat fragmentation, reduced resource availability and/or urban heat island effects—result in maladaptive elevation of glucocorticoids and reduction in immune function and overall body condition is mixed. In fact, while some studies in reptiles do show higher CORT (baseline and/or stress-induced) in more urban populations (e.g., Lucas and French, 2012; Malisch et al., 2020), others show the opposite trend (e.g., French et al., 2008). Meta-analyses have indicated there is no general trend for elevated CORT with increasing urbanization across taxa, even when considering season, life stage, city size, taxon, and methodology (Injaian et al., 2020; Iglesias-Carrasco et al., 2020). Furthermore, while side-blotched lizards did show reduction in immune function with urbanization (Lucas and French, 2012), which supports the possibility of a stress-induced trade-off, a meta-analysis examining immune response in reptiles showed no consistent pattern of difference across an urban gradient (Putman and Tippie, 2020)—though the sample size was perforce limited. Similarly, studies vary with regard to whether they have observed a reduction in body condition with urbanization (e.g., Lazić et al., 2017), an increase in condition (e.g., Hall and Warner, 2017) or no relationship (e.g., Knapp and Perez-Heydrich, 2012).

A study in Claremont and San Bernardino populations of western fence lizards showed no change in either baseline CORT or body condition with urbanization (Putman et al., 2025). Similarly, in our study, we found no change in body condition with urbanization. Furthermore, we found no evidence of higher baseline blood glucose with urbanization, which could be indicative of higher urban temperatures and/or higher frequency of acute stressors (e.g., Gangloff et al., 2016; Telemeco et al., 2017; Neuman-Lee et al., 2020). Nor, in the opposite direction, did we find evidence of lower blood glucose, which could be indicative of lower resource availability (e.g., Alonso‐Alvarez and Ferrer, 2001; Sparkman et al., 2018; McGraw et al., 2020—but see Basile et al., 2022). However, we did find a season-specific increase in baseline CORT with increasing urbanization, and some indication of depression of immune function in one sex, as well as reductions in summer body size, egg volume and overall clutch volume. These findings could indicate that lizards are experiencing adverse responses to one or more stressors associated with urbanization–for instance, an urban heat island effect (Merckx et al, 2018—but see Putman and Tippie, 2020). However, it is widely recognized that glucocorticoid physiology is highly complex, and elevated levels could be evidence of successful coping rather than a maladaptive response to anthropogenic stressors (Romero and Beattie, 2022); furthermore, the changes in life-history traits that we observed could be an adaptive strategy for coping with diverse environmental challenges (see below).

4.3 Pace-of-life

There is some evidence in squamate reptiles that immune function and glucocorticoid levels may correlate with pace-of-life (e.g., Sparkman and Palacios, 2009; Palacios et al., 2011; Palacios et al., 2012), and urbanization has been linked to changes in life histories on an interspecific level, particularly with regard to reductions in avian clutch size (Brown & Graham 2015; Sepp et al., 2018). That said, a meta-analysis of reptile responses to anthropogenic habitat modification suggested there was a negative trend for smaller clutch sizes in reptiles with habitat modification, but the relationship was weak and overlapped zero (Doherty et al., 2020). A pioneering study of the effects of urbanization on side-blotched lizards found evidence to support a pace-of-life framework, with greater investment in reproduction coupled with higher levels of CORT and decreased immune function and survival suggesting less investment in self-maintenance (Lucas and French, 2012). However, a subsequent study of the same species shows differences in reproductive investment between urban and rural lizards varies with rainfall (Smith et al., 2024).

In our study, we found life-history changes with increasing urbanization, with lizards (including reproductive females) having smaller summer body sizes and decreased egg volumes resulting in decreased clutch volume overall, though clutch size remained the same. Furthermore, we also found higher levels of baseline CORT, at least in one season, as well as decreasing agglutination with urbanization in males. Thus there is some support for the possibility that urbanization is selecting for life histories in western fence lizards characterized by smaller body size and reduced reproductive investment (absolute and relative), though the physiological mechanisms involved will require much more study to elucidate.

Trends for increased body size have also been observed in more urban areas in mammals (Hantak et al., 2021) and seem to be common in reptiles as well (Putman and Tippie, 2020). However, smaller body size in urban areas has also been documented in a range of taxa, from birds (Sepp et al., 2018) to toads (Favio et al., 2025), to a population of fence lizards in Claremont—but not San Bernardino (Putman et al., 2019, Putman et al., 2025). A shift towards smaller body sizes could be either adaptive or maladaptive, depending on the cause. It could be a sign of adaptive adjustment to a reduction in resource availability, thermoregulatory challenges, or smaller refuges.

Similar to the present study, we also observed smaller body sizes in urban lizards in the sample of lizards we used to compare morphology and sprint behavior between college campuses in Santa Barbara and San Luis Obispo and nearby rural habitats (Sparkman et al., 2018; results of body size analysis not included), suggesting it is a consistent trend. The fact that body size did not differ in spring in this study either suggests that there could be difference in size-specific survival across the urban gradient, such that larger lizards are more likely to survive to summer, or that more rural lizards grow at a more rapid rate such that body sizes become more evident as the season progresses. Alternatively, it is possible that our sample size in spring (n = 31 vs. n = 107 in summer) was too small to pick up a size difference; if that is the case, it may be that lower egg volumes translate to smaller hatchling sizes (Sinervo and Adolph, 1989; Bosch and Bout, 1998; Tomasek et al., 2019), which are carried through to adulthood. We have previously demonstrated reduced sprint speeds in urban lizards in Santa Barbara (Sparkman et al., 2018). Since larger hatchlings have been shown to have higher sprint speeds in this species (Sinervo and Adolph, 1989), and we found higher sprint speeds in adult urban fence lizards (Sparkman et al., 2018), it is possible there has been a reduction in predation pressure in urban environments resulting in relaxation of selection on larger body sizes and favoring a reduction in egg size.

There is a strong negative relationship between blood glucose and body size on an interspecific level in birds (Tomasek et al., 2019), though studies within species have shown a positive relationship between glucose and nestling mass (e.g., Kaliński et al., 2014, Kaliński et al., 2015). We found no relationship between baseline blood glucose and body size. Investigation of additional physiological mechanisms underlying changes in growth rate, body size and reproductive investment is currently hampered by unavailability of heterologous assays for measuring key hormones such as insulin-like growth factor-1 and 2 in reptiles (Schwartz and Bronikowski, 2016). As these assays are developed in future, it will be interesting to determine whether endocrinological growth factors do better at predicting this life-history shift than other physiological variables commonly considered.

4.4 Conclusion

There has been widespread acknowledgment in the field of urban ecology of the need for studies spanning more taxa, more populations, and additional physiological, morphological, behavioral, and life-history traits examined in relation to specific anthropogenic factors (French et al., 2018; Iglesias-Carrasco et al., 2020; Putman and Tippie, 2020). At present, it remains difficult to draw any general conclusions regarding consistent, intelligible tendencies of urban environments to select for, or induce plasticity within, particular organismal traits. However, the inconsistency among existing studies suggests that how populations of specific species respond to the specific contexts in which they find themselves is perhaps more at the crux of the matter.

A significant factor inhibiting the progress of urban reptile physiology, particularly for small reptiles, is the difficulty of obtaining blood samples of appreciable size (e.g., 50-100µl whole blood) for even one immunological or endocrinological assay, much less several. Skill in obtaining blood samples requires training and time. The development of more sensitive multiplex methods would greatly enhance our ability to look at more physiological endpoints within the same individual. For our study, while we were able to derive glucose measurements from every individual (only a 1µl of blood being required), we were unable to do more than one hormone and a combined assay to measure two indices of innate immunity given limited plasma volumes.

Reproductive and seasonal sampling also present logistical challenges. Individual variation in phenology and the difficulty of locating eggs once laid complicate efforts to link physiological patterns with reproductive status. Furthermore, expanding reproductive sampling beyond a single urban site would help determine whether observed patterns are consistent across the urban gradient. Stress-induced CORT and blood glucose, as well as additional immunological measures, such as leukocyte differentials and microbial killing assays (Field et al., 2022—see also Blackwell and Garcia, 2022) could provide a more comprehensive picture of physiological adaptation. However, physiological methods continue to be limited for those interested in applying relatively non-invasive methods to free-ranging animals in the wild. That said, population genetic, transcriptomic, genomic, and proteomic approaches are ripe for exploration in this system and could provide powerful insights into the immunological and endocrinological responses of reptiles to urbanization (Watson et al., 2017; Miles et al., 2019; Zylberberg, 2019; Vicente-Santos et al., 2025). Our study brings us at least one further step in the understanding of immunological and endocrinological patterns in urban reptiles, demonstrating that it is possible to look at multiple physiological and life-history endpoints in the same population, and showing the feasibility of more extensive, expansive sampling of this kind in future.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Footnotes

Edited by: Lorin Anne Neuman-Lee, Arkansas State University, United States

Reviewed by: Gregory Blair Pauly, Natural History Museum of Los Angeles County, United States

Emily Virgin, Cincinnati Zoo and Botanical Garden, United States

Statements

Conflict of interest

The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Data availability

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics approval

The animal study was approved by Westmont College Institutional Review Board. The study was conducted in accordance with the local legislation and institutional requirements.

Author contributions

AS: Methodology, Formal analysis, Writing – original draft, Software, Visualization, Data curation, Investigation, Validation, Supervision, Funding acquisition, Project administration, Writing – review & editing, Resources, Conceptualization. CM: Data curation, Writing – review & editing, Formal analysis. ER: Writing – review & editing, Data curation, Investigation. AR: Investigation, Data curation, Writing – review & editing. NH: Data curation, Investigation, Writing – review & editing.

Acknowledgements

We acknowledge the support of the Westmont Biology department and Provost office in maintaining the vibrant undergraduate research fellowship program that made this research possible.

References

  1. Ahmad I. M., Zhang Q., Liu X., Ge S., Nabi G., Wingfield J. C.. (2025). Adjusting to urban stress: How Eurasian tree sparrows modulate multiple physiological and nutritional markers across sexes. Current Zoology 71 (6), 703 – 714.
  2. Alonso‐Alvarez C., Ferrer M. (2001). A biochemical study of fasting, subfeeding, and recovery processes in yellow‐legged gulls. Physiol. Biochem. Zool. 74, 703 – 713. doi:. PMID: doi:10.1086/322932
  3. Álvarez-Ruiz L., Pausas J. G., Blumstein D. T., Putman B. J. (2023). Lizards’ response to the sound of fire is modified by fire history. Anim. Behav. 196, 91 – 102. doi:. PMID: doi:10.1016/j.anbehav.2022.12.002
  4. Amdekar M. S., Kakkar A., Thaker M. (2018). Measures of health provide insights into the coping strategies of urban lizards. Front. Ecol. Evol. 6, 128. doi: doi:10.3389/fevo.2018.00128
  5. Basile A. J., Singh K. C., Watson D. F., Sweazea K. L. (2022). Effect of macronutrient and micronutrient manipulation on avian blood glucose concentration: A systematic review. Comp. Biochem. Physiol. Part. A. Mol. Integr. Physiol. 272, 111279. doi:. PMID: doi:10.1016/j.cbpa.2022.111279
  6. Birnie-Gauvin K., Peiman K. S., Gallagher A. J., de Bruijn R., Cooke S. J. (2016). Sublethal consequences of urban life for wild vertebrates. Environ. Rev. 24, 416 – 425. doi:. PMID: doi:10.1139/er-2016-0029
  7. Blackwell A. D., Garcia A. R. (2022). Ecoimmunology in the field: Measuring multiple dimensions of immune function with minimally invasive, field-adapted techniques. Am. J. Hum. Biol. 34, e23784. doi:. PMID: doi:10.1002/ajhb.23784
  8. Bosch H. A. J., Bout R. G. (1998). Relationships between maternal size, egg size, clutch size, and hatchling size in European lacertid lizards. J. Herpetol. 32, 410 – 417. doi: doi:10.2307/1565456
  9. Bonier F. (2023). Future directions in urban endocrinology–the effects of endocrine plasticity on urban tolerance. Molecular and Cellular Endocrinology 565, 111886.
  10. Brown L. M., Graham C. H. (2015). Demography, traits and vulnerability to urbanization: can we make generalizations ?. Journal of Applied Ecology 52 (6), 1455 – 1464.
  11. Brum P. H. R., Gonçalves S. R. A., Strüssmann C., Teixido A. L. (2023). A global assessment of research on urban ecology of reptiles: patterns, gaps and future directions. Anim. Conserv. 26, 1 – 13. doi:. PMID: doi:10.1111/acv.12799
  12. Chen S., Liu Y., Patrick S. C., Goodale E., Safran R. J., Pagani-Núñez E. (2023). A multidimensional framework to quantify the effects of urbanization on avian breeding fitness. Ecol. Evol. 13, e10259. doi:. PMID: doi:10.1002/ece3.10259
  13. Delaney K. S., Riley S. P. D., Fisher R. N. (2010). A rapid, strong, and convergent genetic response to urban habitat fragmentation in four divergent and widespread vertebrates. PloS One 5, e12767. doi:. PMID: doi:10.1371/journal.pone.0012767
  14. Destefano S., Deblinger R. D., Miller C. (2005). Suburban wildlife: Lessons, challenges, and opportunities. Urban Ecosyst. 8, 131 – 137. doi:. PMID: doi:10.1007/s11252-005-4376-8
  15. Deviche P., Sweazea K., Angelier F. (2023). Past and future: Urbanization and the avian endocrine system. Gen. Comp. Endocrinol. 332, 114159. doi:. PMID: doi:10.1016/j.ygcen.2022.114159
  16. Dewitz J. (2011). National Land Cover Database (NLCD) 2006 Land Cover Conterminous United States (ver. 2.0, July 2024). US Geological Survey (USGS) Data Release, 33.
  17. Doherty T. S., Balouch S., Bell K., Burns T. J., Feldman A., Fist C.. (2020). Reptile responses to anthropogenic habitat modification: A global meta-analysis. Global Ecol. Biogeogr. 29, 1265 – 1279. doi:. PMID: doi:10.1111/geb.13091
  18. Elvidge C. D., Baugh K., Zhizhin M., Hsu F. C., Ghosh T. (2017). VIIRS night-time lights. International Journal of Remote Sensing 38 (21), 5860 – 5879.
  19. Favio P., Clarisa B., Mariana B., Manuel O., Adolfo M., Pablo G. (2025). Anuran responses to urbanization: evaluating life history traits of Rhinella arenarum in urban wetlands. Curr. Zool. 71, 233 – 242. doi:. PMID: doi:10.1093/cz/zoae043
  20. Field E. K., Hartzheim A. M., Terry J., Dawson G., Haydt N., Neuman-Lee L. A. (2022). Reptilian innate immunology and ecoimmunology: what do we know and where are we going ? Integr. Comp. Biol. 62, 1557–1571. doi:. PMID: doi:10.1093/icb/icac116
  21. French S. S., Fokidis H. B., Moore M. C. (2008). Variation in stress and innate immunity in the tree lizard (Urosaurus ornatus) across an urban–rural gradient. J. Comp. Physiol. B 178, 997 – 1005. doi:. PMID: doi:10.1007/s00360-008-0290-8
  22. French S. S., Webb A. C., Hudson S. B., Virgin E. E. (2018). Town and country reptiles: a review of reptilian responses to urbanization. Integr. Comp. Biol. 58, 948 – 966. doi:. PMID: doi:10.1093/icb/icy052
  23. Gangloff E. J., Holden K. G., Telemeco R. S., Baumgard L. H., Bronikowski A. M. (2016). Hormonal and metabolic responses to upper temperature extremes in divergent life-history ecotypes of a garter snake. J. Exp. Biol. 219, 2944 – 2954. doi:. PMID: doi:10.1242/jeb.143107
  24. Gilman C. A., Wolf B. O. (2007). Use of portable ultrasonography as a nondestructive method for estimating reproductive effort in lizards. J. Exp. Biol. 210, 1859 – 1867. doi:. PMID: doi:10.1242/jeb.001875
  25. Hall J. M., Warner D. A. (2017). Body size and reproduction of a non-native lizard are enhanced in an urban environment. Biol. J. Linn. Soc 122, 860 – 871. doi:. PMID: doi:10.1093/biolinnean/blx109
  26. Hantak M. M., McLean B. S., Li D., Guralnick R. P. (2021). Mammalian body size is determined by interactions between climate, urbanization, and ecological traits. Commun. Biol. 4, 972. doi:. PMID: doi:10.1038/s42003-021-02505-3
  27. Hau M., Ricklefs R. E., Wikelski M., Lee K. A., Brawn J. D. (2010). Corticosterone, testosterone and life-history strategies of birds. Proc. R. Soc. B. Biol. Sci. 277, 3203 – 3212. doi:. PMID: doi:10.1098/rspb.2010.0673
  28. Her X., Slade J. W. (2025). The Effect of Urbanization and Sampling Date on Blood Immunophysiology and Haemosporidian Parasitemia in Cardueline Finches. Integrative and Comparative Biology 65 (2), 216 – 228.
  29. Iglesias-Carrasco M., Aich U., Jennions M. D., Head M. L. (2020). Stress in the city: meta-analysis indicates no overall evidence for stress in urban vertebrates. Proc. R. Soc. B. Biol. Sci. 287, 20201754. doi:. PMID: doi:10.1098/rspb.2020.1754
  30. Injaian A. S., Francis C. D., Ouyang J. Q., Dominoni D. M., Donald J. W., Fuxjager M. J.. (2020). Baseline and stress-induced corticosterone levels across birds and reptiles do not reflect urbanization levels. Conserv. Physiol. 8, coz110. doi:. PMID: doi:10.1093/conphys/coz110
  31. Kaliński A., Bańbura M., Glądalski M., Markowski M., Skwarska J., Wawrzyniak J.. (2014). Landscape patterns of variation in blood glucose concentration of nestling blue tits (Cyanistes caeruleus). Landscape Ecol. 29, 1521 – 1530. doi:. PMID: doi:10.1007/s10980-014-0071-6
  32. Kaliński A., Bańbura M., Glądalski M., Markowski M., Skwarska J., Wawrzyniak J.. (2015). Long-term variation in blood glucose concentration in nestling great tits (Parus major). Avian Biol. Res. 8, 129 – 137. doi: doi:10.3184/175815515X14294426911072
  33. Knapp C. R., Perez-Heydrich C. (2012). Using non-conspicuous metrics to examine selected impacts of disturbance on a long-lived reptile. Endanger. Species Res. 17, 193 – 200. doi:. PMID: doi:10.3354/esr00424
  34. Lapiedra O. (2018). Urban behavioral ecology: Lessons from Anolis lizards. Integr. Comp. Biol. 58, 939 – 947. doi:. PMID: doi:10.1093/icb/icy109
  35. Lazić M. M., Carretero M. A., Živković U., Crnobrnja-Isailović J. (2017). City life has fitness costs: reduced body condition and increased parasite load in urban common wall lizards, Podarcis muralis. Salamandra 53 (1), 10–17. Available online at: https://www.podarcis.de/AF/Bibliografie/BIB_10816.pdf.
  36. Lucas L. D., French S. S. (2012). Stress-induced tradeoffs in a free-living lizard across a variable landscape: Consequences for individuals and populations. PloS One 7, e49895. doi:. PMID: doi:10.1371/journal.pone.0049895
  37. Malisch J. L., Garland T., Claggett L., Stevenson L., Kohl E. A., John-Alder H. B. (2020). Living on the edge: Glucocorticoid physiology in desert iguanas (Dipsosaurus dorsalis) is predicted by distance from an anthropogenic disturbance, body condition, and population density. Gen. Comp. Endocrinol. 294, 113468. doi:. PMID: doi:10.1016/j.ygcen.2020.113468
  38. Martínez-Torres M., Guzmán-Rodríguez R., Cárdenas-León M., Brunner-Reynaldo N. (2006). Follicular development and ovulation determined by ultrasound imaging in the viviparous lizard Barisia imbricata (Reptilia: Anguidae). swna 51, 401 – 406. doi: doi:10.1894/0038-4909(2006)51%5B401:FDAODB%5D2.0.CO;2
  39. Matson K. D., Ricklefs R. E., Klasing K. C. (2005). A hemolysis–hemagglutination assay for characterizing constitutive innate humoral immunity in wild and domestic birds. Dev. Comp. Immunol. 29, 275 – 286. doi:. PMID: doi:10.1016/j.dci.2004.07.006
  40. McGraw K. J., Chou K., Bridge A., McGraw H. C., McGraw P. R., Simpson R. K. (2020). Body condition and poxvirus infection predict circulating glucose levels in a colorful songbird that inhabits urban and rural environments. J. Exp. Zool. Part A 333, 561 – 568. doi:. PMID: doi:10.1002/jez.2391
  41. Merckx T., Souffreau C., Kaiser A., Baardsen L. F., Backeljau T., Bonte D.. (2018). Body-size shifts in aquatic and terrestrial urban communities. Nature 558, 113 – 116. doi:. PMID: doi:10.1038/s41586-018-0140-0
  42. Miles L. S., Rivkin L. R., Johnson M. T. J., Munshi-South J., Verrelli B. C. (2019). Gene flow and genetic drift in urban environments. Mol. Ecol. 28, 4138 – 4151. doi:. PMID: doi:10.1111/mec.15221
  43. Miller J. R., Hobbs R. J. (2002). Conservation where people live and work. Conserv. Biol. 16, 330 – 337. doi:. PMID: doi:10.1046/j.1523-1739.2002.00420.x
  44. Møller A. P. (2009). Successful city dwellers: a comparative study of the ecological characteristics of urban birds in the Western Palearctic. Oecologia 159, 849 – 858. doi:. PMID: doi:10.1007/s00442-008-1259-8
  45. Murray M. H., Sánchez C. A., Becker D. J., Byers K. A., Worsley-Tonks K. E., Craft M. E. (2019). City sicker? A meta-analysis of wildlife health and urbanization. Front. Ecol. Environ. 17, 575 – 583. doi:. PMID: doi:10.1002/fee.2126
  46. Neuman-Lee L. A., Hudson S. B., Webb A. C., French S. S. (2020). Investigating the relationship between corticosterone and glucose in a reptile. J. Exp. Biol. 223, jeb203885. doi:. PMID: doi:10.1242/jeb.203885
  47. Ochsenbein A. F., Zinkernagel R. M. (2000). Natural antibodies and complement link innate and acquired immunity. Immunol. Today 21, 624 – 630. doi:. PMID: doi:10.1016/s0167-5699(00)01754-0
  48. Ouyang J. Q., Isaksson C., Schmidt C., Hutton P., Bonier F., Dominoni D. (2018). A new framework for urban ecology: an integration of proximate and ultimate responses to anthropogenic change. Integr. Comp. Biol. 58, 915 – 928. doi:. PMID: doi:10.1093/icb/icy110
  49. Palacios M. G., Sparkman A. M., Bronikowski A. M. (2011). Developmental plasticity of immune defence in two life-history ecotypes of the garter snake, Thamnophis elegans – A common-environment experiment. J. Anim. Ecol. 80, 431 – 437. doi:. PMID: doi:10.1111/j.1365-2656.2010.01785.x
  50. Palacios M. G., Sparkman A. M., Bronikowski A. M. (2012). Corticosterone and pace of life in two life-history ecotypes of the garter snake Thamnophis elegans. Gen. Comp. Endocrinol. 175, 443 – 448. doi:. PMID: doi:10.1016/j.ygcen.2011.11.042
  51. Putman B. J., Drury J. P., Blumstein D. T., Pauly G. B. (2017). Fear no colors? Observer clothing color influences lizard escape behavior. PloS One 12, e0182146. doi:. PMID: doi:10.1371/journal.pone.0182146
  52. Putman B. J., Gasca M., Blumstein D. T., Pauly G. B. (2019). Downsizing for downtown: limb lengths, toe lengths, and scale counts decrease with urbanization in western fence lizards (Sceloporus occidentalis). Urban Ecosyst. 22, 1071 – 1081. doi:. PMID: doi:10.1007/s11252-019-00889-z
  53. Putman B. J., Rensel M. A., Schlinger B. A., French S., Blumstein D. T., Pauly G. B. (2024). Comparing fear responses of two lizard species across habitats varying in human impact. J. Urban Ecol. 10, juae002. doi: doi:10.1093/jue/juae002
  54. Putman B. J., Stevens B., Fresco N. A., Urquidi E. R. (2025). Effects of urbanization on ventral patch size and phenotypic correlates of patch expression in male western fence lizards (Sceloporus occidentalis). Ecol. Evol. 15, e70915. doi:. PMID: doi:10.1002/ece3.70915
  55. Putman B. J., Tippie Z. A. (2020). Big city living: A global meta-analysis reveals positive impact of urbanization on body size in lizards. Front. Ecol. Evol. 8, 580745. doi: doi:10.3389/fevo.2020.580745
  56. Putman B. J., Williams R., Li E., Pauly G. B. (2021). The power of community science to quantify ecological interactions in cities. Sci. Rep. 11, 3069. doi:. PMID: doi:10.1038/s41598-021-82491-y
  57. Ricklefs R. E., Wikelski M. (2002). The physiology/life-history nexus. Trends Ecol. Evol. 17, 462 – 468. doi: doi:10.1016/S0169-5347(02)02578-8
  58. Romero L. M., Beattie U. K. (2022). Common myths of glucocorticoid function in ecology and conservation. J. Exp. Zool. Part A 337, 7 – 14. doi:. PMID: doi:10.1002/jez.2459
  59. Rurik A. J., Wilmoth S. C., Dayton K. E., Sparkman A. M. (2022). Rock refuges are strongly associated with increased urban occupancy in the western fence lizard, Sceloporus occidentalis. Diversity 14. doi:. PMID: doi:10.3390/d14080655
  60. Sacchi R., Pellitteri-Rosa D., Capelli A., Ghitti M., Di Paoli A., Bellati A.. (2012). Studying the reproductive biology of the common wall lizard using ultrasonography. J. Zool. 287, 301 – 310. doi:. PMID: doi:10.1111/j.1469-7998.2012.00917.x
  61. Schwartz T. S., Bronikowski A. M. (2016). Evolution and function of the insulin and insulin-like signaling network in ectothermic reptiles: some answers and more questions. Integr. Comp. Biol. 56, 171 – 184. doi:. PMID: doi:10.1093/icb/icw046
  62. Sepp T., McGraw K. J., Kaasik A., Giraudeau M. (2018). A review of urban impacts on avian life-history evolution: Does city living lead to slower pace of life ? Global Change Biol. 24, 1452 – 1469. doi:. PMID: doi:10.1111/gcb.13969
  63. Sheldon B. C., Verhulst S. (1996). Ecological immunology: costly parasite defences and trade-offs in evolutionary ecology. Trends Ecol. Evol. 11, 317 – 321. doi:. PMID: doi:10.1016/0169-5347(96)10039-2
  64. Sinervo B., Adolph S. C. (1989). Thermal sensitivity of growth rate in hatchling Sceloporus lizards: environmental, behavioral and genetic aspects. Oecologia 78, 411 – 419. doi:. PMID: doi:10.1007/BF00379118
  65. Smith G. D., Wilcoxen T. E., Hudson S. B., Virgin E. E., Durso A. M., Van der Walt M. (2024). Anthropogenic and climatic factors interact to influence reproductivetiming and effort. Ecol. Evol. 14, e11306. doi: doi:10.1002/ece3.11306
  66. Sparkman A., Howe S., Hynes S., Hobbs B., Handal K. (2018). Parallel behavioral and morphological divergence in fence lizards on two college campuses. PloS One 13, e0191800. doi:. PMID: doi:10.1371/journal.pone.0191800
  67. Sparkman A. M., Palacios M. G. (2009). A test of life-history theories of immune defence in two ecotypes of the garter snake, Thamnophis elegans. J. Anim. Ecol. 78, 1242 – 1248. doi:. PMID: doi:10.1111/j.1365-2656.2009.01587.x
  68. Stahlschmidt Z., Brashears J., Denardo D. (2011). The use of ultrasonography to assess reproductive investment and output in pythons. Biol. J. Linn. Soc 103, 772 – 778. doi:. PMID: doi:10.1111/j.1095-8312.2011.01671.x
  69. Stebbins R. C. (2003). A field guide to western reptiles and amphibians (Houghton Mifflin Harcourt).
  70. Telemeco R. S., Gangloff E. J., Cordero G. A., Polich R. L., Bronikowski A. M., Janzen F. J. (2017). Physiology at near-critical temperatures, but not critical limits, varies between two lizard species that partition the thermal environment. J. Anim. Ecol. 86, 1510 – 1522. doi:. PMID: doi:10.1111/1365-2656.12738
  71. Timmermans S., Souffriau J., Libert C. (2019). A general introduction to glucocorticoid biology. Front. Immunol. 10, 1545. doi:. PMID: doi:10.3389/fimmu.2019.01545
  72. Tomásek O., Bobek L., Kralova T., Adamkova M., Albrecht T. (2019). Fuel for the pace of life: Baseline blood glucose concentration co-evolves with life-history traits in songbirds. Funct. Ecol. 33, 239 – 249. doi:. PMID: doi:10.1111/1365-2435.13238
  73. Trompeter W. P., Langkilde T. (2011). Invader danger: lizards faced with novel predators exhibit an altered behavioral response to stress. Horm. Behav. 60, 152 – 158. doi:. PMID: doi:10.1016/j.yhbeh.2011.04.001
  74. Urban M. C., Alberti M., De Meester L., Zhou Y., Verrelli B. C., Szulkin M.. (2024). Interactions between climate change and urbanization will shape the future of biodiversity. Nat. Clim. Change 14, 436 – 447. doi:. PMID: doi:10.1038/s41558-024-01996-2
  75. Vicente-Santos A., Sandoval-Herrera N., Czirják G.Á., Neely B. A., Becker D. J. (2025). Proteomics approaches to ecoimmunology: New insights into wildlife immunity and disease. Integr. Comp. Biol. 65 (6), 1744 – 1754. doi:. PMID: doi:10.1093/icb/icaf044
  76. Virgin E. E., Lewis E. L., Lidgard A. D., Kepas M. E., Marchetti J. R., Hudson S. B.. (2023). Egg viability and egg mass underlie immune tradeoffs and differences between urban and rural lizard egg yolk physiology. Gen. Comp. Endocrinol. 337, 114258. doi:. PMID: doi:10.1016/j.ygcen.2023.114258
  77. Watson H., Videvall E., Andersson M. N., Isaksson C. (2017). Transcriptome analysis of a wild bird reveals physiological responses to the urban environment. Sci. Rep. 7, 44180. doi:. PMID: doi:10.1038/srep44180
  78. Winchell K. M., Campbell-Staton S. C., Losos J. B., Revell L. J., Verrelli B. C., Geneva A. J. (2023). Genome-wide parallelism underlies contemporary adaptation in urban lizards. Proc. Natl. Acad. Sci. 120, e2216789120. doi:. PMID: doi:10.1073/pnas.2216789120
  79. Winchell K. M., Maayan I., Fredette J. R., Revell L. J. (2018). Linking locomotor performance to morphological shifts in urban lizards. Proc. R. Soc. B. Biol. Sci. 285, 20180229. doi:. PMID: doi:10.1098/rspb.2018.0229
  80. Winchell K. M., Reynolds R. G., Prado-Irwin S. R., Puente-Rolón A. R., Revell L. J. (2016). Phenotypic shifts in urban areas in the tropical lizard Anolis cristatellus. Evol. 70, 1009 – 1022. doi:. PMID: doi:10.1111/evo.12925
  81. Wingfield J. C., Maney D. L., Breuner C. W., Jacobs J. D., Lynn S., Ramenofsky M.. (1998). Ecological bases of hormone—behavior interactions: the “Emergency Life History Stage. Am. Zool. 38, 191 – 206. doi: doi:10.1093/icb/38.1.191
  82. Wingfield J. C., Sapolsky R. M. (2003). Reproduction and resistance to stress: When and how. J. Neuroendocrinol. 15, 711 – 724. doi:. PMID: doi:10.1046/j.1365-2826.2003.01033.x
  83. Zimmerman L. M. (2020). The reptilian perspective on vertebrate immunity: 10 years of progress. J. Exp. Biol. 223, jeb214171. doi:. PMID: doi:10.1242/jeb.214171
  84. Zylberberg M. (2019). Next-generation ecological immunology. Physiol. Biochem. Zool. 92, 177 – 188. doi:. PMID: doi:10.1086/702440

Citation

Sparkman, A. M., et al. (2026). Urbanization is associated with alterations in immunity, stress physiology, morphology and reproduction in western fence lizards. Frontiers in Amphibian and Reptile Science, Volume 4. https://doi.org/
Received
Accepted
Published
Volume
4 - 2026

Copyright

Copyright © 2026 Sparkman, Muthiah, Reyes, Rurik and Hareb.

License: https://creativecommons.org/licenses/by/4.0/

*Correspondence: Amanda M. Sparkman

Article metrics

Views
0
Downloads
0
Citations
0
Shares
0

Related articles

ReviewCulture and conservation: a One Health approach to Indigenous and ancestral herptile knowledgeAshley N. Morgan, Fortunate Mafeta Phaka, Ida Ayu Dian Kusuma Dewi, Angela Julian, Andres Santiago Carrasco-Medina, Tariq Stark, Jywateju Kayabi, Iauapuru Trumai, Lorena Dall’Ara Guimarães, María Torres-Sánchez, Debra L. MillerCase ReportCase Report: Oviductal adenocarcinoma in an Argentine black and white tegu (Salvator merianae): clinical, imaging, surgical, and histopathological findingsAndreia Garcês, Roberto Sargo, Luís Sousa, Camila Cardoso, Luana Monteiro, Diogo Silva, Nuno Alvura, Justina Prada, Filipe SilvaOriginal ResearchEvaluating invasive reptile control efforts: nocturnal bulk removal of green iguanas (Iguana iguana Linnaeus, 1758) in Florida, USAFrank J. Mazzotti, Sergio A. Balaguera-Reina, Sidney T. Godfrey, Nathan P. Schwartz, Melissa A. Miller