Miami heat: Urban heat islands influence the thermal suitability of habitats for ectotherms

Shedding light on biodiversity: reviewing existing knowledge and exploring hypothesised impacts of agrophotovoltaics

The growing demand for energy and the shift towards green energy solutions have led to the conversion of open spaces and agricultural fields into photovoltaic (PV) power plants, exacerbating the "food-energy-environment" trilemma. Agrophotovoltaics (APVs), a dual-use system combining agriculture and energy production on the same land, presents a potential solution to this challenge. While the environmental impacts of ground-mounted utility-scale PV (USPV) power plants and the effects of APV systems on agricultural yields have been extensively studied and reviewed, the implications for wildlife and biodiversity remain largely unexplored. This knowledge gap is pressing, given the accelerated global adoption of APV systems and the urgency of understanding their broader ecological consequences. In this concise review, we synthesise existing literature on the impacts of USPV installations on biodiversity and the effects of APV on crop production. Building on these foundations, we propose novel hypotheses concerning the potential pathways and mechanisms through which APV systems may influence biodiversity. We explore the complex interactions between agroecosystems and natural ecosystems, examining both direct and indirect effects. Our review culminates in a set of key research questions designed to guide future studies on the biodiversity outcomes of APV deployment. Future research should comprehensively address factors such as habitat type, climate, spatial scale, technology, and agricultural practices, as well as the overarching impacts of climate change. By highlighting the importance of these variables, we aim to facilitate a nuanced understanding of how APV systems can either support or undermine biodiversity. This work not only underscores the critical need for empirical studies in this emerging field but also sets the stage for more informed and sustainable implementation of APV technologies.

Observing character displacement from process to pattern in a novel vertebrate community

Ecological character displacement, whereby shifts in resource use in the presence of competing species leads to adaptive evolutionary divergence, is widely considered an important process in community assembly and adaptive radiation. However, most evidence for character displacement has been inferred from macro-scale geographic or phylogenetic patterns; direct tests of the underlying hypothesis of divergent natural selection driving character displacement in the wild are rare. Here, we document character displacement between two ecologically similar lizards (Anolis sagrei and A. cristatellus) experiencing novel contact. We identify directional selection during the incipient stages of sympatry in a new community that corresponds to repeated trait divergence across multiple established sympatric communities. By identifying the role of natural selection as character displacement unfolds, we connect how natural selection operating at short timescales may drive broader patterns of trait distributions at larger spatial and temporal scales.

Rethinking ecological niches and geographic distributions in face of pervasive human influence in the Anthropocene

Species are distributed in predictable ways in geographic spaces. The three principal factors that determine geographic distributions of species are biotic interactions (B), abiotic conditions (A), and dispersal ability or mobility (M). A species is expected to be present in areas that are accessible to it and that contain suitable sets of abiotic and biotic conditions for it to persist. A species' probability of presence can be quantified as a combination of responses to B, A, and M via ecological niche modeling (ENM; also frequently referred to as species distribution modeling or SDM). This analytical approach has been used broadly in ecology and biogeography, as well as in conservation planning and decision-making, but commonly in the context of 'natural' settings. However, it is increasingly recognized that human impacts, including changes in climate, land cover, and ecosystem function, greatly influence species' geographic ranges. In this light, historical distinctions between natural and anthropogenic factors have become blurred, and a coupled human-natural landscape is recognized as the new norm. Therefore, B, A, and M (BAM) factors need to be reconsidered to understand and quantify species' distributions in a world with a pervasive signature of human impacts. Here, we present a framework, termed human-influenced BAM (Hi-BAM, for distributional ecology that (i) conceptualizes human impacts in the form of six drivers, and (ii) synthesizes previous studies to show how each driver modifies the natural BAM and species' distributions. Given the importance and prevalence of human impacts on species distributions globally, we also discuss implications of this framework for ENM/SDM methods, and explore strategies by which to incorporate increasing human impacts in the methodology. Human impacts are redefining biogeographic patterns; as such, future studies should incorporate signals of human impacts integrally in modeling and forecasting species' distributions.

Does habitat modification impact morphology, performance, and inflammatory responses in an amphibian with limited dispersal capacity (Lisssotriton helveticus)?

The environment of an organism exerts selective pressures that affect mobility, feeding, reproduction as well as predator-prey and conspecific interactions. Land use changes induced by human activities modify these selective pressures and may result in the adaptation of organisms. Amphibians are ectotherms that typically show a biphasic life cycle with an aquatic and terrestrial phase, which makes them particularly sensitive to environmental change. We studied the impact of habitat modifications on palmate newt populations in the Ile de France region across four types of habitats: urban, mixed, agricultural, and natural with at least two replicates for each habitat type. We measured the morphology of newts using callipers, quantified maximal running and swimming speed and acceleration using high-speed video recordings, and quantified the swelling of the hind limb linked to an inflammatory reaction. Our results show that in urban habitats, newts are larger and heavier and have a better body condition. Females, moreover, have a larger head in natural habitats, possibly due to diet specialisation of females during the breeding season. In mixed and agricultural habitats, newts have longer limbs and show a tendency to run faster, possibly associated with the selective pressures on movement in mixed habitats. Differences in inflammatory responses were observed between sexes but not habitat types. Overall, our results show differences in morphology and trends for differences in performance in newts living in different habitats suggesting that animals are adapting to human-induced changes in their environment.

When adaptation is slowed down: Genomic analysis of evolutionary stasis in thermal tolerance during biological invasion in a novel climate

Research conducted during the past two decades has demonstrated that biological invasions are excellent models of rapid evolution. Even so, characteristics of invasive populations such as a short time for recombination to assemble optimal combinations of alleles may occasionally limit adaptation to new environments. Here, we investigated such genetic constraints to adaptation in the invasive brown anole (Anolis sagrei)-a tropical ectotherm that was introduced to the southeastern United States, a region with a much colder climate than in its native Caribbean range. We examined thermal physiology for 30 invasive populations and tested for a climatic cline in cold tolerance. Also, we used genomics to identify mechanisms that may limit adaptation. We found no support for a climatic cline, indicating that thermal tolerance did not shift adaptively. Concomitantly, population genomic results were consistent with the occurrence of recombination cold spots that comprise more than half of the genome and maintain long-range associations among alleles in invasive populations. These genomic regions overlap with both candidate thermal tolerance loci that we identified using a standard genome-wide association test. Moreover, we found that recombination cold spots do not have a large contribution to population differentiation in the invasive range, contrary to observations in the native range. We suggest that limited recombination is constraining the contribution of large swaths of the genome to adaptation in invasive brown anoles. Our study provides an example of evolutionary stasis during invasion and highlights the possibility that reduced recombination occasionally slows down adaptation in invasive populations.

Spatiotemporal and Individual Patterns of Domestic Cat (Felis catus) Hunting Behaviour in France

Domestic cats (Felis catus), one of the most popular pets, are widespread worldwide. This medium-sized carnivore has well-known negative effects on biodiversity, but there is still a need to better understand the approximate causes of their predation. Based on a citizen science project, we assessed the role of spatiotemporal (i.e., latitude, longitude, and seasons), climatic (i.e., rainfall), anthropogenic (i.e., human footprint, HFI), and individual (i.e., sex and age) variables on the number of preys returned home by cats in metropolitan France. Over the 5048 cats monitored between 2015 and 2022, prey from 12 different classes (n = 36,568) were returned home: 68% mammals, 21% birds, and 8% squamates. Shrews brought home by cats peaked during summer, while rodents were recorded during summer-autumn. Birds brought home by cats peaked in spring-summer and in autumn, and lizards peaked in spring and in late summer. Lower HFI was associated with more voles and mice brought home, and the opposite trend was observed for lizards and birds. Younger cats were more prone to bring home shrews, birds, and reptiles. Although environmental factors play a minor role in prey brought home by cats, some geographical characteristics of prey species distribution partly explains the hunting behaviour of cats.

Interactions among spatial configuration aspects of urban tree canopy significantly affect its cooling effects

Increasing urban tree canopy (UTC) has been widely recognized as an effective means for urban heat mitigation and adaptation. While numerous studies have shown that both percent cover of UTC and its spatial configuration can significantly affect urban temperature, the pathways governing these relationships are largely unexplored. Here we present a cross-city comparison aiming to fill this gap by explicitly quantifying the pathways on which percent cover of UTC and its spatial configuration affect land surface temperature (LST) using structural equation modeling (SEM), based on UTC mapped from high resolution imagery and LST derived from Landsat thermal bands. We found: 1) Although both the direct and indirect pathways significantly affected LST regardless of scales and cities, the direct pathway played a more important role in affecting LST in Baltimore, Beijing, and Shenzhen. In contrast, an opposite result was found in Sacramento, likely due to the effects of buildings and their interactions with UTC. 2) Similarly, the direct pathway of mean patch size (MPS) and mean shape index (MSI) played a more important role in affecting LST than their indirect effects via altering edge density (ED). Our results highlighted the necessity for discomposing the effects of different spatial configuration variables on LST. Understanding the pathways through which UTC affects LST can provide insights into urban heat mitigation and adaptation.

Rapid introgression of non-native alleles following hybridization between a native Anolis lizard species and a cryptic invader across an urban landscape

Invasive species can impact native populations through competition, predation, habitat alteration, and disease transmission, but also genetically through hybridization. Potential outcomes of hybridization span the continuum from extinction to hybrid speciation and can be further complicated by anthropogenic habitat disturbance. Hybridization between the native green anole lizard (Anolis carolinensis) and a morphologically similar invader (A. porcatus) in south Florida provides an ideal opportunity to study interspecific admixture across a heterogeneous landscape. We used reduced-representation sequencing to describe introgression in this hybrid system and to test for a relationship between urbanization and non-native ancestry. Our findings indicate that hybridization between green anole lineages was probably a limited, historic event, producing a hybrid population characterized by a diverse continuum of ancestry proportions. Genomic cline analyses revealed rapid introgression and disproportionate representation of non-native alleles at many loci and no evidence for reproductive isolation between parental species. Three loci were associated with urban habitat characteristics; urbanization and non-native ancestry were positively correlated, although this relationship did not remain significant when accounting for spatial nonindependence. Ultimately, our study demonstrates the persistence of non-native genetic material even in the absence of ongoing immigration, indicating that selection favouring non-native alleles can override the demographic limitation of low propagule pressure. We also note that not all outcomes of admixture between native and non-native species should be considered intrinsically negative. Hybridization with ecologically robust invaders can lead to adaptive introgression, which may facilitate the long-term survival of native populations otherwise unable to adapt to anthropogenically mediated global change.

Do Suburban Populations of Lizards Behave Differently from Forest Ones? An Analysis of Perch Height, Time Budget, and Display Rate in the Cuban Endemic Anolis homolechis

Urbanization transforms natural ecosystems into novel habitats, which can result in negative consequences for biodiversity. Therefore, it is important to understand the mechanisms of maintenance of native species in urbanized environments, including behavior—which can act as a fast response to rapid environmental changes. We compared some behavioral traits between two suburban and two forest populations of Anolis homolechis. Direct observations of 779 individuals revealed that perch height was positively influenced by body size, but not by sex. Suburban individuals perched higher than forest ones, and even more so in the afternoon compared to the morning; a behavior that was not observed in forests populations. These differences might be due to a change from foraging activities in the morning to vigilance, display, and/or thermoregulation in the afternoon, promoted by suburban habitat conditions (e.g., higher predator abundance, open habitat structure, and urban heat). Video recordings of 81 focal individuals showed that males were more active than females (i.e., spending less time in stationary behavior and having a higher display rate), with no significant effect of habitat type. As some of our results diverge from previous studies on invasive anoles, we recommend extending comparative studies of urban and non-urban populations to other native Anolis.

An expanding cityscape and its multi-scale effects on lizard distribution

Urbanization results in complex and variable changes to environmental conditions, which translate to shifts in selection pressures for organisms. Size of a city as well as the intensity and extent of urbanization can synergistically influence how organisms are impacted. However, less is known about how landscape heterogeneity, rate of land-use change, and scale of urbanization affect species persistence. We evaluate the ways in which urbanization changes the environment and examine how some of these environmental factors influence the presence of the lizard Psammophilus dorsalis (Peninsular rock agama), in Bengaluru, India. Variability in environmental factors across the study area was characterised by measures of habitat composition and diversity, habitat connectivity, rate of habitat change, predation pressure, land surface temperature (LST) and artificial light at night (ALAN), that were derived from remotely sensed and citizen science data. Most of these factors showed high variance across two measures of urbanization: distance from city center and proportion of built-up area. Habitat diversity and ALAN were the only two factors that changed predictably and in a non-linear way, with distance from the city center and proportion of built-up area. We then used a multi-scale approach to examine the relative importance of some these environmental factors at the landscape scale, as well as additional factors at the microhabitat-scale, in predicting the presence and relative abundance of P. dorsalis respectively. At the landscape scale, LST, which is positively correlated with proportion of cropland, predicted lizard presence; whereas at the microhabitat scale, P. dorsalis was more likely to be found in sites with higher proportions of rocks. Overall, we demonstrate that urbanization can result in environmental predictors that do not vary linearly across the urbanization gradient. For the iconic rock agama, many of these environmental factors do not seem to be strong selection pressures that influence their distribution in the expanding cityscape. Whether this urban utilizer can continue to persist with increasing anthropogenic development is uncertain. To better understand drivers of species persistence, we emphasize the importance of quantifying urbanization across multiple axes, considering environmental factors that are relevant to species at different spatial and temporal scales.

Nesting in Anolis Lizards: An Understudied Topic in a Well-Studied Clade

Maternal nesting behavior in oviparous species strongly influences the environmental conditions their embryos experience during development. In turn, these early-life conditions have consequences for offspring phenotypes and many fitness components across an individual’s lifespan. Thus, identifying the evolutionary and ecological causes and effects of nesting behavior is a key goal of behavioral ecology. Studies of reptiles have contributed greatly to our understanding of how nesting behavior shapes offspring phenotypes. While some taxonomic groups have been used extensively to provide insights into this important area of biology, many groups remain poorly studied. For example, the squamate genus Anolis has served as a model to study behavior, ecology, and evolution, but research focused on Anolis nesting behavior and developmental plasticity is comparatively scarce. This dearth of empirical research may be attributed to logistical challenges (e.g., difficulty locating nests), biological factors (e.g., their single-egg clutches may hinder some experimental designs), and a historical focus on males in Anolis research. Although there is a gap in the literature concerning Anolis nesting behavior, interest in nesting ecology and developmental plasticity in this group has grown in recent years. In this paper, we (1) review existing studies of anole nesting ecology and developmental plasticity; (2) highlight areas of anole nesting ecology that are currently understudied and discuss how research in these areas can contribute to broader topics (e.g., maternal effects and global change biology); and (3) provide guidelines for studying anole nesting in the field. Overall, this review provides a foundation for establishing anoles as models to study nesting ecology and developmental plasticity.

Selection on adaptive and maladaptive gene expression plasticity during thermal adaptation to urban heat islands

Phenotypic plasticity enables a single genotype to produce multiple phenotypes in response to environmental variation. Plasticity may play a critical role in the colonization of novel environments, but its role in adaptive evolution is controversial. Here we suggest that rapid parallel regulatory adaptation of Anolis lizards to urban heat islands is due primarily to selection for reduced and/or reversed heat-induced plasticity that is maladaptive in urban thermal conditions. We identify evidence for polygenic selection across genes of the skeletal muscle transcriptome associated with heat tolerance. Forest lizards raised in common garden conditions exhibit heat-induced changes in expression of these genes that largely correlate with decreased heat tolerance, consistent with maladaptive regulatory response to high-temperature environments. In contrast, urban lizards display reduced gene expression plasticity after heat challenge in common garden and a significant increase in gene expression change that is congruent with greater heat tolerance, a putatively adaptive state in warmer urban environments. Genes displaying maladaptive heat-induced plasticity repeatedly show greater genetic divergence between urban and forest habitats than those displaying adaptive plasticity. These results highlight the role of selection against maladaptive regulatory plasticity during rapid adaptive modification of complex systems in the wild.

Infection risk varies within urbanized landscapes: the case of coyotes and heartworm

BACKGROUND

Urbanization can have profound effects on ecological interactions. For host-pathogen interactions, differences have been detected between urban and non-urban landscapes. However, host-pathogen interactions may also differ within highly heterogeneous, urbanized landscapes.

METHODS

We investigated differences in infection risk (i.e., probability of infection) within urbanized landscapes using the coyote (Canis latrans) and mosquito-borne nematode, Dirofilaria immitis (the causative agent for canine heartworm), as a case study. We focused on a coyote population in Chicago for which extensive behavioral and heartworm infection data has been collected between 2001 and 2016. Our objectives were to: (i) determine how onset and duration of the heartworm transmission season varied over the 16-year period and across the urban-suburban gradient; and (ii) investigate how heartworm infection risk in coyotes varied over the years, across the urban-suburban gradient, by coyote characteristics (e.g., age, sex, resident status), and coyote use of the urbanized landscape (e.g., use of urban areas, mosquito habitats).

RESULTS

While onset of the heartworm transmission season differed neither by year nor across the urban-suburban gradient, it was longer closer to the core of Chicago. Of the 315 coyotes sampled, 31.1% were infected with D. immitis. Older coyotes and coyotes sampled in later years (i.e., 2012-2016) were more likely to have heartworm. While coyote location in the urban-suburban gradient was not a significant predictor of infection, the proportion of urban land in coyote home ranges was. Importantly, the size and direction of this association varied by age class. For adults and pups, infection risk declined with urbanization, whereas for subadults it increased. Further, models had a higher predictive power when focusing on resident coyotes (and excluding transient coyotes). The proportion of mosquito habitat in coyote home ranges was not a significant predictor of infection.

CONCLUSIONS

Our findings suggest that urbanization may affect host exposure to vectors of D. immitis, that risk of infection can vary within urbanized landscapes, and that urbanization-wildlife infection associations may only be detected for animals with certain characteristics (e.g., age class and resident status).

Disentangling controls on animal abundance: Prey availability, thermal habitat, and microhabitat structure

The question of what controls animal abundance has always been fundamental to ecology, but given rapid environmental change, understanding the drivers and mechanisms governing abundance is more important than ever. Here, we determine how multidimensional environments and niches interact to determine population abundance along a tropical habitat gradient. Focusing on the endemic lizard Anolis bicaorum on the island of Utila (Honduras), we evaluate direct and indirect effects of three interacting niche axes on abundance: thermal habitat quality, structural habitat quality, and prey availability. We measured A. bicaorum abundance across a series of thirteen plots and used N-mixture models and path analysis to disentangle direct and indirect effects of these factors. Results showed that thermal habitat quality and prey biomass both had positive direct effects on anole abundance. However, thermal habitat quality also influenced prey biomass, leading to a strong indirect effect on abundance. Thermal habitat quality was primarily a function of canopy density, measured as leaf area index (LAI). Despite having little direct effect on abundance, LAI had a strong overall effect mediated by thermal quality and prey biomass. Our results demonstrate the role of multidimensional environments and niche interactions in determining animal abundance and highlight the need to consider interactions between thermal niches and trophic interactions to understand variation in abundance, rather than focusing solely on changes in the physical environment.

In situ adaptation and ecological release facilitate the occupied niche expansion of a non-native Madagascan day gecko in Florida

AIM

To investigate whether the frequently advocated climate-matching species distribution modeling approach could predict the well-characterized colonization of Florida by the Madagascar giant day gecko Phelsuma grandis.

LOCATION

Madagascar and Florida, USA.

METHODS

To determine the climatic conditions associated with the native range of P. grandis, we used native-range presence-only records and Bioclim climatic data to build a Maxent species distribution model and projected the climatic thresholds of the native range onto Florida. We then built an analogous model using Florida presence-only data and projected it onto Madagascar. We constructed a third model using native-range presences for both P. grandis and the closely related parapatric species P. kochi.

RESULTS

Despite performing well within the native range, our Madagascar Bioclim model failed to identify suitable climatic habitat currently occupied by P. grandis in Florida. The model constructed using Florida presences also failed to reflect the distribution in Madagascar by overpredicting distribution, especially in western areas occupied by P. kochi. The model built using the combined P. kochi/P. grandis dataset modestly improved the prediction of the range of P. grandis in Florida, thereby implying competitive exclusion of P. grandis by P. kochi from habitat within the former's fundamental niche. These findings thus suggest ecological release of P. grandis in Florida. However, because ecological release cannot fully explain the divergent occupied niches of P. grandis in Madagascar versus Florida, our findings also demonstrate some degree of in situ adaptation in Florida.

MAIN CONCLUSIONS

Our models suggest that the discrepancy between the predicted and observed range of P. grandis in Florida is attributable to either in situ adaptation by P. grandis within Florida, or a combination of such in situ adaptation and competition with P. kochi in Madagascar. Our study demonstrates that climate-matching species distribution models can severely underpredict the establishment risk posed by non-native herpetofauna.

Eurythermic Sprint and Immune Thermal Performance and Ecology of an Exotic Lizard at Its Northern Invasion Front

AbstractThermal performance of immunity has been relatively understudied in ectotherms, especially in the context of invasive species or in relation to other fitness-related traits and thermoregulatory patterns in the field. For reptiles, thermal biology is a primary factor determining physiological performance and population viability, and suboptimal thermal conditions may limit the expansion of exotic species along the edges of their invasion fronts. This study examined thermoregulatory ecology and thermal performance of immunity and sprinting in a population of Mediterranean geckos (Hemidactylus turcicus) at the northern edge of their invasion front in a temperate zone of the United States. In the field, we quantified temperatures of geckos of varied age classes in relation to air, wall, and refugia temperatures. We also quantified temperature-dependent sprint performance and immune function in field-collected geckos to detail thermal performance patterns that may contribute to the capacity for this species to invade cool climates. Although body temperature (T_b) of wild-caught geckos correlated with wall temperature, average T_b exhibited wide distributions, suggesting eurythermy. Furthermore, the thermal performance of immune swelling responses to phytohemagglutinin injections and sprinting was optimized over a similarly wide temperature range that overlapped with the field T_b's that suggest eurythermy in this species. The wide thermal performance breadths in these traits could buffer against variation in factors such as pathogen exposure and environmental temperatures that could otherwise suppress functional performance. Thus, eurythermy of sprint and immune performance may facilitate the invasive potential of H. turcicus.

Home climate and habitat drive ecotypic stress response differences in an invasive grass

Invasive plants and agricultural weeds are a ubiquitous and ever-expanding threat to biosecurity, biodiversity and ecosystem services. Many of these species are known to succeed through rapid adaptation to biotic and abiotic stress regimes, often in highly disturbed systems. Given the current state of evidence for selection of weedy genotypes via primary physiological stresses like drought, flooding, heat, cold and nutrient deficiency, we posit that adaptation to land management regimes which comprise suites of these stresses can also be expected. To establish this link, we tested adaptation to water and nutrient stresses in five non-agricultural and five agricultural populations of the invader Johnsongrass (Sorghum halepense) sampled across a broad range of climates in the USA. We subjected seedlings from each population to factorial drought and nutrient stresses in a common garden greenhouse experiment. Agricultural and non-agricultural ecotypes did not respond differently to experimentally applied stresses. However, non-agricultural populations from more drought-prone and nutrient-poor locations outperformed their agricultural counterparts in shoot allocation and chlorophyll production, respectively. We also found evidence for root allocation adaptation to hotter climates, in line with other C4 grasses, while greater adaptation to drought treatment was associated with soil organic carbon (SOC)-rich habitats. These findings imply that adaptation to land-use types can interact with other macrohabitat parameters, which will be fluctuating in a changing climate and resource-needy world. We see that invasive plants are poised to take on novel habitats within their introduced ranges, leading to complications in the prevention and management of their spread.

Heat tolerance of reptile embryos: Current knowledge, methodological considerations, and future directions

Aspects of global change result in warming temperatures that threaten biodiversity across the planet. Eggs of non-avian, oviparous reptiles (henceforth "reptiles") are particularly vulnerable to warming due to a lack of parental care during incubation and limited ability to behaviorally thermoregulate. Because warming temperatures will cause increases in both mean and variance of nest temperatures, it is crucial to consider embryo responses to both chronic and acute heat stress. Although many studies have considered embryo survival across constant incubation temperatures (i.e., chronic stress) and in response to brief exposure to extreme temperatures (i.e., acute stress), there are no standard metrics or terminology for determining heat stress of embryos. This impedes comparisons across studies and species and hinders our ability to predict how species will respond to global change. In this review, we compare various methods that have been used to assess embryonic heat tolerance in reptiles and provide new terminology and metrics for quantifying embryo responses to both chronic and acute heat stress. We apply these recommendations to data from the literature to assess chronic heat tolerance in 16 squamates, 16 turtles, five crocodilians, and the tuatara and acute heat tolerance for nine squamates and one turtle. Our results indicate that there is relatively large variation in chronic and acute heat tolerance across species, and we outline directions for future research, calling for more studies that assess embryo responses to acute thermal stress, integrate embryo responses to chronic and acute temperatures in predictive models, and identify mechanisms that determine heat tolerance.

Differential effects of the urban heat island on thermal responses of freshwater fishes from unmanaged and managed systems

A lack of understanding exists regarding how freshwater species will respond to increases in temperature associated with ongoing changes in climate. Non-urban to urban thermal gradients generated by urban heat islands can serve as models to characterize the effects of relatively consistent increases in temperature on freshwater ecosystems over several decades. This study investigates the apparent responses of two freshwater fish species, Campostoma anomalum (Central Stoneroller) and Lepomis macrochirus (Bluegill), to directional changes in temperature over the past century across the non-urban to urban gradient in the Saint Louis, Missouri region in the central United States. Differences in air temperature across this gradient have increased by approximately 3 °C since 1920. Critical thermal maximum (CTMax) assays were conducted on individuals from fish populations across this gradient from either streams (C. anomalum) or ponds (L. macrochirus) to assess whether thermal tolerance is associated with water temperature among sites. According to expectations based on the effect of an urban heat island, maximum water temperature at stream sites was positively correlated with percent urban landcover around the sites. Moreover, CTMax among populations of C. anomalum was positively correlated with maximum water temperature at each site, suggesting that this species has likely responded to increases in temperature over the past several decades. There was no relationship between percent urban landcover and maximum water temperature in the pond systems. There was also no relationship between CTMax and maximum water temperature among L. macrochirus populations. The pond systems and populations of L. macrochirus are highly managed, which may limit local physical and biological responses to increases in air temperature. Results suggest that freshwater habitats in urban environments and the species inhabiting these areas are responding differently to recent increases in air temperature, highlighting the complexity of the physical and biological components of these systems.

Nestled in the city heat: urban nesting behavior enhances embryo development of an invasive lizard

Urbanization transforms many aspects of natural landscapes and poses many new challenges for individual survival and population persistence. Thus, urbanization provides an opportunity to examine how organisms deal with novel environmental change. Many studies provide evidence of phenotypic adaptation to urban environments, but few focus on responses during early life stages. Filling this information gap is important, because early life stages are particularly sensitive to abiotic factors, and no population is sustainable without successful embryo development. We tested the hypotheses that (i) embryos tolerate warmer temperature conditions of urbanized areas and (ii) maternal nesting behavior protects embryos from potentially lethal thermal conditions in urbanized habitats. We studied introduced populations of a subtropical lizard, Anolis cristatellus, in suburban and forested areas in Miami, Florida. In each habitat, we measured microenvironment variables for locations that females used for nesting vs. locations they did not use. We then incubated eggs from both populations under thermal conditions that mimicked used and unused sites. Nests in the suburban site were warmer than in the forest; however, in the suburban site, locations that females used were relatively cool compared with locations that were not used. We found no evidence that embryos are adapted to their respective suburban or forested thermal environments, but rather maternal nest-site choice enhanced embryo development in the suburban habitat. Maternal nesting behavior is likely an important factor for population persistence under major environmental changes, and a key contributor to the establishment and spread of invasive organisms across urbanized landscapes.

Metropolitan lizards? Urbanization gradient and the density of lagartixas (Tropidurus hispidus) in a tropical city

Urbanization, with its cohort of environmental stressors, has a dramatic effect on wildlife, causing loss of biodiversity and decline in population abundance customarily associated with increasing levels of impervious surface and fragmentation of native habitats. Some studies suggest that faunal species from open habitats, and with higher abundance in natural environments, seem more likely to tolerate and live in urban environments. Here I evaluate how the level of urbanization affects lagartixas (Tropidurus hispidus) one of the most common lizards found in open vegetation ecosystems in NE Brazil. I surveyed a total of 47 transects across sites that differed in proportion of impervious surface (high, mild, peri-urban, and rural). I also collected specific biotic (herbaceous cover, tree, and arthropod abundance) and abiotic (amount of shelters and impervious surfaces) factors that could affect lagartixas abundance. Ants were the most common arthropod both in the rural and urban environment. Lagartixas thrive in urban environments, and trees and shelter were key predictors of their abundance. Lagartixas show a clear association with use of artificial structures. The low densities of lagartixas in rural areas and higher density in urbanized areas suggest that they colonized urban areas due to the hard surfaces and they probably are not exploiting a novel habitat, but somewhat responding to conditions resembling those in which they evolved. Finally, lagartixas are extremely common in tropical cities, they have a suite of features that are associated with selective pressures in cities and they might play a key functional role in urban ecosystems making this lizard an excellent system for the study of ecology and adaptation to the urban environments.

Variation in tail morphology across urban and forest populations of the crested anole (Anolis cristatellus)

Anolis lizards are well known for their specialist ecomorphs characterized by the convergent evolution of suites of traits linked to the use of particular microhabitats. Many of these same traits evolve rapidly in response to novel selection pressures and have been very well studied. In contrast, the tail crest, a feature present in a subset of lineages, has been almost entirely overlooked. Variation in tail crest morphology within and among species remains largely unstudied, as does the function of the trait. Here, we use the natural experiment provided by urbanization to ask whether tail crest size differs between urban and forest populations of the crested anole (Anolis cristatellus) across the Caribbean island of Puerto Rico. We find that tail crest size differs primarily between regions; however, within regions, crests are invariably larger in urban than in forest environments. This difference in size is correlated with the hotter, drier conditions and sparser distribution of perches that typify urban sites, leading to the intriguing possibility that the tail crest might be under differential natural selection for signalling and/or because of the thermoregulatory challenge of urban habitats. Further study is required to shed light on the functional significance and evolution of this under-studied trait.

Ontogenetic scaling patterns of lizard skin surface structure as revealed by gel-based stereo-profilometry

The skin surface structure of squamate reptiles varies greatly among species, likely because it plays a key role in a range of tasks, such as camouflage, locomotion, self-cleaning, mitigation of water loss and protection from physical damage. Although we have foundational knowledge about squamate skin morphology, we still know remarkably little about how intraspecific variation in skin surface structure translates to functional variation. This gap in our understanding can be in part traced back to: (i) our lack of knowledge on how body size determines skin surface structure; and (ii) the lack of means to perform high-throughput and detailed analysis of the three-dimensional (3D) anatomy of reptilian skin surfaces in a non-destructive manner. To fill this gap, we explored the possibilities of a new imaging technique, termed gel-based stereo-profilometry, to visualize and quantify the 3D topography of reptilian skin surface structure. Using this novel approach, we investigated intra-specific and intra-individual variation in the skin surface morphology of a focal lizard species, Anolis cristatellus. We assessed how various characteristics of surface topography (roughness, skew and kurtosis) and scale morphology (area, height, width and shape) scale with body size across different body regions. Based on an ontogenetic series of A. cristatellus males, we show that skin roughness increases with body size. Skin patches on the ventral body region of lizards were rougher than on the dorsum, but this was a consequence of ventral scales being larger than dorsal scales. Dorsal surface skew and kurtosis varied with body size, but surfaces on the ventral skin showed no such relationship. Scale size scaled isometrically with body size, and while ventral scales differed in shape from dorsal scales, scale shape did not change with ontogeny. Overall, this study demonstrates that gel-based stereo-profilometry is a promising method to rapidly assess the 3D surface structure of reptilian skin at the microscopic level. Additionally, our findings of the explanatory power of body size on skin surface diversity provide a foundation for future studies to disentangle the relationships among morphological, functional and ecological diversity in squamate reptile skin surfaces.

Thermal tolerance in the urban heat island: thermal sensitivity varies ontogenetically and differs between embryos of two sympatric ectotherms

Most studies of thermal tolerance use adults, but early-life stages (e.g. embryos) are often more sensitive to thermal agitation. Studies that examine effects on embryos rarely assess the potential for thermal tolerance to change with ontogeny or how effects differ among sympatric species, and often utilize unrealistic temperature treatments. We used thermal fluctuations from nests within the urban-heat island to determine how thermal tolerance of embryos changes across development and differs among two sympatric lizard species (Anolis sagrei and A. cristatellus). We applied fluctuations that varied in frequency and magnitude at different times during development and measured effects on embryo physiology, egg survival, and hatchling morphology, growth, and survival. Thermal tolerance differed between the species by∼2 °C: embryos of A. sagrei, a lizard that prefers warmer, open-canopy microhabitats, were more robust to thermal stress than embryos of A. cristatellus, which prefers cooler, closed-canopy microhabitats. Moreover, thermal tolerance changed through development; however, the nature of this change differed between the species. For A. cristatellus, thermal tolerance was greatest mid-development. For A. sagrei the relationship was not statistically clear. The greatest effects of thermal stress were on embryo and hatchling survival and embryo physiology. Hatchling morphology and growth were less affected. Inter-specific responses and the timing of stochastic thermal events with respect to development have important effects on egg mortality. Thus, research that integrates ecologically-meaningful thermal treatments, considers multiple life-history stages, and examines interspecific responses will be critical to make robust predictions of the impacts of global change on wildlife.