Urosaurus Research Articles

Homing behavior of a tree lizard: influences of mating resource, and habitat structure

Homing behavior of a tree lizard: influences of mating resource, and habitat structure

Territorial status is explained by covariation between boldness, exploration, and thermal preference in a colour polymorphic lizard.

Colour polymorphic species often exhibit variation in morphology, physiology, and behaviour among morphs. In particular, dominance status may be signalled by the interaction between behaviour and colour morph. Behavioural traits associated with dominance include boldness, exploration, and aggression, which influence access to preferred habitat, territorial defence, and mate acquisition. In ectotherms, the social structure associated with morphs may result in the exploitation of structural niches differing in thermal quality. Hence, social interactions among morphs may generate concordant variation in thermal preference and environmental temperature. However, few studies have assessed thermal preference variation in colour polymorphic species and its covariation with behaviour. Doing so can provide insight into niche specialization and the maintenance of colour polymorphism in populations. Here, we investigated the patterns of covariation in boldness behaviour, exploratory behaviour, and thermal preference in the tree lizard, Urosaurus ornatus. We assessed trait variation between territorial and non-territorial male morphs and between orange and yellow female morphs. Boldness and exploratory behaviour were repeatable in male U. ornatus and bolder individuals were significantly more likely to incur tail loss, a potential consequence of bold behaviour. Territorial male morphs were significantly bolder and more exploratory and preferred higher body temperatures with a narrower T set than non-territorial morphs. Female morphs did not vary in behavioural or thermal traits. This study highlights behavioural mechanisms that underly ecological niche segregation and variable habitat use between morphs in a colour polymorphic species.

The Shape of Water: Physiological Adaptations to Habitat Aridity in the Ornate Tree Lizard (Urosaurus ornatus).

Deserts have always amazed researchers due to their high diversity of habitats, where plant and animal species have been able to adapt and diversify, even when these areas impose several constraints on an organism's activity patterns. In particular, deserts support several lizard species adapted to the thermal and water restrictions found in such biomes. Although several studies have attempted to understand how lizard species might respond to water deficits or droughts in deserts, few have addressed how these responses might vary along a latitudinal gradient. This raises the question of whether physiological buffering of the organism or the climatic environment affects water loss in lizards. Here, we used six populations of Urosaurus ornatus to test whether water loss is influenced more by the intrinsic physiology of the lizard or by the climatic niche. We found that water loss is primarily influenced by the climatic niche of the lizard. However, future studies should focus on how microclimatic variables can influence water loss in organisms found across large latitudinal gradients.

Behavioral plasticity during acute heat stress: heat hardening increases the expression of boldness

Climate change is creating novel thermal environments via rising temperatures and increased frequency of severe weather events. Short-term phenotypic adjustments, i.e., phenotypic plasticity, may facilitate species persistence during adverse environmental conditions. A plastic response that increases thermal tolerance is heat hardening, which buffers organisms from extreme heat and may enhance short term survival. However, heat hardening responses may incur a cost with concomitant decreases in thermal preference and physiological performance. Thus, phenotypic shifts accompanying a hardening response may be maladaptive in warming climates. Understanding how heat hardening influences other traits associated with fitness and survival will clarify its potential as an adaptive response to altered thermal niches. Here, we studied the effects of heat hardening on boldness behavior in the color polymorphic tree lizard, Urosaurus ornatus. Boldness in lizards influences traits such as territory maintenance, mating success, and survivorship and is repeatable in U. ornatus. We found that when lizards underwent a heat hardening response, boldness expression significantly increased. This trend was driven by males. Bolder individuals also exhibited lower field active body temperatures. This behavioral response to heat hardening may increase resource holding potential and territoriality in stressful environments but may also increase predation risk. This study highlights the need to detail associated phenotypic shifts with stress responses to fully understand their adaptive potential in rapidly changing environments.

Negative density‐regulated contest performance promotes conflict resolution in a tree lizard

Abstract Territoriality is a behavioural adaptation resulting from intraspecific competition and reflects the strategy of how individuals share limited resources in the environment. As a consequence, territorial contests and levels of aggressiveness are strongly influenced by population density. The positive relationship between population density and the intensity of intraspecific competition may appear straightforward. However, empirical evidence regarding this association remains inconclusive. This ambiguity may be attributed to studies that have predominantly focussed on specific fight‐associated traits while overlooking potential interactions between multiple phenotypic characteristics and population dynamics. To examine the effects of population density and other ecological factors on the variation in fight behaviour as well as fight‐associated morphology and performance. We conducted population surveys and behavioural experiments using the Swinhoe's tree lizard across eight populations. Our findings revealed that males from higher density populations tended to engage in less intense fights and exhibited a weaker resident advantage in fights, which coincided with our findings on lower rates of injuries, weaker bite forces and smaller body sizes (and vice versa). Male‐specific variation in fight behaviour, morphology and performance along a density gradient suggests different evolutionary equilibria in territoriality influenced by local costs and benefits. Our study supports the significant role of negative density dependence as a fundamental regulator of eco‐evolutionary dynamics. The observed phenotypic variation emphasizes the importance of ecological and social factors in shaping ontogenetic growth and life‐history strategies. Our findings provide a basis for future investigations into pace‐of‐life syndromes and shed light on how phenotypic adaptation may shape population structure. Read the free Plain Language Summary for this article on the Journal blog.

Habitat use and body temperature influence push-up display rate in the tree lizard, Urosaurus ornatus

Abstract Lizards engage in push-up displays to signal dominance and to secure access to important resources. The rate and patterns of push-up displays have been shown to vary based on both biotic and abiotic factors. We investigated push-up display rate in tree lizards, Urosaurus ornatus, to determine contributions from potentially conflicting factors including sex, throat colour, microhabitat usage, social context, and thermal traits. We found that display rate was best described by an interaction between microhabitat and body temperature (Tb). The relationship between display rate and Tb was significantly different between three microhabitats: sunny dead trees, the inner branches of trees, and tree trunks. We suggest that this variation in display rate is driven by shifts in microhabitat temperature over the course of the day and spatial and temporal adjustments being made depending on the probabilities of being detected by both conspecifics and predators.

Variation in Melanin Content of Lizard Livers: Hybrids Turning to the Dark Side

AbstractPigments such as melanin are most often associated with the surface of an organism, providing functions such as coloration and protection from UV radiation. However, the internal organs of some species also contain melanin. Internal melanin may also perform protective functions when cellular stress is experienced. We tested liver tissue of two tree lizard species that experienced introgression of their mitochondria to see whether melanin was present and whether it was at higher concentrations in the types of lizards thought to be under cellular stress. Previous work found that mitochondria from livers of hybrid tree lizards (those with introgressed mitochondrial DNA) had higher levels of ATP production at higher temperatures than both parental species and showed indications of dysfunction. Therefore, we predicted that if internal melanin functions to mediate the impact of damaging by-products of metabolism, such as excessive reactive oxygen species (ROS), melanin would be highest in livers of lizards with introgressed mitochondria. To test this, we used a melanin-specific stain on liver tissue sections and measured melanin concentration with spectrophotometry of heavy-membrane fractions from whole-liver homogenates of both parental species and their hybrids with introgressed mitochondria. Slides of liver sections treated with a melanin-specific stain revealed that hybrids contained melanin and had significantly higher levels of it than either parental species. Spectrophotometry gave the same result. This distribution of internal melanin matches the pattern expected if melanin functions as a compensatory mechanism to deal with higher ATP production and the subsequent high levels of ROS expected in these hybrid lizards. Future studies will examine this mechanistically.

Climate mediates color morph turnover in a species exhibiting alternative reproductive strategies

Sexual selection is considered the primary driver of morph turnover in many color polymorphic taxa, yet the potential for other factors (like climate) to contribute to polymorphism maintenance and evolution remains unclear. Appreciation for a role of environmental conditions in the maintenance and evolution of color polymorphisms has grown in recent years, generating evidence suggesting that color morphs linked to sexual selection may also diverge in climate sensitivity. Focusing on the three color components contributing to the male tree lizard (Urosaurus ornatus) color morphs, I reveal a marked concordance between patterns of turnover over space and time, with a general affinity of orange- and yellow-colored males to hotter, more variable conditions, and blue colored males to wetter, cooler conditions. An assessment of long-term turnover in the blue color component in response to recent climate change over the past 60 years reinforces these findings. Overall, behavioral asymmetries attributed to sexual selection likely expose competing morphs to divergent environmental conditions in heterogeneous habitats, creating opportunity for natural selection to shape climate sensitivities that also drive turnover in morph color composition. Ultimately, these processes may favor stark asymmetries in morph persistence over the coming decades.

Internal Melanin and Oxidative Stress: An Investigation of Lizard Livers

The habitats of two brush lizards that reside in Arizona, U. ornatus and U. graciosus, overlap and a hybrid species has arisen over time that has the nuclear DNA from one introgressed with the mitochondrial DNA from the other. Previous studies by Haenel and Del Gaizo Moore have shown that the mitochondria in these hybrid lizards are much more inefficient than those in the two parental species. It was observed that all three species of lizards have internal melanin in their livers, with the hybrids possessing much higher amounts. One hypothesis explaining the higher melanin content in the hybrid’s livers is that it helps protect their inefficient mitochondria from oxidative stress. In order to test this hypothesis, we sought to induce expression of melanin in liver cells using 1,2‐dimethyl‐3,3‐butanadiol (1,2DM‐3,3BD). Initially, human epithelial kidney (HEK) cells were treated with 12.5‐37.5 mM of 1,2DM‐3,3BD for 6 days and their capacity to resist oxidative stress was tested using a CellROX and cell viability flow cytometry assay. Melanin induction in HEK cells was small and therefore no protection was afforded against oxidative stress. Next, a protocol was developed to isolate primary liver cells from North Carolina tree lizards. Currently, different methods are being tested to maintain these primary cell cultures long enough to treat it with 1,2DM‐3,3BD to determine if melanin expression can be induced in the cells.

Application of Gamma-irradiation to Sterilize Nonnative Swinhoe’s Tree Lizards in Miyazaki Prefecture, Japan

Application of Gamma-irradiation to Sterilize Nonnative Swinhoe’s Tree Lizards in Miyazaki Prefecture, Japan

Lizards Are Important Hosts for Zoonotic Flavivirus Vectors, Subgenus Culex, in the Southern USA

Host association is among the most important factors that drive the transmission dynamics of mosquito-vectored pathogens. Competent vectors that feed exclusively upon non-competent hosts will not transmit pathogens, and highly competent hosts that are not bitten by competent vectors will not contribute to pathogen amplification. Therefore, characterizing the blood-feeding ecology of vector mosquitoes is critical to understanding how zoonotic pathogens amplify within ecosystems and spillover to humans and domesticated animals. In North America, mosquito species of the subgenus Culex are considered the most important vectors of zoonotic Flaviviruses, particularly West Nile virus (WNV), St. Louis encephalitis virus (SLEV), and western equine encephalitis virus. Many species of the Culex subgenus Culex are thought to feed predominantly upon birds and mammals, a behavior that facilitates the amplification and spillover of these zoonotic pathogens. Much of our understanding of the host associations of Culex vectors is based on research conducted in the 1960s and 1970s that used serological methods to infer host group(s). Here we reevaluate host associations of six Culex species from the southern US (Florida and Arizona) using DNA barcoding-based blood meal analysis. Our results demonstrate that reptiles, particularly lizards, constitute an important, and previously underappreciated, group of vertebrate hosts for several subgenus Culex mosquitoes. In Florida, >25% of Culex nigripalpus blood meals were derived from lizards (mainly Anolis spp.), and reptile host use generally increased from north to south with ~10%, ~25% and ~60% of Cx. nigripalpus blood meals derived from reptiles in northern, central, and southern Florida, respectively. In southern Arizona, lizards (mainly Sceloporus spp. and Urosaurus ornatus) constituted 40-45% of blood meals of Culex tarsalis, Culex thriambus, and Culex stigmatosoma. Other species of the subgenus Culex, including Culex quinquefasciatus, were not found to feed upon reptiles at the same sites, suggesting host association variation within Culex subgenus Culex. Whether or not lizards contribute to or dilute amplification of zoonotic Flaviviruses depends upon host competency of the lizard species bitten for WNV and SLEV. To date, very few studies have evaluated host competence of lizards for these viruses, so their roles in transmission cycles of zoonotic Flaviviruses remains obscure.

Feeding ecology of Swinhoe's tree lizard (Diploderma swinhonis (Günther, 1864)) in Hyuga City, Miyazaki Prefecture, Japan.

Swinhoe's tree lizard (Diploderma swinhonis: D. swinhonis) is an arboreal agamid that is native to Taiwan. In Taiwan, the lizard is considered to be a generalist that feeds primarily on ants and a diversity of small insect prey by employing an opportunistic sit-and-wait foraging strategy. In Japan, D. swinhonis is considered as an invasive alien species that was discovered in Hyuga city, Miyazaki Prefecture, in 2016. Despite concerns about the impact of D. swinhonis on native fauna, little information about the diet of this alien species has been published to date. This study, therefore, investigated the feeding ecology of D. swinhonis in Hyuga city to evaluate their potential impact on the ecosystem. Specifically, prey preference was investigated by examining the stomach contents of males, females, and juveniles captured from April to December 2020 and in March 2021. The results showed that the lizards in Hyuga preyed upon a wide variety of invertebrates as in Taiwan, while ants accounted for the largest proportion of the prey items consumed regardless of sex, age or changes in season. These findings indicated that D. swinhonis might cause a decrease in the abundance of the native insect fauna of Hyuga city or competition with native lizards for foods in Hyuga city. Since its impact is not currently apparent, it's necessary to monitor its effect in the future.

Species and prevalence of parasitic mites on tree geckos in Purwokerto, Central Java

Parasitic mite infections are very common on virtually all organisms including tree geckos. This research was aimed to determine the species and prevalence of parasitic mites infecting tree lizards in Purwokerto, Central Java. This research employed a survey method with a purposive random sampling technique. One hundred individuals of tree lizards were obtained from trees in 4 different sub-districts in Purwokerto. The results showed that from 3 species of tree geckos namely, Hemidactylus platyurus, H. frenatus and H. garnotii, only the last one was not infected by parasitic mites. The prevalence of parasitic mites in H. garnotii was 0%, while in H. frenatus and H. platyurus were 27% and 29%, respectively. The total prevalence of parasitic mites on tree geckos in Purwokerto, Central Java, was 28%. The results showed that there were 5 (five) species of parasitic mites belonging to the genus Geckobia, namely G. keegani, G. gleadovania, G. turkestana, G. simplex and G. diversipilis. The prevalence of G. gleadovania in H. frenatus geckos was 100%, while in H. platyurus geckos, the prevalence of infection by G. diversipilis was also 100%. The most infected body part was the trunk where the prevalence was 57%.

Flight initiation distance of Urosaurus ornatus from the Sierra de Samalayuca, Mexico

In lizards, flight initiation distance (FID), the distance between a prey individual and a predator when escape begins, can be affected by numerous intrinsic and extrinsic factors, including sex, temperature, and level of conspicuousness. Here we report on a study of FID in a population of Ornate Tree Lizards, Urosaurus ornatus, from the Sierra de Samalyuca, Chihuahua, Mexico which are cryptic due to their dorsal coloration blending into their background. Urosaurus ornatus in our study population allowed close approaches (mean FID = 65 cm). Mean FID did not differ between males and females. We also found no effect of body, air, or substrate temperature on FID. The short FID we observed may be related to the cryptic nature of U. ornatus.

Choleoeimeria spp. Prevalence in Captive Reptiles in Germany and a New Treatment Option in a Lawson's Dragon (Pogona henrylawsoni)

Coccidia are common endoparasites in reptiles, especially lizards. Within this class Choleoeimeria spp. infections are rarely detected, but they may have a high pathogenic potential and treatments are often unsuccessful. A retrospective study was performed evaluating the prevalence of Choleoeimeria in fecal samples from lizards submitted for routine examination to a diagnostic laboratory in Germany. Between 2013 and 2014, 1.5% (n = 24/1,621; 95% confidence interval [CI]: 1.0–2.2%) of coprological samples from different lizard species tested positive for Choleoeimeria oocysts using a fecal flotation technique. This prevalence was similar to data obtained 10 yr earlier at the same laboratory. Infected species included central bearded dragons (Pogona vitticeps), collared lizards (Crotaphytus collaris), unclassified agamids, monitors, one horned tree lizard (Acanthosaura sp.), one gecko, one common bluetongue (Tiliqua scincoides), and one chameleon. Different treatments (toltrazuril in varying intervals or trimethoprim and sulfonamide) in combination with strict environmental hygiene and disinfection with p-Chlor-m-Kresol did not impact fecal oocyst shedding for one juvenile Lawson's dragon (Pogona henrylawsoni). A new therapy approach using 10 mg/kg toltrazuril PO q 24 h for 3 days, with a repeat in 7 days, combined with 5 mg/kg clindamycin PO q 24 h for 7 days, finally resulted in negative oocyst shedding. Possible explanations for the challenging treatment of Choleoeimeria spp. are their localization in the gallbladder or the phylogenetical distance of the genus Choleoeimeria to the typical members of the family Eimeriidae. Further research is needed to increase our knowledge of these parasites and to develop an evidence-based treatment approach for diseased reptiles.

DIET OF EIGHT SPECIES OF LIZARDS FROM GRANITE GAP, HIDALGO COUNTY, NEW MEXICO

Abstract Granite Gap is a desert scrub habitat located in the Chihuahuan Desert in southwestern New Mexico about 200 km from the Texas border. In May 2016, we collected specimens of eight lizard species, six of which range into Texas: Callisaurus draconoides, Cophosaurus texanus, Uta stansburiana, Urosaurus ornatus, Gambelia wislizenii, and Aspidoscelis sonorae (a parthenogenetic species), plus two species not found in Texas: Sceloporus clarkii and Aspidoscelis tigris. We analyzed stomach contents of the preserved lizards and computed diet breadth and overlap for each. All lizard species consumed arthropods only. Considering the entire sample, there was a significant correlation between lizard snout-vent length (SVL) and total volume of arthropods consumed, and between lizard SVL and mean volume per prey item, but not between lizard SVL and number of arthropods consumed. This suggests larger lizards did not consume more arthropods than smaller lizards, but they did consume larger ones. Overall, A. sonorae was the most specialized lizard species at Granite Gap whereas C. texanus seemed to be the most generalized owing to its high numeric and high volumetric diet breadth. The dietary overlap data suggest there were two groups of lizards at Granite Gap: one that consumes a large number and volume of termites (Callisaurus, Cophosaurus, and the two species of Aspidoscelis) and the other that consumes a large number and volume of ants (Uta, Urosaurus, small Sceloporus) plus cicadas when lizard size is large enough to consume them (large Sceloporus and Gambelia).

Thermoregulation in a saxicolous population of the lizard Urosaurus ornatus from the northern Chihuahuan Desert, Mexico

Abstract Environmental temperatures often regulate the activity and physiological processes of ectotherms. Because environmental temperatures can vary significantly among seasons, lizards exposed to different thermal conditions in different months could differ in how they thermoregulate or behave. Here, we present a combination of field, laboratory, and modeling approaches to examine thermoregulation, habitat thermal quality, and hours of thermal restriction on activity in a saxicolous population of Urosaurus ornatus in two thermally contrasting months (June and October) in a micro-insular mountain system in the northern Chihuahuan Desert in Mexico. Both active and preferred body temperatures did not vary between months. In this population, U. ornatus is an active thermoregulator with highly accurate and efficient thermoregulation despite the thermal quality in both months. However, during the breeding season (June) activity is restricted (i.e., high number of hours of restriction) compared to the non-breeding season (October). Therefore, our results suggest that this saxicolous population of U. ornatus could be threatened by global climate change and it is essential to determine a conservation strategy for this population.

Niche Partitioning between Two Sympatric Lizards in the Chiricahua Mountains of Arizona

Competition for resources between sympatric species can result in reduced fitness. Resource partitioning allows the minimization of competitive pressures, consequently promoting the coexistence of a diversity of species. We tested the hypothesis that the Striped Plateau Lizard (Sceloporus virgatus) and the Ornate Tree Lizard (Urosaurus ornatus) that occur in sympatry in the Chiricahua mountains of Arizona, USA have distinct ecological niches to minimize interspecific competition. We compared the activity times, perch microhabitat characteristics, and diet of these insectivorous lizards to test the prediction that they partition resources. Although we found no difference between the two species in the time at which lizards become active in the morning nor in the composition of their diets, the two species used different structural perch microhabitats. The Ornate Tree Lizard selected higher and narrower perches with more closed canopy than the Striped Plateau Lizard, and males generally occupied higher perches than females. These differences in perch microhabitat use may reduce interspecific competition and allow these two sympatric species to cohabitate.

High tolerance of two parasites in ornate tree lizards reduces the fitness costs of parasitism

AbstractParasites are ubiquitous and are presumed to have strong negative effects on host fitness. Despite this expectation, many parasites have negligible effects on their hosts in nature. Two hypotheses can explain why this might occur. Hosts can evolve resistance to parasites where their immune system attacks parasites (resistance hypothesis). The resistance hypothesis predicts that parasite load will decrease through time because of immune activity and that parasites have fitness costs to hosts. Alternatively, hosts can evolve tolerance to parasites and invest little energy in repelling attacks (tolerance hypothesis). The tolerance hypothesis predicts that parasites have no fitness costs to hosts. We tested these hypotheses with mark‐recapture data from six populations of a lizard host (Urosaurus ornatus) and two common parasites (ectoparasitic Trombiculid mites and haemoparasitic Plasmodium). We found that parasite load was unrelated to lizard growth rates or survival. In addition, mite parasite load did not decrease through time. Thus, our data support the tolerance hypothesis. Ectoparasitic mites and haemoparasitic Plasmodium are therefore unlikely to be strong drivers of variation in Urosaurus ornatus population density at our study sites because of their negligible effects on host fitness. We encourage ecologists to measure carefully the effects of parasites on hosts, rather than assuming fitness costs of parasitism are present.

Insularity effects on the morphological space and sexual dimorphism of a tropical tree lizard in western Mexico

AbstractEcological interactions of lizards on islands tend to differ from those on the mainland, with a decrease in predation and interspecific competition and an increase in intraspecific competition. This may drive morphological divergences from their mainland counterparts, presenting gigantism and frequently sexual dimorphism. The aim of this study was to determine morphological divergence (i.e. head and limbs) and sexual dimorphism in the arboreal lizard Urosaurus bicarinatus on San Agustin Island off the Mexican Pacific Coast. We measured several morphological structures of U. bicarinatus on San Agustin Island, as well as on the adjacent mainland in the state of Jalisco, Mexico. Additionally, we measured individuals from the state of Michoacán and from a preserved collection with individuals from Michoacán and Guerrero. Our results indicated a divergence and an expansion of the morphological space of the island population compared with the mainland. The divergence was accompanied by dwarfism (reduction of the head and limbs with respect to body size) and a lack of sexual dimorphism in morphology and size. Our study contributes to understanding the effect of insularity on lizards’ populations and enriches the knowledge concerning phrynosomatids such as U. bicarinatus.