Living on the edge: Lower thermal quality but greater survival probability at a high altitude mountain for the mesquite lizard (Sceloporus grammicus)

Viviparity imparts a macroevolutionary signature of ecological opportunity in the body size of female Liolaemus lizards

Viviparity evolved ~115 times across squamate reptiles, facilitating the colonization of cold habitats, where oviparous species are scarce or absent. Whether the ecological opportunity furnished by such colonization reconfigures phenotypic diversity and accelerates evolution is unclear. We investigated the association between viviparity and patterns and rates of body size evolution in female Liolaemus lizards, the most species-rich tetrapod genus from temperate regions. Here, we discover that viviparous species evolve ~20% larger optimal body sizes than their oviparous relatives, but exhibit similar rates of body size evolution. Through a causal modeling approach, we find that viviparity indirectly influences body size evolution through shifts in thermal environment. Accordingly, the colonization of cold habitats favors larger body sizes in viviparous species, reconfiguring body size diversity in Liolaemus. The catalyzing influence of viviparity on phenotypic evolution arises because it unlocks access to otherwise inaccessible sources of ecological opportunity, an outcome potentially repeated across the tree of life.

DNA metabarcoding reveals seasonal changes in diet composition across four arthropod-eating lizard species (Phrynosomatidae: Sceloporus)

Diet composition and its ecological drivers are rarely investigated in coexisting closely related species. We used a molecular approach to characterize the seasonal variation in diet composition in four spiny lizard species inhabiting a mountainous ecosystem. DNA metabarcoding revealed that the lizards Sceloporus aeneus, S. bicanthalis, S. grammicus, and S. spinosus mostly consumed arthropods of the orders Hemiptera, Araneae, Hymenoptera, and Coleoptera. The terrestrial lizards S. aeneus and S. bicanthalis mostly predated ants and spiders, whereas the arboreal-saxicolous S. grammicus and saxicolous S. spinosus largely consumed grasshoppers and leafhoppers. The taxonomic and phylogenetic diversity of the prey was higher during the dry season than the rainy season, likely because reduced prey availability in the dry season forced lizards to diversify their diets to meet their nutritional demands. Dietary and phylogenetic composition varied seasonally depending on the species, but only dietary composition varied with altitude. Seasonal dietary turnover was greater in S. spinosus than in S. bicanthalis, suggesting site-specific seasonal variability in prey availability; no other differences among species were observed. S. bicanthalis, which lives at the highest altitude in our study site, displayed interseasonal variation in diet breadth. Dietary differences were correlated with the species' feeding strategies and elevational distribution, which likely contributed to the coexistence of these lizard species in the studied geographic area and beyond.

Maternal transmission of bacterial microbiota during embryonic development in a viviparous lizard

IMPORTANCE

We investigated the presence and diversity of bacteria in the embryos of the viviparous lizard Sceloporus grammicus and their amniotic environment. We compared this diversity to that found in the maternal intestine, mouth, and cloaca. We detected bacterial DNA in the embryos, albeit with a lower bacterial species diversity than found in maternal tissues. Most of the bacterial species detected in the embryos were also found in the mother, although not all of them. Interestingly, we detected a high similarity in the composition of bacterial species among embryos from different mothers. These findings suggest that there may be a mechanism controlling the transmission of bacteria from the mother to the embryo. Our results highlight the possibility that the interaction between maternal bacteria and the embryo may affect the development of the lizards.

Is Habitat More Important than Phylogenetic Relatedness for Elucidating the Gut Bacterial Composition in Sister Lizard Species?

The gut microbiota influences the phenotype and fitness of a host; however, limited information is currently available on the diversity and functions of the gut microbiota in wild animals. Therefore, we herein examined the diversity, composition, and potential functions of the gut microbiota in three Sceloporus lizards: Sceloporus aeneus, S. bicanthalis, and S. grammicus, inhabiting different habitats in a mountainous ecosystem. The gut bacterial community of S. bicanthalis from alpine grasslands at 4,150‍ ‍m a.s.l. exhibited greater taxonomic, phylogenetic, and functional alpha diversities than its sister species S. aeneus from cornfields and human-induced grasslands at 2,600‍ ‍m‍ ‍a.s.l. Bacteria of the genus Blautia and metabolic functions related to the degradation of aromatic compounds were more abundant in S. bicanthalis than in S. aeneus, whereas Oscillibacter and predicted functions related to amino acid metabolism and fermentation were more abundant in S. aeneus. The structure of the dominant and most prevalent bacteria, i.e., the core microbiota, was similar between the sister species from different habitats, but differed between S. grammicus and S. aeneus cohabiting at 2,600‍ ‍m‍ ‍a.s.l. and between S. grammicus and S. bicanthalis cohabiting at 4,150‍ ‍m a.s.l. These results suggest that phylogenetic relatedness defines the core microbiota, while the transient, i.e., non-core, microbiota is influenced by environmental differences in the habitats. Our comparisons between phylogenetically close species provide further evidence for the specialized and complex associations between hosts and the gut microbiota as well as insights into the roles of phylogeny and ecological factors as drivers of the gut microbiota in wild vertebrates.

Exceptional parallelisms characterize the evolutionary transition to live birth in phrynosomatid lizards

Viviparity, an innovation enhancing maternal control over developing embryos, has evolved >150 times in vertebrates, and has been proposed as an adaptation to inhabit cold habitats. Yet, the behavioral, physiological, morphological, and life history features associated with live-bearing remain unclear. Here, we capitalize on repeated origins of viviparity in phrynosomatid lizards to tease apart the phenotypic patterns associated with this innovation. Using data from 125 species and phylogenetic approaches, we find that viviparous phrynosomatids repeatedly evolved a more cool-adjusted thermal physiology than their oviparous relatives. Through precise thermoregulatory behavior viviparous phrynosomatids are cool-adjusted even in warm environments, and oviparous phrynosomatids warm-adjusted even in cool environments. Convergent behavioral shifts in viviparous species reduce energetic demand during activity, which may help offset the costs of protracted gestation. Whereas dam and offspring body size are similar among both parity modes, annual fecundity repeatedly decreases in viviparous lineages. Thus, viviparity is associated with a lower energetic allocation into production. Together, our results indicate that oviparity and viviparity are on opposing ends of the fast-slow life history continuum in both warm and cool environments. In this sense, the ‘cold climate hypothesis’ fits into a broader range of energetic/life history trade-offs that influence transitions to viviparity.

There have been five independent transitions from egg laying to live birth in the phrynosomatid lizards. Here, Domínguez-Guerrero et al. identify parallel changes in physiology, life history and behaviour that characterize these transitions to live birth.

Post-exercise Hypothermia Varies Between High- and Low-Altitude Populations in the Asiatic Toad (Bufo gargarizans)

Whether and how poikilothermic animals change their thermal performance to cope with global warming are crucial questions to predict the future of biodiversity. Intraspecific comparison among populations that occur in different climatic zones can provide insight into how poikilotherms may alter their thermal performance under a particular climatic event. We compared populations of the Asiatic toad (Bufo gargarizans) from two altitudinal zones (3239 and 926 m above sea level) to explore variations of post-exercise hypothermia, which can lead to lower temperature preference than normal conditions. Common garden experiment was also employed to test plasticity of hypothermic performance in adult toads. As results, exhaustive exercise induced measurable reduction in body temperature for both populations. Furthermore, high-altitude population experienced larger reduction in body temperature than low-altitude conspecifics in both original habitat and common garden conditions. Therefore, low-altitude toads may to enhance their hypothermic reaction if they shift their ranges to higher altitudes to survive warming climate; However, the relatively limited plasticity of hypothermic performance may constraint their adaptative process.

Season-sex interaction induces changes in the ecophysiological traits of a lizard in a high altitude cold desert, Puna region

Functional traits are those characteristics of organisms that influence the ability of a species to develop in a habitat and persist in the face of environmental changes. The traits are often affected by a multiplicity of species-dependent and external factors. Our objective was to investigate thermal biology of Liolaemus ruibali in a high altitude cold desert at the arid Puna region, Argentina. We address the following question: do sex and seasonal variations in environmental temperature induce changes in the ecophysiological traits? We measured and compared the operative temperatures between fall and spring; and between sexes and seasons, we compared the ecophysiological traits of lizards, microenvironmental temperatures and thermoregulatory behavior. Air and operative temperatures were different between seasons. We found an effect of season-sex interaction on field body temperatures, preferred temperatures, panting threshold and thermal quality. The voluntary and critical temperatures presented seasonal variation in relation to changes in environmental temperatures, suggesting thermal acclimatization. We note behavioral changes between seasons, with the substrate being the main resource for gaining heat in spring. We conclude that Liolaemus ruibali is an efficient thermoregulator; it is a eurythermic lizard and presents phenotypic plasticity in different ecophysiological and behavioral traits induced by sex and seasonality. In addition, we predict that this population could buffer the effects of projected global warming scenarios.

Fast and dark: The case of Mezquite lizards at extreme altitude

Sprint speed is a major performance trait in animal fitness involved in escaping from predators, obtaining food, and defending territory. Biotic and abiotic factors may influence sprint speed in lizards. Temperature decreases at higher altitude. Therefore, lizards at high elevations may require longer basking times to reach optimal body temperatures, increasing their vulnerability to predation and decreasing their time for other activities such as foraging or reproduction. Here, we tested whether the maximum sprint speed of a lizard that shows conservative thermal ecology varied along an altitudinal gradient comprising low (2500 m), middle (3400 m) and high-altitude (4300 m) populations. We also tested whether sprint speed was related to dorsal reflectance at different ecologically relevant temperatures. Given that the lizard Sceloporus grammicus shows conservative thermal ecology with altitude, we expected that overall average sprint speed would not vary with altitude. However, given that darker lizards heat up quicker, we expected that darker lizards would be faster than lighter lizards. Our results suggest that S. grammicus at high altitude are faster and darker at 30 °C, while lizards from low and middle altitude are faster and lighter in color at 20 °C than high altitude lizards. Also, our results suggest a positive relationship between sprint speed and dorsal skin reflectance at 10 and 20 °C. Sprint speed was also affected by snout-vent length, leg length, and leg thickness at 10 °C. These results suggest that, even though predation pressure is lower at extreme altitudes, other factors such as vegetation cover or foraging mode have influenced sprint speed.