Effects of microhabitat features on the intraspecific variability of the distribution and functional traits in a highest elevational distributed lizard

Exploring the microhabitat determinants of organisms distribution and functional traits differences can help us better understand the importance of intraspecific variations in ecological niches. Investigations on animals functional niche primarily focused on differences among species and tended to neglect the potential variability within species, despite the fact that the ecological and evolutionary importance of intraspecific variations was widely recognized. In this study, we examined the influence of microhabitat features on the intraspecific variability of the distribution and functional traits of a highest elevational distributed lizard species Phrynocephalus erythrurus. To do so, field work was conducted between July and August, 2020 and August and September, 2021 in Namtso watershed in central Xizang, China. Specifically, 11 transects were sampled for P. erythrurus individuals, which were measured for a set of 10 morphological traits. Moreover, 11 microhabitat variables that potentially affect the distribution of lizards were also measured for each transect. Our results indicated that juveniles, males, and females exhibited different functional traits, allowing them to occupy distinct functional space. The distribution of juveniles, males, and females was determined by different microhabitat variables such as illuminance and air temperature. More importantly, these variables also determined the intraspecific functional traits variability in this lizard species. All of these results supported previous claims that intraspecific traits variation should be incorporated into functional ecological studies, and diverse microhabitat features should be conserved to maintain high intraspecific diversity. Future studies can focus on the food analysis to explore the linkage between functional traits and resources utilization within animal populations.

Female lizards (Eremias argus) reverse Bergmann's rule across altitude

The evolution of body size within and among species is predicted to be influenced by multifarious environmental factors. However, the specific drivers of body size variation have remained difficult to understand because of the wide range of proximate factors that covary with ectotherm body sizes across populations with varying local environmental conditions. Here, we used female Eremias argus lizards collected from different populations across their wide range in China, and constructed linear mixed models to assess how climatic conditions and/or available resources at different altitudes shape the geographical patterns of lizard body size across altitude. Lizard populations showed significant differences in body size across altitudes. Furthermore, we found that climatic and seasonal changes along the altitudinal gradient also explained variations in body size among populations. Specifically, body size decreased with colder and drier environmental conditions at high altitudes, reversing Bergmann's rule. Limited resources at high altitudes, measured by the low vegetative index, may also constrain body size. Therefore, our study demonstrates that multifarious environmental factors could strongly influence the intraspecific variation in organisms' body size.

Intra-specific variation of thermal performance, skin reflectance and body size partially co-vary with climate in a lizard

Thermal adaptation theory posits that variation of thermal traits such as those affecting thermal budgets and the performance of ectotherms should be associated with climate gradients. Under a simple scenario, thermal traits should also co-vary to shape optimal thermal phenotypes under a particular climate. However, geographical variation and covariation of thermal traits can result from other sources of selection and a wide range of other mechanisms. Here, we explore variation and covariation of skin reflectance (melanization), body size and thermal performance traits among three populations of the lizard Cordylus cordylus, a species endemic to South Africa. We also examine relationships between skin reflectance and substrate reflectance, body size and crevice size to test alternative hypotheses. We found partial support for predictions of thermal adaptation to climate regimes for body size, melanization and chill-coma recovery time. Darker lizards also performed optimally at higher temperatures than lighter coloured lizards but there was limited individual covariation between morphological and performance traits. Despite partial support for thermal adaptation, the complex interactions between sex and body size and between substrate reflectance and size underlying skin reflectance emphasized the importance of testing multiple hypotheses when exploring drivers of thermal trait variation within species.

Evidence for ephemeral ring species formation during the diversification history of western fence lizards (Sceloporus occidentalis)

Divergence is often ephemeral, and populations that diverge in response to regional topographic and climatic factors may not remain reproductively isolated when they come into secondary contact. We investigated the geographical structure and evolutionary history of population divergence within Sceloporus occidentalis (western fence lizard), a habitat generalist with a broad distribution that spans the major biogeographical regions of Western North America. We used double digest RAD sequencing to infer population structure, phylogeny and demography. Population genetic structure is hierarchical and geographically structured with evidence for gene flow between biogeographical regions. Consistent with the isolation-expansion model of divergence during Quaternary glacial-interglacial cycles, gene flow and secondary contact are supported as important processes explaining the demographic histories of populations. Although populations may have diverged as they spread northward in a ring-like manner around the Sierra Nevada and southern Cascade Ranges, there is strong evidence for gene flow among populations at the northern terminus of the ring. We propose the concept of an "ephemeral ring species" and contrast S. occidentalis with the classic North American ring species, Ensatina eschscholtzii. Contrary to expectations of lower genetic diversity at northern latitudes following post-Quaternary-glaciation expansion, the ephemeral nature of divergence in S. occidentalis has produced centres of high genetic diversity for different reasons in the south (long-term stability) vs. the north (secondary contact).

Morphological evolution in relationship to sidewinding, arboreality and precipitation in snakes of the family Viperidae

Compared with other squamates, snakes have received relatively little ecomorphological investigation. We examined morphometric and meristic characters of vipers, in which both sidewinding locomotion and arboreality have evolved multiple times. We used phylogenetic comparative methods that account for intraspecific variation (measurement error models) to determine how morphology varied in relationship to body size, sidewinding, arboreality and mean annual precipitation (which we chose over other climate variables through model comparison). Some traits scaled isometrically; however, head dimensions were negatively allometric. Although we expected sidewinding specialists to have different body proportions and more vertebrae than non-sidewinding species, they did not differ significantly for any trait after correction for multiple comparisons. This result suggests that the mechanisms enabling sidewinding involve musculoskeletal morphology and/or motor control, that viper morphology is inherently conducive to sidewinding (‘pre-adapted’) or that behaviour has evolved faster than morphology. With body size as a covariate, arboreal vipers had long tails, narrow bodies and lateral compression, consistent with previous findings for other arboreal snakes, plus reduced posterior body tapering. Species from wetter environments tended to have longer tails, wider heads and reduced anterior tapering. This study adds to the growing evidence that, despite superficial simplicity, snakes have evolved various morphological specializations in relationship to behaviour and ecology.