Climate‐mediated adaptation after mainland colonization of an ancestrally subtropical island lizard, Anolis carolinensis

Abstract

Climate-mediated evolution plays an integral role in species migration and range expansion. Gaining a clearer understanding of how climate affects demographic history and adaptation provides fundamental insight into the generation of intra- and interspecific diversity. In this study, we used the natural colonization of the green anole (Anolis carolinensis) from the island of Cuba to mainland North America to investigate the role of evolution at the niche, phenotypic and genetic levels after long-term establishment in a novel environment. The North American green anole occupies a broader range of thermal habitats than its Cuban sister species. We documented niche expansion in the mainland green anole, mediated primarily through adaptation to winter temperatures. Common garden experiments strongly suggest a genetic component to differences in thermal performance found between populations in different temperature regimes. Analysis of geographic variation in population structure based on 53 486 single nucleotide variants from RAD loci revealed increased genetic isolation between populations in different vs. similar thermal environments. Selection scans for environment-allele correlations reveal 19 genomic loci of known function that may have played a role in the physiological adaptation of A. carolinensis to temperate environments on the mainland.

Physiological and regulatory underpinnings of geographic variation in reptilian cold tolerance across a latitudinal cline

“…There was no significant interaction between latitude and acclimation, suggesting that acclimatization responses do not differ among populations. The correlation between latitude of origin and cold tolerance observed in this study is congruent with other studies of wild populations of green anoles (Campbell‐Staton et al., ; Wilson & Echternacht, ). Given that cold tolerance is heritable in green anoles (Campbell‐Staton et al., ), the correlation between cold tolerance and environmental variables along a latitudinal cline supports a hypothesis of local adaptation via genotypic specialization in the green anole (Campbell‐Staton et al., ; Wilson & Echternacht, ).…”

“…Taken together, these data suggest that suppressed rates of oxygen consumption allow for the maintenance of function at cold temperatures via decreased oxygen demand. This further supports our hypothesis that local adaptation via genotypic specialization plays an important role in clinal variation of thermal physiology in this species (Campbell‐Staton et al., ). The physiological mechanisms that result in plastic increases in cold tolerance following cold acclimation are unclear, and warrant further study.…”

“…To assess the lower thermal limits of each lizard, we employed a common metric used to estimate thermal tolerance in ectotherms, critical thermal minimum [CT min , (Campbell‐Staton et al., ; Cowles & Bogert, )]. During CT min testing, internal body temperature ( T b ) was monitored continuously via a 20‐gauge digital thermocouple inserted approximately 5 mm inside the cloaca and secured with tape.…”

“…Green anoles ( Anolis carolinensis ) colonized the continental United States from Cuba during the Miocene–Pliocene (Campbell‐staton et al., ) and subsequently expanded their range northward to occupy the highest latitudes of any member of the neotropical genus (~400 species; Michaud & Echternacht, ). Winter temperatures are hypothesized to limit the northern edge of the species’ range (Williams, ), and cold tolerance of this species is highly correlated with winter temperature across its range (Campbell‐Staton, Edwards, & Losos, ; Wilson & Echternacht, ). However, the relative roles of seasonal acclimatization, genotypic specialization (constitutive genetically based differences) and evolution of plasticity in shaping geographic variation in thermal tolerance are not clear.…”

Are Historical Biogeographical Events Able to Promote Biological Diversification?

“…Finally, studies undoubtedly need to include detailed research from the field of the genetics of the adaptation to new environments [8,22]. These studies are useful to understand why some clades diversified extensively after a dispersal or vicariance events and others not.…”