Phylogeographic and phenotypic outcomes of brown anole colonization across the Caribbean provide insight into the beginning stages of an adaptive radiation

Some of the most important insights into the ecological and evolutionary
processes of diversification and speciation have come from studies of
island adaptive radiations, yet relatively little research has examined
how these radiations initiate. We suggest that Anolis sagrei is a
candidate for understanding the origins of the Caribbean Anolis adaptive
radiation and how a colonizing anole species begins to undergo
allopatric diversification, phenotypic divergence and, potentially,
speciation. We undertook a genomic and morphological analysis of
representative populations across the entire native range of
A. sagrei, finding that the species originated in the early
Pliocene, with the deepest divergence occurring between western and
eastern Cuba. Lineages from these two regions subsequently colonized the
northern Caribbean. We find that at the broadest scale, populations
colonizing areas with fewer closely related competitors tend to evolve
larger body size and more lamellae on their toepads. This trend follows
expectations for post‐colonization divergence from progenitors and
convergence in allopatry, whereby populations freed from competition with
close relatives evolve towards common morphological and ecological optima.
Taken together, our results show a complex history of ancient and recent
Cuban diaspora with populations on competitor‐poor islands evolving away
from their ancestral Cuban populations regardless of their phylogenetic
relationships, thus providing insight into the original diversification of
colonist anoles at the beginning of the radiation. Our research also
supplies an evolutionary framework for the many studies of this
increasingly important species in ecological and evolutionary research.

关于物种分化与物种形成的生态及演化过程，学界诸多关键认知均源自岛屿适应辐射（adaptive radiation）相关研究，但针对此类辐射如何起始的探究却相对匮乏。我们认为，棕安乐蜥（Anolis sagrei）可作为理想研究对象，用以解析加勒比安乐蜥适应辐射的起源，以及拓殖性安乐蜥物种如何启动异域分化、表型分歧乃至潜在的物种形成过程。我们针对棕安乐蜥整个原生分布范围内的代表性种群开展了基因组与形态学分析，结果显示该物种起源于上新世早期，最深的遗传分化发生在古巴西部与东部种群之间；这两个区域的支系随后拓殖了加勒比海北部地区。研究发现，从宏观尺度来看，定居于近亲竞争者较少区域的种群，往往会演化出更大的体型以及更多的趾垫鳞瓣（lamellae）。该趋势契合以下演化预期：拓殖后的种群会与祖先种群产生分化，且在异域环境中发生趋同演化——即脱离近亲竞争的种群，会朝着共同的形态与生态最优表型方向演化。综合来看，本研究结果揭示了古巴种群古代与近代扩散的复杂历史：无论系统发育关系如何，竞争者匮乏的岛屿上的种群均会与其祖先古巴种群产生分化，这为理解适应辐射起始阶段拓殖性安乐蜥的初始分化过程提供了重要视角。此外，本研究还为这一在生态与演化研究中愈发重要的物种的众多相关研究，提供了一套系统的演化框架。