Data from: Defining spatial and temporal patterns of phylogeographic structure in Madagascar's iguanid lizards (Genus Oplurus)

Understanding the remarkably high species diversity and levels of endemism found among Madagascar’s flora and fauna has been the focus of many studies. One hypothesis that has received much attention proposes that Pleistocene climate fluctuations spurred diversification. However, while spatial patterns of distribution and phylogenetic relationships can provide support for biogeographic predictions, temporal estimates of divergence are required to determine the fit of these geospatial patterns to climatic or biogeographic mechanisms. We use multilocus DNA sequence data to test whether divergence times among Malagasy iguanid lizards of the subfamily Oplurinae are compatible with a hypotheses of Quaternary diversification. We estimate the oplurine species tree and associated divergence times under a relaxed clock model. In addition, we examine the phylogeographic structure and population divergence times within two sister-species of Oplurus primarily distributed in the northwest and southwest of Madagascar (O. cuvieri and O. cyclurus, respectively). We find that divergence events among oplurine lineages occurred in the Oligocene and Miocene and are thus far older and incompatible with the hypothesis that recent climate fluctuations are related to current species diversity. However, the timing of intraspecific divergences and spatial patterns of population genetic structure within O. cuvieri and O. cyclurus suggest a role for both intrinsic barriers and recent climate fluctuations at population-level divergences. Integrating information across spatial and temporal scales allows us to identify and better understand the mechanisms generating patterns diversity.

探究马达加斯加动植物区系中极高的物种多样性与特有性（endemism）水平，一直是诸多研究的核心聚焦方向。其中一则受到广泛关注的假说提出，更新世（Pleistocene）气候波动推动了物种分化进程。然而，尽管物种分布的空间格局与系统发育关系（phylogenetic relationships）可为生物地理学预测（biogeographic predictions）提供佐证，但要验证这些地理空间格局是否适配气候或生物地理机制，仍需获取分化时间的时序估算（temporal estimates of divergence）数据。本研究采用多位点DNA序列数据（multilocus DNA sequence data），检验马达加斯加鬣蜥科盾尾蜥亚科（Oplurinae）蜥蜴的类群分化时间是否契合第四纪（Quaternary）物种分化假说。我们基于宽松分子钟模型（relaxed clock model）估算了盾尾蜥类的物种树及其伴随的分化时间。此外，我们还分析了两种盾尾蜥属（Oplurus）姊妹物种的系统地理学结构（phylogeographic structure）与种群分化时间：二者分别主要分布于马达加斯加西北部与西南部，即库氏盾尾蜥（O. cuvieri）与环尾盾尾蜥（O. cyclurus）。研究结果显示，盾尾蜥类各支系的分化事件发生于渐新世（Oligocene）与中新世（Miocene），其分化时间远早于第四纪，因此与"近期气候波动与当前物种多样性相关"的假说相悖。不过，库氏盾尾蜥与环尾盾尾蜥的种内分化（intraspecific divergences）时间以及种群遗传结构的空间格局表明，内在屏障（intrinsic barriers）与近期气候波动均在种群水平分化（population-level divergences）过程中发挥了作用。整合不同空间与时间尺度的信息，有助于我们识别并更深入地理解塑造物种多样性格局的内在机制。