Data from: Geographic variation in hybridisation and ecological differentiation between three syntopic, morphologically similar species of montane lizards

To understand factors shaping species boundaries in closely related taxa, a powerful approach is to compare levels of genetic admixture at multiple points of contact, and determine how this relates to intrinsic and extrinsic factors, such as genetic, morphological and ecological differentiation. In the Australian Alps, the threatened alpine bog skink Pseudemoia cryodroma co-occurs with two morphologically and ecologically similar congeners, P. entrecasteauxii and P. pagenstecheri, and all three species are suspected to hybridise. We predicted that the frequency of hybridisation should be negatively correlated with genetic divergence, morphological differentiation, and microhabitat separation. We tested this hypothesis using a mitochondrial locus, 13 microsatellite loci, morphological and microhabitat data, and compared results across three geographically isolated sites. Despite strong genetic structure between species, we detected hybridisation between all species pairs, including evidence of backcrossed individuals at the two sites where all three species are syntopic. Hybridisation frequencies were not consistently associated with genetic, morphological or ecological differentiation. Furthermore, P. entrecasteauxii and P. pagenstecheri only hybridised at the two sites where they are syntopic with P. cryodroma, but not at the largest site where P. cryodroma was not recorded, suggesting that P. cryodroma may serve as a bridging species. This study reveals the complex dynamics within a three species hybrid zone and provides a baseline for assessing the impact of climate change and anthropogenic habitat modification on future hybridisation frequencies.

为解析近缘类群物种边界的塑造机制，一种强有力的研究方法是比较多个接触区域的遗传混杂（genetic admixture）水平，并明确其与遗传、形态、生态分化等内在与外在因素的关联。在澳大利亚阿尔卑斯山，受威胁的高山泥炭石龙子Pseudemoia cryodroma与两个形态、生态特征相似的同属物种P. entrecasteauxii和P. pagenstecheri同域分布，且推测三者均可发生杂交。我们提出预测：杂交频率应与遗传分化、形态分化及微生境分离程度呈负相关。本研究采用1个线粒体基因座（mitochondrial locus）、13个微卫星位点（microsatellite loci）的遗传标记，结合形态与微生境数据对该假说进行了检验，并对比了3个地理隔离样点的研究结果。尽管物种间存在强烈的遗传结构，但我们仍检测到所有物种类群对之间均可发生杂交，且在三者同域分布的2个样点中发现了回交个体（backcrossed individuals）的证据。杂交频率并未与遗传、形态或生态分化呈现稳定的关联。此外，P. entrecasteauxii与P. pagenstecheri仅在与P. cryodroma同域分布的2个样点中发生杂交，而在未记录到P. cryodroma的最大样点中未检测到杂交，这表明P. cryodroma可能充当了桥梁物种（bridging species）。本研究揭示了三物种杂交带内的复杂动态过程，并为评估气候变化与人为生境改造对未来杂交频率的影响提供了基准参照。