Data from: Recent rapid speciation and ecomorph divergence in Indo-Australian sea snakes

The viviparous sea snakes (Hydrophiinae) are a young radiation of at least 62 species that display spectacular morphological diversity and high levels of local sympatry. To shed light on the mechanisms underlying sea snake diversification, we investigated recent speciation and eco-morphological differentiation in a clade of four nominal species with overlapping ranges in Southeast Asia and Australia. Analyses of morphology and stomach contents identified the presence of two distinct ecomorphs: a ‘macrocephalic’ ecomorph that reaches >2 m in length, has a large head and feeds on crevice-dwelling eels and gobies; and a ‘microcephalic’ ecomorph that rarely exceeds 1 m in length, has a small head and narrow fore-body and hunts snake eels in burrows. Mitochondrial sequences show a lack of reciprocal monophyly between ecomorphs and among putative species. However, individual assignment based on newly developed microsatellites separated co-distributed specimens into four significantly differentiated clusters corresponding to morphological species designations, indicating limited recent gene flow and progress towards speciation. A coalescent species tree (based on mitochondrial and nuclear sequences) and isolation-migration model (mitochondrial and microsatellite markers) suggest between one and three transitions between ecomorphs within the last approximately 1.2 million to approximately 840 000 years. In particular, the macrocephalic ‘eastern’ population of Hydrophis cyanocinctus and microcephalic H. melanocephalus appear to have diverged very recently and rapidly, resulting in major phenotypic differences and restriction of gene flow in sympatry. These results highlight the viviparous sea snakes as a promising system for speciation studies in the marine environment.

胎生海蛇（海蛇亚科Hydrophiinae）是一类处于较晚近演化辐射的类群，目前已知至少包含62个物种，展现出显著的形态多样性与极高的局部同域分布频率。为阐明海蛇物种分化的潜在机制，我们对东南亚与澳大利亚分布范围重叠的4个名义物种组成的演化支开展了近期物种形成与生态形态分化相关研究。通过形态学与胃容物分析，我们发现该类群存在两种截然不同的生态型：一种为"大头型"生态型，体长可超过2米，头部宽大，以穴居鳗类和虾虎鱼为食；另一种为"小头型"生态型，体长罕有超过1米者，头部小巧且躯干前部狭窄，于洞穴中捕猎蛇鳗。线粒体序列分析显示，不同生态型之间以及候选物种之间均未形成互为单系的类群。不过基于新开发的微卫星标记（microsatellites）开展的个体分型结果，将同域分布的样本划分为4个分化显著的类群，与形态学物种界定结果相符，表明近期基因流有限且物种形成进程正在推进。基于线粒体与核基因序列构建的溯祖物种树，以及基于线粒体序列与微卫星标记构建的隔离迁移模型结果均显示，在距今约120万年至84万年的时间范围内，该类群的生态型之间共发生了1至3次演化转换。其中，青环海蛇（Hydrophis cyanocinctus）的大头"东部种群"与黑头海蛇（Hydrophis melanocephalus）的分化时间极近且分化速率极快，造就了显著的表型差异，并在同域分布区域限制了基因交流。上述研究结果表明，胎生海蛇是开展海洋环境物种形成研究的极具潜力的研究体系。