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（Hydrophiinae，海蛇亚科）是一类经历了近期辐射演化的类群，包含至少62个物种，展现出显著的形态多样性与极高的局地同域分布（sympatry）水平。为阐明海蛇物种分化的内在机制，本研究针对东南亚与澳大利亚分布区重叠的4个指名物种构成的演化支，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，本研究鉴定出两类截然不同的生态型（ecomorph）：其一为“大头型”生态型，体长可超过2米，头部宽大，以穴居鳗类与虾虎鱼为食；其二为“小头型”生态型，体长罕有超过1米者，头部小巧且躯体前部狭窄，以洞穴中的蛇鳗为捕食对象。线粒体序列分析显示，不同生态型之间以及各推定物种之间均未形成互惠单系群。但基于新开发的微卫星标记（microsatellites）进行的个体分型分析，将同分布的标本划分为4个与形态学物种定名相符的显著分化聚类簇，表明近期基因流有限且物种形成进程正在推进。基于线粒体与核序列构建的溯祖物种树（coalescent species tree），以及基于线粒体和微卫星标记的隔离迁移模型（isolation-migration model）均表明，在距今约120万年至84万年间，生态型之间共发生了1至3次演化转变。尤为值得注意的是，青环海蛇（Hydrophis cyanocinctus）的大头型“东部”种群与小头型黑头海蛇（Hydrophis melanocephalus）似乎发生了极为近期且快速的分化，造就了显著的表型差异，并在同域分布区限制了基因交流。本研究结果凸显出胎生海蛇是开展海洋环境物种形成研究的极具潜力的实验体系。