Data from: Reduced genetic diversity and increased reproductive isolation follow population-level loss of larval dispersal in a marine gastropod

Population-level consequences of dispersal ability remain poorly understood, especially for marine animals in which dispersal is typically considered a species-level trait governed by oceanographic transport of microscopic larvae. Transitions from dispersive (planktotrophic) to non-dispersive, aplanktonic larvae are predicted to reduce connectivity, genetic diversity within populations, and the spatial scale at which reproductive isolation evolves. However, larval dimorphism within a species is rare, precluding population-level tests. We show the sea slug Costasiella ocellifera expresses both larval morphs in Florida and the Caribbean, regions with divergent mitochondrial lineages. Planktotrophy predominated at 11 sites, 10 of which formed a highly connected and genetically diverse Caribbean metapopulation. Four populations expressed mainly aplanktonic development and had markedly reduced connectivity, and lower genetic diversity at one mitochondrial and six nuclear loci. Aplanktonic dams showed partial post-zygotic isolation in most inter-population crosses, regardless of genetic or geographic distance to the sire's source, suggesting outbreeding depression affects fragmented populations. Dams from genetically isolated and neighboring populations also exhibited pre-mating isolation, consistent with reinforcement contingent on historical interaction. By increasing self-recruitment and genetic drift, the loss of dispersal may thus initiate a feedback loop resulting in the evolution of reproductive isolation over small spatial scales in the sea.扩散能力的种群级效应迄今仍未得到充分解析，尤其针对海洋动物而言——这类生物的扩散通常被视作由海洋环流驱动微小幼虫扩散的物种类群固有特征。从扩散型（浮游营养型）幼虫向非扩散型非浮游幼虫的转变，据推测会降低种群间连通性、种群内遗传多样性，以及生殖隔离演化的空间尺度。不过，同一物种内的幼虫二态性极为罕见，这使得种群水平的实证检验难以开展。本研究证实，眼斑海蛞蝓（Costasiella ocellifera）在佛罗里达与加勒比海区域均存在两种幼虫形态，且这两个区域存在分化的线粒体谱系。11个采样点以浮游营养型幼虫占主导，其中10个采样点构成了连通性极强、遗传多样性丰富的加勒比海集合种群。剩余4个种群主要表现为非浮游型发育，其种群连通性显著下降，且在1个线粒体位点与6个核基因位点上的遗传多样性更低。无论与父本来源地的遗传距离或地理距离如何，非浮游型个体在多数跨种群杂交中均呈现出部分合子后生殖隔离的表型，这表明远交衰退会对碎片化种群造成影响。来自遗传隔离种群与邻近种群的非浮游型个体还表现出交配前生殖隔离，这与依赖历史交互作用的生殖强化机制相符。综上，通过提升种群自我补充率与遗传漂变效应，扩散能力的丧失可能会启动一个反馈循环，进而推动海洋环境中极小空间尺度下生殖隔离的演化。