DISSERTATION RESEARCH: Is mitochondrial DNA lying about its age? Assessing diversification history in a species complex of sea cucumbers (Echinodermata: Holothuroidea)

鉴于物种主要在地理隔离中分化，当地多样性的动态取决于这些物种共存（次级同域）所需的时间。基于线粒体DNA和形态学证据，一些棘皮动物似乎能够比其他海洋无脊椎动物群体更快地实现次级同域性。拟议的研究旨在调查这些模式是否可能是由渐渗杂交掩盖早期的分歧，或反映高水平的种内多态性掩盖了类似的二级同域性。梳理除了这些假设，隔离与迁移（IM）模型的参数将估计从一个复杂的海参四个推定的，最近分歧，物种组成的多位点数据集。此外，计算机模拟将被用来确定是否有一些位点的历史偏离这个模型，暗示渐渗杂交，结果将有助于我们了解物种的限制，在具有挑战性的群体，在最丰富的海洋地理区域的多样化。他们还将产生关于产生这种多样性的机制的假设。特别是，基因流和人口规模的估计将导致预测这些人口参数在物种形成中的作用。此外，这些估计数将有助于改善海参这一热带沿海社区的主要海洋资源的种群划分和估计。

Given that species diverge mostly in geographical isolation, the dynamics of local diversity is governed by the time it takes for these species to co-occur (secondary sympatry). Based on mitochondrial DNA and morphological evidence, some echinoderms seem able to achieve secondary sympatry an order of magnitude faster than other groups of marine invertebrates. The proposed research seeks to investigate whether these patterns could alternatively be caused by introgressive hybridization masking an earlier divergence, or reflect high levels of intraspecific polymorphism obscuring similar rates of secondary sympatry. To tease apart these hypotheses, the parameters of the isolation-with-migration (IM) model will be estimated from a multilocus dataset in a complex of sea cucumbers comprised of four putative, recently diverged, species. Furthermore, computer simulations will be used to determine whether the history of some loci deviates from this model, suggesting introgressive hybridization.Results will contribute to our understanding of species limits in challenging groups, and diversification in the richest marine biogeographic region. They will also generate hypotheses on the mechanisms involved in the generation of this diversity. In particular, the estimation of gene flow and population sizes will lead to predictions on the role of these demographic parameters in speciation. Furthermore, these estimates will help improve stock delineation and estimation of sea cucumbers, a major marine resource in tropical coastal communities.