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

鉴于物种大多在地理隔离的情况下分化，本地多样性的动态取决于这些物种共同发生所需的时间（次级同栖）。根据线粒体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二级共感。提出的研究旨在调查这些模式是否可能是由掩盖早期分化的渐渗杂交引起的，或者反映了高水平的种内多态性，从而掩盖了相似的次级共情率。为了区分这些假设，隔离-迁移（IM）模型的参数将从一个由四个假定的、最近分化的物种组成的海参复合体的多位点数据集进行估计。此外，计算机模拟将用于确定某些位点的历史是否偏离该模型，表明渐渗杂交。研究结果将有助于我们了解具有挑战性的类群的物种限制，以及最丰富的海洋生物地理区域的多样性。他们还将就产生这种多样性所涉及的机制提出假设。特别是，对基因流动和种群大小的估计将导致对这些人口统计学参数在物种形成中的作用的预测。此外，这些估计将有助于改善海参的存量划定和估计，海参是热带沿海社区的一种主要海洋资源。

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.