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

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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.