KRUG LAB - EVOLUTIONARY AND LARVAL ECOLOGY OF MARINE INVERTEBRATES
Elena Hidalgo, M.S. 2007
For her M.S. thesis, Elena studied population connectivity in two Caribbean sea slugs, Elysia velutinus (=tuca) and E. crispata, which differ in larval dispersal potential. Elysia velutinus has short-lived, non-feeding larvae that settle only upon contacting the host alga Halimeda. In contrast, larvae of E. crispata metamorphose within their benthic egg capsules and have no free-swimming period. Elena sequenced a portion of the cytochrome c oxidase I gene from slugs collected at a dozen sites across the Caribbean, ranging from Panama to Bermuda. She found 6 highly divergent clades
within E. crispata that are largely restricted to different islands or regions,
with limited gene flow as expected given its non-dispersive larval stage.
In contrast, there was comparatively little phylogeographic structure in E. velutinus. Using population genetic methods of data analysis, Elena showed that most sites in the central Caribbean are connected and share a common haplotype, whereas populations at the range edges and in the northern
Bahamas experience little gene flow with the rest of the basin. Her data suggested that Panama and Bermuda may have retained ancestral polymorphism that was lost from the central Caribbean during Pleistocene sea level fluctuations. Overall, our results do not match well the predictions of biophysical coupling models that predict source-sink relationships for Caribbean marine animal populations, based on ocean circulation and larval lifespan; phylogeographic patterns may be quite idiosyncratic among different taxa.