Phylogeography is the study of how genetic lineages (typically traced through mitochondrial DNA) are distributed geographically. The signature of historical forces, such as sea level fluctuations during Pleistocene ice ages, remains in the mitochondrial DNA of today’s organisms, and can be decoded through genetic studies. To understand how larval dispersal affects population structure, we are assessing phylogeography and population genetic structure in Caribbean sacoglossans with and without dispersing larvae.
Preliminary results support the hypothesis that species with non-planktonic development (E. crispata, E. pratensis) have highly divergent, geographically restricted lineages. However, a species with dispersing larvae (Costasiella ocellifera) exhibits a deep genetic break between Florida and the rest of the Caribbean, suggesting that larval dispersal has not historically maintained connectivity between all regions. In several species, populations at the southern range edge are more genetically diverse than the central Caribbean. These results have implications for the design of marine protected areas in threatened shallow-water ecosystems, revealing regions that harbor unique lineages and retain ancestral polymorphism.