Albert Rodriguez, M.S. 2009

Albert used molecular methods to assess gene flow in the Caribbean sea slugs Elysia pratensis and E. subornata. These sister species both show high levels of genetic structure expected for species that lack a planktonic larval stage, but surprisingly, analysis of mitochondrial COI haplotypes revealed that populations of E. pratensis in the northern Bahamas have mitochondria descended from their sister species E. subornata.  Past hybridization events led to introgression and local fixation of the foreign E. subornata mitochondria within a few E. pratensis  populations. The species have fixed differences in nuclear genes and morphology, and are partitioned onto different host algae.  Ecological speciation by host shifting may thus allow divergence even in the face of hybridization.  As E. subornata has been proposed as a biological control agent for invasive Caulerpa algae; its potential for hybridization with native species warrants careful attention.