62.6 Saturday, Jan. 5 Parallel sexual rekeying supports non-geographic planktonic speciation CHURCHILL, C.K.C.*; ALEJANDRINO, A.; VALDÉS, A.; Ó FOIGHIL, D.; University of California, Santa Barbara; Iowa State University; California State Polytechnic University, Pomona; University of Michigan, Ann Arbor firstname.lastname@example.org
The relative roles of geographic and biological barriers as mechanisms of genetic isolation are highly debated in evolutionary biology, yet knowing how speciation occurs is essential to our understanding of biodiversity. In the open ocean, differentiating between the two is particularly difficult because of the high levels of gene flow found in pelagic communities. The marine neuston is a promising system for investigating planktonic speciation mechanisms; located at the surface of the planet’s subtropical oceans, the neuston’s isobathic nature renders it exceptionally tractable both for sampling and understanding localized ecological variation. Here, we use molecular phylogenetics to test the hypothesis that geography is the primary isolating mechanism in a group of predatory neustonic nudibranchs with simultaneous hermaphroditic reproduction (Glaucinae). Glaucinae comprises two valid species with different distributions: Glaucus atlanticus is circumtropical and G. marginatus is Indo-Pacific. Our results are the inverse of allopatric expectations: G. atlanticus is panmictic, whereas G. marginatus contains four species in two clades with overlapping distributions. Within the G. marginatus species complex, a parallel reproductive change has occurred in each cryptic species pair: the loss of a bursa copulatrix. We hypothesize that its presence or absence affects mating behavior by changing the mechanics of penial insertion. Our results show that details of genital morphology are better predictors of latent evolutionary relationships among glaucinid lineages than biogeography, and support biological isolation as the primary driver of speciation—a novel result in a planktonic system.