Parallel changes in genital morphology delineate cryptic diversification of planktonic nudibranchs

Abstract

The relative roles of geographical and non-geographical barriers in the genesis 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. Here, we use molecular phylogenetics to test the hypothesis that geography is the primary isolating mechanism in a clade of pelagic nudibranchs, Glaucinae. Our results contradict allopatric expectations: the cosmopolitan Glaucus atlanticus is panmictic, whereas the Indo-Pacific Glaucus marginatus contains two pairs of cryptic species 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. Available G. marginatus data are most consistent with non-geographical speciation events, but we cannot rule out the possibility of allopatric speciation, followed by iterative range extension and secondary overlap. Irrespective of ancestral range distributions, our results implicate a central role for reproductive character differentiation in glaucinin speciation-a novel result in a planktonic system.

Multilocus evidence for globally distributed cryptic species and distinct populations across ocean gyres in a mesopelagic copepod

“…; Churchill et al . ). However, a number of studies have found evidence for allopatric speciation in the plankton (Fleminger ; Darling et al .…”

A Radical Solution: The Phylogeny of the Nudibranch Family Fionidae

“…The addition of more slowly evolving unlinked markers should help resolve some poorly supported node at the base of the phylogenies presented here. Recently, Churchill et al [104] included the nuclear 28S gene in their phylogeny of Glaucidae. This provided a good resolution in deeper nodes, and therefore their 28S protocol will be included in further analyses as potentially useful in resolving within-aeolid relationships.…”

Molecular phylogeny of Glossodoris (Ehrenberg, 1831) nudibranchs and related genera reveals cryptic and pseudocryptic species complexes

“…These species, originally recognized by molecular phylogenetics, were then corroborated by both internal and external morphological features (Hoover et al., ). Additionally, a phylogenetic analysis revealed two cryptic pairs in the aeolid nudibranch Glaucus marginatus (Churchill et al., ). However, in this instance, all four share the same external coloration, but each pair differs morphologically (presence or absence of the bursa copulatrix; Churchill et al., ).…”