title: More than bindin divergence: reproductive isolation between sympatric subspecies of a sea urchin by asynchronous spawning.
abstract: The evolution of reproductive barriers is crucial to the process of speciation. In the Echinoidea, studies have focused on divergence in the gamete recognition protein, bindin, as the primary isolating mechanism among species. As such, the capacity of alternate mechanisms to be effective reproductive barriers and the phylogenetic context in which they arise is unclear. Here, we examine the evolutionary histories and factors limiting gene exchange between two subspecies of Heliocidaris erythrogramma that occur sympatrically in Western Australia. We found low, but significant differentiation between the subspecies in two mitochondrial genes. Further, coalescent analyses suggest that they diverged in isolation on the east and west coasts of Australia, with a subsequent range expansion of H. e. erythrogramma into Western Australia. Differentiation in bindin was minimal, indicating gamete incompatibility is an unlikely reproductive barrier. We did, however, detect strong asynchrony in spawning seasons; H. e. erythrogramma spawned over summer whereas H. e. armigera spawned in autumn. Taken together, we provide compelling evidence for a recent divergence of these subspecies and their reproductive isolation without gamete incompatibility. Western Australian H. erythrogramma may therefore present an intriguing case of incipient speciation, which depends on long-term persistence of the factors underlying this spawning asynchrony.
authors.affiliation: School of Animal Biology, The University of Western Australia, Crawley, Western Australia 6009, Australia. rachel.binks@grs.uwa.edu.au
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Binks
authors.forename: Jane
authors.initials: J
authors.lastname: Prince
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Evans
authors.forename: W Jason
authors.initials: WJ
authors.lastname: Kennington
mesh_terms: D000818:Animals; D047329:Anthocidaris / Q000235:genetics / Q000502:physiology*; D004272:DNA, Mitochondrial / Q000235:genetics; D003576:Electron Transport Complex IV / Q000235:genetics; D005260:Female; D008297:Male; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics*; D012098:Reproduction; D060047:Reproductive Isolation; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D061350:Sympatry; D013997:Time Factors; D014904:Western Australia
chemical_list: D004272:DNA, Mitochondrial; D012336:RNA, Ribosomal, 16S; D011956:Receptors, Cell Surface; C035027:egg surface sperm receptor; D003576:Electron Transport Complex IV