Meeting Abstract

31.7  Tuesday, Jan. 5  Natural hybridization in echinoderms: a case study from the sea urchin genus Pseudoboletia ZIGLER, Kirk S*; BYRNE, Maria; RAFF, Rudolf A; RAFF, Elizabeth C; LESSIOS, H A; Sewanee: The University of the South; University of Sydney; Indiana University ; Indiana University; Smithsonian Tropical Research Institute kzigler@sewanee.edu

Confirmed cases of natural hybridization in echinoderms are limited to six genera, spread across the echinoids, asteroids, and holothuroids. We suspected hybridization between the sea urchins Pseudoboletia indiana and P. maculata based on the presence of morphologically intermediate individuals in a sympatric population at Sydney, Australia. We confirmed that hybridization was occurring by determining the mitochondrial cytochrome oxidase I haplotype, nuclear bindin genotype, and, when possible, egg size of individuals with a range of morphologies. We then characterized the conditions related to hybridization between these species by examining their distribution in the field, annual spawning cycles, cross-fertilization efficiencies, molecular divergence at the sperm protein bindin, and time since divergence from a common ancestor. We found that, (1) morphology is a good indicator of genetic background; (2) members of the two species can be found within a meter of one another in the field; (3) the two species have partially overlapping annual reproductive cycles; (4) they cross-fertilize easily, which is correlated with minimal bindin divergence; and (5) that the two species last shared a common ancestor around 2 mya. We compare these results to other examples of natural hybridization in echinoderms, and other animal taxa.