MCFADDEN, C.S.*; RETTIG, P.M.; BECKMAN, E.J.; Harvey Mudd College: Molecular Evidence for Hybridization Between Two Alcyoniid Soft Coral Species With Contrasting Life Histories

Numerous studies have now documented both the potential for and past occurrence of interspecific hybridization events in scleractinian corals and other anthozoan cnidarians. The evolutionary importance of hybridization in these groups is still widely debated, however, with views ranging from hybrids as evolutionary dead-ends (�immortal mules�) to the idea that coral populations represent syngameons within which species boundaries are fluid over space and time. We report evidence for a probable case of hybridization between two soft coral species giving rise to a hybrid lineage that reproduces predominantly by asexual propagation. Alcyonium digitatum is a gonochoric, broadcast spawning soft coral that is common throughout the NE Atlantic. In the Irish Sea it is sympatric with an undescribed sibling species, A. sp. A, that is hermaphroditic and broods its larvae. In two mixed-species populations we have found numerous individuals that resemble A. sp. A morphologically but are white, a color typically found only in A. digitatum. Data from allozymes, RAPD fingerprints and rDNA ITS polymorphisms support the hypothesis that these white individuals are F1 hybrids between A. digitatum and A. sp. A. Moreover, all white individuals shared the same multi-locus genotype, suggesting that the hybrid genotype is being maintained in the population by asexual reproduction. To our knowledge, this is the first report of hybridization between species with such different modes of reproduction.