MCFADDEN, C.S.*; HUTCHINSON, M.B.: Hybrid Origin of Soft Coral Species Suggested by Ribosomal DNA Sequence Heterogeneity

Throughout its broad Atlanto-Mediterranean geographic range, the soft coral Alcyonium coralloides occurs in sympatry with three closely related species, A. hibernicum, A. sp. M2 and Bellonella bocagei. Although a recent allozyme study indicates the 4 species are reproductively isolated, intraindividual polymorphisms of the multicopy ribosomal ITS gene regions suggest A. hibernicum and B. bocagei may have arisen by hybridization between A. coralloides and another species, perhaps A. sp. M2. We screened 15-20 ITS-1 clones from each of 44 individuals and identified them as ‘C-type’ (A. coralloides clade) or ‘H-type’ (A. hibernicum clade) sequences. All individuals of A. coralloides had C-type sequences only, and only H-type sequences were found in A. sp. M2. However, 83% of A. hibernicum individuals, including those from populations allopatric with A. coralloides, contained sequences of both types. In addition, several A. hibernicum individuals had sequences that appear to be recombinants between H- and C-type sequences. Recombinant H/C sequences were also present at high frequency in 5 of 6 individuals of B. bocagei, even though no pure C-type sequences were found in this species. These results suggest that hybridization between A. coralloides and an A. hibernicum-clade species or ancestor may have occurred in the lineages leading to both A. hibernicum and B. bocagei.