THE EVOLUTION OF MATING SYSTEMS IN A GROUP OF BROODING SEA-ANEMONES (EPIACTIS)

The sea anemone genus Epiactis provides an unusually good opportunity to study the evolution of brooding and mating systems. The four Epiact is species on the Pacific coast of North America all brood their offsp ring up to the juvenile stage, but each has a different combination of internal vs. external brooding and gonochory vs. simultaneous or gyno dioecious hermaphroditism. Two of the four species (E. prolifera and E . lisbethae) were indistinguishable with allozymes (20 loci), but coul d be differentiated using multilocus DNA fingerprinting. Phylogenetic analyses of the allozyme data by distance and parsimony methods using three outgroups suggest that the four nominal Epiactis species are pol yphyletic, with the two internal brooders evolving independently of th e two external brooders. This topology does not allow inferences about the evolutionary order of hermaphroditism, dioecy and gynodioecy. Sep arate sexes and obligate outcrossing are often believed to be ancestra l, with hermaphroditism and the potential for self-fertilization being favored in taxa where restricted dispersal promotes inbreeding. Previ ous studies of population genetic structure in these Epiactis species is consistent with this hypothesis, as even the cross-fertile species were highly inbred.