Reproductive isolation with little genetic divergence between Urticina (=Tealia) felina and U. eques (Anthozoa: Actiniaria)

There has long been doubt as to whether there are one or two British species of the sea anemone genus Urticina. In the present study, populations of both putative species, which occur sympatrically in the Isle of Man, have been compared by electrophoresis of isozymes and nematocyst analysis. The analysis of fourteen isozyme loci exhibited a high genetic identity between the two taxa (I=0.907), but four loci showed significant differences in gene frequencies; thus indicating reproductive isolation. The populations displayed highly significant differences in the sizes of the various nematocyst types. The individual analysis of data for each type of nematocyst revealed that the basitrics from the actinopharynx and from the tentacles contribute most to the observed difference. Consequently, U. felina (L.) and U. eques (Gosse) are assumed to be valid species, as suggested by Manuel (1981). The mean heterozygosities for each species (0.410 and 0.436, respectively) are the highest reported for cnidarians.