Biological and population-genetic aspects of the sea anemone Actinia equina (Cnidaria: Anthozoa) along the Mediterranean coast of Israel

The population genetics of most cnidarians remain poorly understood, in part due to the complexities of their modes of reproduction and hybridization among closely related species. Actinia equina is the most common species of sea anemone along coastal areas in Europe and the Mediterranean. Members of this species vary in reproductive modes and presumably in genetic diversity among sites. Here we follow genetic variation of Actinia populations along the Mediterranean coasts of Israel, at the southern limit of the species range. Three sites, Yafo, Mikhmoret and Akhziv (south to north along a distance of 120 km; showing a decreased abundance of polyps towards the south) were chosen. Genetic profiles using amplified fragment length polymorphism (AFLP) markers indicated that each individual had a unique banding pattern and thus a distinct genetic identity. This suggests exclusive sexual reproduction, in contrast to clonal replication known in other Actinia populations. Nei's mean genetic distance analysis revealed that all three studied populations interbreed, marked by reduced genetic diversity and polymorphism in the northernmost population at Akhziv. The Israeli populations exhibit a higher genetic polymorphism than other Actinia populations from the Mediterranean Sea. We conclude that environmentally stressful conditions, especially high temperatures at the southernmost limit of this species in the Mediterranean, restrict these populations to sexual reproduction, generating higher levels of genetic heterogeneity.