Asterina burtoni (Asteroidea; Echinodermata) in the Mediterranean and the Red Sea: does asexual reproduction enhance colonization?

Abstract

The starfish Asterina burtoni is a Lessepsian colonizer which penetrated the Mediter- ranean Sea from the Red Sea. Populations of A. burtoni are found under rocks and stones in shallow waters along the northern Israeli and southern Lebanese Mediterranean coasts. In the Red Sea, A. burtoni is found in 2 forms, a pentamerous form with 5 equal arms that reproduces sexually, and a pluriradiate form with 3 to 8 arms of unequal length that reproduces both sexually and by fission. In the Mediterranean Sea only the pluriradiate fissiparous form is found. Only male gonads were observed in Mediterranean populations, suggesting reproduction by fission only. It is possible that the successful colonization of the Mediterranean by A. burtoni was mainly due to rapid proliferation by fissiparity. In the present study we used the random amplified polymorphic DNA (RAPD) method to address this question. Genetic diversity was determined within and between different pluriradiate populations from the Mediterranean and the Red Sea, and between the pentaradiate and the pluri- radiate populations of the Red Sea. Our RAPD analysis revealed very low genetic diversity both within and between the localities in the Mediterranean, indicating clonal structure of these popula- tions. These populations are similar to a fissiparous population from the south of the Gulf of Elat (Gulf of Aqaba), indicating that the probable origin of the Mediterranean populations is a fissiparous pop- ulation from the Red Sea. On the other hand, there is high genetic diversity between the pentaradi- ate and the pluriradiate populations from Elat, at the north end of the Gulf of Elat. Phylogenetic trees based on these results distinguished between the populations from Elat and those of the Mediter- ranean, but did not show a clear separation between the 2 populations from Elat. This supported our assumption that the Israeli Mediterranean populations of this starfish are exclusively fissiparous, while in Elat the fissiparous population of A. burtoni also reproduces sexually.