GENETIC UNIFORMITY OF WIDELY SEPARATED POPULATIONS OF THE CORAL-REEF STARFISH LINCKIA-LAEVIGATA FROM THE EAST-INDIAN AND WEST PACIFIC OCEANS, REVEALED BY ALLOZYME ELECTROPHORESIS

Gene flow among 18 widely separated populations of the starfish Lincki a laevigata was investigated using allozyme electrophoresis at seven p olymorphic enzyme loci. Little genetic differentiation was observed am ong East Indian-West Pacific populations separated by thousands of kil ometres. Gene flow was estimated to be of the same order of magnitude as that found in the highly connected Great Barrier Reef region. The a bsence of genetic structure over such a broad geographic range is cons istent with any of three conclusions: (1) there is extensive dispersal among widely separated populations across the range examined, (2) the re has been a rapid expansion of the East Indian-West Pacific populati ons in the recent past, or (3) the loci surveyed are under the influen ce of balancing selection. The first two conclusions are not totally e xclusive, since a recent expansion over several thousand generations w ould also require rapid dispersal at some stage, although present-day levels of dispersal need not be of the same order. With the available data, it is not possible to distinguish which of these mechanisms is t he most likely. The most parsimonious conclusion is that extremely low levels of population differentiation are consistent with the existenc e of a large, homogeneous, panmictic population, with extensive disper sal occurring throughout the East Indian-West Pacific.