INDO-WEST PACIFIC PATTERNS OF GENETIC DIFFERENTIATION IN THE HIGH-DISPERSAL STARFISH LINCKIA-LAEVIGATA

Genetic variation in four natural populations of the starfish Linckia laevigata from the Indo-West Pacific was examined using restriction fr agment analysis of a portion of the mtDNA including the control region . Digestion with seven restriction enzymes identified 47 haplotypes in a sample of 326 individuals. Samples collected from reef sites within each location were not significantly differentiated based on Phi(ST) or spatial distribution of haplotypes, indicating that dispersal is hi gh over short to moderate distances. Evidence of gene flow is further supported by the low divergence among haplotypes and the lack of any c lear geographical structuring among different haplotypes in the gene p hylogeny. However, analysis of molecular variance (AMOVA), Phi(ST) and contingency chi(2) analyses of the spatial distribution of haplotypes demonstrate the presence of significant broad scale population geneti c structure among the four widespread locations examined. RFLP data ar e consistent with high gene flow between the Philippines and Western A ustralia and moderate gene flow between the Great Barrier Reef (GBR) a nd Fiji, but only limited gene flow between either the Philippines or Western Australia and either the GBR or Fiji. The presence of mtDNA st ructure contrasts with previous allozyme data which suggest that dispe rsal among widely separated locations is equivalent to dispersal among populations within the highly connected GBR studies. This discordance between patterns of gene flow inferred from these two markers cannot be fully accounted for by differences in effective population size for mtDNA. This might suggest that while mtDNA variation may represent co ntemporary patterns of gene flow, allozyme variation among populations is yet to reach equilibrium between drift and migration over the rang e surveyed.