GENETIC-STRUCTURE OF DASCYLLUS-ARUANUS POPULATIONS IN FRENCH-POLYNESIA

Dascyllus aruanus were collected from 13 different locations in French Polynesia between 15 November 1990 and 15 February 1991 in order to e xamine larval dispersal on four spatial scales: within-reef, within-is land, within-archipelago, among-archipelagoes. Average polymorphism wa s analysed by protein electrophoresis at two levels (P-95 = 0.285 and P-90 = 0.107) from 12 and 3 polymorphic loci, respectively. Spatial ge netic variation displayed a low level of differentiation between popul ations among archipelagoes, and homogeneity at lower spatial scales. T wo hypotheses are proposed to explain the genetic structure observed. The first suggests substantial gene flow between the islands during th e pelagic larval phase, the second that the absence of differentiation is the result of recent colonisation. Genetic variation amongst size classes showed a significant heterozygote deficiencies at two loci (PG M() and EST-2(*)) in the smallest size class. This suggests a ''cycli c selection'' which affects larvae and adults differentially. The data revealed little differentiation among populations at the different lo calities, despite the short larval duration of D. aruanus; this sugges ts that larval duration is not the main factor presently affecting gen etic structure in an insular model.