Genetic differentiation among populations of the amphidromous shrimp Atya innocous (HERBST) and obstacles to their upstreaming migration

Abstract

In order to determine whether the amphidromous shrimp Atya innocous can breed successfully in freshwater above major obstacles to its upstream migration, we investigated the reproductive interactions among three local populations above high waterfalls or stream sections without runoff in Guadeloupe, Lesser Antilles. Reproductive interactions were investigated through the rates of genetic divergence (based on 8 allozyme loci) between populations. We also investigated four populations from streams without major obstacles. We recorded a high level of dispersal (N m >13) between six local populations (from streams with or without major obstacles) resulting in the mixing of alleles (pairwise F st values never significantly different from 0). Major obstacles did not separate upstream populations from those of neighbouring drainage basins and our results did not support the hypothesis that A. innocous can breed successfully in freshwater. As stressed elsewhere, shrimps (and particularly juveniles) are probably able to climb high waterfalls. Moreover, they probably use subsurface passages to colonise upstream sections of certain rivers. On the contrary the seventh population (from a more distant stream without major obstacles) displayed a high degree of genetic differentiation (pairwise F st >0.8, P<0.001). The detailed mechanism of its reproductive isolation remains to be solved. According to the published literature on decapods, the genetic distance recorded (mean D = 0.278) between the two groups of A. innocous in Guadeloupe falls within the range of sub-species.