Allozyme variation and genetic divergence in populations of Talitrus saltator (Crustacea: Amphipoda) around the Atlantic coast, the Azores and the Canary Islands

Abstract

Individuals from 15 supralittoral populations of the marine amphipod Talitrus saltator collected in a range from northern Portugal to south-west Spain, as well as from the Azores, and the Canary Islands, were electrophoretically analysed and compared with specimens from two NW-Atlantic populations. Patterns of significant differences in gene frequencies and geographic divergence were examined, using starch-gel electrophoresis. Out of ten enzymes loci investigated, 4 (glutamate- oxalacetate-transaminase-2, Got-2, mannose-phosphate-isomerase, Mpi, phosphoglucoisomerase, Pgi, phosphoglucomutase, Pgm,) were highly polymorphic. A clinal variation in allele frequency was obvious, and especially at two loci (Pgi, Pgm). Estimates of Nm (effective number of migrants per generation between populations) revealed reduced gene flow which is related to the restricted dispersal capacity of T. saltator. UPGMA cluster analysis, based upon polymorphic loci, shows two different groups of populations: (1) those form Portugal, including the populations of the Azores, and (2) those from the gulf of Cadiz which extends with modifications of allele frequencies to the Gibraltar region and to the Canary Islands. Genetic differentiation is proposed to be promoted by random genetic drift and natural selection.