Large scale population structure and gene flow in the planktonic developing periwinkle, Littorina striata, in Macaronesia (Mollusca : Gastropoda)

Allozymes were used to investigate the genetic structure of 42 populations of the planktonic developing, Macaronesian periwinkle Littorina striata, th roughout its entire geographic range (Azores, Madeira, Canary Islands and C ape Verde Islands). This periwinkle is presumed to have a high dispersal an d gene flow potential, because it has a planktonic development. It is there fore expected to show little population genetic differentiation. Indeed, ba sed on Wright's hierarchical F-statistics, no significant genetic different iation could be detected among populations, at any of the specified hierarc hical levels (i.e. population, island, and archipelago). Nevertheless, the Cape Verde Islands seemed genetically more diverse (highest mean number of alleles per locus). The number of loci revealing a significant genetic hete rogeneity increased with increasing distance between populations, while pri vate alleles based gene flow (Nm) estimates also revealed a tendency toward s a geographical pattern. The distribution of rare and private alleles, mig ht account for these observations which suggested some geographical effect. Because of the low frequency at which these alleles occur, their influence on the genetic population structure is negligible, and not picked up by F- statistics. (C) 2000 Elsevier Science BN. All rights reserved.