MOLECULAR INSIGHTS INTO THE POPULATION STRUCTURES OF COSMOPOLITAN MARINE FISHES

Many marine fishes are cosmopolitan, occurring in continuous (e.g., ci rcumtropical) or discontinuous (e.g,, antitropical) distributions. Lit tle is known of the genetic basis of population structure of these spe cies, even though several support extensive fisheries. To develop a da tabase that would facilitate comparison of the population structures a mong cosmopolitan fishes we consistently included restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) as a common approach to our investigations of these species. This article presents a review of those analyses. Considerable intraspecific geneti c variation was revealed within all cosmopolitan marine species. Conti nuously distributed species displayed population structures ranging fr om a lack of significant heterogeneity between ocean samples to shallo w but significant structuring within an ocean basin. In general, great er intraspecific genetic divergence was revealed within discontinuousl y distributed fishes. Levels of population structuring ranged from spe cies comprising conspecific populations with no mtDNA haplotypes in co mmon to those comprising populations with homogeneous distributions of mtDNA haplotypes across ocean basins. The close affinity of haplotype s among conspecific populations of all discontinuously distributed spe cies was consistent with contact since the Pleistocene, Although gener al patterns of genetic population structure were similar among continu ously and discontinuously distributed cosmopolitan marine species, the re were some striking differences. These differences underscore the ne ed for a thorough understanding of the genetic basis of population str ucture of each species for proper management.