A comparison of genetic diversity levels in marine, freshwater, and anadromous fishes

Abstract

Electrophoretic data were analysed from 49 species of freshwater fish, 57 species of marine fish, and seven anadromous species. For each species, at least 15 individuals had been assayed for at least 15 loci in two or more subpopulations. The results showed that while average total heterozygosity (H̄T) was approximately equal in freshwater and marine species (0·062 and 0·064 respectively), subpopulation heterozygosity (H̄s) was significantly less in the former group (0·046 and 0·059 respectively). Consequently the average degree of genetic subpopulation differentiation (H̄ST) was significantly greater for freshwater species (0·222 v. 0·062). On average, it is likely that marine subpopulations exchange between 10 and 100 times more migrants per generation than freshwater subpopulations, presumably because of the relative absence of barriers to dispersal in the marine environment. The reduced values of Hs in freshwater species are likely to reflect reduced effective subpopulation sizes relative to marine species. The few andromous species that have been analysed show intermediate levels of GST.

Genetic and morphologic differentiation of the Lusitanian toadfish (<i>Halobatrachus didactylus</i>) between estuarine and coastal areas in Portugal

“…Allozymes revealed that the genetic variability of H. didactylus along the Portuguese coast was similar to that determined by Smith and Fujio (1982) over a large number of marine teleosts (mean heterozygosities of 0.006). The mean F ST value found in the analysis of all loci (0.042) was lower than that reported by Ward et al (1994) for fishes (0.14) but was in accordance with the low spatial genetic heterogeneity suggested by Gyllensten (1985) for marine teleosts. The Mantel test showed that genetic and geographic distances were not correlated, thus refuting the hypothesis of isolation by distance, and that morphological distances were independent of genetic ones.…”

Fine-scale spatial and temporal genetic structure of Atlantic cod off the Atlantic coast of the USA

“…This classical view of marine fish species (Hauser & Carvalho 2008) was supported by tagging studies that demonstrated long distance migrations (Templeman 1974) and by early genetic studies that revealed high levels of gene flow (Ward et al 1994). This perspective influenced management regimes, such that many marine fisheries are managed as broadly distributed, panmictic populations .…”

Contrasts in genetic structure and historical demography of marine and riverine populations of Atherina at similar geographical scales

“…Fish species that are closely tied to brackish water ecosystems, at least during a part of their life cycle, may present a genetic structure that is the result of two opposing factors: (1) the tendency for differentiation among populations due to geographic isolation, and (2) the homogenizing effects of gene flow among populations which is a function of each species dispersal capability (Ward et al, 1994).…”