Genotypic variation amongGammarus fasciatus(Crustacea: Amphipoda) from the Great Lakes - St. Lawrence River: implications for the conservation of widespread freshwater invertebrates

Abstract

We examined the population genetic structure of the amphipod Gammarus fasciatus (Crustacea: Amphipoda) over two years from a total of 11 sites within the Great Lakes - St. Lawrence River system using allozyme electrophoresis. In 1995, we examined differences within the St. Lawrence River (Cornwall to Quebec City), and in 1996, we focused on larger scale, whole-system differences from Lake Superior to Lake Champlain. We found very low levels of genetic differentiation among sites (Wright's FST < 0.03). This was not unexpected for an active disperser in a relatively contiguous system. However, we also found low levels of genetic variability within sites (Hobs = 0.07- 0.15), a result that was not anticipated. We surveyed the available literature on gammarid and other amphipods and found that limited genetic variability is characteristic of continuously distributed taxa, contrary to the expectations of current conservation theory. This is potentially of concern, especially in light of recently reported declines of G. fasciatus at several locations within the St. Lawrence River and Great Lakes. Given the importance of species such as G. fasciatus in aquatic food webs, further work is clearly needed on the consequences of population genetic structure to species' responses to novel environmental changes (e.g., exotic species introductions).

Genetic diversity in the Gammarus pecos species complex: Implications for conservation and regional biogeography in the Chihuahuan Desert

“…2). A similar result was seen by Hogg et al (1998) when studying the population genetic structure of Hyalella azteca from the Laurentian Great Lakes basin. Their analysis of genetic distance revealed a cluster of similar populations (D Ͻ 0.15) occupying sites widely separated geographically (Hogg et al 1998).…”

“…A similar result was seen by Hogg et al (1998) when studying the population genetic structure of Hyalella azteca from the Laurentian Great Lakes basin. Their analysis of genetic distance revealed a cluster of similar populations (D Ͻ 0.15) occupying sites widely separated geographically (Hogg et al 1998). The authors suggested that the individuals from those locations might have been a more widely distributed species, in contrast to genetically distinct populations from the other sites (Hogg et al 1998).…”

“…The Sitting Bull population also has two alleles at MPI, AAT-1, AAT-2, and MDH-2 (Table 2), but no heterozygotes at these loci. The high level of genetic diversity among the nine populations of the G. pecos complex ( ϭ 0.59) further supports the hypothesis of the presence of cryptic species (Hogg et al 2000). Both the BL1 and SB populations contain unique alleles.…”

“…In the case of the G. pecos complex, the high number of loci significantly different from HW expectations and the resulting high inbreeding coefficients (f) suggest nonrandom mating as the main cause of heterozygote deficiency. Two populations, BL1 and SB, showed very high proportions of polymorphic loci, heterozygote deficiencies at over half of all loci sampled, and high values of inbreeding; together, these factors provide further evidence of the presence of cryptic species (Hogg et al 2000). Indeed, in population BL1 there are two alleles at AAT-1 (Table 2), but no heterozygotes.…”

“…Hogg et al (2000) suggested that the high levels of variation they observed in amphipod species was due to incomplete knowledge of amphipod taxonomy and the presence of cryptic species. Moreover, they suggested using Wright's F statistic F ST ( in our study) as an indication of the presence of cryptic species; large F ST values indicate distinct subspecific or specific status (Hogg et al 2000). Our similar results suggest that cryptic species may be found within populations of the G. pecos complex.…”