Phylogeography and environmental diversification of a highly adaptable marine amphipod, Gammarus duebeni

Abstract

Genetic diversity and phylogeographic population structure in the gammarid amphipod, Gammarus duebeni, were investigated across its broad latitudinal distribution in the NE and NW Atlantic by analysis of mitochondrial DNA sequence. Gammarus duebeni has exceptional tolerance of salinity change and inhabits environments ranging from marine to freshwater. The longstanding debate on whether there are distinct marine and freshwater subspecies was assessed by sampling populations from sites characterized by different salinities. Our sequence data demonstrates that there are two major lineages, with little internal geographic structuring. Evidence is provided to suggest a pre-glacial divergence of these two clades, involving segregation between a region historically associated with the freshwater form and the majority of the marine localities on both sides of the Atlantic. A modern contact zone between the marine and freshwater forms is proposed in western Britain.

Linking functional molecular variation with environmental gradients: Myosin gene diversity in a crustacean broadly distributed across variable thermal environments

“…The high levels of mitochondrial genetic divergence between the 7 gammarid species are consistent with other phylogenetic work on north Atlantic gammarids (Hou et al 2007;Rock et al, 2007). Even though there was no overarching phylogenetic basis to the interspecific patterns of MyHC form diversity, G. oceanicus displayed unique patterns of MyHC expression for both loop 1 and loop 2.…”

“…Total genomic DNA was extracted from a minimum of five individuals for each species and a fragment of CO1 gene amplified as described in Rock et al (2007). Phylogenetic tree reconstructions were carried out in MEGA4 (Tamura et al, 2007) using neighborjoining methods with bootstrap tests performed to 1000 replications.…”

Congeneric Amphipods Show Differing Abilities to Maintain Metabolic Rates with Latitude

“…It appears that the subarctic population of G. oceanicus displays some cold-water characteristics that are more in keeping with highly stenothermal marine invertebrates endemic to the Southern Ocean, where evolution to the low and stable conditions has occurred over 25-35 myr. In sharp contrast, G. oceanicus in the Northern Hemisphere migrated north to arctic latitudes from southern refugia about 20,000 yr ago (Rock et al 2007. Despite this relatively short period in environments that are extremely cold and stable with limited resources, the lowering of thermal tolerances suggest some physiological diversification in the subarctic population.…”

“…Four species of marine gammarid amphipod were investigated, including the circumpolar arctic/boreal species Gammarus setosus, the subarctic/boreal species Gammarus oceanicus, the temperate species Gammarus locusta, and the more eurythermal boreal/temperate species and marine haplotype Gammarus duebeni duebeni (Rock et al 2007). All species inhabit the low intertidal except G. d. duebeni, which inhabits areas under freshwater influence in the mid to high intertidal ).…”

“…The study benefits from recent phylogenetic analysis based on the mitochondrial cytochrome c oxidase I gene sequences from 16 putative Gammarus species because the analysis provides information on the genetic differentiation among the populations and species of interest (Costa et al 2009). Moreover, the ability of the four species to tolerate environmental change differs, as does their vertical distribution in the intertidal (Bulnheim 1979;Rock et al 2007). Subsequently, it was possible to examine intraspecific variations in metabolic rate in gammarid species with similar ecologies and known phylogeny but different latitudinal and vertical distribution patterns and therefore environmental tolerances.…”