Evolutionary ecology of the North Atlantic Talitridae (Crustacea, Amphipoda): A review

Abstract

Four primary estuarine/marine ecotopes recognized in the North Atlantic continental littoral and continental terrestrial margins give rise to the following ecotypes: wrack generalists (=beach-hoppers), psammophilic talitrids (=sandburrowing-hoppers), palustral talitrids (=salt marsh-hoppers), and xylophagous talitrids (=driftwood hoppers). On the European continent, there are freshwater riverine and lacustrine talitrids. In addition, there are a few terrestrial ecotypes in the Northeast Atlantic Islands: rainforest leaflitter talitrids and one troglobiont (=cave-hopper). Wrack generalist species are phenotypically plastic and can live in one or more secondary ecotopes. It is hypothesized herein that switching on/off appropriate genes by cellular mechanisms (epigenesis) occurs during the microevolution of Talitridae. The generalist/specialist continuum concept supports our understanding of both the ecology and microevolution of talitrids. Microevolutionary characteristics of wrack generalists are that they exhibit the most phenotypic variability and occurrences of epigenesis, have the most extensive zoogeographic range, and have the lowest speciation potential and endemism rate. Examples where epigenesis may be part of the microevolutionary process include low/high salinity and hypogean/epigean combined switches giving rise to sibling (sister) species pairs. Current views of the phylogeny of the Talitridae based on either morphological characters used in taxonomy or molecular genetic methods are still under development. Molecular genetic methods show promise of providing a scientifically reproducible phylogeny and temporal history of talitrids (macroevolution), but insufficient coverage of genera within talitrids and of related groups is available to do so yet.