Hidden Biodiversity in an Ecologically Important Freshwater Amphipod: Differences in Genetic Structure between Two Cryptic Species

Abstract

Cryptic species, i.e. species that are morphologically hard to distinguish, have been detected repeatedly in various taxa and ecosystems. In order to evaluate the importance of this finding, we have to know in how far cryptic species differ in various aspects of their biology. The amphipod Gammarus fossarum is a key invertebrate in freshwater streams and contains several cryptic species. We examined the population genetic structure, genetic diversity and demographic history of two of them (type A and type B) using microsatellite markers and asked whether they show significant differences. We present results of population genetic analyses based on a total of 37 populations from the headwaters of two major European drainages, Rhine and Rhone. We found that, in both species, genetic diversity was geographically structured among and within drainages. For type A in the Rhine and type B in the Rhone, we detected significant patterns of isolation by distance. The increase of genetic differentiation with geographical distance, however, was much higher in type A than in type B. This result indicates substantial interspecific differences in population history and/or the extent of current gene flow between populations. In the Rhine, type B does not show evidence of isolation by distance, and population differentiation is relatively low across hundreds of kilometres. The majority of these populations also show signatures of recent bottlenecks. These patterns are consistent with a recent expansion of type B into the Rhine drainage. In summary, our results suggest considerable and previously unrecognized interspecific differences in the genetic structure of these cryptic keystone species.

Trouble at the top? Restricted distribution and extreme population isolation in an alpine crustacean assemblage with unexpected lineage diversity

“…However, molecular studies of freshwater invertebrates have resulted in numerous examples of unexpected species diversity (Bickford et al ., ). This pattern appears to be a particularly common feature of freshwater amphipods over a wide range of habitats, with species complexes common in both desert spring amphipods (Witt et al ., ; Murphy et al ., ) and many mesic environments, such as the streams, ponds and lakes of the Great Lakes District, USA (Witt & Hebert, ) and in European rivers (Müller, ; Weiss et al ., ; Westram, Jokela & Keller, ). While the freshwater isopods in this study appear to exhibit less lineage diversity than amphipods in the Bogong High Plains, Wilson () estimates more than 200 undescribed species may be present in freshwater phreatoicid isopods).…”

Habitat requirements and ecological niche of two cryptic amphipod species at landscape and local scales

“…Specific allelic combinations in these 10 microsatellite markers have been described as a diagnostic tool to tell types A and B apart (for details see Westram et al. , , ). The microsatellite markers diagnostic for type A is gf27 polymorphic with alleles >200 bp (but ≠205), whereas for type B the marker is monomorphic at 205 bp.…”

“…The streams were inhabited either only by types A or B, as known from previous studies based on molecular markers (Westram et al. , Altermatt et al. , A. M. Westram et al., unpublished data ).…”

Fluvial network topology shapes communities of native and non‐native amphipods

“…Previous studies confirm low dispersal rates in native Gammarus species (Westram et al. , Weiss et al. ).…”