Phylogeographic Patterns in Riverine Crustaceans

Abstract

Riverine crustaceans -- freshwater crayfish, river crabs, freshwater shrimps, and amphipods -- are among the most phylogeographically informative organisms in continental biogeography: obligately aquatic and largely unable to disperse overland between river drainages, their population genetic structure directly reflects historical river capture events, glacial refuge locations, drainage divide crossings, and post-glacial recolonisation pathways in a way that vertebrates -- with their greater dispersal capacity -- cannot. This study presents the most comprehensive multi-taxon phylogeographic analysis of European riverine crustaceans yet conducted, sequencing 1,847 individuals from 247 sites across 84 river drainages in 18 countries at three molecular markers (COI + 16S rRNA + one nuclear marker per taxon) for 18 focal crustacean species from four orders. Phylogeographic structure was strongly drainage-concordant for most species: mean FST between drainages = 0.487 +- 0.084 vs. within-drainage FST = 0.084 +- 0.028 (t = 18.4; p < 0.001). Bayesian phylogenetic analysis resolved 47 independent clades not currently recognised in taxonomic classifications, with 18 clades showing divergences > 3% COI consistent with cryptic species-level differentiation. Coalescent demographic modelling identified two major glacial refugia for European freshwater crustaceans -- the Danube basin and the Iberian drainages -- as primary sources of post-glacial recolonisation, consistent with the stream capture hypothesis for European freshwater biodiversity patterns. Drainage history reconstruction identified 8 likely historical river capture events explaining anomalous cross-drainage gene flow signatures.