Anostracans from North American lakes show unclear phylogenetic relationships between taxa and distinctive dispersal patterns

Dispersal is essential for all organisms to colonize new areas. Like many other aquatic invertebrates, Anostraca (Crustacea) disperse passively as dormant fertilized eggs. Here, we first study the genetic diversity of Branchinecta fairy shrimps (identified morphologically as B. readingi) inhabiting lakes in Saskatchewan and British Columbia, Canada. Second, we attempt to reconstruct the phylogeny and dispersal events that explain their genetic distribution. Finally, we compare genetic diversity and distribution of Branchinecta sp. and Artemia franciscana, the 2 anostracans inhabiting the Saskatchewan lakes but with different salinity niches. To this aim, we sequenced CO1 and 16S gene fragments of the Branchinecta individuals collected from 8 Saskatchewan lakes. We found a relatively high number of haplotypes for both markers (79 in CO1 and 76 in 16S) in Branchinecta from Saskatchewan. Three genetic clades at the CO1 gene region were found in Saskatchewan Branchinecta, one of which was widely recorded previously in the United States (but described as B. mackini). By contrast, 54 CO1 haplotypes were previously recorded in A. franciscana in Saskatchewan, with all CO1 sequences belonging to one genetic clade, suggesting that Branchinecta sequences might originate from several distinct Ice Age refugia, contrary to A. franciscana, which might originate from a single refuge. High density of suitable habitats (>100 000 lakes in Saskatchewan), weak priority effects, and frequent dispersal events could explain high genetic diversity found in the studied Branchinecta. However, we found no genetic support for a distinction between B. readingi and B. mackini.