Data from: Secrets of the spring-keepers: Phylogeographic analyses of a freshwater amphipod uncover dispersal pathways in eastern North America

Aim: While the Nearctic freshwater amphipod, Gammarus minus, is known for
its adaptation to groundwater environments, relatively little is known
about other aspects of the species evolutionary history throughout its
range, which spans much of the eastern United States. As a result, the
phylogeography of the species is investigated here. Location: Eastern
United States Taxon: Gammarus minus Methods: Sequence data for two nuclear
and two mitochondrial loci were generated for 13 populations of Gammarus
minus. These data were combined with 15 populations obtained from GenBank.
From this partitioned dataset, phylogenetic trees were reconstructed using
both maximum-likelihood (IQTREE) and Bayesian Inference (MrBayes/BEAST),
and haplotype networks were generated using POPART. BEAST trees were
time-calibrated based on a set of 4 mixed calibration points. RASP
software was used to investigate ancestral areas. Ecological niche models
were generated in R using the dismo/ENMeval packages. Results:
Investigations revealed the presence of three clades within Gammarus
minus: (I) a “Susquehanna-Potomac” clade containing populations from
central Pennsylvania and northern West Virginia; (II) an “Ozark” clade
containing populations from Missouri/Illinois; and (III) a widely
distributed “Circum-Appalachian” clade containing populations from the
Appalachians, Interior Plateau, and Piedmont. Time-calibrated phylogenies
place the origin of the G. minus lineage during the Miocene, with clades
diverging in the late Miocene to early Pliocene. Phylogenetic
reconstructions recovered populations from the Susquehanna-Potomac clade
as basally derived, with other clades likely dispersing southward and
westward to reach the Ozarks and Appalachians. Main conclusions:
Diversification within Gammarus minus, likely was promoted by climatic
changes and uplift of the Appalachians during the Miocene. These results
provide a novel model for how drainage reorganizations, climate shifts,
and geological processes in eastern North America have shaped lineage
diversification in freshwater taxa. More broadly, this study demonstrates
the value of phylogeographic analyses in revealing hidden patterns of
biotic assembly and dispersal across complex landscapes.