Data from: Genomic data clarify Aquarana systematics and reveal isolation-by-distance dominates phylogeography of the wide-ranging frog Rana clamitans

Wide-ranging species are often polytypic, span geographic dispersal
barriers, and experience opportunities for divergence via genetic drift or
natural selection. Such conditions can be favorable for speciation and
wide-ranging taxa are frequently subdivided into multiple species by
modern molecular studies. However, with wide-ranging species, it is
important to explicitly test for isolation-by-distance (IBD) which can
produce continuous genetic variation that may be misinterpreted as
discrete population structure or even distinct species. Here we examine
the Green Frog (Rana clamitans), a wide-ranging species of the Aquarana
clade distributed across much of North America. Although Rana clamitans is
phenotypically variable enough to previously merit description of two
subspecies, patterns of genetic diversity remain unclear. Additionally,
the broader phylogenetic context for R. clamitans is poorly understood,
particularly its relationship with the closely related and IUCN Vulnerable
Bog Frog (Rana okaloosae). Using genome-wide ddRAD markers, we largely
resolve relationships within Aquarana and unambiguously identify R.
okaloosae as the sister lineage to R. clamitans. Within R. clamitans we
find two well-supported and geographically divided clades which are
identified as distinct species by a widely used genetic species
delimitation method, BPP. However, the two clades exhibit low genealogical
divergence and population genetic analyses reveal that genetic variation
within R. clamitans is best described by a pattern of IBD rather than
independently evolving lineages. We conclude that R. clamitans is indeed a
single species and the subspecies concept is of limited use. Our analysis
emphasizes how existing approaches can erroneously split species
characterized by continuous genetic variation and highlights the power of
combining population genetic and phylogenetic perspectives to better
understand diversity within wide-ranging taxa.