Revisiting the comparative phylogeography of unglaciated eastern North America: 15 years of patterns and progress

WashU affiliated authors: Christine E. Edwards ( Dept. of Biology)

Abstract
In a landmark comparative phylogeographic study, “Comparative phylogeography of
unglaciated eastern North America,” Soltis et al. (Molecular Ecology, 2006, 15, 4261)
identified geographic discontinuities in genetic variation shared across taxa occupying unglaciated eastern North America and proposed several common biogeographical discontinuities related to past climate fluctuations and geographic barriers. Since
2006, researchers have published many phylogeographical studies and achieved
many advances in genotyping and analytical techniques; however, it is unknown how
this work has changed our understanding of the factors shaping the phylogeography
of eastern North American taxa. We analyzed 184 phylogeographical studies of eastern North American taxa published between 2007 and 2019 to evaluate: (1) the taxonomic focus of studies and whether a previously detected taxonomic bias towards
studies focused on vertebrates has changed over time, (2) the extent to which studies
have adopted genotyping technologies that improve the resolution of genetic groups
(i.e., NGS DNA sequencing) and analytical approaches that facilitate hypothesistesting (i.e., divergence time estimation and niche modeling), and (3) whether new
studies support the hypothesized biogeographic discontinuities proposed by Soltis
et al. (Molecular Ecology, 2006, 15, 4261) or instead support new, previously undetected discontinuities. We observed little change in taxonomic focus over time, with
studies still biased toward vertebrates. Although many technological and analytical
advances became available during the period, uptake was slow and they were employed in only a small proportion of studies. We found variable support for previously
identified discontinuities and identified one new recurrent discontinuity. However,
the limited resolution and taxonomic breadth of many studies hindered our ability to
clarify the most important climatological or geographical factors affecting taxa in the
region. Broadening the taxonomic focus to include more non-vertebrate taxa, employing technologies that improve genetic resolution, and using analytical approaches
that improve hypothesis testing are necessary to strengthen our inference of the forces shaping the phylogeography of eastern North America.

Citation: Rachel Ann Lyman, Christine E Edwards, Revisiting the comparative phylogeography of unglaciated eastern North America: 15 years of patterns and progress, Ecology and Evolution, 2022, 12:e8827, https://doi.org/10.1002/ece3.8827