Abstract

Regional phylogeographic studies have long been conducted in the southeastern United States for a variety of species. With some exceptions, many of these studies focus on single species or single clades of organisms, and those considering multiple species tend to focus on deep historical breaks causing differentiation. However, in many species more recent factors may be influencing genetic diversity. To understand the roles of historic and contemporary processes in structuring genetic diversity, we reanalyzed existing genetic data from Southeast of North America using approaches gleaned from phylogeographic and landscape genetic literature that were implemented across species including AMOVAs, PCoAs, Species Distribution Modelling, and tests of isolation by distance, environment, and habitat instability. Genetic variance was significantly partitioned by ecoregions, watersheds, and across phylogeographic breaks in the majority of species. Similarly, genetic variation was significantly associated with some combination of geographic or environmental distance or habitat instability in most species. Patterns of genetic variation were largely idiosyncratic across species. While habitat instability over time is significantly correlated with genetic diversity in some species, it appears generally less important than isolation by geographic or environmental distance. Our results suggest that many factors, both historical and contemporary, impact genetic diversity within a species, and more so, that these patterns aren’t always similar in closely related species. This supports the importance of species- specific factors and cautions against assumptions that closely related species will respond to historical and contemporary forces in similar ways.

Highlights

  • Phylogeography aims to understand how climatic and geologic events have structured genetic diversity; while comparative phylogeography seeks this understanding in multiple species

  • Data repurposing (Sidlauskas et al 2010) provides a more comprehensive approach than meta-analysis for comparative phylogeography because data collected from species that share a geographic distribution can be analyzed and interpreted in a common framework

  • Our results support the viewpoint that many forces combine to influence genetic diversity within species (e.g., Zhang et al 2018)

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Summary

Introduction

Phylogeography aims to understand how climatic and geologic events have structured genetic diversity; while comparative phylogeography seeks this understanding in multiple species. This discipline interprets similar patterns (e.g., genealogies, STRUCTURE plots, etc.) across species as evidence for a shared species response to climate and/or geologic events (Avise 1987, Sullivan et al 2000). Soltis et al (2006) reviewed phylogeographic patterns from the Southeastern US and suggested that these patterns could be categorized into three categories: populations structured by 1) river basins, 2) mountain ranges, and 3) the locations of glacial refugia. These categories are not independent or exclusive; for example, species with population structure across a given river or the Appalachian Mountains may have been isolated across these barriers in separate refugia during Pleistocene glaciation

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