Abstract
Prehistoric climate and landscape features play large roles structuring wildlife populations. The amphibians of the northern Great Plains of North America present an opportunity to investigate how these factors affect colonization, migration, and current population genetic structure. This study used 11 microsatellite loci to genotype 1,230 northern leopard frogs (Rana pipiens) from 41 wetlands (30 samples/wetland) across North Dakota. Genetic structure of the sampled frogs was evaluated using Bayesian and multivariate clustering methods. All analyses produced concordant results, identifying a major east–west split between two R. pipiens population clusters separated by the Missouri River. Substructuring within the two major identified population clusters was also found. Spatial principal component analysis (sPCA) and variance partitioning analysis identified distance, river basins, and the Missouri River as the most important landscape factors differentiating R. pipiens populations across the state. Bayesian reconstruction of coalescence times suggested the major east–west split occurred ~13–18 kya during a period of glacial retreat in the northern Great Plains and substructuring largely occurred ~5–11 kya during a period of extreme drought cycles. A range‐wide species distribution model (SDM) for R. pipiens was developed and applied to prehistoric climate conditions during the Last Glacial Maximum (21 kya) and the mid‐Holocene (6 kya) from the CCSM4 climate model to identify potential refugia. The SDM indicated potential refugia existed in South Dakota or further south in Nebraska. The ancestral populations of R. pipiens in North Dakota may have inhabited these refugia, but more sampling outside the state is needed to reconstruct the route of colonization. Using microsatellite genotype data, this study determined that colonization from glacial refugia, drought dynamics in the northern Great Plains, and major rivers acting as barriers to gene flow were the defining forces shaping the regional population structure of R. pipiens in North Dakota.
Highlights
Prehistoric climatic trends have played large roles in shaping the cur‐ rent biogeographic population structures of many North American species from a wide variety of lineages, including trees (Roberts & Hamann 2015), aquatic insects (Peterson, O'Grady, & Resh, 2017), fish (David & Wright, 2017; Tarpey et al, 2018), and mammals (Puckett, Etter, Johnson, & Eggert, 2015; Sim et al, 2016)
The expected range is split between parts of the American Atlantic Plain and areas around the Ohio River Valley, while most of the Great Plains region appears unsuitable, and areas stretching from eastern Colorado to the Gulf coast of Texas could have supported R. pipiens populations during this period
Popu‐ lations rapidly expanded (Mushet 2010). This interaction between drought and the hydrological structure of river basins in the northern Great Plains drives contraction–recolonization dynamics of R. pipi‐ ens populations and could explain the river basin‐associated pattern of genetic structuring seen in R. pipiens populations in North Dakota
Summary
Prehistoric climatic trends have played large roles in shaping the cur‐ rent biogeographic population structures of many North American species from a wide variety of lineages, including trees (Roberts & Hamann 2015), aquatic insects (Peterson, O'Grady, & Resh, 2017), fish (David & Wright, 2017; Tarpey et al, 2018), and mammals (Puckett, Etter, Johnson, & Eggert, 2015; Sim et al, 2016). Amphibians of the northern Great Plains provide an opportunity to evaluate prehistoric climate signatures on genetic variation This region was partially glaciated and has been characterized by glacial retreat (Mickelson et al, 1983) followed by cycles of drought and wet periods throughout the Holocene (~11 kya – present; Valero‐ Garcés et al, 1997; Xia, Haskell, Engstrom, & Ito, 1997). This study applies population genetic tools on a finer scale than previous range‐wide studies to understand what regional landscape features and aspects of climate history have played important roles in how R. pipiens populations have been structured This information will be useful for conservation efforts by delineating populations, identi‐ fying natural and anthropogenic barriers to gene flow, and assessing how climate‐related factors have influenced species distributions in the past. Spe‐ cies distribution model for R. pipiens was developed to investigate how changes in climate and climate refugia may explain the evolution‐ ary relationships between distinct populations of R. pipiens
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