The Corrected Taxonomic History of the North American Ratsnakes ( Pantherophis obsoletus Complex) POINTS OF VIEW POINTS OF VIEW POINTS OF VIEW

Genomic data now permit investigations into speciation that yield unprecedented detail on processes of diversification. In herpetology, this has helped cement broad understanding of relationships within amphibians and major reptile groups (Burbrink et al. 2020; Milián-Garcia et al. 2020; Singhal et al. 2020; Hime et al. 2021), as well as revealing that hybridization and introgression are common at both deep and shallow phylogenetic scales (O’Connell et al. 2017; Portik et al. 2017; Leaché et al. 2020; Myers et al. 2020; Reyes-Velasco et al. 2020). Furthermore, phylogeographic studies since the naming of the field (Avise et al. 1987) have increasingly shown that many wideranging species are composed of multiple geographic lineages, and that these evolutionarily lineages often conflict with traditional, taxonomic arrangements that are typically based on a few morphological characters (Leaché et al. 2002; Lemmon et al. 2007; Burbrink et al. 2008; Myers et al. 2013; Burbrink and Guiher 2015; Weinell and Austin 2017; Cox et al. 2018). Many studies have demonstrated that divergence with gene flow either in primary or secondary contact is a common part of the speciation process, and that strict reproductive isolation is often not observed across the genome. Differential isolation across the genomes of geographic lineages is possible, with some chromosomal regions showing low levels of introgression and others showing considerable admixture (Canestrelli et al. 2015; Martin et al. 2019; Burbrink et al. 2021). Nevertheless, it is possible for ancient lineages to persist in the face of ongoing gene flow dating back as early as the Miocene (e.g., Barth et al. 2020). Additionally, migration may not be equal for all loci, as some alleles are adapted to particular environments and resist introgression. This differential level of migration among loci is expected under a process of speciation with ecological adaptation via natural selection (Mayr 1963; Van Valen 1976; Coyne and Orr 2004; Nosil 2008, 2012; Feder et al. 2012; Harrison and Larson 2014; Ravinet et al. 2017). In a recent paper on the North American ratsnakes of the Pantherophis obsoletus complex, Burbrink et al. (2021) examined the phylogeographic history of the group using 2491 ultraconserved elements (UCEs) from 288 individual samples (filtered to 238) to better understand the formation of lineages across the landscape and address consequences of hybridization between species pairs. Like previous mtDNA-based analysis (Burbrink et al. 2000) and a morphological investigation of the taxa (Burbrink 2001), this recent paper confirmed the presence of four evolutionary lineages with varying degrees of introgression (Fig. 1). These corresponded (for the most part) to species previously designated (Burbrink 2001) as: 1) Pantherophis bairdi, distributed primarily in the Chihuahuan Desert of western Texas and northern Mexico; 2) Pantherophis obsoletus, mostly occurring west of the Mississippi River; 3) Pantherophis "spiloides" (corrected to P. alleghaniensis by Hillis and Wüster [2021] and Burbrink et al. [2021]), found east of the Mississippi River to the Atlantic Seaboard Fall Line in Virginia; and 4) Pantherophis "alleghaniensis" (corrected to P. quadrivittatus by Hillis and Wüster [2021] and Burbrink et al. [2021]), found southeast of the Fall Line in Virginia to the Florida Keys. The range of Pantherophis "spiloides" (now corrected to P. alleghaniensis), referred to as the Central lineage in Burbrink et al. (2021), was found to extend farther east and southeast relative to the Central mtDNA lineage of Burbrink et al. (2000) and the morphological clade of Burbrink (2001). For P. alleghaniensis (now corrected to P. quadrivittatus), referred to as the Eastern lineage POINTS OF VIEW