Fuzzy Boundaries: Color and Gene Flow Patterns among Parapatric Lineages of the Western Shovel-Nosed Snake and Taxonomic Implication

Abstract

Accurate delineation of lineage diversity is increasingly important, as species distributions are becoming more reduced and threatened. During the last century, the subspecies category was often used to denote phenotypic variation within a species range and to provide a framework for understanding lineage differentiation, often considered incipient speciation. While this category has largely fallen into disuse, previously recognized subspecies often serve as important units for conservation policy and management when other information is lacking. In this study, we evaluated phenotypic subspecies hypotheses within shovel-nosed snakes on the basis of genetic data and considered how evolutionary processes such as gene flow influenced possible incongruence between phenotypic and genetic patterns. We used both traditional phylogenetic and Bayesian clustering analyses to infer range-wide genetic structure and spatially explicit analyses to detect possible boundary locations of lineage contact. Multilocus analyses supported three historically isolated groups with low to moderate levels of contemporary gene exchange. Genetic data did not support phenotypic subspecies as exclusive groups, and we detected patterns of discordance in areas where three subspecies are presumed to be in contact. Based on genetic and phenotypic evidence, we suggested that species-level diversity is underestimated in this group and we proposed that two species be recognized, Chionactis occipitalis and C. annulata. In addition, we recommend retention of two subspecific designations within C. annulata (C. a. annulata and C. a. klauberi) that reflect regional shifts in both genetic and phenotypic variation within the species. Our results highlight the difficultly in validating taxonomic boundaries within lineages that are evolving under a time-dependent, continuous process.

Łeghágots'enetę (learning together): the importance of indigenous perspectives in the identification of biological variation

“…In the case of todzı in the Sahtú, the mtDNA haplogroups do not coincide geographically with the microsatellite markers. Similar divergence among markers has been shown in shovel-nosed snakes (Wood et al 2014) and chipmunks (Good et al 2008, Hird andSullivan 2009). Surprisingly, results from the pairwise mtDNA analysis indicated that boreal woodland/todzı and barren-ground appear to be more closely related than either are to the mountain group (Table A2.4).…”

“…Examining multiple markers concurrently can provide information about how phenotypic differences may be contributing to historical isolation and present patterns of gene flow (Wood et al 2014). In the case of todzı in the Sahtú, the mtDNA haplogroups do not coincide geographically with the microsatellite markers.…”

“…Variation below the species level is an important component of biodiversity because it provides the genetic variation required for incipient speciation and local genetic adaptation (Wood et al 2014, Mee et al 2015, Hamilton and Miller 2016. Cryptic intraspecific diversity, as is displayed between caribou ecotypes and subspecies (Pond et al 2016), can be especially contentious because it is not always clear how to best identify, delimit, or maintain genetic lineage diversity (Mace 2004, Wood et al 2014, Fitzpatrick et al 2015.…”

“…Cryptic intraspecific diversity, as is displayed between caribou ecotypes and subspecies (Pond et al 2016), can be especially contentious because it is not always clear how to best identify, delimit, or maintain genetic lineage diversity (Mace 2004, Wood et al 2014, Fitzpatrick et al 2015. Further, from a purely scientific perspective, there can exist multiple valid interpretations because rules for finding discontinuity in genetic or spatial ecological data are at some level arbitrary.…”

A legacy of geo‐climatic complexity and genetic divergence along the lower Colorado River: Insights from the geological record and 33 desert‐adapted animals

“…Many species exhibit divergence associated with the ecological boundary dividing the Mojave and Sonoran deserts (Mojave‐Sonoran “ecotone”). Of studies referencing ecotone divergence (Inman et al, ; Wood, Fisher, & Vandergast, ), most attribute this to the vegetation transition (Devitt, ; Graham et al, ; Jezkova et al, ; Mulcahy, Spaulding, Mendelson, & Brodie, ; Wood et al, ) despite the likelihood of an underlying abiotic control (a proximate mechanism) on the change in plant composition. The Mojave Desert has higher average elevation, a wider range of annual temperatures, and lower annual precipitation compared to the Sonoran Desert (Norris, ).…”