Is the Eastern Wolf a Species?
Genotypic Clusters in Practice:
Algonquin Wolf Speciation
Uncertainty in the wolf and coyote Canis lineage has complicated conservation efforts throughout eastern North America. One point of contention revolves around the designation of Algonquin Provincial Park’s eastern wolf population as a distinct species, or as a hybrid of two Canis species, the grey wolf (C. lupus) and western coyote (C. latrans). Ultimately, this paper aims to support the three-species model, which considers the eastern wolf as the species C. lycaon on the basis of the genotypic clusters concept.
Photo: © Michael Runtz,
from Gov’t of Canada Eastern Wolf proposed management plan.
Firstly, the results of SNP and genotypic distribution analyses conducted by Wilson et al. disputes the previous classification of C. lycaon as a hybrid of C. lupus and latrans (2000). The researchers first compared the allele frequencies of eight microsatellites in western coyote, eastern and grey wolf populations across North America to identify allelic origins. Clusters of associations were formed by plotting relative genetic distances between individuals. They used mitochondrial DNA (mtDNA) to generate bootstrapped phylogenies as well.
C. lycaon and its putative sub-species rufus (red wolves) aggregated away from grey wolves and coyotes. Bootstrapped lineages also placed the eastern and red wolves on a distinct branching node, rather than extending from grey wolves or coyotes – which would be expected under the two-species model (Wilson et al., 2000). Collectively, these early findings helped inspire further investigations into the genetic basis of eastern wolf speciation.
A consequent study expanded the range of genetic markers used to evaluate eastern wolf identity, utilizing paternal Y-chromosome markers in addition to maternal mtDNA to further illustrate speciation. Researchers sampled coyote, grey and eastern wolf populations from three regions in Ontario, hypothesizing that Algonquin eastern wolves were the agents of sex-biased gene flow via a history of hybrid backcrossing (Rutledge et al., 2010). After examining marker assortment in Y-chromosome and mtDNA, they discovered a larger frequency of distinct eastern wolf Y-chromosome haplotypes in Algonquin than what would be expected under random mating. Algonquin eastern wolf females had mtDNA originating from both coyotes and grey wolves. Likewise, both grey wolf and coyote samples had individuals with eastern wolf mtDNA. The presence of grey wolf DNA in coyotes (and vice-versa) despite behavioral mating barriers between them suggests that eastern wolf females act as the agents of gene flow. Results of sex-based genetic analysis also denote the persistence of a unique Algonquin eastern wolf genetic identity, despite an extensive history of hybridization and sympatry.
Lastly, concerns regarding the limited number of genetic markers used in previous studies were addressed in a subsequent study. Researchers analyzed 127K autosomal SNPs to measure the presence of autosomal grey wolf genes in the eastern wolf genome (Rutledge et al., 2015). Instead of the 8 microsatellites, mtDNA or Y-chromosome markers used in previous experiments, 127K autosomal SNPs were generated using RAD-sequencing; researchers used these genotypes to run simulations under different hybridization mechanisms and generate autosomal genotype frequencies. Contrary to the expectations of the two-species model, eastern wolves were not identified as hybrids of grey wolves and western coyotes – instead, eastern wolf lineages aggregated away from both, forming a distinct cluster of autosomal genotypes similar to mtDNA/Y-chromosome clusters. Although the secondary f3 statistics program identified admixture in the eastern wolf (which would support the two-species model), it failed to identify admixture in the pre-established eastern coyote hybrid, bringing into question the reliability of the f3 results without context (Rutledge et al., 2015).
Nonetheless, the aforementioned studies collectively provide evidence of speciation per the genotypic cluster concept. Despite living in sympatry with several Canis lineages, the Algonquin population of eastern wolves have maintained a distinct genetic identity. Wide-spread recognition of Canis lycaon as a species may address current sociopolitical barriers to conservation, and allow for unified efforts to be made in support of the eastern wolf.
References:
Rutledge, L. Y., Devillard, S., Boone, J. Q., Hohenlohe, P. A., & White, B. N. (2015). RAD sequencing and genomic simulations resolve hybrid origins within North American Canis. Biology Letters, 11(7), 20150303. https://doi.org/10.1098/rsbl.2015.0303
Rutledge, L. Y., Garroway, C. J., Loveless, K. M., & Patterson, B. R. (2010). Genetic differentiation of eastern wolves in Algonquin Park despite bridging gene flow between coyotes and grey wolves. Heredity, 105(6), 520–531. https://doi.org/10.1038/hdy.2010.6
Wilson, P. J., Grewal, S., Lawford, I. D., Heal, J. N., Granacki, A. G., Pennock, D., Theberge, J. B., Theberge, M. T., Voigt, D. R., Waddell, W., Chambers, R. E., Paquet, P. C., Goulet, G., Cluff, D., & White, B. N. (2000). DNA profiles of the eastern Canadian wolf and the red wolf provide evidence for a common evolutionary history independent of the gray wolf. Canadian Journal of Zoology, 78(12), 2156–2166. https://doi.org/10.1139/z00-158
Written for BIOL 336: Fundamentals of Evolutionary Biology (Population Genetics), taken in 2019W T2.