Meeting Abstract
Cities are the Earth’s newest major habitat and we can learn a great deal about how populations cope with environmental change by studying the species that colonise them. Eastern grey squirrels (Sciurus carolinensis) are strongly associated with humans and occur, at spatially varying densities, in grey, brown-black, and black colour morphs. These morphs are produced by a single deletion in a gene associated with melanin production. The melanistic allele is incompletely dominant over the wild type. Heterozygotes produce the brown-black morph. We were interested in determining whether melanistic morphs are more closely associated with urban areas than grey morphs. Some data suggests that there may be phenotypic traits, related to temperament and physiology, linked to the melanistic allele that make melanistic morphs better suited to living in urban areas than grey morphs. To test this we downloaded 6782 georeferenced photos of grey squirrels from iNaturalist.org and designated colour morphs as melanistic (black/black-brown) or not. We first used presence only species distribution modelling of environmental variables and human density to identify correlates of the distribution of all morphs pooled. Mixed wood forest cover and human density were the most important variables in the final model, each contributing ~32% to the model’s explanatory power. We then fit the same model to the 896 melanistic morph samples, comparing environments where melanistic morphs occurred to those where grey morphs were sampled. Melanistic morphs were much more closely tied to the presence of humans. Human density contributed ~63% to this model’s explanatory power. This suggests that there may be genetically based traits linked to the melanistic allele that contribute to urban adaptation. What these traits are remains poorly understood.
