Urban areas around the world are an interesting combination of non-native and native species. In London, urban foxes are a common sight and because of this, we would predict that urban foxes have evolved due to differing selection factors in cities. For mammalogists, examing and comparing skulls is a common way to measure changes that have occurred. For example, altered food sources could lead to shifts in dentition, complex urban environments could lead to shifts in braincases, and artificial light at night could result in changes to the size of eye sockets. Recently we wrote about comparisons between historic and contemporary rat skulls in New York City and a study published this summer by Dr. Kevin Parsons et al. conducted a similar comparison between urban and rural foxes in London.
Dr. Parsons led a team that measured 111 red fox (Vulpes vulpes) skulls using homologous landmarks (points on the dorsal and ventral sides of the skull) from natural history collections in London and the surrounding boroughs. The team also collected the same measurements on 12 species from the fox clade to understand if and how phylogenetics influences variation in fox skull shape. The researchers found no support for phylogenetic signal contributing to skull shape allowing the team to directly compare urban and rural foxes.
The researchers found variation in skull shape between urban and rural red foxes with urban foxes having a shorter snout and larger sagittal crest — likely related to the greater bite-force required to access discarded human food (i.e. food in trash bags). Despite the shorter snout, urban foxes had an increased nasal region which the authors suggest may be due to urban foxes being more dependant on smell than other senses. Additionally, urban foxes showed reduced sexual dimorphism which may be linked to self-domestication.
Overall, this research suggests that, at least for some urban organisms, urbanization may relax selection by providing ample sources of food (in the form of anthropogenic food waste) and decreasing the need to hunt for live animals. The author’s next steps are to compare the heritability of the morphological traits measured here and use the recently assembled fox genome to identify genes under selection that contribute to craniofacial development.
Check out the full paper here: Parsons, K. J., Rigg, A., Conith, A. J., Kitchener, A. C., Harris, S., & Zhu, H. (2020). Skull morphology diverges between urban and rural populations of red foxes mirroring patterns of domestication and macroevolution. Proceedings of the Royal Society B, 287(1928), 20200763.
Featured image: “Photo 58698234” by Dan Brickley is licensed under CC0.
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