For most urban wildlife, elements of a city environment such as built environments, limited predation pressure, and highly fragmented habitats pose conditions that they would be unlikely to face in the wild. But could altered selection processes in urban environments lead to a rise in uncommon fur and feather coloring for species that dwell there? A recent study led by SEFS graduate student Samantha Kreling conceptualizes how wildlife in metropolitan or suburban areas could develop different coloration patterns from their neighbors in non-urban areas in response to the differing environmental conditions they face.
Kreling first arrived at this question while watching a group of coatis, a raccoon-like mammal native to South America, Central America, Mexico, and the southwestern United States, on a golf course in Mexico. Several young individuals in the group had light coloring compared to the rest due to a condition called leucism resulting from decreased melanin production. In the wild, the conspicuous coloring would likely attract predators, but on the relative safety of the groomed course, the coloring could have neutral or even beneficial effects.
“I visited Mexico when I was 19 or 20, and thought, I don’t think this would happen in a place with more predation. The photos of those coatis inspired me on this paper,” said Kreling.
Kreling theorized that factors for urban wildlife such as different predation patterns, exposure to chemicals, low-nutrition diets, limited gene flow with larger populations, and the effect of human presence or domestic species could create an environment that serves as hotspots for rapid evolution. Where it may be beneficial for animals to blend into their surroundings in natural environments, standing out in urban environments could help individuals avoid vehicle collisions, tolerate heat, or even receive preferential treatment such as feeding from humans.
“Color in mammals and birds has largely been studied in naturalized systems where we understand that it’s caused a combination of avoiding detection by predators and prey, sexual selection, and thermoregulation, among other things. But the constraints that would have led to evolutionary colorations aren’t necessarily upheld in urban areas,” said Kreling.
The study, published this week in Bioscience, theorized that the varying selection pressures in cities may be working against each other, limiting the benefits of certain colorations and making it less likely for them to persist. Because physical appearances in wildlife serve distinct and important purposes, the benefits of atypical coloration in a species could be outweighed by other factors. For example, lighter colorations could give a thermoregulatory advantage to urban-dwelling individuals but might be detrimental for sexual selection.
In situations where uncommon colorations in wildlife are protected based on human interests, such as laws protecting albino species of squirrels or deer for tourism purposes, this human-driven selection could have unintended consequences for those populations. In some species, leucism and albinism have been linked to negative health attributes in wildlife, such as weakened feathers in birds.
Cities are a relatively new landscape from an evolutionary perspective, and there is little research on the coloration of wildlife in urban and non-urban areas outside of a few key species. Further research on how urban wildlife species adapt to changing environmental conditions could shed light on species resiliency and the survival and reproduction rates of species.