Farmers depend on hybrid vigor for improved crop yields, as seeds produced from different strains of, say, corn, can lead to superior crops. Hybrid vigor seems to have worked for coyotes in the Northeastern United States as well, according to a genetic study and physical analysis of the animals: Coyotes in this part of the United States are bigger than their western counterparts because, as their ancestors migrated into the territory, they mated with wolves along the way.
Interested in how animals spread from one region to another, Roland Kays has long been fascinated by coyotes. Originating in the Great Plains, these wild canids have moved eastward over the past 90 years into a mix of forests and fields well suited for the deer and small prey these animals thrive on. Curiously, though, coyotes expanded five times faster via a northern route through Ontario, Canada, than through a more southern route through Ohio. Kays, a wildlife biologist with the New York State Museum in Albany, New York, wondered if mating and hybridization with Canadian wolves influenced this rapid spread. Wolves had been extirpated from Ohio long ago, but they still survive in Ontario.
Over the past 9 years, Kays has photographed coyotes with remote motion sensor cameras, collected roadkill and scat, and obtained tissue and bones from fur trappers, hunters, and others. This material provided Kays and his colleagues with data to nail down the influence of wolves on eastern coyotes. The researchers sequenced a piece of mitochondrial DNA from more than 680 coyotes and measured the skulls of 196 animals. They grouped the DNA sequences by similarity and thus were able to trace the lineages of the various animals and determine their migration patterns.
The data showed that indeed coyotes arrived along southern and northern routes, with the descendents of the southern travelers having DNA much like that of their western counterparts, the researchers report today in Biology Letters. But the offspring of animals that had come along the northern route are much less genetically diverse--suggesting that a few individuals took this route--and have wolf DNA, most likely because their ancestors interbred with Great Lakes wolves. "The wolves are gone, but part of their genomes are still here," says collaborator Jeremy Kirchman, also with the New York State Museum. "This has allowed these coyotes to be so successful." The researchers did not find evidence of much hybridization with domestic dogs, as some have expected, says Kirchman.
Northeastern coyotes are not just larger but they also have wolflike features, the researchers found. These coyotes have wider mouths, with more surface area on the skull where chewing muscles attach, giving them a stronger bite for killing bigger prey. They eat more deer and they are comfortable in forests, much like wolves. More genetic studies are needed to pin down that wolf genes are responsible for all of these changes. But it's clear that "in many ways they are acting like a small wolf, but they look like coyotes," says Matthew Gompper, a wildlife biologist at the University of Missouri, Columbia, who was not involved in the study.
The findings also put an interesting twist on hybrid vigor, say Gompper. Although such crossbreeding often yields hardier plants, "the rule of thumb [for animals] is that hybrids do less well," he says. "In this case, the hybrids appear to have greater fitness. It shows the importance of hybridization in providing the meat for adaptation."
So what exactly are the wild canids in Northeastern America--coyotes or wolves? That puzzler will give evolutionary biologists a bone to gnaw on for a while.