Jeff Renaud

Wildlife populations that become small and isolated, often due to habitat loss, inevitably experience inbreeding which can lead to the loss of fitness and eventual extinction. One solution is to perform a genetic rescue: a management intervention where new blood is brought in by introducing outsiders to a population to reduce inbreeding and restore diversity. But how do researchers know the inbreeding problem has been solved? A new long-term study from Western, led by biology professor and chair David Coltman, shows DNA-based tools detected changes in inbreeding more accurately than traditional pedigree methods in a wild population of bighorn sheep that was recently genetically rescued. Pedigree approaches estimate genetic health from family history, whereas genomic approaches directly analyze DNA. Coltman, graduate student Carson Mitchell and their collaborators compared genomic and pedigree inbreeding estimates in wild bighorn sheep (Ovis canadensis) from Ram Mountain, Alberta, Canada, from 1972 to the present. The DNA-based method was more responsive to population changes and revealed trends that pedigrees missed. This new study is the first to compare these two widely used inbreeding metrics during a genetic rescue.

Importance of genomic monitoring

Conservation translocation is the deliberate movement of organisms from one site to another where the primary objective is conservation. In North America, wildlife managers sometimes move bighorn sheep to areas where populations have declined (like Ram Mountain, Alta.) to strengthen herds and increase genetic diversity. These efforts can help stabilize smaller populations and support the long-term health of the species. “Translocations are a critical tool used in bighorn sheep management and in the past century more than 1,500 translocations of bighorn sheep have been performed in the United States and Canada,” said Coltman, a faculty member of Western’s Centre for Animals on the Move. “These are expensive and risky undertakings, and sometimes they succeed at genetically rescuing a struggling population and sometimes they fail.” Because inbreeding threatens the long-term viability of many small wildlife populations, these findings have important implications for conservation management and highlight the importance of genomic monitoring at-risk wildlife populations. “Using a snapshot of the genome from a DNA sample, we can now clearly see the genetic consequences of a translocation, we can better monitor populations at risk and post-rescue, and we can plan for more successful translocations in the future,” said Coltman. For 55 years, graduate students like Mitchell have dedicated their summers to investigating bighorn sheep at the Ram Mountain field site in Alberta. The resulting long-term datasets are extremely valuable for conducting studies like this one. “We tracked changes in inbreeding around a translocation event using the population’s family tree and DNA samples. While we expected the DNA-based approach to be more accurate, we didn’t expect them to tell completely different stories,” said Mitchell, the study’s first author who is pursuing her PhD in the Coltman lab. “The pedigree suggested inbreeding was increasing, while the DNA showed it declined after the translocation. Without the DNA data, we could have reached the wrong conclusion about how this population is responding to management.” The study was published in the journal Evolutionary Applications.