Wageningen University & Research: Danish wild boars are doing surprisingly well, despite a century of inbreeding

A population of isolated wild boars in Denmark that all descend from just four ancestors appear surprisingly fit and healthy. A Wageningen University & Research study revealed strong inbreeding in this population. Remarkable, as inbreeding is considered bad for a population. The study offers new perspectives on the release of endangered species into the wild by, for example, zoos.

Wild boars had gone extinct in Denmark one hundred years ago. The species was reintroduced in Lille Vildmose, Denmark, from Germany in 1926. Only four animals, two of them male and two females, were released into the wild. Almost a century later, these four have produced a healthy population of 150 animals. There is no doubt that this population results from years of inbreeding. Still, the population is surprisingly healthy and resilient, states a study published in Evolutionary Applications.

‘Very remarkable’
‘The introduction of fresh blood is normally seen as essential to the population’s development and biodiversity’, Mirte Bosse of Wageningen University & Research states. She led the study in collaboration with Copenhagen Zoo. Bosse is a conservation geneticist and is involved in, for example, the conservation of endangered species such as the Asian elephant through her research.

Bosse does, however, feel more research on the population is needed to determine the exact level of fitness. Bosse: ‘The rangers report low mortality, and the boar look healthy, but objective measurements to determine the precise level of fitness should be done.’ This is one of the reasons their genes are being sequenced to determine the possible presence of harmful mutations or whether these mutations have been selectively removed from the population generations ago.

New perspectives
A myriad of factors determines the success of a population. Geneticists consider inbreeding an important detrimental factor. A well-known example is provided by the isolated population of wolves in Isle Royale in the United States. Inbreeding and the resulting exposure of harmful mutations have brought this population to the brink of extinction. The population of wild boar in Denmark now shows that a healthy population can, indeed, spring from just a few animals. It is precisely this fact that piqued the interest of Copenhagen Zoo. ‘When endangered species from a zoo are reintroduced into the wild, there are generally only a few animals available’, Bosse explains, ‘this study provides new perspectives on the protection of endangered species.’