25 March 2012

The Alpine ibex - a lesson in outbreeding depression

The Alpine ibex, Capra ibex, is a species of wild goat that lives in the European Alps. Historically the goat ranged throughout the whole mountain range, but the heavy hunting beginning in the 1500s caused dramatic declines in its populations. As a result of this overexploitation, the goat became extinct in France, Switzerland and Germany by the 18th Century and in Austria and north-east Italy by the 19th. Fortunately, the Italian Gran Paradiso National Park was established in 1922 in order to protect the ibex and its population was used to help recolonise other areas of its historical range.

The anti-poaching enforcement efforts in Gran Paradiso were successful and, as a result, the population of the ibex began to rise. Once the population had grown large enough the next stage of the conservation plan was implemented and the ibex were used in the recolonisation efforts of the species in the Tatra Mountains in Czechoslovakia, one of the areas that it was now extinct. However, this was where a massive and unpredicted problem began. Capra ibex ibex from the park was not the only subspecies of the mountain goat used the scheme, since conservationists believed that their population would grow faster and the scheme would be more successful if they used as many goats as possible to recolonise the mountain range. Thus, the subspecies Capra ibex nubiana from Sinai and Capra aegagrus from Turkey were also used in the scheme and bred with Capra ibex ibex. The problem with is was that these additional subspecies of goat were from much warmer drier climates; climates to which they had become locally adapted to.

The Alpine ibex, Capra ibex ibex.

Consequently, when the additional ibex subspecies' mated with Capra ibex ibex, the hybrid offspring had genes that had been selected for by the environmental conditions of the hotter climates. As a result, the hybrids rutted in autumn instead of winter and the resulting kids (baby goats) were born in February, the coldest month of the year and the whole population rapidly became extinct. Thus, the scheme failed because conservationists had failed to predict the effects of mixing different sub-populations, with slightly different adaptations, together.

This problem is known as outbreeding depression, which occurs because populations in different geographical areas do not breed with each other and are under selection pressures from their environment. Over time, these selection pressures cause different alleles to be most favourably expressed in the different populations and if they breed, the young will likely have reduced fitness (survival and reproductive ability). This problem of local adaptation is an issue for all conservation schemes that move species from one habitat to another; so, before such a scheme's implementation, conservationists must first research whether or not outbreeding depression will be an issue. If it is, the scheme will likely fail at great monetary expense and expense to the endangered species itself, which will already have a small population. Unfortunately, extensive research isn't always possible because of the rapid rate at which species are disappearing and often, management decisions have to made very quickly, without complete genetic knowledge.

However, even though this particular reintroduction scheme failed, the population of the Alpine ibex is now well over 20, 000 and the species is listed under 'Least Concern' by the IUCN

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