Alpine ibex are wild relatives (although not direct ancestors) of the domestic goat. These animals are majestic creatures found throughout the Alps. But the species underwent drastic fluctuations in their census over the past centuries. Overhunting in the Alps brought Alpine ibex to virtual extinction in the 19th century (that’s about the same time bears and wolfs practically vanished from the Alps too). Paradoxically, Alpine ibex only survived because a 19th century Italian king, Vittorio Emmanuele, loved hunting them so much. The king ordered that a park in the Italian Alps be set apart for his private hunting pleasure. The hunting ban for underlings essentially protected the Alpine ibex in the park. During the 20th century, Alpine ibex from the park were used for captive breeding and reintroduction across the Alps. Despite the current census in the ten thousands of animals, Alpine ibex are genetically impoverished which is a testimony to the severe bottleneck imposed by the near extinction in the 19th century.
After her PhD, Christine decided to get to the bottom of why Alpine ibex share a MHC allele with domestic goats. Finally, a combination of Sanger sequencing, microsatellites, SNP chip and restriction site associated DNA sequencing (RADseq) showed that the Alpine ibex MHC allele shared with domestic goats is the result of an introgression event into Alpine ibex. We found that the sequence identity between goat and Alpine ibex extended far into other exons and introns of the MHC locus. Furthermore, the MHC region showed a strong signature of linkage disequilibrium suggesting that linkage introduced by the introgression has not been fully broken down yet.
Introgression at the MHC, despite the very small number of documented cases, should not be very surprising. Diversity at the MHC is maintained by balancing selection, favouring rare variants over more frequent variants. Introgression, by definition, introduces (initially) rare variants and may, therefore, be favoured by selection at the locus.