Surviving despite reduce MHC variation: selection patterns and genetic variation of the endangered Huillín (Lontra provocax)
2021
The major histocompatibility complex (MHC) is a highly polymorphic gene group that mediates the vertebrate immune response through antigen recognition and presentation. The ability to face an emerging infectious disease is greatly attributable to the genetic diversity of the MHC genes due to its main role in the adaptive immune response of vertebrates. The Huillín (Lontra provocax) is an endangered otter from southern Chile whose populations have been threatened due to illegal fur trade and displaced as a result of land use change in southern Chile, facilitating contact with domestic animals and allowing the transmission of infectious diseases. In this study, MHC loci from wild populations of L. provocax were assessed for the first time. Variation and signature of selection were estimated for MHC class I exons 2 and 3, and MHC class II DRB exon 2. Low genetic diversity was found for MHC whereas signatures of historical positive selection are suggested but inconclusive. The recent population bottleneck that occurred in L. provocax due to anthropogenic pressures might have unchained a strong genetic drift that overcomes the effects of positive selection in the MHC loci, diminishing genetic diversity and erasing signatures of selection. These results suggest that L. provocax has a low adaptive capacity and, therefore a great susceptibility to the spread of diseases from domestic and invasive animals towards the endangered L. provocax. This should be considered as a warning about the vulnerability of the species to face emerging infectious diseases.
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