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bioRxiv · 10.1101/2023.04.17.537178

Female reed warblers in social pairs with low MHC dissimilarity achieve higher MHC compatibility through random extra-pair matings

Halupka, L.·O'Connor, E. A.·Strandh, M.·Sztwiertnia, H.·Klimczuk, E.·Hasselquist, D.·Westerdahl, H.
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Abstract

Major Histocompatibility Complex (MHC) polymorphism is maintained by balancing selection through host-pathogen interactions and mate choice. MHC-based mate choice has been proposed across a wide range of vertebrates. However, the likelihood of its existence in songbirds has been questioned because of their poorly developed olfactory sense, which is a trait considered crucial in pre-copulatory mate choice to determine both own MHC and the MHC of putative partners. In this study, we show that female reed warblers, Acrocephalus scirpaceus, with extra-pair young in their nests have a lower MHC class I (MHC-I) dissimilarity with their social mate than females without extra-pair young in their nests. We also show that the MHC-I dissimilarity of successfully siring extra-pair males is not different from that of either the other males with territories surrounding the social nest (i.e. putative extra-pair males) or the pairs without extra-pair young in their nests. Taken together with the observation that extra-pair mating in reed warblers is common, we argue that these results support a scenario where extra-pair mating is more likely to lead to successful fertilisation when there is a high similarity in MHC-I between the female and her social male. Furthermore, as our data suggest that extra-pair mating at random can result in a higher MHC-I dissimilarity this scenario does not require any active female mate choice for MHC-I dissimilar males to drive this pattern.

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Halupka, L., O'Connor, E. A., Strandh, M., Sztwiertnia, H., Klimczuk, E., Hasselquist, D., Westerdahl, H.. 2023-04-18. Female reed warblers in social pairs with low MHC dissimilarity achieve higher MHC compatibility through random extra-pair matings. https://doi.org/10.1101/2023.04.17.537178

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