MHC, preen oil and mate choice in bluethroats

The major histocompatibility complex (MHC) genes are highly diverse in vertebrates and have demonstrated to yield a higher fitness with an optimal diversity that is neither too high nor too low. MHC based mate choice has proven to be a strategy for several vertebrate species, yet the mechanism behind this mate choice is not fully understood. Passerine species has a large diversity of MHC genes and preen oil composition is postulated to be the discriminating factor in MHC based mate choice, where odour cues are the assumed mechanism. The passerine bird species bluethroat is particularly diverse for MHCII genes. As a socially monogamous species with high extra pair paternity, the bluethroat is a good study organism to further explore the mechanisms behind MHC and preen oil mate choice. The previous study by Rekdal et al. (2019) showed that female bluethroats chose extra pair males that sired extra pair young closer to the population mean. The present study uses MHCIIβe2 amplified from 590 bluethroats captured over three field seasons and will aim to replicate the previous study by Rekdal et al. (2019). Data regarding MHC similarity and preen oil composition are also used to further explore bluethroat mate choice. I found that females with her extra pair male had a higher MHCII diversity compared to the diversity between females and her social male. I further found no significant difference in preen oil dissimilarity for females and her extra pair male compared to the female and her social male. My results do not coincide with the findings in Rekdal et al. (2019) and there was no apparent correlation between MHC dissimilarity and preen oil similarity in adult pairs. As the sample size used in this study is rather small, more work with larger datasets is needed in order to more accurately draw conclusions regarding MHC-based mate choice in bluethroats