Molecular Ecology (2010) 19, 3444–3455
doi: 10.1111/j.1365-294X.2010.04750.x
MHC-dependent survival in a wild population: evidence for hidden genetic benets gained through extra-pair fertilizations
L Y A N N E B R O U W E R , * I A I N B A R R , * M A R T I J N V A N D E P O L , T E R R Y B U R K E , § J A N K O M D E U R – and D A V I D S . R I C H A R D S O N * * * *Centre for Ecology, Evolution and Conservation, School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK, Department of Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway, Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia, §Department of Animal & Plant Sciences, University of Shefeld, Shefeld, S10 2TN, UK, –Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 14, 9750 AA, Haren, The Netherlands, **Nature Seychelles, PO Box 1310, Mahe, Republic of Seychelles
Abstract
Females should prefer to be fertilized by males that increase the genetic quality of their offspring. In vertebrates, genes of the major histocompatibility complex (MHC) play a key role in the acquired immune response and have been shown to affect mating preferences. They are therefore important candidates for the link between mate choice and indirect genetic benefits. Higher MHC diversity may be advantageous because this allows a wider range of pathogens to be detected and combated. Furthermore, individuals harbouring rare MHC alleles might better resist pathogen variants that have evolved to evade common MHC alleles. In the Seychelles warbler, females paired with low MHC-diversity males elevate the MHC diversity of their offspring to levels comparable to the population mean by gaining extra-pair fertilizations. Here, we investigate whether increased MHC diversity results in higher life expectancy and whether there are any additional benefits of extra-pair fertilizations. Our 10-year study found a positive association between MHC diversity and juvenile survival, but no additional survival advantage of extra-pair fertilizations. In addition, offspring with a specific allele (Ase-ua4) had a fivefold longer life expectancy than offspring without this allele. Consequently, the interacting effects of sexual selection and pathogen-mediated viability selection appear to be important for maintaining MHC variation in the Seychelles warbler. Our study supports the prediction that MHC-dependent extra-pair fertilizations result in genetic benefits for offspring in natural populations. However, such genetic benefits might be hidden and not necessarily apparent in the widely used fitness comparison of extra- and within-pair offspring.

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