Résumé
Sexual selection theory suggests that choice for partners carrying
dissimilar genes at the major histocompatibility complex (MHC) may play a
role in maintaining genetic variation in animal populations by limiting
inbreeding or improving the immunity of future offspring. However, it is
often difficult to establish whether the observed MHC dissimilarity among
mates drives mate choice or represents a by-product of inbreeding
avoidance based on MHC-independent cues. Here, we used 454-sequencing and
a 10-year study of wild grey mouse lemurs (Microcebus murinus), small,
solitary primates from western Madagascar, to compare the relative
importance on the mate choice of two MHC class II genes, DRB and DQB, that
are equally variable but display contrasting patterns of selection at the
molecular level, with DRB under stronger diversifying selection. We
further assessed the effect of the genetic relatedness and of the spatial
distance among candidate mates on the detection of MHC-dependent mate
choice. Our results reveal inbreeding avoidance, along with disassortative
mate choice at DRB, but not at DQB. DRB-disassortative mate choice remains
detectable after excluding all related dyads (characterized by a
relatedness coefficient r > 0), but varies slightly with the
spatial distance among candidate mates. These findings suggest that the
observed deviations from random mate choice at MHC are driven by
functionally important MHC genes (like DRB) rather than passively
resulting from inbreeding avoidance and further emphasize the need for
taking into account the spatial and genetic structure of the population in
correlative tests of MHC-dependent mate choice.