Sexual conflict inhibits female mate choice for major histocompatibility complex dissimilarity in Chinook salmon

Abstract

In many species females prefer major histocompatibility complex (MHC) dissimilar mates, which may improve offspring resistance to pathogens. However, sexual conflict may interfere with female preference when males attempt to mate with all females, regardless of compatibility. Here we used semi-natural spawning channels to examine how mating behaviour and genetic similarity at the MHC class II peptide binding region affected parentage patterns in Chinook salmon (Oncorhynchus tshawytscha). We found that females directed aggression at more MHC-similar males than expected by chance, providing a possible mechanism of female MHC choice in salmon. Males also directed aggression towards MHC-similar females, which was consistent with males harassing unreceptive mates. Males' aggression was positively correlated with their reproductive success, and it appeared to overcome female aversion to mating with MHC-similar males, as females who were the target of high levels of male aggression had lower than expected MHC divergence in their offspring. Indeed, offspring MHC divergence was highest when the sex ratio was female-biased and male harassment was likely to be less intense. These data suggest that male harassment can reduce female effectiveness in selecting MHC-compatible mates, and sexual conflict can thus have an indirect cost to females.

Behavioural and genetic analyses of mate choice and reproductive success in two Chinook salmon populations

“…This technique has been used previously to assess behavioural interaction rates in both the coho (Oncorhynchus kisutch) and Chinook salmon (Fleming and Gross 1994;Garner et al 2010). In total, we observed spawning behaviour for Little Qualicum and Quinsam fish over 20 days and 15 days, respectively.…”

Social discrimination by quantitative assessment of immunogenetic similarity

“…The pool of peptide ligands cleaved by MHC molecules reflects structural properties of the peptide-binding groove that are determined by the PBR amino acid sequence. Discrimination thresholds based on MHC-PBR amino acid sequence similarity have been documented in mammals [21], birds [22] and fishes [23][24][25][26]. This suggests that peptides restricted by the peptide-binding groove of MHC molecules directly or indirectly generate social recognition signals.…”

The Relationship between Sexual Selection and Sexual Conflict

“…For example, what if females seek genetic benefits that are uncorrelated with a male's ability to acquire mates? As an illustrative example, female Chinook salmon are more aggressive toward major histocompatibility complex (MHC)-similar males ( potentially indicating choice for MHC dissimilarity), but males appear to be able to overcome this preference (Garner et al 2010). Intriguingly, this study provides evidence that females are better able to control the decision to mate when the sex ratio becomes more female-biased, as offspring MHC diversity was found to increase under such conditions.…”