The MHC and non-random mating in a captive population of Chinook salmon

Abstract

Detailed analysis of variation in reproductive success can provide an understanding of the selective pressures that drive the evolution of adaptations. Here, we use experimental spawning channels to assess phenotypic and genotypic correlates of reproductive success in Chinook salmon (Oncorhynchus tshawytscha). Groups of 36 fish in three different sex ratios (1:2, 1:1 and 2:1) were allowed to spawn and the offspring were collected after emergence from the gravel. Microsatellite genetic markers were used to assign parentage of each offspring, and the parents were also typed at the major histocompatibility class IIB locus (MHC). We found that large males, and males with brighter coloration and a more green/blue hue on their lateral integument sired more offspring, albeit only body size and brightness had independent effects. There was no similar relationship between these variables and female reproductive success. Furthermore, there was no effect of sex ratio on the strength or significance of any of the correlations. Females mated non-randomly at the MHC, appearing to select mates that produced offspring with greater genetic diversity as measured by amino-acid divergence. Females mated randomly with respect to male genetic relatedness and males mated randomly with respect to both MHC and genetic relatedness. These results indicate that sexual selection favours increased body size and perhaps integument coloration in males as well as increases genetic diversity at the MHC by female mate choice.

Sexual selection for genetic compatibility: the role of the major histocompatibility complex on cryptic female choice in Chinook salmon (Oncorhynchus tshawytscha)

“…Studies in Atlantic salmon (Landry et al, 2001;Consuegra and de Leaniz, 2008) and Chinook salmon (Neff et al, 2008) revealed that reproductive success was positively correlated with MHC class II allelic distance of mates (disassortative). In these studies, females and males were allowed to spawn freely without interference and it is not possible to differentiate between the impact of female choice and male competitiveness pre-and post-spawning on the reproductive success.…”

“…Neff et al (2008) detected that females produced more offspring with MHC class II dissimilar males in Chinook salmon but since individuals were allowed to spawn without interference, it was impossible to disentangle female choice prior to and post mating. However, it allows to hypothesize that CFC might be biased towards MHC class II dissimilar males…”

Mate-guarding by male mandrills (Mandrillus sphinx) is associated with female MHC genotype

“…Among species with conventional sex roles, captive male chinook salmon (Oncorhynchus tshawytscha) also mated randomly with respect to female MHC genotype (Neff et al 2008). …”

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

“…DNA was extracted from parents and offspring, and genetic variation was then evaluated using seven microsatellite loci (for details see Neff et al 2008). Parental allocation was based on maximum likelihood procedures implemented in the program Cervus (v. 3.0, Marshall et al 1998;Kalinowski et al 2007).…”

“…We predicted that intrasexual aggression would correlate with reproductive success, as dominant females may obtain preferred nest sites, and dominant males may monopolize access to spawning females. We also examined how intersexual aggression related to MHC genotypes, as we predicted that female aggression towards MHC similar males may be the mechanism that leads to the higher observed MHC amino acid divergence in a female's offspring than expected by chance (Neff et al 2008). We likewise examined the role of MHC genotype in male aggression towards females.…”