The effect of a cluster of genes known as the major histocompatibility complex (MHC) on the survival rates of grey seal pups is examined in a Scientific Reports paper. The study indicates that as much as 70% of grey seal pup mortality may be attributable to MHC genotype, with one allele in particular being strongly associated with pup survival.
William Amos and colleagues studied the relationship between MHC genotype and mortality in the grey seal (Halichoerus grypus). They found a strong correlation between the number of MHC alleles a seal pup exhibits and its chances of surviving to reproduce: pups with four alleles are almost certain to reach adulthood, whereas those with only one are very unlikely to survive. One particular allele - allele 5 - was implicated as a strong predictor of whether a pup will die before weaning. It is unusual to find such a high proportion of mortality attributable to one immune-related gene, the authors note.
The MHC is a key genetic component of the vertebrate immune system and is thought to inform mate choice in some species by providing olfactory cues. These results suggest why it may be beneficial for female grey seals to mate with MHC-dissimilar males that will father pups that are more likely to survive to adulthood, given their increased MHC heterozygosity and greater chance of carrying allele 5. The authors do caution, however, that the analysis is quite preliminary - they didn't measure the age of the adult seals or the season quality, for example - and that further research could help to shed light on the mechanisms underlying these processes.