Data from: Exploring the mechanisms underlying a heterozygosity-fitness correlation for canine size in the Antarctic fur seal Arctocephalus gazella

Although heterozygosity-fitness correlations (HFCs) are widely reported in
the literature, most studies use too few markers to allow the proximate
mechanisms to be convincingly resolved. Two competing hypotheses have been
proposed: the general effects hypothesis, in which marker heterozygosity
correlates with genome-wide heterozygosity and hence the inbreeding
coefficient f, and the local effects hypothesis, in which one or more of
the markers by chance exhibit associative overdominance. To explore the
relative contributions of general and local effects in a free-ranging
marine mammal population, we revisited a strong HFC found using nine
microsatellite loci for canine tooth size in 84 male Antarctic fur seals
Arctocephalus gazella (Hoffman et al. 2010). Increasing the number of
markers to 76, we find that heterozygosity is uncorrelated across markers,
indicating that inbred individuals are rare or absent. Similarly, while
the HFC based on overall heterozygosity is lost, stochastic simulations
indicate that when an HFC is due to inbreeding depression, increasing
marker number effectively invariably strengthens the HFC. Together these
observations argue strongly that the original HFC was not due to
inbreeding depression. In contrast, a subset of markers show individually
significant effects, and these are non-randomly distributed across the
marker panel, being preferentially associated with markers cloned from
other species. Using BLAST searches, we were able to locate 94% of loci to
unique locations in the dog genome, but the local genes are functionally
diverse, and the majority cannot be linked directly to growth. Our results
suggest that inbreeding depression contributes little if at all to the
relationship between heterozygosity and tooth size, but that instead the
primary mechanism involves associative overdominance. These findings
contribute to a growing body of evidence suggesting that general effects
are likely to be uncommon in natural populations