Exploring the Relationship Between Parental Relatedness and Male Reproductive Success in the Antarctic Fur Seal Arctocephalus Gazella

Abstract

Recent genetic studies of natural populations have shown that heterozygosity and other genetic estimates of parental relatedness correlate with a wide variety of fitness traits, from juvenile survival and parasite resistance to male reproductive success. Many of these traits involve health and survival, where the underlying mechanism may involve changes in the effectiveness of the immune system. However, for traits such as reproductive success, the likely mechanisms remain less obvious. In this paper, we examine the relationship between heterozygosity and a range of traits that contribute to male reproductive success, including time spent on territories and competitiveness. Our analysis is based on observational and genetic data from eight consecutive breeding seasons at a colony of the Antarctic fur seal, Arctocephalus gazella. Overall, male reproductive success was found to correlate strongly with internal relatedness (IR, a form of heterozygosity). When different components of success were analyzed, we found that IR correlates independently with reproductive longevity, time spent ashore, and competitive ability per unit mating opportunity on the study beach, with more heterozygous males being more successful. Behavioral observations were sufficiently detailed to allow examination of how daily mean IR values for males present on the beach varied within seasons and from year to year. Again, significant variation was found both among and within seasons, with more homozygous males appearing less able to hold territories in poor seasons when pup production is low and, within a season, at both the start of the season and to some extent around the peak of female estrus. Finally, we tested whether the benefits of high heterozygosity are due mainly to a genomewide effect (e.g. inbreeding depression) or to single locus heterosis by asking whether the relationship between IR and male success was robust to the removal of any single locus or to any pair of loci. Since the relationship remained significant in all cases, we favor a multilocus explanation for the effects we report.

Quantifying the increase in average human heterozygosity due to urbanisation

“…This resulted in negative mean F A values in all six subsamples (as a proportion of the failed genotypes were likely to be heterozygotes). 16,18 Quantifying increase in human heterozygosity I Rudan et al through application of the sMLH yielded similar results, with successive increase among investigated subsamples of 0.037, 0.043, 0.079, 0.064 and 0.101 (Po0.001). This shows that the two methods are highly comparable, although opposite in sign (direction) of their measurement scale.…”

“…16,18 To control for this we excluded marker data from individuals for whom there were data on less than 750 markers, and corrected for any remaining effect statistically. This resulted in negative mean F A values in all six subsamples (as a proportion of the failed genotypes were likely to be heterozygotes).…”

“…This is because sMLH is a robust method that does not distinguish between an individual's homozygosity for rare and common alleles, whereas F A gives more weight to homozygosity of rare than common alleles. 16 Therefore, although sMLH has been consistently shown to be a very useful method for studying heterozygosity levels in natural animal and plant populations with fewer number of markers used in genotyping, 18,19 we gave more weight to results based on F A measure in this manuscript as it provides more insight into homozygosity in rare genetic variation, which is one of the key features of recent inbreeding that could be affecting human quantitative traits with relevance to health.…”

“…16,17 The first approach was to measure the standardised multilocus heterozygosity (sMLH), the ratio of the proportion of the heterozygous loci of an individual to the mean heterozygosity of those loci at which the individual was typed. 18,19 Weighted averages of chromosome-based heterozygosity estimates were calculated. The scale of this measure is essentially identical to the scale of the inbreeding coefficient, but reversed in sign.…”

Does kin selection influence fostering behaviour in Antarctic fur seals (Arctocephalus gazella)?

“…(a) Study site and field methods This study was conducted at a small fur seal breeding beach at Bird Island, South Georgia (54 800 0 S, 38 802 0 W) and is based on a dataset spanning seven consecutive pupping seasons (Hoffman et al 2003;Hoffman & Amos 2005) that was subsequently expanded to incorporate an additional season (Hoffman et al 2004). Tissue samples and observational data were collected during the austral summers of 1994/1995-2001/2002 (hereafter, breeding seasons are referred to by the year in which they began).…”