Genetic diversity and fitness traits in fur seals
Many important fitness traits such as parasite resistance, survivorship and reproductive success often correlate with heterozygosity, whereby there are two different forms of a particular gene in a population. Such heterozygosity-fitness correlations (HFCs) have been found to influence interactions between pathogens and their hosts and the evolution of mate selection. To date, most studies have only used around 10 microsatellite markers (tracts of repetitive DNA), so the mechanisms underlying HFCs remain unclear. This was addressed by the project FURSEALFITNESS (Elucidating the relationship between heterozygosity and fitness in a natural marine mammal population), which used next-generation sequencing of single-nucleotide polymorphisms to investigate HFCs in a natural population. Researchers studied a breeding colony of Antarctic fur seals (Arctocephalus gazella) at Bird Island, South Georgia as a model system to determine the basis of HFCs in a natural population. The aim was to investigate whether HFCs in this species are due to inbreeding or due to a small number of genes that have a major effect (the so-called local effect). Analysis of a microsatellite data set covering 21 consecutive breeding seasons plus 3 decades of individual-based data from the study colony indicated that heterozygosity was strongly associated with multiple fitness traits in females. These traits ranged from early survival to breeding success. Scientists also found that climate change has led to increasing selection against lower-quality, homozygous females. A novel approach was developed for estimating genome-wide heterozygosity based on high-throughput sequencing and applied to an HFC for parasite load in harbor seals (Foca vitulina). It showed unequivocally that HFC is due to inbreeding, and suggested that heterozygosity may explain far more variation in fitness than previously believed. FURSEALFITNESS set out to explain the primary mechanism underlying HFCs for a range of fitness traits in a model system. It has resulted in a clearer understanding of how key fitness traits, including female survivorship under increasing climate stress, correlate with an individual's genotype. Results will contribute to understanding the role of a key species in the fragile Antarctic ecosystem, while increasing our knowledge of the link between genotype and fitness and how it underpins breeding behaviour. The work has been published in the leading peer-reviewed scientific journal Nature and in the Proceedings of the National Academy of Sciences of the United States of America.
Keywords
Genetic diversity, fitness traits, fur seals, heterozygosity-fitness correlations, FURSEALFITNESS
