Genomic dissection of climate change impacts on a declining Antarctic top predator population

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Predicting how species will respond to climate change requires an understanding of the genetic basis of variation in individual fitness. This is particularly important for long-lived species, which have relatively few generations in which to respond, and species inhabiting polar regions where many of the most rapid and profound environmental changes are occurring. However, long-term studies of polar vertebrates are rare owing to the difficulty and expense of collecting individual-based phenotypic and genetic data from large numbers of individuals under challenging field conditions.Rapid climate change is likely to impose strong selection pressures on traits that are important to fitness, yet few empirical studies have been able to directly quantify altered selective regimes under climate change and their demographic consequences. Furthermore, most studies have focused on additive genetic effects (i.e. allele frequency changes) in response to climate change. However, there is a growing awareness of the fact that heterozygosity can also be a major component of individual fitness that feeds into population growth and extinction probability.An outstanding opportunity to elucidate the genomic and phenotypic consequences of altered selective regimes under climate change is provided by a study of Antarctic fur seals in the South Atlantic. We recently reported a 25% decline in the number of breeding females and an 8% fall in pup birth mass since the 1980s due to locally reduced krill availability. Concurrently, breeding female heterozygosity has increased by 17% over two decades, suggesting that the strength of viability selection against homozygous pups has been increasing over time. However, because heterozygosity was only quantified from nine genetic markers, it remains unclear whether these patterns could reflect inbreeding depression or chance linkage of individual markers to biologically relevant genes. Elucidating the importance of these mechanisms and identifying the genes involved is crucial for understanding the nature of selection, the genetic architecture of fitness-relevant traits and their ecological and evolutionary dynamics in a changing world.We will tackle this question by genotyping 576 individuals spanning three decades at 80,000 genome-wide distributed single nucleotide polymorphisms. The resulting dataset will offer great power to quantify the contribution of inbreeding depression to fitness variation, while several complementary approaches will also be taken to evaluate the explanatory power of specific parts of the genome and the possible involvement of key candidate genes. Finally, we will delve deeper into early acting fitness variation by testing whether heterozygosity influences the ability of individual pups to gain body mass during the critical period from birth to nutritional independence. This project will thereby provide an unprecedented window on the impacts of climate change on an Antarctic top predator.