Genetic diversity and demographic history of the leopard seal: A Southern Ocean top predator

Leopard seals (Hydrurga leptonyx) are top predators that can exert substantial top-down
control of their Antarctic prey species. However, population trends and genetic diversity of
leopard seals remain understudied, limiting our understanding of their ecological role. We
investigated the genetic diversity, effective population size and demographic history of leopard
seals to provide fundamental data that contextualizes their predatory influence on Antarctic
ecosystems. Ninety leopard seals were sampled from the northern Antarctic
Peninsula during the austral summers of 2008–2019 and a 405bp segment of the mitochondrial
control region was sequenced for each individual. We uncovered moderate levels of
nucleotide (π = 0.013) and haplotype (Hd = 0.96) diversity, and the effective population size
was estimated at around 24,000 individuals (NE = 24,376; 95% CI: 16,876–33,126). Consistent
with findings from other ice-breeding pinnipeds, Bayesian skyline analysis also revealed
evidence for population expansion during the last glacial maximum, suggesting that historical
population growth may have been boosted by an increase in the abundance of sea ice.
Although leopard seals can be found in warmer, sub-Antarctic locations, the species’ core
habitat is centered on the Antarctic, making it inherently vulnerable to the loss of sea ice
habitat due to climate change. Therefore, detailed assessments of past and present leopard
seal population trends are needed to inform policies for Antarctic ecosystems.