Differential resource allocation strategies in juvenile elephant seals in the highly seasonal Southern Ocean

Environmental conditions experienced in early life affect growth and influence life history strategies, especially in seasonal environments. We studied the seasonal and sexual variation in resource allocation in juvenile southern elephant seals to investigate whether they show a seasonal decline in growth. We also examined whether sexual differences in growth may lead to separate growth strategies that suit each sex in maximizing fitness. We examined the variation in length (as a measure of somatic growth), body mass and condition of 470 individual 1to 4-yr-old elephant seals relative to their different growth strategies. Applying a novel growth function, we observed increased somatic growth in summer compared to winter. Males were larger, had higher proportions of lean tissue and grew faster than females, demonstrating the evolution of a male growth strategy of attaining maximum size quickly, and a female strategy of achieving primiparity at an early age. This evidence supports the idea that seasonal patterns reflect seasonal variation in prey availability and quality, and differential growth strategies promote optimal resource allocation and increase an individual’s probability of survival and future breeding success in the highly dynamic and seasonal Southern Ocean.