Development of fasting abilities in subantarctic fur seal pups: balancing the demands of growth under extreme nutritional restrictions

1. Surviving prolonged food deprivation requires various metabolic adaptations such as energy and protein sparing, which can be highly conflicting with energy-demanding stages of an animal's life history such as growth. 2. Due to the maternal attendance pattern, subantarctic fur seal (Arctocephalus tropicalis Gray) pups must repeatedly endure exceptionally long fasts of increasing duration throughout the 10-month lactation period. Little is known of (i) how these infants adapt to such extreme energetic constraints while sustaining growth and development; and (ii) the ecological implications of repeated prolonged fasting in early life in terms of offspring survival, maternal care and growth strategy in this species, as well as the evolutionary consequences of such life history trait. 3. Physiological responses to prolonged fasting and how they change with development throughout the pre-weaning period were investigated. Results show that beginning with their first fast, subantarctic fur seal pups are able to mobilize lipid reserves preferentially while conserving protein stores in response to nutritional deprivation. As pup age, profound changes in energy expenditure allow the implementation of an efficient strategy of fat storage and lean body mass preservation, which proves highly adaptive in the face of the low maternal provisioning rates experienced. 4. Despite increasing fasting durations, pup mortality decreased markedly throughout the maternal dependence period. Consistent with predictions, field measurements indicate that fasting endurance, although limited in early life, increases up to durations of nearly 3 months with age. Results suggest that the maternal provisioning strategy could be constrained by these ontogenetic changes in pup fasting abilities. 5. Furthermore, extreme energetic constraints and local density-dependent effects appear to exert a strong selective pressure upon the adoption of a convergent growth strategy between the sexes aiming to maximize fat storage and pre-weaning survival. 6. The issues of resulting trade-offs between pre-and post-weaning survival and the evolutionary consequences of extreme fasting abilities are also addressed.