Extreme polygyny results in intersex differences in age-dependent survival of a highly dimorphic marine mammal

• Published in: Royal Society Open Science
• Main Authors: Sophia Volzke, Jaimie B. Cleeland, Mark A. Hindell, Stuart P. Corney, Simon J. Wotherspoon, Clive R. McMahon
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2023
• Subjects: Cormack–Jolly–Seber model; demography; southern elephant seal; mark–recapture; Mirounga leonina; Science; Q; Elephant Seal; Elephant Seals; Southern Elephant Seal; Southern Elephant Seals
• Online Access: https://doi.org/10.1098/rsos.221635; https://doaj.org/article/dbe85a3abba644e8b14656a992039a5e

Developmental differences in vital rates are especially profound in polygamous mating systems. Southern elephant seals (Mirounga leonina) are highly dimorphic and extremely polygynous marine mammals. A demographic model, supported by long-term capture–mark–recapture records, investigated the influence of sex and age on survival in this species. The study revealed clear differences between female and male age-dependent survival rates. Overall juvenile survival estimates were stable around 80–85% for both sexes. However, male survival estimates were 5–10% lower than females in the same age classes until 8 years of age. At this point, male survival decreased rapidly to 50% ± 10% while female estimates remained constant at 80% ± 5%. Different energetic requirements could underpin intersex differences in adult survival. However, the species' strong sexual dimorphism diverges during early juvenile development when sex-specific survival rates were less distinct. Maximizing growth is especially advantageous for males, with size being a major determinant of breeding probability. Maturing males may employ a high-risk high-reward foraging strategy to compensate for extensive sexual selection pressures and sex-specific energetic needs. Our findings suggest sex-specific adult survival is a result of in situ ecological interactions and evolutionary specialization associated with being a highly polygynous marine predator.