Rules of death across ontogeny in sexually dimorphic mammals

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In many animals, males are notably larger, forage in different habitats, and experience higher mortality than females. Although physiological constraints, behavioral strategies, and predator-prey interactions have been proposed as possible links between body size and mortality, their relative importance is unknown. This project will determine the benefits and consequences of large body size in northern elephant seals, in which adult males are 6x larger than females. Diving abilities and food requirements will be quantified and compared between males and females from birth to age four. During their foraging migrations, each seal will carry a newly-developed biologger that transmits data on diving behavior, migration route, and feeding success via satellites even if animals die at sea. Identifying the mechanisms that drive differences in foraging habitat and mortality rates between males and females will transform our understanding of top predators including marine mammals and birds that exert strong influences on ecosystems around the world. The project will also build research capacity among students traditionally underrepresented in biology and provide education opportunities for K-12 students and the public through an interactive animal tracking website. For sexually size dimorphic species, it is unknown how ecological processes such as starvation and predation act upon the disparate physiological and behavioral phenotypes of males and females. This project aims to determine how male and female body size differences throughout ontogeny lead to divergent use of the risk-reward landscape. Male and female northern elephant seals will be anesthetized, measured, weighed, instrumented, and sampled from birth through age four. The resulting data will link three biological disciplines: physiological measurements of diving development and energy demands, behavioral partitioning of 3-dimensional space use and diet due to physiological constraints, and ecological consequences of variation in physiology and niche partitioning. A meta-analysis across all seal, sea lion, and walrus species will be used to evaluate how sex-specific mortality rates correlate with the degree of polygyny and sexual size dimorphism more broadly. Together, these aims will determine how ecological risk and reward interact with physiological constraints to drive the ontogenetic development of behavioral strategies in sexually dimorphic mammals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.