Project Summary:  The survival and reproductive success of polar marine mammals depends on the individual's ability to efficiently manage their energy stores despite large-scale intra- and inter-annual environmental variation. How individuals balance energetic costs to reproduce successfully year-in and year-out depends on physiological and behavioral plasticity, as well as their underlying genotype. Weddell seals  (Leptonychotes weddellii) offer an unparalleled opportunity to assess the nature and underlying mechanisms that contribute to the significant heterogeneity observed in reproductive rates and animal fitness that exist within any wild animal population. This species is a particularly tractable study model due to a long-term demographic study that can distinguish high- and low-quality females a priori (based on past reproductive history), the predictability with which animals return to breeding colonies, the fact
that study animals are easily approachable, and a published genome. This project will take a two-stage approach to understanding the causes of observed differences in
reproductive output by comparing high- and low-quality females' energy dynamics, aerobic capacity, and fertility. The Organismal Energetics component aims to identify key differences in how high-quality females navigate critical 'bottlenecks' within the annual cycle that facilitate both current and future reproductive success, as compared to low-quality females that fail to produce pups year after year. We will focus on the interplay between current and future reproductive success by tracking lactation costs,
midsummer foraging success and the probability of getting pregnant, and overwinter foraging patterns and the probability of pupping the next year in both study cohorts. A strength of the proposed study will be having repeated samplings of animals' physiological status (body composition, endocrinology, ovulation and pregnancy timing), paired with a genome study in the same individuals. The Genome to Phenome aim will identify genetic differences between high- and low-quality females through whole genome sequencing, and we will test that sequence variants (i.e., SNPs) ultimately translate to functional differences in downstream products and phenotype. This will be accomplished through a suite of targeted assays tracking alterations in transcription, translation, through to pathway function through dual luciferase reporter experiments, RT-qPCR, and protein and metabolite quantification. In combination, this project will make strides in distinguishing the roles that plastic (physiological, behavioral) and fixed
(genetic) factors play in complex, multifaceted traits such as fitness in a long-lived wild mammal.