Abstract
Trends in modern society show an increase in maternal age due to deferred childbearing, and assisted reproductive technologies often make this possible. However, there are still numerous challenges in the field of reproductive health, ranging from conception to delivery and beyond. Wild animals may provide answers to some of the field's pressing problems because these species have acquired adaptations to maximize reproductive output under some of the world's most extreme conditions. Here, I focus on 3 key aspects of marine mammal life history that could provide significant insight into reproductive physiology and function for future study. First, marine mammals are fasting-adapted species that cease feeding activities during portions of their reproductive cycle. Strong selective pressures for lipid mobilization to support energetic demands during fasts result in reversible insulin resistance, similar to gestational diabetes mellitus. Second, marine mammals extensively forage as they recover from fasts, engaging in repeated, long-duration dives. This exposes the females and their pregnancies to prolonged hypoxia, extending far past the limits that human fetuses could withstand during delivery without hypoxic ischemic encephalopathy or asphyxiation. Finally, pinnipeds and polar bears use embryonic diapause to time birth with optimal conditions for successful offspring rearing. The ability to "pause" pregnancy until conditions improve could substantially enhance successful outcomes for assisted reproductive technologies in humans. Lessons learned from marine mammal physiology highlight the value in applying comparative studies toward a One Health approach in reproductive medicine.