Developmental conditions shape lifetime reproductive strategies in a wild mammal

Coping with developmental hardship is a defining feature of resilience across the tree of life. Compensatory strategies that preserve fitness after a poor start are hypothesized to be favored by natural selection, but empirical evidence is rare. Using over three decades of data on >1,000 reproductive attempts across the lifetimes of 405 wild female red squirrels, we show that developmental adversity prompts adaptive reorganization of reproductive investment across the lifespan. Hardships reduced lifetime reproductive opportunities, but triggered opposing strategies. Extrinsic mortality risk predicted frontloading of reproduction at debut, while poor maternal investment predicted terminal reproductive effort at a cost to future generations. Both strategies preserved lifetime fitness, revealing how context-dependent reproductive plasticity over the life course can rescue the fitness consequences of developmental hardship.