Sex-specific Tradeoffs With Growth and Fitness Following Life-span Extension by Rapamycin in an Outcrossing Nematode, Caenorhabditis remanei

Rapamycin inhibits the nutrient-sensing TOR pathway and extends life span in a wide range of organisms. Although life-span extension usually differs between the sexes, the reason for this is poorly understood. Because TOR influences growth, rapamycin likely affects life-history traits such as growth and reproduction. Sexes have different life-history strategies, and theory predicts that they will resolve the tradeoffs between growth, reproduction, and life span differently. Specifically, in taxa with female-biased sexual size dimorphism, reduced growth may have smaller effects on male fitness. We investigated the effects of juvenile, adult, or life-long rapamycin treatment on growth, reproduction, life span, and individual fitness in the outcrossing nematode Caenorhabditis remanei. Life-long exposure to rapamycin always resulted in the strongest response, whereas postreproductive exposure did not affect life span. Although rapamycin resulted in longer life span and smaller size in males, male individual fitness was not affected. In contrast, size and fitness were negatively affected in females, whereas life span was only extended under high rapamycin concentrations. Our results support the hypothesis that rapamycin affects key life-history traits in a sex-specific manner. We argue that the fitness cost of life-span extension will be sex specific and propose that the smaller sex generally pay less while enjoying stronger life-span increase.