Experimental evidence for physiological costs underlying the trade-off between reproduction and survival

P>1. A central tenet of life-history theory is that investment in reproduction compromises survival. However, the underlying physiological mechanisms that link reproduction to survival are poorly understood, particularly in wild populations. 2. Previous experiments in the brown anole lizard (Anolis sagrei) show that the elimination of reproduction via surgical ovariectomy results in a dramatic increase in the survival of wild females. We hypothesized that this trade-off reflects underlying differences in energy allocation between reproduction and physiological processes that influence survival. 3. To test this hypothesis, we compared ovariectomized (OVX) females to reproductive controls (SHAM) with respect to four physiological parameters that are thought to influence survival: energy storage, haematocrit, immune function and parasitemia. 4. Consistent with previous studies, we found that OVX females exhibited increased survival and growth relative to reproductive SHAM females. At the end of the breeding season, OVX also exceeded SHAM with respect to energy storage, haematocrit and immune response to phytohemagglutinin challenge. 5. Contrary to our predictions, OVX were more likely than SHAM to exhibit high levels of parasitemia. However, growth and parasite load were positively correlated in OVX and negatively correlated in SHAM, suggesting that reproductive investment may compromise parasite tolerance rather than parasite resistance. 6. Collectively, our results provide direct experimental evidence that reproductive investment affects several key physiological traits that likely interact to influence survival in wild populations.