65.1 Sunday, Jan. 6 Experimental egg removal reveals costs of reproduction in a lizard, Anolis sagrei COX, Robert M*; CALSBEEK, Ryan; Dartmouth College; Dartmouth College email@example.com
Life history theory is structured around the assumption that current reproductive investment incurs costs (e.g., reduced survival or growth) that compromise future reproduction. Despite the theoretical importance of such trade-offs, clear experimental demonstrations of reproductive costs are uncommon. In this study, we used surgical egg removal and ovariectomy to eliminate the physical burden and presumed energetic cost of reproduction in a wild Bahamian population of brown anoles (Anolis sagrei). Anoles are notable among lizards because they exhibit reduced clutch sizes consisting of one or occasionally two eggs, ostensibly as an adaptation to minimize the physical burden of reproduction in light of their arboreal lifestyle. However, our experiment revealed that even a single-egg clutch incurs performance costs in A. sagrei. Surgical removal of oviductal eggs increased stamina by an average of 10.5% relative to pre-treatment values, whereas sham-surgery controls exhibited a slight decrease in stamina. Egg removal also increased maximal sprint speed by 11.9% relative to pre-treatment values, whereas sham-surgery controls did not differ in pre- and post-treatment sprint speed. Previous studies show that stamina and sprint speed can be subject to strong viability selection in this species. To link these performance costs of reproduction with their ultimate fitness consequences, we compared the growth and survival of surgically ovariectomized (i.e., permanently non-reproductive) females with that of intact controls (i.e., continuously reproductive) in their natural environment. We describe the form and intensity of viability selection acting on experimentally induced variation in reproductive burden and resultant locomotor performance. Our results illustrate a powerful experimental approach for elucidating the relationship between morphology, performance and fitness in wild populations.