Costs of reproduction in a lizard species: a comparison of observational and experimental data

Life history theory predicts that increasing investments into reproduction compromises survival and future reproduction. However, demonstrating such c osts is confounded by positive correlations between life history traits. Fo r example, individuals in good condition may be good at both surviving and reproducing. We studied such processes in a viviparous snow skink lizard (N iveoscincus microlepidotus) from high elevation sites in Tasmania, Australi a. Our results show a stark difference in costs of reproduction between unm anipulated females from the natural population versus experimentally manipu lated females (using follicle stimulating hormones). In the unmanipulated f emales, females with relatively larger reproductive investments survived be tter than females with smaller reproductive investments. In the experimenta l group, however, females forced to 'over-invest' into a larger clutch surv ived less well than controls. Thus, our study confirms the potential danger s of non-experimental estimation of costs of reproduction.