To accurately estimate potential limits of phenotypic evolution we must understand how phenotypes interact to determine fitness in natural populations. In heterogeneous environments, understanding the determinants of fitness is further complicated by variation in the presence and intensity of multiple environmental pressures. In many animal species, females can directly influence the selective environment experienced by their offspring. Proximate cues such as temperature, humidity, shade, and substrate type can all influence maternal nest site choice and offspring success. By studying the physiological and behavioral strategies maintaining fitness in turtle populations today, we hope to demarcate their capacity to respond to the uncertainty of tomorrow.