53.2 Saturday, Jan. 5 Miles to go before I sleep: reduced fitness at older ages in a long-lived reptile JANZEN, F*; WARNER, D; BRONIKOWSKI, A; MILLER, D; Iowa State Univ.; Univ. Alabama, Birmingham; Iowa State Univ.; Penn State Univ. email@example.com
Theory predicts that senescence will evolve when selection operates less strongly on traits that are expressed at an old age relative to those expressed at a young age. Although identifying reproductive deterioration and reduced survival at old ages provides an indication of senescence, how age-related changes in reproductive output and survival translate to actual fitness is largely unknown. We quantify the strength and direction of age-specific natural selection and its temporal consistency concerning reproductive output and survival of >1000 mature female painted turtles (Chrysemys picta) across 20 field seasons to further our understanding of how selection affects deterioration of reproductive function and/or survival (or lack thereof) in long-lived organisms. Clutch size and choice of vegetation cover over nests did not differ with maternal age, but older females laid larger eggs and nested more frequently, earlier in the season, and farther from water than younger females. Despite this moderate increase in reproductive function at old ages, fitness declined with advancing age, particularly for individuals with relative high egg output. Moreover, demographic analyses revealed fairly low mortality across reproductive ages, yet detected an unmistakable acceleration in mortality rate with age in these female turtles. To our knowledge, these findings provide the first evidence of reduced fitness at old age in putatively “immortal” reptiles, and suggest that senescence may be observed in populations that exhibit long chronological life spans.