Why do we senesce? This question has intrigued many, perhaps since the dawn of our species. Remarkably, recent work on turtles has detected no evidence of demographic senescence, i.e. - no mortality and reproductive aging. Theory predicts the circumstances under which aging should evolve, implying that such senescence may be evolutionarily labile and its occurrence context-dependent. While predictions from theory have been borne out in short-lived organisms under controlled conditions, our understanding of the ecology and evolution of senescence in long-lived organisms in the wild, where it evolved, is lacking. Moreover, evolutionarily conserved molecular networks underlie aging in a wide array of animal taxa (fruit flies, mice, nematode worms). Whether and how such genetic and cellular mechanisms underlie mortality and reproductive senescence outside of the realm of laboratory models remains unknown. Quantifying aging and the evolutionary, ecological, and physiological determinants of such senescence in exceptional taxa will yield valuable insights into the evolution and persistence of senescence, and its co-regulation with other life-history traits. We will investigate key aspects of the evolution, ecology and genetics of aging in a wild population of painted turtles (Chrysemys picta), which has been studied in detail since 1988. We will answer the following questions. 1) Do these C. picta exhibit age-related declines in reproduction and increases in mortality, which is evidence for senescence? 2) Are there differences between the sexes and are there long-lasting impacts of early- age experiences on late-life mortality and fertility trajectories? 3) Are sex differences and early-life impacts on aing rates context dependent? 4) Is offspring lifespan positively related to maternal age or maternal and paternal genotype, thereby suggesting the inheritance of lifespan? 5) Do age-specific physiological profiles (specifically, gene-expression and mitochondrial energetics) underlie mortality and reproduction trajectories similar to mammals and model genetic organisms? We will address these questions with coordinated experimental and analytical approaches. Existing informatics and collections-based resources accumulated over the past 24 yrs., including TurtleBase - a database comprising integrated ecological, environmental, evolutionary, and genetic information corresponding to hundreds of turtles and nests - will provide the input to an analytical pipeline for modeling the biodemography of aging. Importantly, our on-the-ground turtle population has individuals of known age ranging from hatchling to maximum lifespan (ca. 25 yrs.). Samples of these individuals combined with our archived tissue and DNA bank will be leveraged to render us uniquely able to test these important questions.
In this proposal we develop a new vertebrate model for the study of aging; develop a new analytical framework for understanding the biodemography of aging in the context of life history theory; and test the aging profiles (mortality, reproduction, gene expression, physiological) of an ecological model system - the painted turtle. Recent reports of turtle demography suggest that turtles may not age - i.e., they may have no mortality increases and fecundity decreases with advancing age. We will test these assertions, test for the inheritance of lifespan, and test for evolutionary mechanisms of senescence in a long-term study population. By comparing non- traditional organismal biodemography and senescence with mammalian patterns, this approach promises to yield insights into the evolution and genetic control of aging, and has relevance to the practice of geriatric medicine and clinical research in that comparative biology can shed light on conserved vs. flexible aging mechanisms.
| Warner, Daniel A; Miller, David A W; Bronikowski, Anne M et al. (2016) Decades of field data reveal that turtles senesce in the wild. Proc Natl Acad Sci U S A 113:6502-7 |
