Life History and Demographic Aspects of Aging in the Long-Lived Turtle (Emydoidea blandingii)

Abstract

More than 40 years ago Williams (1957) asked, “Why is it that after achieving the seemingly miraculous feat of morphogenesis, a complex metazoan is unable to perform the apparently much simpler task of merely maintaining that which is already formed?” Answering that question remains central to understanding the evolution of life histories in general, and aging and longevity specifically. The preponderance of relatively short-compared to long-lived organisms suggests that morphogenesis is easier to accomplish than is maintenance of soma, whereas the broad range of longevities of organisms (Finch 1999) demonstrates that maintaining soma for extended periods of time is possible. The underlying assumption of the “disposable soma” theory of aging (Kirkwood 1999) is that the expense of maintaining the immortal germ cells is always warranted, whereas investing in maintaining somatic cells depends on their contribution to the welfare of the germ cells. Because the death of many individuals results from extrinsic factors (predators, disease, accidents), large investiments in maintaining somatic cells are often not warrented. Kirkwood (1999) restated Williams’ (1957) question to ask, “. . . how long do germ cells need soma to last?” From a life history perspective, the question becomes, under what environmental conditions can selection favor prolonged investment in maintenance of soma?