Hypotheses of aging in a long-lived vertebrate, Blanding's turtle (Emydoidea blandingii)

For 35 of the past 47 years, Blanding's turtles were studied on the University of Michigan's E.S. George Reserve in southeastern Michigan. Blanding's turtle is one of the longest-lived emydid turtles with individuals reaching ages greater than 75 years. We compared body sizes, reproductive traits and survival of Young, Middle, and Oldest age groups of Blanding's turtles to test predictions from two contrasting hypotheses of aging. The relative reproductive rate hypothesis predicts traits that increase the reproductive output or survival rates of older compared to younger individuals, whereas the senescence hypothesis predicts a reduction in reproductive output or survival in older versus younger individuals. Body size did not increase with age among groups; therefore, indeterminate growth was not a mechanism for increased reproductive output of the oldest individuals. Survivorship, reproductive frequency and size-adjusted mean clutch size were all higher in the Oldest age group compared to the younger age groups. Nest predation rate was highest in the Young age group compared to either group of older turtles. In nests that survived predation, the proportion of nests that failed entirely due to developmental problems was lowest in the Young, intermediate in the Middle, and highest in the Oldest age group. Successful nests produced similar numbers of hatchlings and similar sized hatchlings in all three age groups. Traits such as egg and offspring size, and offspring produced per nest did not support either the relative reproductive rate or the senescence hypothesis of aging. Increased embryo mortality in nests of older females compared to younger turtles supports predictions from the senescence hypothesis. Three traits; increased clutch size, reproductive frequency, and survivorship of individuals in the Oldest age group compared to younger turtles support the relative reproductive rate hypothesis for evolution of longevity.