Justin D. Congdon1,3, Roy D. Nagle2, Owen M. Kinney3, Todd Quinter2, and R. C. van Loben Sels4

For 42 of the past 53 years, three species of turtles (Chrysemys picta, Emydoidea blandingii, and Chelydra serpentina) were studied on the University of Michigan’s E. S. George Reserve in southeastern Michigan. Maximum longevities recorded to date are 75 yr, 60 yr, and 50 yr for Blanding’s, Painted, and Snapping turtles, respectively. We examined indeterminate growth as a mechanism for increasing the proportion of late to early births of individuals. We compared age or age group specific body sizes, reproductive traits and survival for all three species to test the contrasting predictions of the Relative Reproductive Rate Hypothesis (predicts traits that will increase the reproductive output or survival of older compared to younger individuals) and the Senescence Hypothesis (predicts a reduction in reproductive output or survival in older versus younger individuals). In order of importance, indeterminate growth was most influential in determining the traits of older individuals in Painted turtles, Snapping turtles, and Blanding’s turtles; however, juvenile growth rates and ages at maturity are a more important determinant of variation in adult body size in the populations. Increased reproductive output of older individuals of all three species was primarily related to higher reproductive frequency. Other factors such as nest predation rates were not related to age. Egg size increased substantially with age in Painted and Snapping turtles, but less so in Blanding’s turtles. Increased reproductive output combined with no reduction in survivorship of the older turtles in all three species provides support for the Relative Reproductive Rate Hypothesis as a mechanism for evolution of longevity.
International conservation/field research Oral

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