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 Univers ity 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 an d survival of Young, Middle, and Oldest age groups of Blanding's turtles to test predictions from two contrasting hypotheses of aging. The relative re productive rate hypothesis predicts traits that increase the reproductive o utput or survival rates of older compared to younger individuals, whereas t he senescence hypothesis predicts a reduction in reproductive output or sur vival in older versus younger individuals. Body size did not increase with age among groups; therefore, indeterminate growth was not a mechanism for i ncreased reproductive output of the oldest individuals. Survivorship, repro ductive frequency and size-adjusted mean clutch size were all higher in the Oldest age group compared to the younger age groups. Nest predation rate w as highest in the Young age group compared to either group of older turtles . In nests that survived predation, the proportion of nests that failed ent irely due to developmental problems was lowest in the Young, intermediate i n the Middle, and highest in the Oldest age group. Successful nests produce d similar numbers of hatchlings and similar sized hatchlings in all three a ge groups. Traits such as egg and offspring size, and offspring produced pe r nest did not support either the relative reproductive rate or the senesce nce hypothesis of aging. Increased embryo mortality in nests of older femal es compared to younger turtles supports predictions from the senescence hyp othesis. Three traits; increased clutch size, reproductive frequency, and s urvivorship of individuals in the Oldest age group compared to younger turt les support the relative reproductive rate hypothesis for evolution of long evity, (C) 2001 Elsevier Science Inc. All rights reserved.