X-Message-Number: 23923
Date: Sun, 18 Apr 2004 12:06:45 -0700 (PDT)
From: Doug Skrecky <>
Subject: negligible senescence in some turtles

(How do they do it?)
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Exp Gerontol. 2003 Jul;38(7):765-72.
Testing hypotheses of aging in long-lived painted turtles (Chrysemys picta).

For 38 of the past 50 years, Painted Turtles were studied on the
University of Michigan's E.S. George Reserve in southeastern Michigan. We
compared age specific body sizes, reproductive traits and survival of
Painted Turtles ranging from 9 to 61 years of age to test contrasting
predictions of the Relative Reproductive Rate and Senescence Hypotheses of
aging. Indeterminate growth (i.e. continued body growth of adults) was
important in increasing reproductive output of older turtles; however,
growth rate of the oldest age-group was reduced compared to that of
younger adults. Although clutch size and among year reproductive frequency
did not increase with age, within year reproductive frequency (production
of second clutches), egg size, and hatchling size did. Nest predation
rates and the proportion of surviving nests that produced hatchlings were
similar among age groups, and embryo mortality in nests was not related to
age. Survivorship of males was less than that of females, and
survivorship of the oldest group of females was not statistically
different from that of a younger group of females. No decline in
reproductive output or survivorship was detected in the oldest
females as predicted by the Senescence Hypothesis. Thus, the majority of
data on reproductive traits and survivorship support the Relative
Reproductive Rate Hypothesis. We also compared Painted Turtles to
Blanding's Turtles, another species studied on the E.S. George Reserve.
That Painted Turtles exhibit indeterminate growth whereas Blanding's
Turtles do not, appears to be a primary mechanism for some differences
between species in the relationships between reproductive traits and age.
An important mechanism for increasing reproductive output in both species
was increased reproductive frequency in older females. Painted Turtles
also increased offspring quality (egg and hatchling size) with age,
whereas Blanding's Turtles did not. Compared to younger individuals,
there was no reduction in survivorship in the oldest Painted Turtles and
survivorship increased in the oldest Blanding's Turtles.

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