SREL Reprint #3244

Indeterminate growth in long-lived freshwater turtles as a component of individual fitness

Justin D. Congdon1,2, J. Whitfield Gibbons2, Ronald J. Brooks3, Njal Rollinson4, and Ria N. Tsaliagos2

1Bar Boot Ranch, PO Box 1128, Douglas, AZ 85608, USA
2Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802, USA
3Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada
4Department of Biology, Dalhousie University, Halifax, NS B3H 4J1, Canada

Abstract: Although evidence that reptiles exhibit indeterminate growth remains equivocal and based on inadequate data, the assumption that they do is still widely accepted as a general trait of reptiles. We examined patterns of variation in adult growth using long-term mark-recapture data on 13 populations of 9 species representing 3 families of freshwater turtles located in South Carolina, Michigan, and Arizona in the USA and in Ontario, Canada. Across 13 study populations, growth rates of all adults and only those that grew averaged 1.5 and 1.9 mm/yr respectively. Sources of variation in growth rates included species, population, sex, age, and latitude. Most adults of both sexes with recapture intervals greater than 10 years grew, but across all populations an average of 19% of individuals did not grow (some with recapture intervals up to 30 years). For known-age adults of three species, the highest growth rates occurred during the 10 years following sexual maturity, and the proportions of non-growing individuals increased with age. Growth rates of adults were on average 92% lower than those of juveniles. Based on linear relationships of clutch size and body size of females at average juvenile and adult growth rates it would take 0.7 (0.2–1.2) years and 8.6 (min–max = 2.3–18.5) years, respectively, to grow enough to increase clutch size by one egg. The majority of within population variation in adult body size in 3 species appeared to be a combination of differences in ages at maturity and juvenile and early adult growth, rather than indeterminate growth. The results from our study populations indicate that increases in body size (and associated reproductive output) that results from indeterminate growth are not substantial enough to represent a major factor in the evolution of life histories in general or the evolution of longevity and aging specifically.

Keywords: Indeterminate growth, Turtles, Life-history evolution

SREL Reprint #3244

Congdon, J. D., J. W. Gibbons, R. J. Brooks, N. Rollinson, and R. N. Tsaliagos. 2013. Indeterminate growth in long-lived freshwater turtles as a component of individual fitness. Evolutionary Ecology 27(2): 445-459.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).