Wolak 2010 - Contributed Paper A Contemporary Sex-Limited...

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Contributed Paper A Contemporary, Sex-Limited Change in Body Size of an Estuarine Turtle in Response to Commercial Fishing MATTHEW E. WOLAK, ‡ GEORGE W. GILCHRIST,† VICTORIA A. RUZICKA, DANIEL M. NALLY, AND RANDOLPH M. CHAMBERS W.M. Keck Environmental Field Laboratory, College of William and Mary, Williamsburg, VA 23187, U.S.A. †Department of Biology, College of William and Mary, Williamsburg, VA 23187, U.S.A. Abstract: Juvenile growth rate and adult body size are important components of life-history strategies because of their direct impact on fitness. The diamondback terrapin ( Malaclemys terrapin ) is a sexually dimorphic, long-lived turtle inhabiting brackish waters throughout the Atlantic and Gulf coasts of the United States. In parts of its range, terrapins face anthropogenically imposed mortality: juveniles of both sexes inadvertently enter commercial crab traps and drown. For adult females, the carapace eventually grows large enough that they cannot enter traps, whereas males almost never reach that critical size. We compared age structure, carapace dimensions, growth curves, and indices of sexual dimorphism for a Chesapeake Bay population of terrapins (where mortality of turtles is high due to crab traps) with contemporary terrapins from Long Island Sound and museum specimens from Chesapeake Bay (neither group subject to commercial crab traps). We also calculated the allochronic and synchronic rates of evolutionary change (haldanes) for males and females to measure the rate of trait change in a population or between populations, respectively. We found a dramatic shift to a younger male age structure, a decrease in the length of time to terminal female carapace size, a 15% increase in female carapace width, and an increase in sexual dimorphism in Chesapeake Bay. In a new twist, our results implicate a fishery in the selective increase in size of a reptilian bycatch species. These sex-specific changes in life history and demography have implications for population viability that need to be considered when addressing conservation of this threatened turtle. Keywords: anthropogenic selection, haldanes, fisheries, Malaclemys terrapin , rapid evolution, sexual dimor- phism, size-selective mortality. Un Cambio Contempor´ aneo, Limitado por el Sexo, en el Tama˜no Corporal de una Tortuga Estuarina en Respuesta a la Pesca Comercial Resumen: La tasa de crecimiento de juveniles y el tama˜no corporal de adultos son componentes importantes de las estrategias de historia de vida debido a su impacto directo sobre la eficacia biol´ogica. La tortuga Malaclemys terrapin es una especie longeva, dim´orfica sexualmente, que habita aguas salobres a lo largo de las cosas del Atl´antico y Golfo de M´ exico de Estados Unidos. En algunas partes de su distribuci´on, las tortugas enfrentan mortalidad de origen antropog´enico: juveniles de ambos sexos entran inadvertidamente a trampas para cangrejos y se ahogan. En hembras adultas, el carapacho eventualmente crece lo suficiente y no pueden
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This note was uploaded on 07/13/2011 for the course PCB 4034C taught by Professor Osenberg during the Spring '11 term at University of Florida.

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Wolak 2010 - Contributed Paper A Contemporary Sex-Limited...

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