Evol Ecol Res 4: 563-576 (2002)     Full PDF if your library subscribes.

Fitness consequences of delayed maturity in female wood ducks

Madan K. Oli,1* Gary R. Hepp2 and Robert A. Kennamer3

1Department of Wildlife Ecology and Conservation, University of Florida, 303 Newins-Ziegler Hall, Gainesville, FL 32611, 2School of Forestry and Wildlife Sciences, Auburn University, 108 M. White Smith Hall, Auburn, AL 36849-5418 and 3Savannah River Ecology Laboratory, The University of Georgia, PO Drawer E, Aiken, SC 29802, USA

Author to whom all correspondence should be addressed.
e-mail: olim@wec.ufl.edu


Age at maturity has been suggested to be an important life-history trait with substantial potential for influencing the evolution of life histories. Using known reproductive histories of 90 female wood ducks (Aix sponsa) from a long-term study (1982–96), we investigated the fitness consequences of changes in age at maturity. Female wood ducks that attained sexual maturity as yearlings had a significantly shorter lifespan than those that delayed reproduction until 2 years of age or later. However, females that delayed reproduction neither produced a larger number of ducklings during their first reproductive event, nor did they have a greater number of successful lifetime breeding attempts than those maturing as yearlings. Females that attained sexual maturity as yearlings had the greatest individual fitness; the results indicated a directional selection for early maturity. These results are consistent with life-history theory predictions and suggest that reduced lifespan in female wood ducks is the primary cost associated with early maturity; however, costs of early maturity are outweighed by the associated benefits in fitness currency. Regression of individual fitness on age at maturity indicated strong directional selection for early maturity. These results suggest that attaining sexual maturity as yearlings may be an evolutionarily stable strategy in our study population, and that females delaying reproduction do so because they are genetically or environmentally constrained, not because of the potential fitness benefits of delayed maturity.

Keywords: age at maturity, Aix sponsa, cost of reproduction, demography, fitness, individual fitness, life-history evolution, life-history trade-offs, lifetime reproductive success, wood duck.

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