Evol Ecol Res 6: 955-973 (2004)     Full PDF if your library subscribes.

Natural selection acting on body size, growth

rate and compensatory growth: an empirical

test in a wild trout population

Stephanie M. Carlson,1* Andrew P. Hendry2 and Benjamin H. Letcher3

1Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003-5810, USA,  2Redpath Museum and Department of Biology, McGill University, 859 Sherbrooke St. W, Montréal, Québec H3A 2K6, Canada and  3S.O. Conte Anadromous Fish Research Center, US Geological Survey–Leetown Science Center, PO Box 796, One Migratory Way, Turners Falls, MA 01376, USA

Address all correspondence to Stephanie Carlson, School of Aquatic and Fishery Sciences, University of Washington, Box 355020, Seattle, WA 98195, USA.
e-mail: scar@u.washington.edu


Organisms usually grow slower than their maximum potential under a given set of conditions, suggesting that fast growth carries a corresponding fitness cost. A pattern of growth that might influence such costs is compensatory (or catch-up) growth, where individuals grow faster than expected. One form of compensatory growth occurs when small individuals grow faster for their size than do large individuals, thereby decreasing (or slowing the increase in) size disparity between themselves and larger conspecifics. We tested these ideas over several seasons in wild brown trout (Salmo trutta) by estimating selection acting on individual size, growth and compensatory growth. We then examined population-level growth patterns to determine whether they influence individual-level selection. Selection generally did not favour large individuals or those with slow growth; indeed, the opposite was more likely. Moreover, selection did not act against small/fast-growing individuals (i.e. those expressing compensatory growth). Population-level growth was proportional (i.e. mass increases were a constant percentage of initial mass across the range of body sizes) in all seasons except for the spring and, to a lesser degree, the early summer of the second year of life. In these two intervals, small fish showed greater proportional growth than large fish and small/fast-growing fish had higher (or at least not lower) survival. An intriguing explanation for these results is that fast (and compensatory) growth is only exhibited when the costs of fast growth are low. Our study introduces a novel approach for assessing growth at the population level, as well as the survival costs associated with individual size and growth.

Keywords: brown trout, compensatory growth, correlational selection, costs of growth, life-history trade-offs, Salmo trutta.

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        © 2004 Stephanie M. Carlson. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

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