Behavioral Ecology Advance Access originally published online on May 19, 2008
Behavioral Ecology 2008 19(5):949-959; doi:10.1093/beheco/arn051
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Effects of experimentally increased costs of activity during reproduction on parental investment and self-maintenance in tropical house wrens
a Department of Biology, University of Missouri–St Louis, 1 University Drive, St Louis, MO 63121, USA b Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 14, 9750 AA Haren, the Netherlands c Department of Animal Science, University of California, Davis, CA 95616, USA d Center for Isotope Research, University of Groningen, Nijenborgh 4, 9747 AG Groningen, the Netherlands e Behavioral Biology, University of Groningen, PO Box 14, 9750 AA Haren, the Netherlands f Department of Ecology, Evolution, and Organismal Biology, Ohio State University, 318 West 12th Avenue, Columbus, OH 43210, USA
Address correspondence to B.I. Tieleman. E-mail: B.I.Tieleman{at}rug.nl.
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Abstract |
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Life-history theory assumes that organisms trade-off current against future reproduction to maximize fitness. Experimental explorations of the costs of reproduction have not yielded a clear understanding of the nature of these costs but rather point to a complex set of allocation possibilities among several physiological functions and behaviors. We investigated how experimentally increased flight costs affected the trade-off between parental investment and self-maintenance in tropical house wrens, which have relatively high annual survival and multiple breeding opportunities per year. We predicted that handicapped wrens would not increase their energy expenditure but instead decrease their effort to rear young in order to maintain their own body condition. Our results largely supported these predictions: handicapped parents decreased their nestling feeding frequency but did neither alter their field metabolic rate (FMR) nor compromise their body condition as measured by basal metabolic rate (BMR) and several measures of innate immune function. Reduced feeding rates did not affect nestling body mass growth but resulted in decreased structural growth (length of tarsus). The latter result can be explained if parents shifted the type of prey brought to offspring or altered the amount of food brought per trip. The experiment-wide positive correlations among FMR, BMR, and feeding frequency are in agreement with the hypothesis that hard work requires elevated levels of BMR. These correlations, in combination with the absence of a handicap treatment effect on FMR or BMR, do not lend support for predictions from studies in the laboratory that birds compensate hard work during the day by lowering their BMR at night. Considering a complex set of allocation possibilities among several physiological functions and behaviors, we conclude that tropical wrens take out the costs of a handicap largely on their offspring quality not on self-maintenance processes.
Key words: cost of reproduction, handicap experiment, life-history evolution, physiological trade-offs.
* Deceased, 3 June 2007
Received 23 January 2008; revised 26 March 2008; accepted 9 April 2008.