Behavioral Ecology Advance Access originally published online on December 4, 2008
Behavioral Ecology 2009 20(2):403-409; doi:10.1093/beheco/arn147
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Competition and brood reduction: testing alternative models of clutch-size evolution in parasitoids
a Department of Entomology, North Dakota State University, Fargo, ND 58105, USA b Department of Entomology, University of Minnesota, St. Paul, MN 55108, USA c Laboratory of Entomology, Wageningen University, 6709 PD Wageningen, the Netherlands d Department of Entomology, University of Illinois, Urbana, IL 61801, USA
Address correspondence to P.J. Ode, who is now at the Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523-1177, USA. E-mail: paul.ode{at}colostate.edu. J.G. de Boer is now at the Evolutionary Genetics and Evolutionary Studies, University of Groningen, PO Box 14, NL-9750 Haren, the Netherlands.
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Abstract |
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Competition between siblings occurs in many taxa including parasitoid wasps. Larvae of solitary species eliminate competitors by engaging in aggressive behavior, thus restricting brood size to a single individual. In gregarious species, more than one offspring can develop per host. There are 2 models by which gregariousness can arise in a population of solitary individuals: 1) through a reduction in larval mobility (with the retention of aggressive behavior) or 2) through a reduction in fighting behavior or ability. When more larvae are present than can be supported by available host resources, these 2 models make opposing predictions regarding the process of brood size reduction: Mortality occurring early in larval development under the reduced mobility hypothesis versus mortality occurring throughout larval development under the reduced aggression hypothesis. Here, we measure changes in brood size over the course of larval development of the gregarious parasitoid, Cotesia flavipes. Superparasitized hosts contained approximately twice as many C. flavipes eggs as hosts parasitized by a single parasitoid female. Brood sizes in superparasitized hosts declined gradually as C. flavipes individuals developed, whereas brood sizes remained constant during larval development in singly parasitized hosts. An absence of wounded or destroyed larvae suggested no aggressive behavior. Collectively, these results support the reduced aggression hypothesis.
Key words: brood reduction, clutch-size evolution, contest competition, Cotesia flavipes, parasitic Hymenoptera, scramble competition, sibling rivalry.
Received 29 January 2008; revised 24 October 2008; accepted 30 October 2008.