Evol Ecol Res 5: 559-570 (2003)     Full PDF if your library subscribes.

Interspecific brood parasitism and the evolution of host clutch sizes

Mark E. Hauber*

Department of Integrative Biology, Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720-3140, USA

e-mail: hauberm@socrates.berkeley.edu


Life-history theory predicts that, over evolutionary time, increased juvenile mortality should decrease parental investment in the number of offspring produced at each breeding attempt. Because interspecific brood parasitism in birds typically reduces the survival of host eggs, nestlings and fledglings, but not that of adult hosts, a specific prediction of the theory is that co-evolution with interspecific brood parasites should lead to smaller avian clutch sizes. Furthermore, the severity of juvenile mortality caused by parasitism in the hosts, due to the parasites’ activities and the hosts’ rejection behaviours, should correlate negatively with clutch size. In a comparative analysis, both of these predictions were supported among hosts of obligate brood parasitic brown-headed cowbirds (Molothrus ater). Reduced clutch sizes appeared to be part of a trade-off strategy as parasitism was also associated with more annual breeding attempts. These findings suggest that, on an evolutionary time-scale, hosts’ prolonged interactions with interspecific brood parasites lead to reduced clutch sizes at the taxon level and, qualitatively, these changes in life-history traits are similar to those associated with other types of parasitism and diseases whose main effects also lead to reduced juvenile survival.

Keywords: co-evolution, conspecific brood parasitism, cowbirds, optimal clutch sizes.

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