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Experimental evidence for helper effects in a cooperatively breeding cichlid
Authors:Brouwer  Lyanne; Heg  Dik; Taborsky  Michael
Institution:a Department of Behavioural Ecology, Zoological Institute, University of Bern, CH-3032 Hinterkappelen, Switzerland, and b Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, P.O. Box 14 Haren, The Netherlands
Abstract:Neolamprologus pulcher is a cooperatively breeding cichlid fish,in which helpers stay in their natal territory and help withbrood care, territory defense, and maintenance. In this studywe investigated helper effects by an experimental group sizereduction in the field. After this manipulation, focal helpersin reduced groups tended to feed less, and small helpers visitedthe breeding shelter significantly more often than same-sizedhelpers in control groups. No evidence was found that remaininghelpers compensated for the removed helpers by increasing territorydefense and maintenance behavior. Breeders, however, did showa lower defense rate, possibly caused by an increase in broodcare effort. Survival of fry was significantly lower in removalthan control groups, which provides the first experimental proofin a natural population of fish that brood care helpers do effectivelyhelp. The data suggest that in small, generally younger, helpers,kin selection may be an important evolutionary cause of cooperation.Large helpers, however, who are generally older and less relatedto the breeders than small helpers are suggested to pay to beallowed to stay in the territory by helping. All group membersbenefit from group augmentation.
Keywords:cooperative breeding  group size reduction  helping behavior  Lake Tanganyika cichlids  reproductive success  
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