Mothers Adjust Egg Size to Helper Number in a Cooperatively Breeding Cichlid

Taborsky B, Skubic E, & Bruintjes R (2006). Mothers Adjust Egg Size to Helper Number in a Cooperatively Breeding Cichlid. IIASA Interim Report. IIASA, Laxenburg, Austria: IR-06-056

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Abstract

Mothers should adjust the size of propagules to the selective forces to which these offspring will be exposed. Usually a larger propagule size is favored when mortality risk or competition for young are high. Here we test two predictions on how egg size should vary with these selective agents. When offspring are cared for by parents and/or alloparents, protection may reduce the predation risk to young, which may allow mothers to invest less per single offspring. In the cooperatively-breeding cichlid "Neolamprologus pulcher", brood care helpers protect group offspring and reduce the latters' mortality rate. Therefore females are expected to reduce their investment per egg when more helpers are present. In a first experiment, we tested this prediction by manipulating the helper number. In "N. pulcher" helpers compete for dispersal opportunities with similar-sized individuals of neighboring groups. If the expected future competition pressure on young is high, females should increase their investment per offspring to give them a headstart. In a second experiment, we tested whether females produce larger eggs when perceived neighbor density is high. Females indeed reduced egg size with increasing helper number. However, we did not detect an effect of local density on egg size, although females took longer to produce the next clutch when local density was high. We argue that females can use the energy saved by adjusting egg size to reduced predation risk to enhance future reproductive output. Adaptive adjustment of offspring size to helper number may be an important, as yet unrecognized strategy of cooperative breeders.

Item Type: Monograph (IIASA Interim Report)
Uncontrolled Keywords: cooperative breeding, maternal effects, maternal investment, offspring size, intraspecific competition, cichlids
Research Programs: Evolution and Ecology (EEP)
Depositing User: IIASA Import
Date Deposited: 15 Jan 2016 08:38
Last Modified: 23 Oct 2016 09:20
URI: http://pure.iiasa.ac.at/8043

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