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 young are exposed to high mortality risk or conspecific competition. Here we test 2 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 head start. 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.
Translated title of the contribution | Mothers adjust egg size to helper number in a cooperative breeding cichlid |
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Original language | English |
Pages (from-to) | 652 - 657 |
Journal | Behavioral Ecology |
Volume | 7 |
Publication status | Published - 2007 |