Female preference for nests with many eggs: a cost-benefit analysis of female choice in fish with paternal care

In several fish species with paternal care, females prefer malesguarding many eggs in their nest. This preference might be advantageousbecause the presence of many other eggs dilutes the risk ofnewly laid eggs being eaten by the father. To evaluate thishypothesis quantitatively, we constructed a simulation modelthat mimics the breeding biology of the blenny Aidablenniussphynx. In contrast to earlier verbal models, the costs of choiceare explicitly taken into account We systematically varied factorssuch as the stringency of choosiness and the level and natureof the costs of choice. For realistic parameter values femalechoosiness may result in a fitness advantage of more than 50%.The optimal choice strategy created a distribution of eggs overthe nests which resembles that found in the field for A. sphynx.Our model shows that the relative fitness of a choice strategyis not constant but frequency dependent in a complicated way.If most females are choosy, a bimodal distribution of eggs overthe nests results, with many nests containing few and some nestscontaining many eggs. In such a situation choosiness is profitable,since randomly laying females will often lay their eggs in nestswith few eggs, producing a high mortality per egg due to filialcannibalism. If, on the other hand, only few choosers are present,their influence on the egg distribution is limited. A unimodaldistribution results which is profitable for nonchoosers, sincethe average egg mortality is low and nonchoosers do not bearthe costs of choice. The positive relation between chooser frequencyand chooser fitness makes it easy to understand why choosinessis evolutionarily stable. However, it is not obvious how thetrait is established by selection in the first place.[BehavEcol 7: 353–361 (1996)