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 males guard ing many eggs in their nest. This preference might be advantageous bec ause the presence of many other eggs dilutes the risk of newly laid eg gs being eaten by the father. To evaluate this hypothesis quantitative ly, we constructed a simulation model that mimics the breeding biology of the blenny Aidablennius sphynx. In contrast to earlier verbal mode ls, the costs of choice are explicitly taken into account. We systemat ically varied factors such as the stringency of choosiness and the lev el and nature of the costs of choice. For realistic parameter values f emale choosiness mali result in a fitness advantage of more than 50%. The optimal choice strategy created a distribution of eggs over the ne sts which resembles that found in the field for A. sphynx. Our model s hows that the relative fitness of a choice strategy is not constant bu t frequency dependent in a complicated way. If most females are choosy a bimodal distribution of eggs over the nests results, with many nest s containing few and some nests containing many eggs. In such a situat ion choosiness is profitable, since randomly laying females will often lay their eggs in nests with few eggs, producing a high mortality per egg due to filial cannibalism. If, on the other hand, only few choose rs are present, their influence on the egg distribution is limited. A unimodal distribution results which is profitable for nonchoosers, sin ce the average egg mortality is low and nonchoosers do not bear the co sts of choice. The positive relation between chooser frequency and cho oser fitness makes it easy to understand why choosiness is evolutionar ily stable. However, it is not obvious how the trait is established by selection in the first place.