Parental Care and the Evolution of Egg Size in Fishes

Abstract

The quality of parental care appears to correlate positively with egg size, both among and within species of fishes. Past models of the trade-off between quantity and quality of offspring have been inadequate in explaining this correlation. Using features of models by Smith and Fretwell (1974), Shine (1978), and Taylor and Williams (1984), we constructed a model to explain continuous covariation between the quality of parental care and egg size. Our model contains three major assumptions about the dependence of offspring survival on egg size: offspring from larger eggs develop more slowly and take longer to resorb their yolk sacs and become juveniles; egg size determines initial juvenile size; and larger juveniles, which hatch from larger eggs, have lower mortalities, experience faster growth, and take less time to become adults. Under these assumptions, as parental care reduces instantaneous egg mortality, the optimal egg size increases. This increase is expected both among and within populations. Thus, the general conclusion that each population should have a single optimal egg size (see, e.g., Smith and Fretwell 1974; Maynard Smith 1978) may be incorrect.