MATERNAL AND ENVIRONMENTAL GRADIENTS IN THE EGG SIZE OF AN ITEROPAROUS FISH

Abstract

Life history theory predicts that organisms inhabiting environments with relatively poor conditions for the growth and survival of their offspring should produce fewer and larger offspring. We examined egg size (an index of offspring size) of an iter- oparous, broadcast-spawning, freshwater fish-the walleye (Stizostedion vitreum)-from 34 populations across 260 of latitude in order to determine whether egg size varied with respect to environmental indices of juvenile habitat quality. Variation among populations (among environments) was compared to variation within populations (among females). Within populations, egg size generally increased with maternal size and age. Slopes of these relationships were much more variable among populations (cv > 100%) than inter- annually within populations (cv 10%) than interannually within populations (cv < 5%), but only slightly more variable than among females within populations (mean cv = 8.5%). Nev- ertheless, among-population variability in egg size was related to environmental conditions. Mean egg size decreased with increasing latitude/decreasing mean annual temperature, contrary to our predictions. However, as predicted, egg size decreased with increasing lake productivity following adjustment for the latitudinal/temperature effect. These results sug- gest that egg size in fishes may be influenced by multiple environmental factors across populations, as well as by maternal effects within populations.