Condition-dependent nesting in bluegill sunfish Lepomis macrochirus

There are two prominent, nonmutually exclusive hypotheses to explain the timing of reproduction in animals: energetic constraint and adaptive behaviour. We tested these hypotheses by quantifying the costs and benefits of nesting at different times in the season for male bluegill sunfish Lepomis macrochirus, a species with paternal care, in Lake Opinicon (Ontario, Canada). The value of nesting at different times during the breeding season (RSb) was determined from spawning individuals as RSb = P-b x C-b x S-b x O-b, where P-b is the probability of spawning during each bout b, C-b is the expected brood size, S-b is the expected brood survivorship to 'swim-up', and O-b is the survivorship of free-swimming fry to age 1 year. The results show that the value of nesting peaks during the middle of the season. However, nesting patterns varied with male condition and not all males nested at the peak. Larger males, which were able to nest multiple times, first nested early in the season when overwinter survivorship of offspring and renesting opportunities later in the season were maximized. These males had the highest seasonal reproductive success. Smaller males, which nested a single time, delayed nesting until the middle of the season when spawning opportunities and brood sizes were greatest. These data suggest that both energetics and adaptive behaviour play roles in determining the timing of reproduction.