Unpredictable offspring survivorship in the damselfly, Megaloprepus coerulatus, shapes parental behavior, constrains sexual selection, and challengestraditional fitness estimates

Evolutionary biologists typically assume that the number of eggs fertilized or developing embryos produced is correlated with an individual's fitness. Using microsatellite markers, we document for the first time estimates of realized fitness quantified as the number of offspring surviving to adultho od in an insect under field conditions. In a territorial damselfly whose ma les defend tree hole oviposition sites, patterns of offspring survivorship could not be anticipated by adults. Fewer than half of the parents contribu ting eggs to a larval habitat realized any reproductive success from their investment. The best fitness correlate was the span over which eggs in a cl utch hatched. Among parents, female fecundity and male fertilization succes s were poor predictors of realized fitness. Although body size was correlat ed with female clutch size and male mating success, larger parents did not realize greater fitness than smaller ones. The uncoupling of traditional fi tness surrogates from realized fitness provides strong empirical evidence t hat selection at the larval stage constrains selection on mated adults.