Where do Harris’ Checkerspots Lay their Eggs and what are the Consequences?

Abstract

Where a female lays her eggs has strong implications for the survival of her offspring, an impetus that takes on particular significance for species that exhibit highly specific requirements. The preference-performance (optimal oviposition) hypothesis predicts that an individual will place its eggs where the resulting offspring experience their highest success. We assessed the spatial patterns of ovipositioning of the rare, monophagous Harris’ checkerspot butterfly (Chlosyne harrisii: Nymphalidae) and related this pattern to the survival of their early offspring, and the initial foraging-site decisions of the young. Harris’ checkerspots laid their egg masses exclusively on flat-topped white asters (Doellingeria umbellata: Asteraceae), exhibiting a strong preference for tall plants (> 40 cm). However, they frequently laid multiple egg masses on a single plant, seemingly contradicting the preference-performance hypothesis, since even a single brood usually consumed all the leaves of its natal plant, eventually forcing the caterpillars to find another host plant. Larvae in the second instar recruiting to their next aster experienced extremely high losses, though some individuals usually managed to locate the closest site. Accordingly, the average success of single broods on a foodplant significantly exceeded that of multiple ones. We thus found little evidence that plant characteristics associated with oviposition choice benefitted overall survival. Although occasional second broods prevailed over first broods, they typically had fewer food resources than on an unoccupied plant. This study presents an apparent conundrum for the preference performance hypothesis with potential implications for the conservation of this rare butterfly.