Variation in butterfly egg adhesion: adaptation to local host plant senescence characteristics?

James A. Fordyce* and Chris C. Nice Section of Evolution and Ecology, Center for Population Biology, University of California, Davis, CA 95616, USA Department of Biology, Southwest Texas State University, San Marcos, TX 78666, USA *Correspondence: E-mail: [email protected] Abstract Most butterflies that overwinter as diapausing eggs have evolved oviposition behaviours where egg placement is near or on perennating portions of their host plant. We describe an alternative strategy used by alpine populations of a Lycaenid butterfly species complex where eggs are not attached strongly to the leaf substrate and subsequently fall off the plant. Other populations occurring at lower elevations attach their eggs strongly to the plant. In the laboratory, we measured the amount of force required to detach eggs from the leaf substrate. Eggs of the non-alpine populations required more than five times the force required to detach eggs of the alpine population. Field surveys of the host plant characteristics used by various populations suggest that easy detachment may be adaptive for alpine populations because, unlike the host plants used by other populations, nearly all of the preceding year’s vegetative growth is blown away by strong winds during the winter months.