Is male puddling behaviour of tropical butterflies targeted at sodium for nuptial gifts or activity?

An apparent sexual difference in adult feeding behaviour in many species of Lepidoptera relates to puddling on mud, dung and carrion. In most butterfly species, puddling is exclusively a male behaviour. A possible explanation for this division in feeding behaviour is that nutrients derived from puddling are transferred to the female in the spermatophore during mating as a nuptial gift. Sodium derived from puddling has been shown to act as a nuptial gift in a few Lepidoptera species. It can also be used for neuromuscular activity in both males and females and may therefore correlate with flight morphology. In this study, we examine the generality of these two hypotheses in comparative work on a community of African fruit-feeding butterflies. We investigated puddling behaviour of males and females on carrion and dung together with sodium preferences, polyandry, relative wing-size, sexual size dimorphism and sodium concentrations in the bodies and spermatophores of several species. The results show that sodium as a nuptial gift can explain the sexual division in puddling in some species, but not in all. Species in which both sexes puddle transfer little sodium in the nuptial gift, which is consistent with the nuptial gift theory. Wing loading and puddling are not significantly correlated, but the trend followed the direction predicted by the activity hypothesis. However, the sodium concentration in the species with the smallest wing area to thoracic volume (WA/TV) ratio (the largest Charaxes spp.), was relatively low. Moreover, in all investigated species, the sodium concentration was higher in the abdomen than in the thorax. The results are discussed in the light of differences between the sexes in foraging behaviour in both larvae and adults, and with respect to alternative explanations for puddling. (c) 2005 The Linnean Society of London.