Gender differences and individual variation in the immune system of the scorpionfly Panorpa vulgaris (Insecta : Mecoptera)

From investigations of the vertebrate immune system gender specific differe nces in individual immunocompetence are well known. In general, females see m to possess more powerful immune systems than males. In invertebrates, the situation is much less clear. Therefore, we investigated the immune system of an invertebrate species, the scorpionfly Panorpa vulgaris. We found a h igh degree of individual variation in both traits studied, the lysozyme-lik e antibacterial activity of hemolymph and the capacity for in vitro phagocy tosis of artificial particles. These two immune traits were positively corr elated. As expected, hemolymph derived from females had higher lysozyme-lik e activity and hemocytes from females phagocytosed more particles. The diff erence in phagocytosis was mainly based on higher total hemocyte counts and higher proportions of phagocytically active cells in females, while the av erage number of ingested particles per active phagocyte was not significant ly different. The observed gender differences are discussed in the contest of reproductive strategies and parasite-mediated sexual selection. (C) 2000 Elsevier Science Ltd. All rights reserved.