Nuptial feeding in the scorpionfly Panorpa vulgaris: maintenance of genetic variance in sexual advertisement through dependence on condition influencing traits

In Panorpa vulgaris scorpionflies, females choose males on the basis of their saliva secretion ability depending on salivary gland weight. Condition dependent salivary gland weight indicates male quality in terms of food acquisition ability (FAA). In the present study we compare standardised estimates of additive genetic variance (V _a) in conditional status and salivary gland weight under conditions including and excluding food competition. Estimates of V _a were high when individuals compete for food and significantly lower when food competition was excluded, indicating that a large proportion of V _a in conditional status as well as salivary gland weight attributes to V _a in FAA. As FAA is likely to be determined by various underlying traits, maintenance of V _a in FAA, and therewith in salivary gland weight, is easily conceivable. Furthermore, we found a strong genetic correlation between condition and salivary gland weight under conditions including food competition that decreased when food competition was excluded and thereby diminished the strength of sexual selection on condition influencing traits. In sum, our results demonstrate that estimates of V _a in sexual signals (especially if estimated using standardised breeding conditions) will be strongly influenced by the presence/absence of environmental factors related to male performance in natural selection context.