Love for sale and its fitness benefits: nuptial gifts in the scorpionfly Panorpa vulgaris represent paternal investment

Nuptial feeding is a very common strategy shown by males of various insect taxa in order to obtain copulations. In the majority of cases these gifts presented during or after courtship and/or copulation can be considered as mating effort. In this study we present data which indicate that nuptial feeding in Panorpa vulgaris (Mecoptera: Panorpidae) represents paternal investment. During copulations males produce salivary secretions which are consumed by the females. The more salivary masses a male produces the longer the copulation will last. Since sperm are transferred continuously during copulation and fertilization of eggs follows the fair raffle principle, females allocate paternity in accordance to copulation duration and therefore to the amount of nuptial gifts they receive from a certain male. In the present study we are able to show that the number of salivary masses consumed significantly affects the number of eggs a female produces. Thus, in P. vulgaris the nuptial gift increases the reproductive output of females and hence must not only be considered as mating effort but also as paternal investment. The mechanism by which salivary masses increase female fecundity is yet unknown. We hypothesize that the secretions may not only transfer nutrients but may possibly operate as carriers for an allohormone that manipulates the females' physiology in terms of increasing egg production.