Nuptial gift consumption influences female remating in a scorpionfly: male or female control of mating rate?

Abstract

In the scorpionfly Panorpa cognata, males provide females with saliva secretions as nuptial food gifts. Consequently, females derive material benefits and possibly also genetic benefits from multiple matings. Females therefore generally should have a high motivation to remate. Males, on the other hand, do not share this interest, which will generate a sexual conflict over remating interval, possibly leading to male adaptations that prevent females from remating with other males. In this study, I found that mated females were less prone to copulate than virgin females, despite female benefits of multiple matings. Further, I found that the remating interval was significantly longer if the first copulation was long compared to shorter matings. This effect does not entirely depend on copulation duration per se, but on the amount of saliva, that a female is consuming during copulation. These results suggest a mating-induced refractory period and can be interpreted as male manipulation of female remating behaviour mediated through substances in the nuptial gift. Alternatively, receiving large nuptial gifts may decrease the prospective direct fitness benefits from further copulations, and thus change optimal female remating rate. Furthermore, gift size has been shown to correlate with male nutritional condition, which may be an indicator of male genetic quality. Females may therefore benefit indirectly by not remating following copulations involving large saliva gifts. In this scenario, female remating interval would be an effect of cryptic female choice.

Nuptial food gifts influence female egg production in the scorpionfly Panorpa cognata

“…In light of the relatively small influence on egg production in relation to the extent of female polyandry, it seems reasonable to conclude that the current selection pressures on male salivary secretions in the function of paternal investment are at most marginal. The selection pressures on the function mating effort appear more intense, as male nuptial gift offering is necessary to achieve matings ( Engqvist & Sauer, 2003b ) and the size of the salivary secretion influence both copulation duration and sperm transfer ( Engqvist & Sauer, 2001, 2003a and female remating ( Engqvist, 2007 ), important traits in a mating system characterised by female multiple mating and intense sperm competition. Therefore, it is presumably more appropriate to regard the effect of nuptial gift consumption on female reproductive output as an incidental side-effect of its evolved function, namely a device for acquiring matings and increasing male fertilisation success.…”

Should I stay or should I go? Condition- and status-dependent courtship decisions in the scorpionfly Panorpa cognata

“…Mated females would benefit from additional matings because of nuptial gift consumption (Engqvist 2007b), although these nutritional benefits may not always outweigh the costs of enduring a long-lasting courtship interaction. In a recent study, experimental mating trials with mated females were less likely to result in copulations than mating trials involving virgin females (Engqvist 2007c). The present results confirm these findings and suggest that the reduced success of mating attempts with mated females can at least partly be explained by their reduced motivation to remain in courtship for long.…”

“…An alternative explanation is that sexual conflict has driven the evolution of male and female preferences (reviewed in Arnqvist & Rowe 2005). There is some indication that in P. cognata, malederived substances in the salivary masses enable males to manipulate female remating and reproduction (Engqvist 2007c). It is at least possible that males in good condition might be particularly potent manipulators and thus more harmful to females.…”

“…Reduced receptivity following mating may be induced by an adequate sperm supply (Wedell 2005), but other male-produced compounds transferred during copulation are known to induce female receptivity (Leopold 1976;Chapman et al 1998;Wedell 2005), possibly as a male adaptation to reduce the risk and intensity of sperm competition (Parker & Simmons 1989;Simmons & Gwynne 1991;Stockley 1997). In P. cognata, the reduced receptivity following mating is at least partly mediated by salivary mass consumption during mating (Engqvist 2007c), which may either indicate that the saliva secretions are instruments for male manipulation of female mating behaviour or that optimal female mating frequency is influenced by salivary mass consumption (see discussion in Engqvist 2007c;Gwynne 2008).…”

“…Females feed on the salivary mass during copulation, and terminate copulation when they have consumed it. By producing a larger salivary mass before copulation, males increase copulation duration (Engqvist & Sauer 2001), sperm transfer (Engqvist & Sauer 2003a) and, thus, fertilization success (Engqvist et al 2007), and also reduce the likelihood of female remating (Engqvist 2007c). Males produce and store saliva in their salivary gland.…”