Temporal Variation in Male Copulatory Behaviour in the Solitary Bee Nomadopsis Puellae (Hymenoptera: Andrenidae)

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Abstract
1. Females of the solitary bee, Nomadopsis puellae, foraging for pollen at flowers will copulate with any male that can reach them but the duration of copulation is not constant over the daily foraging-mating period (which lasts from about 0900-1300). Early on, copulations are brief (usually less than 1 min). As the morning progresses, males tend not to release their mates spontaneously but remain in copula for as long as it takes a female to collect a full pollen load and return to her nest. In addition, late in the mating period males that have not secured a single female may begin to assault pairs in attempts to usurp a female from a copulating male. 2. We propose that males control the duration of mating in ways that reflect a change in the genetic gains associated with brief versus prolonged copulations over the course of the morning. We assume that sperm precedence occurs in this species and that females are more likely to oviposit at the end of the foraging period than at the beginning. If these assumptions are correct, guarding a mate through prolonged copulation could become increasingly advantageous as the mating period draws to a close each day. Given a high degree of competition for mates, a male that secured a female on her last trip of the morning could greatly improve the chance that his mate would use his sperm for fertilization if he prevented other males from reaching her until she was safely back inside her nest burrow. 3. An alternative hypothesis that the variation in copulation length is due to changes in the readiness of females to receive sperm from a male over the mating period is considered. Limited data suggest that females do not signal degrees of sperm receptivity to males. Males probably determine how long they will copulate, switching from the tactic of securing many short (unguarded) copulations to a few lengthy (guarded) matings in the course of a morning. 1. Females of the solitary bee, Nomadopsis puellae, foraging for pollen at flowers will copulate with any male that can reach them but the duration of copulation is not constant over the daily foraging-mating period (which lasts from about 0900-1300). Early on, copulations are brief (usually less than 1 min). As the morning progresses, males tend not to release their mates spontaneously but remain in copula for as long as it takes a female to collect a full pollen load and return to her nest. In addition, late in the mating period males that have not secured a single female may begin to assault pairs in attempts to usurp a female from a copulating male. 2. We propose that males control the duration of mating in ways that reflect a change in the genetic gains associated with brief versus prolonged copulations over the course of the morning. We assume that sperm precedence occurs in this species and that females are more likely to oviposit at the end of the foraging period than at the beginning. If these assumptions are correct, guarding a mate through prolonged copulation could become increasingly advantageous as the mating period draws to a close each day. Given a high degree of competition for mates, a male that secured a female on her last trip of the morning could greatly improve the chance that his mate would use his sperm for fertilization if he prevented other males from reaching her until she was safely back inside her nest burrow. 3. An alternative hypothesis that the variation in copulation length is due to changes in the readiness of females to receive sperm from a male over the mating period is considered. Limited data suggest that females do not signal degrees of sperm receptivity to males. Males probably determine how long they will copulate, switching from the tactic of securing many short (unguarded) copulations to a few lengthy (guarded) matings in the course of a morning.

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