Male copulation frequency, sperm competition and genital damage in the golden orb-web spider (Nephila plumipes)

Abstract

Abstract. Copulation in many sexually cannibalistic spiders is associated with a loss of function of the male reproductive organs and, as a consequence, males that survive sexual cannibalism may nevertheless be unable to subsequently copulate successfully. Sexual cannibalism is common in the Australian golden orb-web spider (Nephila plumipes), in which the tip of the conductor typically breaks during copulation. Thus, male mating frequency may be physiologically limited to two females, irrespective of the male's ability to avoid cannibalism or the opportunity to locate and court additional, receptive females. Laboratory experiments revealed that the likelihood of the conductor breaking depends upon the copulatory history of the female insemination duct: males were more likely to break their conductor if they inseminated a 'virgin' rather than 'mated' insemination duct. However, the choice of insemination duct did not influence the duration of copulation or quantity of sperm transferred. In field populations, the proportion of males with both conductors broken increased during the course of the mating season, but while males with broken conductors did not copulate successfully with virgin females, they were nevertheless observed on the webs of immature females. We suggest that male N. plumipes with broken conductors on the webs of females are most likely mate guarding, as this appears to be the most effective mechanism of securing paternity.

Securing paternity in spiders? A review on occurrence and effects of mating plugs and male genital mutilation

“…Contrary to N. fenestrata, fragments of the male palp in the female genitalia did not prevent females from remating, and males who copulated transferred similar amounts of sperm into used and unused ducts (Schneider et al 2008) and first and second males sired similar numbers of offspring . Paternity share in this species is correlated with the duration of copulation .…”

Reproductive Foragers: Male Spiders Choose Mates by Selecting among Competitive Environments

“…A potential mechanism we did not test directly is the movement of males even under low competition. While we have evidence from previous studies that male movement is limited unless competition is increased (Kasumovic et al 2007;Schneider et al 2008), it would be interesting to compare the level of movement under different competitive regimes (including a treatment with no new males added). Indeed, the patterns we observe may be consistent across social contexts and not only a consequence of our competition treatment; males might make adjustments to their choices even when competition is low, using the same behavioral patterns we observe here to increase the fitness payoffs of their choice among potential mates.…”

“…Settlement decisions are therefore equivalent to mate choice in this species, making measurement of male choice straightforward and unambiguous. Previous studies strongly suggest that males do not move once they have settled on a female's web in the wild (Kasumovic et al 2007) or in captivity (Schneider et al 2008), and our own pilot observations show that male settlement decisions are stable in the absence of male-male competition. Once on a female's web, males wait until the female captures a prey item before attempting to assume a mating position (Elgar and Fahey 1996;Schneider et al 2008).…”

“…Previous studies strongly suggest that males do not move once they have settled on a female's web in the wild (Kasumovic et al 2007) or in captivity (Schneider et al 2008), and our own pilot observations show that male settlement decisions are stable in the absence of male-male competition. Once on a female's web, males wait until the female captures a prey item before attempting to assume a mating position (Elgar and Fahey 1996;Schneider et al 2008). Males may attempt to placate females by web plucking, but females typically react aggressively to all males that they detect on the web, and males that attempt to approach females without a current prey item are killed and eaten (Elgar and Fahey 1996;L.…”

“…We ensured that males were all adult virgins by checking for the presence of a full embolus on each of the two pedipalps (mating organs found on the cephalothorax). Each embolus has a scleritized tip that breaks off after mating, such that males cannot reuse their pedipalps (Schneider et al 2008).…”