Resource availability, mating opportunity and sexual selection intensity influence the expression of male alternative reproductive tactics

Abstract

The expression of alternative reproductive tactics can be plastic and occur simultaneously depending on cues that vary spatially or temporally. For example, variation in resources and sexual selection intensity is expected to influence the pay-off of each tactic and shape the decision of which tactic to employ. Males of the nuptial gift-giving spider Pisaura mirabilis can adopt three tactics: offering a genuine prey gift, a 'worthless' non-nutritious gift or no gift. We hypothesized that resources and/or male body condition, and mating opportunity and sexual selection intensity, vary over the course of the mating season to shape the co-existence of alternative traits. We measured these variables in the field over two seasons, to investigate the predictions that as the mating season progresses, (i) males become more likely to employ a gift-giving tactic, and (ii) the likelihood of switching from worthless to genuine gifts increases. Prey availability increased over the season and co-varied with the propensity of males to employ the gift-giving tactic, but we found no support for condition-dependent gift giving. Males responded to an increase in female availability by increasing their mating effort (gift production). Furthermore, the frequency of genuine gift use increased with sexual selection intensity, consistent with the assumption that sperm competition intensity increases with time. Our results suggest that the frequency of alternative tactics is shaped by seasonal changes in ecological factors and sexual selection. This leads to relaxed selection for the gift-giving tactic early in the season when females are less choosy and resources more scarce, and increased selection for genuine gifts later in the season driven by mating opportunity and risk of sperm competition.

Challenging monogamy in a spider with nontraditional sexual behavior

“…They court virgin females and mount without courtship already copulated females, a tactic that larger males with better body condition more frequently perform. Another example has been documented in the spider Pisaura mirabilis , in which males can perform three different mating tactics: offering a prey gift, offering a non-nutritious gift, or not offering any gift depending on prey availability and sperm competition intensity 51 . Scott et al 52 reported that in Latrodectus hesperus males can perform conventional tactics for mate search, courtship and copulation, or they can adopt mate guarding and mating with immatures as the reproductive season progresses.…”

Silk-borne chemicals of spider nuptial gifts elicit female gift acceptance

“…Males may instead benefit from mating with mated females due to their gained paternity share [41]. Enticing reluctant females into mating may be particularly relevant as males often offer females nutritionally worthless gifts consisting of silkwrapped prey leftovers or plant parts [23]. Silk-borne chemicals may potentially ease such cheating behaviour, with males being known to add higher amounts of silk to worthless gifts [22].…”

“…The silk around the gift facilitates keeping the mating position and prolongs copulation [20,21]. Silk-wrapping generally occurs prior to female encounters as mate-searching males are found in the field carrying gifts in their mouthparts [22,23]. Regardless of the gift being silkwrapped, males that are rejected by the female during courtship are known to add silk to their gift before re-offering, a behaviour eventually leading to successful mating [20,24].…”

Metabolic cost of holding nuptial food gifts for male spiders

“…For example males in poor condition emitted less vibratory pulses than good‐condition males and are more likely to be accepted by the female for copulation (Eberhard et al, 2020). One field study carried out over two seasons, however, found no evidence for condition dependence in P. mirabilis males (Ghislandi et al ., 2018), suggesting that condition effects are not universal. Interestingly, if not given to females during mating, an unused nuptial gift can serve as food supply for the male (Ghislandi et al ., 2017), potentially lowering its energetic cost to males.…”