Results
The mating duration of the treatment males was significantly affected by the cues of rival presence to which males were exposed (X2=15.61, df=2, p=0.00041; Figure 1a). Males exposed to the full repertoire of rival cues (+ all; p=0.0047) and those that had been exposed to rivals with the auditory cue removed (+ no sound; p=0.00078) both significantly extended mating duration relative to males that had not encountered rivals. This is consistent with previous research showing that removing one cue signalling the presence of competitors does not impede a male’s ability to respond by significantly increasing mating duration.
Latency to mate was significantly predicted by treatment (X2=5.92, df=2, p=0.052; Figure 1b). Males exposed to a rival with all cues intact (+ all) took significantly longer to start mating than males kept alone (- all; p=0.041). Males exposed to a rival with the auditory cue removed (+ no sound) demonstrated an intermediate mating latency, which did not significantly differ from either of the other treatment groups.
Following mating with the treatment males, females were allowed to oviposit for 24 h before remating. This allowed us to quantify the reproductive success of the treatment males in the absence of sperm competition before remating. A Kruskal-Wallis test showed that the number of offspring produced was significantly affected by rival cues to which males were exposed (X2=11.00, df=2, p=0.0041). However, as the offspring count data were zero-inflated, a hurdle model was then used in which zeroes and non-zeroes were separated and modelled. Neither the number of zeros (X2=4.50, df=2, p=0.11), nor the non-zero offspring counts (X2=3.67, df=2, p=0.16) were significantly predicted by treatment. Contrary to predictions, the distribution of the data suggested an overall pattern of males who had not been exposed to rivals (- all) fathering a higher number of offspring than males exposed to rivals, either with all cues intact (+ all) or the auditory cue removed (+ no sound; Figure 2a).
Females were given the opportunity to remate to an Sb male 24 h after their first matings, in order to assess the reproductive success of the first-mating treatment males under sperm competition. The proportion of females that remated was low across treatments (+ no sound: 38%; + all: 28%; - all: 35%), and was not significantly affected by the rival cues the focal males were exposed to (X2=2.38, df=2, p=0.30). Neither latency to remate (X2=2.76, df=2, p=0.25; Figure S3) nor remating duration (X2=2.23, df=2, p=0.32; Figure S4) were predicted by the rival cues to which the first males were exposed.
The proportion of offspring produced in the 24 h following the second mating that were fathered by the first (focal) male was not significantly affected by the rival exposure treatment (X2=2.05, df=2, p=0.36; Figure 2b). This is contrary to the expectation that males exposed to rivals, either with all cues intact or with the auditory cue removed, would show equivalent increases in sperm competitiveness, compared to males that had not encountered rivals.