Experiment #1. Male Mating With Multiple Females Within Two Hours.
Mating Behavior in Homotypic Matings. Table 1 summarises the mating statistics for Cs pairs. 178 males (73.3%) mated with at least one female; two males mated four times.
Table 1
Courtship and mating performance in homotypic and heterotypic pairs. We tested flies of two genotypes: control Cs (Cs) and desat1 mutant flies. Values shown indicate the total number of pairs tested, courting and mating (N) or mating frequency (%) relative to the total number of males tested. These values are shown relative to the number of male matings over two hours.
| | Courtship | Number of copulations |
| | | | 0 | 1 | 2 | 3 | 4 |
Female x male | n | n | % | n | % | n | % | n | % | n | % | n | % |
(Homotypic) | | | | | | | | | | | | | |
Cs x Cs | 243 | 231 | 95.1 | 65 | 26.7 | 104 | 42.8 | 43 | 17.7 | 29 | 11.9 | 2 | 0.9 |
desat1 x desat1 | 231 | 212 | 91.8 | 151 | 65.4 | 74 | 32 | 6 | 2.6 | 0 | 0 | 0 | 0 |
(Heterotypic) | | | | | | | | | | | | | |
Cs x desat1 | 12 | 11 | 91.7 | 4 | 33.3 | 7 | 58.3 | 1 | 8.3 | 0 | 0 | 0 | 0 |
desat1 x Cs | 10 | 9 | 90 | 3 | 30 | 3 | 30 | 2 | 20 | 1 | 10 | 1 | 10 |
We compared the performance of Cs males of different ages (2, 4 and 10-days old) and social experience (kept alone: x1; in groups of 5 : x5; x5 isolated one or two days before testing : -1S and − 2S; Suppl. Figure 1A). While the variation of these conditions did not alter the proportion or propensity of male mating, it slightly affected (i) mating latency (or the interval between successive mating) and (ii) copulation duration (Suppl. Figure 1B,C). More precisely, with ♀1 females 4-day old males reared alone showed a significantly shorter mating latency (23 ± 3.8 min) than 2-day old reared in similar conditions or 10 day old males held in groups of five (38.0 ± 4.8 min and 37.9 ± 4.8 min). Mating intervals did not vary between conditions. Mating duration was significantly shorter in 4-day old males held singly (17.1 ± 1.3 min) than in 10-day old males kept in groups (24.9 ± 0.9 min). There was no change in mating duration in males that mated more than once.
Table 1 summarises the mating statistics for desat1 males. 80 males (37.3%) mated with at least one female; six males mated twice. Age and experience significantly affected the proportion of males mating once (Suppl. Figure 2A): significantly more 4-day old males held singly mated (73.7%) than 10-day old males held in groups (20.0%) copulated compared to other males. Mating latency was significantly shorter in 2-day old males held singly (28.3 ± 5.6 min) than in 10-day old males held in the same conditions (53 ± 7.2 min; Suppl. Figure 2B). Mating durations with ♀1 were significantly shorter in 2 day-old males held singly (12.8 ± 0.4 min) than in 10 day-old males held singly or in 4 day-old males held in groups (16.1 ± 1.9 and 16.9 ± 0.8 min, respectively; Suppl. Figure 2C).
Overall, mating frequency was significantly lower in desat1 males than in Cs males, although courtship levels were similar (Fig. 2A). No difference was observed between the strains for mating latency or interval, although mating duration was consistently significantly longer in Cs than in desat1 males. Multiple component analysis of the behaviour of Cs and desat1 homotypic pairs revealed that mating latency and duration with ♀1 were positively correlated. Both parameters were negatively correlated with the number of male copulation(s) (Suppl. Figure 3A&B) – perhaps unsurprisingly, males who mated more quickly and with a shorter duration tended to have more matings in the 2-hour test period.
Mating Behavior in Heterotypic Matings. Although the sample sizes were relatively small, comparison of reciprocal pairs of the two genotypes (Cs female x desat1 male and desat1 female x Cs male) suggests that only the male genotype influenced the frequency of multiple male matings (Suppl. Figure 4). No differences between the two crosses were observed for mating latency with ♀1 flies while mating duration was significantly longer in desat1 x Cs than in Cs x desat1. Based on the differences between homotypic matings of these two strains, this indicates that mating duration depends on male genotype – see Fig. 2A.
Pheromones - cVa. We measured the amount of cVa transferred to females by males who mated with more than one female (Fig. 2B, left) and the amount of cVa left in those males (Fig. 2B, right). Pooling across male age and rearing conditions, Cs ♀1 flies received significantly more cVa than desat1 females (387 ± 11 and 273 ± 32 ng, respectively; P = 0.05). ♀2 flies received significantly less cVa (167 ± 30 ng; P = 0.05) with no significant differences between the two types of female. The amount of cVa received by ♀3 and ♀4 Cs individuals was not significantly different than in ♀2 flies. In males, residual cVa significantly decreased after the first and second matings (0 vs 1 and 1 vs 2; P = 0.05) in both strains – Cs males copulating once or twice retained 650 ± 64 and 404 ± 49 ng cVa respectively, while desat1 males copulating once or twice retained 483 ± 52 and 327 ± 59 ng cVa, respectively.
Pheromones − 7-T and 7,11-HD. Cuticular pheromones in both sexes showed only a slight variation depending on the number of matings by a male (Fig. 2C, D). The only significant variation was found for 7,11-HD, which increased between virgin and mated Cs males; no further significant increase was observed in males that mated more than once.
Experiment #2. Male Mating With Multiple Females On Two Successive Days
Mating Behavior. Cs males were relatively consistent in their mating performance over the two days of testing (D1, D2; Fig. 3A). Males that did not mate on D1 mated at most once on D2; males that mated once on D1 mated at most twice on D2. Males that mated twice on D1 mated up to 3 times on D2, while males that mated three times on D1 mated 2 or 3 times on D2 (3/2; 3/3). desat1 males were also relative consistent in their mating frequency on the two days (Fig. 3B).
Pheromones - cVa Transferred To Cs Females. Overall, Cs females that mated with virgin Cs males received an average of 337 ± 21 ng cVa, generally ranging between 270 and 400 ng cVa (in two outlying cases the figures were 154 and 525 ng). Females that mated with a male that had mated more than once received less cVa as the male mated more: ♀1 received significantly more cVa than ♀2 and ♀3 on both days (Fig. 4A; P < 0.001). The amounts of cVa received from males who had mated the same number of times showed a significant decrease on D2 for both in ♀1 and ♀2 individuals (P < 0.001 and P = 0.001, respectively), but not for ♀3 flies (Fig. 4B).
To evaluate the ability of males to replenish their cVa, we compared cVa levels between ♀1-D1 and ♀1-D2 flies that mated with males showing a similar D1 copulation performance (Fig. 4C). The cVa decrease was not significant in ♀1-D2 females mating with males which had copulated once on D1 but was highly significant with males that copulated twice on D1 (P < 0.001), suggesting that these males had not been able to sufficiently replenish their cVa levels overnight.
Pheromones - Residual cVa Left In Cs Males. The mean amount of cVa in an unmated male was 885 ng (D1 and D2 pooled; Fig. 3A). The levels of cVa in males that did not mate or mated once on D2 were not significantly different to this value, irrespective of their mating frequency on D1. Males that mated twice on D2 showed differences between them depending on their mating frequency on D1 – cVa levels were significantly lower in males that mated three times on D1 compared to males that mated once or twice (P = 0.028 and 0.019, respectively), suggesting that they had not sufficiently replenished their cVa levels. No differences were found for the few males that mated three times on D2. Differences were also observed between males that mated the same number of times on D1: males that mated once on D1 but twice on D2 showed significantly lower levels of cVa (compare 1/0 and 1/1 vs 1/2; P = 0.042); similar declines were observed between males that mates twice on D1 but did not mate on D2 (2/0) and those males that mated twice (2/2) or three times (2/3) on D2 (P = 0.019 and 0.034, respectively).
Pheromones - cVa Transferred To desat1 Females.
desat1 females that mated with virgin desat1 males received 120–440 ng cVa (mean = 337 ± 21 ng cVa). No significant variation was found between the two days, perhaps due to the small number of desat1 males mating (Fig. 5).
Pheromones - cVa Remaining In desat1 Males
Males with a similar number of matings on D2 did not vary in their cVa levels depending on the number of times they mated on D1 (Fig. 3B). Males with a similar number of D1 matings showed a significant cVa decrease according to their number of D2 matings (P < 0.001).
Pheromones − 7-T And 7,11-HD
No variation was observed in either female or male flies of either genotype, irrespective of the number of times the male had mated (Fig. 2C, D).