3.2 ǀ Colony growth rate and female mating frequency
A considerable percentage of female sexuals, which had been transferred to the laboratory and kept in isolation, died within the first four weeks of the experiment (40% of 43 female sexuals with and 26% of 112 female sexuals without temporary access to males in the lab). Of the surviving individuals with access to males, 23 (88%) produced at least one worker compared to 13 (16%) of those without. Female sexuals, which succeeded in producing offspring over the 530 days of the experiment (n = 36), lived significantly longer than those that did not (n = 80; log-rank test, test statistic = -7.57, p< 0.0001, Figure 1). Dissection of four female sexuals that died or did not produce any workers revealed an empty spermatheca, suggesting that also other unproductive female sexuals had been unmated.
While it initially appeared that female sexuals, which had been given temporary contact with two or three males in the lab, produced considerably more offspring than those with contact with only one male or without contact (data not shown), paternity analyses of ten offspring workers per female sexual revealed the opposite pattern. The number of offspring varied significantly with mating frequency (Kruskal-Wallis test, H (6,18) = 14.97, p = 0.02) and surprisingly average productivity declined with mating frequency (Spearman rank correlation, rS = -0.816, p< 0.001, Figure 2). Furthermore, a comparison between these field-collected and lab-reared female sexuals, which could only have mated with their brothers, did not reveal a difference in the number of offspring reared during the first three months after hibernation (Kruskal-Wallis test, H (19,40) = 20.80, p= 0.348, Figure 2).