Offspring production
Our results revealed a higher and faster production of workers and soldiers in inbred colonies. This result may be driven by the prevalence of inbred AA pairings and their weak microbial load. The higher productivity of inbred colonies may therefore stem from a trade off in resource investment between pathogen defense and offspring production (Schwenke et al. 2016). In Z. angusticollis , pathogen pressure experienced by primary couples during colony foundation leads to a decrease in the likelihood of oviposition and the total number of eggs (Cole et al. 2018), and sibling pairs had higher survival than non-related couples when exposed to pathogens (Calleri et al. 2005). In C. formosanus , outbred pairings also suffered higher mortality than inbred pairings; but in this species, the decreased success of outbred pairings was offset by their increased productivity (Fei & Henderson 2003). Importantly, most studies investigating differences in survival or productivity between inbred and outbred colonies have not taken into account the colony of origin, nor used equal numbers of the various pairing combinations tested. These studies may have failed to provide deeper insight into this process due to potentially strong differences between alates originating from different colonies and the lack of proper control to account for these differences. In our study, the equal pairing of every combination accounted for differences between colonies and resulted in similar survival between inbred and outbred pairings. However, a bias toward inbred or outbred colonies could be observed in the case of an association of alates from different colonies in different proportions (more inbred pairings from the healthy colony A and less from the susceptible colony E would have resulted in better survival of inbred pairings compared to outbred pairings).