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).