Survival and microbial load of inbred and outbred offspring
Inbred and outbred offspring differentially survive when challenged with pathogens (P = 0.001), with inbred offspring exhibiting a higher mortality rate than those from outbred pairings (Figure 5b). However, no significant difference was found between the microbial load of inbred and outbred offspring (P = 0.401; Figure 5c), with the mean number of CFUs being 26.21 (±SD = 19.14) in inbred offspring and 30.93 (±SD = 25.30) in outbred offspring (Figure S8).
DISCUSSION
Our study shed light on the roles inbreeding and outbreeding play in the success of termite colonies over the course of their development. First, our results revealed comparable survival between inbred and outbred pairings during the first weeks of colony foundation, despite high survival differences between alates from different colonies. This suggests that inbreeding per se has no effect on survival at this stage of colony foundation; rather, the survival of incipient colonies is strongly influenced by the colony of origin of the constituent partners. The pairing with the highest survival was an inbred combination of alates from a low microbial-load colony, while the pairing with the lowest survival was also an inbred combination, but with alates from a high microbial-load colony. Our results show that the susceptibility of pairings increases with their cumulative and maximum levels of microbial load carried by the partners and only provide weak support for different colonies harboring distinct microbial communities; the susceptibility of a pairing was only marginally associated with the fungal dissimilarity between partners. Together with the failure of pairings typically caused by the death of the partner with the highest microbial load, our results highlight the risk of unhealthy mate pairings, regardless of their level of relatedness. Yet, our results suggest that inbreeding takes its toll later when incipient colonies face pathogen pressure, as inbred offspring exhibited higher mortality toward pathogens. These findings suggest that although the choosiness for a lifetime partner is initially influenced by the immediate benefit of a healthy partner rather than the long-term potential of fit offspring, inbreeding depression during colony development may restore the proportion of outbred mature colonies.