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.