Kin recognition in Drosophila: Rearing environment and relatedness can modulate gut microbiota and cuticular hydrocarbon odour profiles

From inbreeding avoidance to kin-selected cooperation, social behaviours
are frequently reliant on kin recognition. However, kin recognition
mechanisms are costly to evolve and currently not very well understood.
Recent evidence suggests that, by altering their host’s odour, gut and
other host-associated microorganisms may provide a promising avenue for
understanding kin recognition. In Drosophila melanogaster, kin recognition
can mediate mate choice, sexual conflict and larval
competition/cooperation, underscoring its important functional role. As is
commonly the case, kin recognition in this species depends on both
familiarity (i.e. shared rearing environment) and relatedness, and seems
to rely mainly on body odours determined by cuticular hydrocarbons. Here,
we investigated the degree to which larval rearing environment and
relatedness (full-sibs vs. unrelated) determine co-variation between gut
microbiota and cuticular hydrocarbons in D. melanogaster. We found that
rearing environment strongly determined both microbiota and cuticular
hydrocarbon composition, but that these effects were independent from each
other. In contrast, relatedness did not influence microbiota composition,
but had a strong influence on microbiota diversity, which in turn covaried
significantly with cuticular hydrocarbon composition. Our results show
that, in D. melanogaster, odours may convey information about both
familiarity and relatedness via an interaction between: a) direct effects
of the rearing environment on cuticular hydrocarbons and b) indirect
effects of relatedness on cuticular hydrocarbons via gut microbiota
diversity.