Young but not defenseless: antifungal activity during embryonic development of a social insect

Termites live in environments heavily colonized by diverse microbial communities, including pathogens. Eggs laid within the nest likely experience similar pathogenic pressures as their older nestmates. Consequently, they may have also been under selective pressures to be immune-competent. Through in vitro experiments, we tested the ontogeny, location and strength of embryos’ antifungal activity against the fungus Metarhizium brunneum. Extraembryonic washes and intraembryonic components were incubated with fungal conidia, which was then scored for viability. Fungistatic activity was location- and stage-dependent. Extraembryonic washes had relatively weak antifungal activity. Conversely, intraembryonic contents were highly antifungal, exhibiting increased potency through development. Boiling both embryonic washes and intraembryonic contents rescued conidia viability, indicating the antifungal agent(s) is (are) likely proteinaceous. Embryonic protein profiles shifted from putative vitellog...