Data from: 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 vitellogenins in young embryos to multiple proteins in subsequent stages, suggesting that the increase in fungistatic activity may be due to the expression of endogenous proteins during embryogenesis. This study is the first to address embryonic antifungal activity in a hemimetabolous eusocial taxon. Our results support the hypothesis that microbes have been significant agents of selection, fostering the evolution of antifungal properties even in the most immature and supposed, most vulnerable stage of development.

白蚁栖息于被多样微生物群落（含病原体）高度定殖的环境中。巢内产下的卵，其面临的致病压力大概率与成年巢伴相似。因此，它们或许也经受了演化选择压力，从而具备免疫能力。本研究通过体外实验，针对布氏白僵菌(Metarhizium brunneum)，探究了白蚁胚胎抗真菌活性的个体发育规律、分布特征与活性强度。我们将胚外洗脱液与胚内组分分别与真菌分生孢子共孵育，随后对孢子存活率进行评分。结果显示，抑菌活性呈现位置依赖性与阶段依赖性：胚外洗脱液仅表现出较弱的抗真菌活性；与之相反，胚内组分具备极强的抗真菌活性，且其活性随胚胎发育进程逐渐增强。对胚外洗脱液与胚内组分均进行煮沸处理后，孢子存活率得以恢复，这表明抗真菌因子大概率为蛋白质类物质。胚胎蛋白质组谱随发育发生动态变化，早期胚胎中以疑似卵黄蛋白原为主，后续发育阶段则出现多种蛋白质组分，这提示抑菌活性的提升或许源于胚胎发生过程中内源性蛋白质的表达。本研究首次针对半变态真社会性类群的胚胎抗真菌活性展开相关研究。研究结果支持如下假说：微生物是重要的选择压力驱动因子，即便在发育最不成熟且通常被认为最脆弱的阶段，也推动了抗真菌特性的演化。