Data from External immunity in ant societies: sociality and colony size do not predict investment in antimicrobials.

Social insects live in dense groups with a high probability of disease transmission and have therefore faced strong pressures to develop defences against pathogens. For this reason, social insects have been hypothesized to invest in antimicrobial secretions as a mechanism of external immunity to prevent the spread of disease. However, empirical studies linking the evolution of sociality with increased investment in antimicrobials have been relatively few. Here we quantify the strength of antimicrobial secretions among 20 ant species that cover a broad spectrum of ant diversity and colony sizes. We extracted external compounds from ant workers to test whether they inhibited the growth of the bacterium <i>Staphylococcus epidermidis</i>. Because all ant species are highly social, we predicted that all species would exhibit some antimicrobial activity and that species that form the largest colonies would exhibit the strongest antimicrobial response. Our comparative approach revealed that strong surface antimicrobials are common to particular ant clades, but 40% of species exhibited no antimicrobial activity at all. We also found no correlation between antimicrobial activity and colony size. Rather than relying on antimicrobial secretions as external immunity to control pathogen spread, many ant species have likely developed alternative strategies to defend against disease pressure.

社会性昆虫栖息于高密度种群中，疾病传播概率极高，因此面临着极强的演化压力以进化出抵御病原菌的防御策略。基于此，学界曾提出假说：社会性昆虫会投入资源产生抗菌分泌物，以此作为外部免疫机制阻止疾病传播。然而，将社会性演化与抗菌物质投入增加联系起来的实证研究相对较少。本研究针对20种涵盖广泛蚂蚁多样性与蚁群规模的蚂蚁，定量测定其抗菌分泌物的活性强度。我们从工蚁体表提取体表化合物，以测试其是否能抑制表皮葡萄球菌（Staphylococcus epidermidis）的生长。鉴于所有蚂蚁均为高度社会性类群，我们预测所有蚂蚁物种均会表现出一定的抗菌活性，且蚁群规模越大的物种，其抗菌应答越强。本研究采用比较分析方法发现，强效体表抗菌物质在特定蚂蚁演化支中较为普遍，但40%的物种完全未表现出任何抗菌活性。同时，我们未发现抗菌活性与蚁群规模之间存在显著相关性。诸多蚂蚁物种或许并未依赖抗菌分泌物作为抵御病原体传播的外部免疫机制，而是演化出了其他应对疾病压力的防御策略。