Disrupting butterfly microbiomes does not affect host survival and development

Abstract

Associations with gut microbes play a crucial role in the physiology, immune function, development, and behavior of many insects. However, butterflies may be an exception to this pattern since butterfly microbiomes do not show the host-specific and developmental shifts that are expected to evolve under strong host-microbial associations. Here, we present the first experimental test of this hypothesis by disrupting gut microbial communities of two butterfly species, Danaus chrysippus and Ariadne merione. Larvae of both the species fed on host plant leaves that were either chemically sterilized or treated with antibiotics had significantly reduced bacterial loads and disrupted gut bacterial communities substantially. However, neither host species treated this way suffered a significant fitness cost. We did not find significant variation in survival, growth and development between test larvae and control larvae. This suggested that butterflies do not rely on their gut bacteria for digestion, detoxification, resource accumulation and metamorphosis. Thus, our results provide empirical support for the growing realization that dependence on gut bacteria for growth and survival is not a universal phenomenon across insects.