The microbiome affects a wide spectrum of host physiological traits, from growth, development, to nutrition and behavior. It has been generally assumed that the microbiome makeup is key to lifetime health, yet, inter-individual microbiome variability is profound in many animals, suggesting there is a certain degree of plasticity that different microbiomes can promote the same physiological outcome. Understanding the factors that govern the plasticity of host-microbe association is relevant to whole organism physiology and can help define the concept of “dysbiosis”, i.e. when host development or physiology is compromised by maladaptive changes of the microbiome. Here, we use two insect systems (the chironomid midges and Drosophila flies) to determine the developmental consequences of microbiome variation, by manipulating the eggs to be colonized by microbes transplanted from parental, closely-related or distantly-related insects. Our null hypothesis is that larval developmental is equally supported by different makeups of the microbiome predisposed from the egg microbiome, and that there is no difference between the insect hosts.
Results/Conclusions
Both insects require microbes to complete development to adulthood, but showed distinct patterns of plasticity in development in response to microbiome shifts. Axenic midges exhibited developmental arrest but remained viable, while axenic flies failed to survive, on their respective dietary habitats. Reciprocal microbiome transplantation showed that midge development can be supported by a more flexible microbiome than flies, as microbiome transplants from the flies could rescue axenic midge development, but not vice versa. Together, our results demonstrated a causal effect of the egg microbiome on insect development, and host-dependent plasticity in response to varying microbiome composition.