Defining the microbiota's response to and influence on the evolution of Drosophila melanogaster

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Understanding the mechanisms of fast adaptive evolution has direct applications to healthcare. But there remains a major gap in the field: associated microorganisms (‘microbiota’), a key potential contributor to animal adaptive evolution are often entirely ignored in evolution studies. The continued existence of this gap is problematic because microbiota can directly affect host health-related traits. Indeed, many animal traits that can evolve in response to laboratory selection can also be influenced by the microbiota. Moreover, when populations undergo laboratory selection for divergence in health-related traits, they also become differentiated in their microbiota. The long-term goal of this project is to define the role of microorganisms in animal evolution. The overall objective is to explain how animals select on their microbiota during evolution and how variation or constancy in the microbiota affects animal evolution. Our central hypothesis is that microbiota affect and are affected by animal evolution. This hypothesis is supported by our preliminary results using a system of experimentally-evolved Drosophila melanogaster (laboratory fruit fly) populations. Thus, the rationale for the proposed project is that we have a demonstrably high-powered and unique system in which we can answer questions about causation when determining the role of microbiota in host evolution. We will achieve our overall objective through two specific aims. Preliminary results show that populations of D. melanogaster selected for fast development have higher abundance of gut microbes but are nearly devoid of the endosymbiont Wolbachia compared to controls; in Aim 1.1 we hypothesize that host genetic control of Wolbachia is under strong and constant selection in these populations. In Aim 1.2 we will determine whether the evolution in host traits drives the changes to the microbiota, or vice versa in a laboratory selection experiment. Aims 2.1 and 2.2 will also use the laboratory selection approach to test if bacterial functions can affect selection pressures acting on hosts, and to what extent variation or constancy of the microbiota affect host rate of evolution. Our approach is innovative because it evolves an animal under bacteria-controlled conditions and extends correlation to causation. The significance of this project is that it will explain how host evolution impacts and depends on the microbiota and determine to what extent microbiota can influence selection pressures experienced by hosts. This project will support research opportunities for undergraduate and Master’s students.