Impact of microbiota on the life-history traits of a polyphagous fly

The microbiota is a key modulator of fitness and disease resistance in insects. Yet, the extent to which the insect microbiota affects host performance and well-being of current and future generations remains to be elucidated. My thesis aims to better understand direct and transgenerational effects of the microbiota on life-history traits and foraging of the polyphagous fly Bactrocera tryoni. I first reviewed the literature to show the state of the art in the field of microbiota research in insects (Chapter 1). Then, I explored the interaction between the insect microbiota and some ecological factors in the early life stage. Results revealed that microbes acquired from both maternal transmission and the environment influence larval food choice whereby larvae that microbiota has been suppressed have a greater preference for diets rich in either protein or sugar (Chapter 2). The results also showed that microbial growth in the larval diet interacts with larval density and diet composition to influence body weight of pupae and adults (Chapter 3). Using axenic lines, I showed that the lack of microbiota negatively affects female fecundity and modulates nutrient intake and body fat reserve differently in males and females (Chapter 4). Transgenerational effects of the microbiota were also observed in offspring that parents’ microbiota had been manipulated whereby developmental traits were negatively affected in offspring of axenic parents (Chapter 5). Furthermore, body mass and fecundity decreased in offspring of axenic parents suggesting that the disruption of the microbial communities has long-lasting effect on offspring’s fitness (Chapter 5). Lastly, I discuss the significance of my results to the field of ecology and evolution, contextualizing my findings into the broader eco-evolutionary framework (Chapter 6). My thesis increases our understanding of the complex interplay between the insect host and its microbiota, highlighting the profound impacts of the microbiota on host fitness at the developmental and generational levels.