Unravelling the genetics of fat accumulation in the house fly to foster circular economy
Authors:   , Boatta Francesco 
Published: December 2023

The world population is growing at an unprecedent rate and solutions to sustainably feed the increasing population are urgently needed. Insects are rich in protein and lipids hence they represent a valid alternative source of these nutrients.
Selecting for leaner or fatter phenotype in insects could improve their application as feed and food or allow to convert organic material into resources destined for other applications respectively.
To become a successful target of selection, a trait must meet specific criteria such as being genetically determined, being heritable, and showing the potential to respond to selection. In this thesis I aim to explore the genetics of fat accumulation in the house fly to answer if this trait meets these three criteria.
In Chapter 2, I provide a general overview and most up-to-date information on the biology of the house fly with particular emphasis on its nutritional ecology, potential industrial applications of this species, and other relevant aspects, particularly in light of the potential application of this insect at industrial level. Chapter 2 wants to be a compendium for those interested in the biology of this intriguing organism and a guide for those that want to harness the potential of this insect for industrial purposes.
Chapter 3 I answer the first important question to understand of fat accumulation could become target of artificial selection: is it genetically determined? In this Chapter, I used three house fly strains originated from different European locations. These were tested in a common environment at two different temperatures to investigate the ontogeny of fat reserves. The results of this experiment show that there is a strong effect of the strain in the ontogeny of fat reserves, suggesting that a genetic component determines this trait.
In Chapter 4 I aim at answering the second important question about fat accumulation in the house fly: is it a heritable trait? Here I estimated the narrow sense heritability of the fat accumulation in one strain by using a half-sib paternal experimental design and two different statistical models. High heritability estimates were found for fat accumulation with the models giving similar results. I discuss the meaning of our result in the light of selecting house flies with improved fat characteristics.
In Chapter 5 the last question regarding fat accumulation is answered: can this trait respond to selection? Here I used experimental evolution to test the response of fat accumulation to a selective pressure. I exposed house fly larvae for multiple generations to two nutritionally challenging diets. In this work we show that the diets induced direct, plastic responses on fat storage. Moreover, I also show that when reversed on the ancestral diet, the lines administrated the experimental diets differed significantly providing the proof that long lasting changes have occurred in these strains.
Lastly, I dedicate Chapter 6 to the discussion of the experimental results obtained and give a general synthesis on the possibility to select for fat-tailored phenotypes and if fat content can be included as a goal in a selection program.