Food choice in Drosophila melanogaster: the role of diet type, sex and social environment

Abstract

INTRODUCTION: Insect nutrition is a widely researched topic, since diet affects many biological processes, which can be monitored from cellular to behavioral level. As one of the most important environmental factors, food quality and balance in the amount of key nutrients, strongly affect fruit fly Drosophila melanogaster fitness. A number of genes involved in multiple sensory pathways and complex physiological systems are consequently included in the regulation of feeding behavior. The fruit fly food-related behavior is primarily influenced by nutritional needs, and may change throughout life. Also, food choice may be determined by sex and the social environment, i.e. by the presence of other individuals. OBJECTIVES: The aim of this study was to determine whether there were differences in food choice between D. melanogaster strains reared on two different substrates for more than 20 years. For that purpose, five food items were offered. Further, it was examined whether sex and social environment influenced food choice in these two strains. METHOD / DESIGN: D. melanogaster strains used in this experiment were maintained for more than 450 generations on two different substrates, standard cornmeal substrate and substrate modified by adding apple. Transparent plastic boxes, dimensions: 220 × 140 × 90mm, which contained five Petri dishes (r = 30mm) were used for monitoring food choice. Petri dishes were filled with five different substrates: standard cornmeal substrate and substrates that contain tomato, banana, carrot and apple. Flies were starved for 18h before being placed into each box. Virgin females and males, 3 - 5 days old, were separated and tested individually and in groups of five individuals, and foraging flies were sampled every 3 min for 1h. Four-way ANOVA was applied in order to determine difference in time that flies spent on different diets, between individuals and groups, and between sexes. RESULTS: Results pointed out significant differences in the time that flies spent by occupying different food items. On the other hand, sex, strain and social environment revealed no significant influence on D. melanogaster food choice. However, significant interaction between strain and food choice was observed. In both strains, the preference toward standard cornmeal substrate was noticed. Even more, flies reared on apple substrate spent significantly more time on Petri dish filled with standard cornmeal diet, compared to flies reared on standard substrate. CONCLUSIONS: These results indicated that flies chose nutritionally richer food (standard cornmeal substrate, rich in sugar and yeast), especially if they were reared on poor diet (the apple substrate). According to data from our previous surveys, substrates that we offered to flies differ in protein content and in the proportion of protein relative to the total content of organic carbon (C/N ratio), which accurately reflected the protein/carbohydrate ratio. Contrary to standard substrate, apple substrate contained smaller amount of protein and higher C/N ratio. The fact that food choice was not influenced by sex or social environment might suggest the same nutritional requirements for the best available food in both sexes, regardless of whether flies were tested individually or in a group.