Social information use and its consequences in adult and larval stages of fruit flies

Abstract

Recent evidence has shown that fruit fly adults and larvae are heavily attracted to food sites occupied by larvae. This attraction is especially strong in mated females that are looking for a suitable site for egg laying. In the first set of experiments, we compared the value assigned to social information provided by larvae at a site to the nutritional information that a female has access to by sampling a food. Lowering food quality did decrease egg-laying preference for a food, but females still showed a much stronger preference for occupied foods. We theorized that the social egg-laying preference may be due to an advantage of developing near older larvae. However, eggs that developed near larvae showed lower survival to adulthood, slower development time, and lower adult body mass. Females were also not able to reduce their social egg-laying preference, even when foods were already heavily occupied by larvae. Finally, we found that larvae were not better able to identify a high quality food site than an adult female, and thus the smell of used food was not a reliable cue to the quality of a site. These results provide evidence that the preference for females to lay eggs near larvae is very robust but the exact benefit it provides for the female and her offspring is unknown. We then ran a series of experiments to test larval social information use to see if they value it as heavily as adult females. Our experiments consisted of focal larvae being put on lower quality food and trying to find a higher quality food nearby that was either occupied or unoccupied by a single model larva. Larvae did not reliably use this social information. Overall, it is unclear whether the larvae are using social information to help them find higher quality foods.