Light exposure inhibits the locomotion of fly larvae.
Adaptation to circumstances and environments is vital to an organism's survival. According to neurobiologist Bruce McEwen, these responses are a "double-edged sword" -- while they promote survival, they also can have long-standing, damaging effects. Drosophila melanogaster larvae feed by burrowing into a food source. During this time, the larvae are repulsed by light and will actively move away from light sources, according to an article in the Journal of Neuroscience Methods. When larvae leave their food source to find a suitable site for pupation, their repulsion to light diminishes and the larvae eventually become unresponsive to bright light.
Abstract
Organisms are continually faced with stressful situations and must be able to adapt to survive. A study published in the January 2005 issue of the Journal of Neuroscience Methods described an assay to measure behavioral responses of Drosophila melanogaster larvae, the common fruit fly, to bright light. Control and experimental (light-exposed) fly larvae were placed equal distances from a food source and the times required to reach the food source were recorded. The researchers found that exposure to bright light resulted in slower movement. However, given time to recover from the light treatment, the experimental larvae regained normal locomotion.
Materials and Methods
Flies were maintained at room temperature and allowed to breed. The newly hatched larvae (72 to 78 hours old) were divided into two groups: a control group that received no treatment and an experimental group, which was exposed to bright light. A small amount of yeast paste was placed in a hole in the middle of a plate. The larvae were placed near the edge of the plate and observed for 60 minutes. Quantitative scores were assessed by counting the number from each group that reached the yeast for each minute of the assay. Those that did not crawl were omitted from the study.
Results
Almost 600 larvae were observed for this experiment -- 305 in the control group and 278 in the experimental group. Results were calculated by counting the number of larvae arriving at the food source every minute for the duration of the experiment. The control larvae reached the food source at an average time of 4.099 minutes, whereas the experimental larvae took an average of 16.27 minutes.
Larvae were exposed to light for durations of 10, 20, 30 and 40 minutes. However, 10 to 30 minutes of light exposure did not influence the amount of time to reach the food source. Increasing the duration of light beyond 30 minutes resulted in a response similar to the control larvae.
Discussion
The researchers concluded that the quantification of the adaptive behavioral responses to bright light in Drosophila larvae is a measure of behavioral flexibility. They further stated that this assay could be a useful genetic screen for behavioral modifications in respect to the larval adaptation to bright light. The study concluded that future studies should be performed to determine changes at the molecular level in factors promoting behavioral responses to better define adaption to stress.
Tags: food source, bright light, behavioral responses, larvae were, concluded that