Date Published: July 26, 2017
Publisher: Public Library of Science
Author(s): Miguel de la Flor, Lijian Chen, Claire Manson-Bishop, Tzu-Chun Chu, Kathya Zamora, Danielle Robbins, Gemunu Gunaratne, Gregg Roman, Amit Singh.
Novel stimuli elicit behaviors that are collectively known as specific exploration. These behaviors allow the animal to become more familiar with the novel objects within its environment. Specific exploration is frequently suppressed by defensive reactions to predator cues. Herein, we examine if this suppression occurs in Drosophila melanogaster by measuring the response of these flies to wild harvested predators. The flies used in our experiments have been cultured and had not lived under predator threat for multiple decades. In a circular arena with centrally-caged predators, wild type Drosophila actively avoided the pantropical jumping spider, Plexippus paykulli, and the Texas unicorn mantis, Phyllovates chlorophaena, indicating an innate defensive reaction to these predators. Interestingly, wild type Drosophila males also avoided a centrally-caged mock spider, and the avoidance of the mock spider became exaggerated when it was made to move within the cage. Visually impaired Drosophila failed to detect and avoid the Plexippus paykulli and the moving mock spider, while the broadly anosmic orco2 mutants were fully capable of detecting and avoiding Plexippus paykulli, indicating that these flies principally relied upon vison to perceive the predator stimuli. During early exploration of the arena, exploratory activity increased in the presence of Plexippus paykulli and the moving mock spider. The elevated activity induced by Plexippus paykulli disappeared after the fly had finished exploring, suggesting the flies were capable of habituating the predator cues. Taken together, these results indicate that despite being isolated from predators for decades Drosophila will visually detect these predators, retain innate defensive behaviors, respond by increasing exploratory activity in the arena rather than suppressing activity, and may habituate to normal predator cues.
Exploratory behaviors allow animals to gather information about their environment [1, 2]. These behaviors can be classified by how the animal explores its surroundings as well as categorized by the underlying motivational drive to explore. Specific exploration is motivated by novelty or a lack of information about the direct environment, and hence is driven by curiosity [1, 3]. Specific exploration is frequently accomplished through locomotor exploration which occurs when the animal moves to explore its environment . The drive to explore novel features in the environment can be compelling in many species, superseding hunger, thirst, and even escape from predatory danger [4–6]. However, defensive reactions due to anxiogenic stimuli, which include predatory threats, can also strongly influence specific and locomotor exploration of novel environments in some species [7–9].
Herein, we have examined the effect of natural and artificial predators on the exploratory behavior of Drosophila melanogaster. Canton-S flies detect and avoid both the pantropical jumping spiders and the Texas unicorn mantis nymphs in a circular arena. Since our flies have been kept in culture and under no predation threat for decades, the predator avoidance is clearly an innate defensive behavior. Canton-S flies demonstrate an even stronger avoidance of a mobile mock spider. These flies rely primarily on visual cues to detect the pantropical jumping spider and the moving mock spider. The flies’ responses to the pantropical jumping spider and the mock spider display some interesting differences. Wild type flies initially increase their activity in the presence of the pantropical jumping spider, but this activity undergoes habituation to normal levels of spontaneous activity as the fly explores the arena, whereas the activity in the presences of the moving mock spider remains higher throughout the experiment. Differences in the exigency of the mock spider threat vs. the pantropical spider threat are probably responsible for the exaggerated responses to the continually moving mock spider. It is likely that these increases in exploratory activity represent an anxiety-like response to perceived predatory threats.