Scared stiff: Effects of a nematode parasite on fearfulness in bess beetles

Anna Shattuck, a student from Tulane University, worked in the lab of Dr. Andy Davis.

Abstract Freezing is a defensive behavior seen in many different animals as a response to extreme threats such as predators. While research on freezing behavior is widespread, there is little known about how parasites may influence it. A non-lethal nematode parasite, Chondronema passali, can be found in the hemocoel cavity of bess beetles, Odontotaenius disjunctus. A single beetle can carry the burden of hundreds of these nematodes. Previous research has shown that parasitized beetles eat more and are more active, suggesting they are bolder and may be less prone to freezing. This experiment tests whether the nematode parasite influences fearfulness in beetles by exposing a population of bess beetles to different stressors and observing their freezing behavior in response to each. Following the trial period, beetles were dissected, and parasite load and sex were assessed. Out of 161 beetles, 14% were unparasitized by C. passali. We found that heavier parasite loads increase freezing durations in males and decrease freezing durations in females in response to a stressor. We suspected that female beetles experienced greater energy loss from being parasitized and laying eggs, making them more inclined to move and forage. To test this idea, we deprived 22 beetles of food for 48 hours in hopes they would display freezing behavior less when responding to a stressor. After being starved, only 4 beetles displayed freezing behavior, indicating fearfulness is tied to hunger.  Further investigation is needed in order to elucidate this relationship.