Around this time of year, as the weather gets warmer, Prof. Cole Gilbert, entomology, challenges the students in his department to bring him the first live tiger beetle of the season. The hunt for this metallic, green predator with six white spots is not just a scavenger hunt for the entomology students. The unique predatory behavior of this beetle provides an extreme example for the study of visual processing in all animals.
Gilbert found himself pursuing entomology and neuroscience in graduate school after taking the two classes in close proximity as an undergraduate student. His interest in animals started as a child, but his college courses challenged him to understand the mechanisms of behavior.
Gilbert has researched a particular tiger beetle, which is common in the Ithaca area with over 2,000 related species world-wide. The predator is one-half inch in size with large eyes and big jaws.
According to Gilbert, tiger beetles “eat anything” with a distinct predatory style. They hunt at relatively high speeds — up to 53.8 centimeters per second in Ithacan beetles. Australian beetles have recorded rates up to 2.5 meters per second.
They chase prey in a strange manner. They run, stop momentarily and then, resume the chase. “It was the stopping part that interested me,” said Gilbert.
Gilbert’s lab analyzed the beetle’s tactic. They found that the behavior is neither an act of sneakiness nor a moment of rest. When the beetles in his lab chased fruit flies, they displayed the same odd behavior. However, when controlled with an artificial prey item, Gilbert saw contradictory results.
When a white prey item moved along a black background, or vice-versa, the beetles did not show the stop-and-go behavior despite moving as fast. However, they maintained their stop-and-go behavior while chasing grey prey, and did not to chase white-on-white.
“A contrast of prey item relative to the background was key,” explained Gilbert.
As Gilbert found out, the beetles stop because they go blind.
“They run so fast that the world goes blurry, and loses contrast. They stop and the world snaps back. They get their aim, then they run, they go blind again, but they’re closer.”
According to Gilbert, by inserting an electrode photoreceptor in the beetle’s retina they are able to, “test how fast the shutter speed is in their eyes, and it’s not very fast.”
The computer-generated images of the beetle’s retina excited Gilbert. They demonstrated the effects of the moving environment. He said, while images from an insect’s perspective alone are not new, these images from a moving perspective provide insight into beetle behavior.
The basic visual process remains the same in every creature. At high rates of movement, fish and birds experience the same blurring effect. Humans are never able to naturally see these effects.
The tiger beetle’s faulty speed arouses many evolutionary questions, which Gilbert hopes to tackle. Why has evolution not reduced the hazardous speed of tiger beetles? Would they benefit from moving slower?
These trade-offs in nature intrigue Gilbert.
As the professor of introductory biology, BioG 1101, Gilbert also sees a trade-off in the university’s new biology curriculum and major requirements. The introductory biology course, which was originally introduced at Cornell, will be replaced. Next year, incoming students in the biology major will choose two of three elective courses to replace introductory biology: Ecology and the Environment, Physiology or Cell and Developmental biology.
While he believes this will benefit individuals with distinct goals, many undecided student may fail to find their ideal concentration. “The lack of a survey course and lack of exposure to everything in biology might hurt those students,” said Gilbert.
If Cornell maintains its high medical and graduate school placement in the future, Gilbert believes that time will indicate that the university wisely altered the program.
Original Author: Tajwar Mazhar