Praying Mantids Adjust Head and Thorax Saccades to Track Visual Stimuli Moving at Different Speeds
摘要
Animals frequently use movements of their eyes or heads to visually track objects in their environment. Visual tracking movements can be classified into two primary categories: smooth pursuit and saccadic. Of these, invertebrates primarily utilize saccadic tracking movements. Saccadic tracking is characterized by rapid movements that shift to reduce blurring of an image on the retina during tracking. While saccadic movements are commonly observed as rapid eye rotations, they can also be induced by moving other parts of the body. Insects with immoveable, fixed eyes are known to have saccades that include moving their head, thorax, or abdomen. These movements are punctuated by fixations, or periods of time where the gaze is centered on a visual target. Insects are known to use this saccade-fixate strategy to stabilize their gaze onto a visual stimulus. Saccadic tracking behaviors in praying mantids are influenced from the speed of a visual stimulus. Saccade magnitude increases with stimulus speed, where a larger deviation of the retinal image leads to higher velocity saccades. While it is known that stimulus speed influences the saccadic tracking of mantids, it is unclear how mantids adjust the fine components of saccadic movements to accommodate for changes in stimulus speed. Here, we report that the praying mantis Tenodera sinensis adjusts the frequency and duration of their head and thorax saccades as visual stimuli change speed. Since praying mantids are ambush predators, adapting their saccadic movements to prey speed may help them stabilize their gaze onto prey to improve hunting success.