Homing in the Benthos: Navigation and Orientation in a Mantis Shrimp

Abstract

Stomatopods, better known as mantis shrimp, are crustaceans which commonly inhabit holes in benthic marine environments for use as burrows. Many stomatopod species forage at extended distances before returning to their burrows, risking predation. By using large, semi-naturalistic arenas, I investigated the navigational strategies these animals use to find their way home. First, by laterally displacing foraging stomatopods, I demonstrated that the mantis shrimp, Neogonodactylus oerstedii, uses path integration, a vector-based strategy, to navigate home, making them the first fully aquatic path-integrating animals yet discovered. Next, by passively rotating stomatopods during foraging, I found that they use celestial and idiothetic (self-motion) orientation cues during path integration. By manipulating the apparent position of the sun and by rotating overhead polarization patterns while animals were foraging, I demonstrated that N. oerstedii hierarchically rely on these cues when orienting. During these experiments, I found that path integration in N. oerstedii was prone to error proportional to error accumulated over the course of foraging paths. To combat this error inherit in path integration, stomatopods enacted stereotyped search patterns when path integration did not lead them directly to their burrows. I found that this search behavior forms continuously expanding, non-oriented loops that are centered near the point of search initiation. Also, the radius of this search appeared to be scaled to the animal'saccumulated error during path integration, improving the effectiveness of the search. Next, by comparing homeward paths in the presence and absence of a landmark placed near the burrow and by displacing the landmark to an alternate location while animals were foraging, I showed that stomatopods navigate using landmarks in parallel with their path integration system. Finally, I aimed to understand what makes a landmark salient to a mantis shrimp when identifying it. Using dichotomous choice behavioral tests, I, with a team of undergraduates, found that the shape of an object is more important that its color for identification by N. oerstedii, suggesting that N. oerstedii identifies landmarks more by their shapes than their colors. These experiments uncover for the first time the robust navigational toolkit N. oerstedii relies upon to find home.