Running the distance: robustness of embodied distance measurement despite social interference in fiddler crabs

Path integration (PI), a spatial memory process, is an essential navigation strategy. Through PI, animals integrate their movements during foraging into a ‘‘home vector” that allows direct return to the origin. In humans, feedback from body movement contributes to readout of the home vector: physical estimation by walking toward the origin improves people’s ability to identify the origin point. However, how such feedback affects home vector readout in other animals remains unclear. Here, we suggest that leg movement feedback contributes to a robust readout of the home vector against errors induced by social behavior in fiddler crabs. Depending on whether they engaged in territorial behavior before homing runs, fiddler crabs altered their response to visual cues (fake burrow entrances) placed along their homing path. When social behavior was absent, the crabs showed a clear transition in behavior, initially suppressing visual cues in favor of PI but prioritizing visual cues as they approached their burrow. But when social behavior was present, this clear transition was disrupted, suggesting that error was induced into the internal estimation of burrow locations when the crabs attempted to interact with visual cues. Nevertheless, when crabs ignored the fake burrow entrance, they returned to their masked true burrow with equal precision regardless of the presence or absence of social behavior. These results suggest that the internal estimation of burrow location during the return is subject to induced errors, whereas the physical estimation is not, and feedback from leg movement contributes to robust distance measurement.