ABSTRACT
Upon visually detecting a moving predator, animals often freeze, i.e. stop moving, to minimize being uncovered and to gather detailed information of the object's movements and properties. In certain conditions, the freezing behavior can be enough to avoid a predatory menace but, when the risk is high or increases to a higher level, animals switch strategy and engage in an escape response. The neural bases underlying escape responses to visual stimuli have been extensively investigated both in vertebrates and arthropods. However, those involved in freezing behaviors are much less studied. Here, we investigated the freezing behavior displayed by the crab Neohelice granulata when confronted with a variety of looming stimuli simulating objects of distinct sizes approaching on a collision course at different speeds. The experiments were performed in a treadmill-like device. Animals engaged in exploratory walks responded to the looming stimulus with freezing followed by escaping. The analysis of the stimulus optical variables shows that regardless of the looming dynamic, the freezing decision is made when the angular size of the object increases by 1.4 deg. In vivo intracellular recording responses of monostratified lobula giant neurons (MLG1) to the same looming stimuli show that the freezing times correlate with the times predicted by a hypothetical spike counter of this neuron.
Footnotes
Author contributions
Conceptualization: D.O., D.T.; Methodology: D.O., M.G., A.C., D.T.; Software: D.O., D.T.; Validation: D.O., D.T.; Formal analysis: D.O., M.G., A.C., D.T.; Investigation: D.O., D.T.; Resources: D.O., D.T.; Data curation: D.O., M.G., A.C., D.T.; Writing - original draft: D.O., D.T.; Writing - review & editing: D.O., M.G., A.C., D.T.; Visualization: D.O., M.G., A.C., D.T.; Supervision: D.T.; Project administration: D.T.; Funding acquisition: D.O., D.T.
Funding
This work was supported by the following grant to D.O. Programas I+D UNQ EXPTE. 2297/22, to D.T. PICT 2019–00724 from Agencia Nacional de Promoción Científica y Tecnológica and grant no. 20020170100254BA from Universidad de Buenos Aires.
Data availability
All relevant data can be found within the article and its supplementary information.
