Shelter use during exploratory and escape behaviour of the crab Chasmagnathus granulatus: a field study

The use of shelters has had a predominant adaptive value in many species throughout evolution. Shelters provide protection and reduce the risk of predation during the search for food and mates. However, they imply the additional danger of having the refuge appropriated by an intruder because of intraspecific competition, especially in densely populated communities. In this work we studied the burrow-centred strategies of exploration and the burrow-oriented escape responses of the crab Chasmagnathus granulatus during surface activity outside their burrows. Exploratory excursions were described through diverse characteristics that enabled their functional analysis and categorization. Results showed that surface exploration is mainly accomplished by slow and near-the-burrow excursions that could be composed of two or three stages. Exploratory behaviour is drastically replaced by a conspicuous burrow-oriented escape response when crabs are faced with an aerial stimulus or the approach of a conspecific neighbour. We describe and compare this escape run with regard to whether individual survival or burrow resource is at risk. This study provides evidence of the effect of the crabs' shelter on surface activity and social interactions in the natural habitat of C. granulatus and supplies valuable tools for field and laboratory studies using this crab as an animal model.