Shelter size influences self-assessment of size in crayfish, Orconectes rusticus: Consequences for agonistic fights

Abstract Theoretical models of animal assessment and decision strategies have assumed animals possess accurate information about themselves. The imperfect nature of self-assessment could cause animals to make inaccurate decisions during agonistic encounters. By manipulating sensory information used in self-assessment in crayfish, Orconectes rusticus, it may be possible to alter either decision-making paradigms or outcomes associated with agonistic encounters. We examined the role of self-assessment in the agonistic behaviour of crayfish by using differing shelter sizes to alter self-assessment of size. Similar-sized crayfish were kept in tanks with small, medium, and large shelters (relative to body size) and subsequently were fought against size-matched, naive opponents in novel chambers to remove resource value as a variable. Crayfish in small shelter treatments initiated and won more fights than crayfish in other shelters. Crayfish in the small shelter treatment had shorter durations of fight when compared to crayfish with the medium and large shelters. These results are consistent with the concept that crayfish placed in smaller shelters may be self-assessing their physical size and, thus, their fighting ability, higher than crayfish in larger shelters. Based on these results, current theoretical models need to include the role of inaccurate self-assessments in agonistic decision making paradigms.