Startle durations reveal visual assessment abilities during contests between convict cichlids

Abstract

In animal contests, the widespread ability of contestants to assess their opponents' resource holding potential (RHP) relative to their own, termed mutual assessment, has recently been questioned. It is possible that each contestant may only have information about its own abilities or state, incurring costs up to a particular threshold then giving up, termed self-assessment. We used a technique that provides a measure of fight motivation to discriminate between different assessment models during aggressive encounters between male convict cichlids, Amatitlania nigrofasciata. A novel stimulus was applied to cause a startle response in one contestant of an aggressively interacting, size mis-matched pair, whereby the animal temporarily stops fighting. The time taken to resume the contest has been verified to provide a measure of the motivation to fight, from which it is possible to infer if any visual information concerning opponent asymmetries has been gathered. The data showed support for two differing types of assessment. There was some support for self-assessment, with startle duration being negatively related to own size, and, in a later trial series some support for an opponent only assessment strategy, with startle duration being positively related to opponent size. These results are consistent with individuals learning to use visual information about opponents when deprived of other sensory cues. Evidence within a trial supporting visual mutual assessment was lacking and possible reasons for this are discussed.