Manipulations of signalling environment affect male competitive success in three-spined sticklebacks

Abstract

Breeding adult male three-spined sticklebacks,Gasterosteus aculeatusL., develop an elaborate breeding signal, the primary component of which is ventral red coloration. In laboratory dominance tests staged under illumination conditions that maintained or eliminated male perceived coloration, this study examined (1) the relationship between male coloration and fighting ability and (2) the applicability of three hypotheses for the current function of male coloration in male–male competitive interactions. In pairs of males from a Long Island, NY, population matched for size and prior dominance experience, the more brightly coloured males were more likely to initiate and win under white light. The effect of colour on dominance success was lost under replicates illuminated by coloured-light treatments that masked the signal by eliminating its visual contrast. The loss of competitive advantage associated with more conspicuous coloration was not an artefact of illumination manipulations, since the effects seen under white light were maintained under a coloured-light treatment that maintained male coloration. These data suggest that red belly coloration of males functions as a threat signal.