Meeting Abstract
Animals use signals to assess quality, motivation, and other factors in contexts ranging from mate choice to aggression. Current models of signal evolution often assume that continuous variation in signal form is perceived in an equally continuous fashion by receivers; that is, any incremental change in the signal is perceived and equally influences subsequent decision-making. This assumption has rarely been tested, however, despite growing evidence showing that stimuli across modalities may be perceived in a categorical fashion. Carotenoid-based color signals are used in assessment of quality across diverse vertebrate taxa, yet few studies have asked how receivers perceive variation in these signals. We tested how female zebra finches (Taeniopygia guttata) perceive the continuum of carotenoid-based colors used in mate assessment. We identified eight colors along a range of orange-red coloration that approximate variation in male beak color, a signal used in mate choice, and that are approximately equidistant in a well-established color space based on avian color vision. After females had been trained to find food under bicolor discs, we then varied the colors comprising the two sides of the discs to determine the extent to which females perceived these colors as same or different. Female responses met both criteria of categorical perception: they (1) labeled colors along the continuum as falling into two distinct categories and (2) showed heightened discrimination of color pairs that crossed the category boundary as compared to equally-spaced pairs from within a category. Similar tests with grey scale stimuli showed that variation in brightness alone cannot account for these results. We discuss how categorical perception of assessment signals may inform models of signal evolution.
