Behaviour 2019
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Bigger is not always better: proportional processing of body size in the green swordtail Xiphophorus helleri
Eleanor M Caves, Laura A Kelley. Centre for Ecology and Conservation, Exeter University, Penryn, Cornwall, United Kingdom

During mate choice, females often assess the magnitude (duration, size, etc.) of male signals that vary along a continuum, with signal variation reflecting variation in male quality. It is often implicitly assumed that signal perception is continuous, i.e. that females perceive and respond to each minute difference in signaling traits. However, many sensory systems adhere to Weber’s Law (proportional processing), which states that animals discriminate between stimuli of different magnitudes based on their proportional rather than absolute difference. We used two-choice tests to examine the preferences of female green swordtails, Xiphophorus helleri, for animations of courting males that differed in size, since female X. helleri are known to prefer larger males. We found that proportional difference in size was a significantly better predicter of female association time with the larger male than absolute difference. This is the first demonstration of proportional processing of a visual signal in the context of mate choice, with implications for understanding how receivers act as a selective force on signal elaboration.