According to Weber’s law of proportional processing, perceptual discrimination between stimuli of different magnitudes is based on their proportional differences in magnitude (not absolute differences). Proportional processing operates in various sensory modalities and behavioural contexts. However, whether female mate preference for colour patterns in animals follows Weber’s law of proportional processing remains untested. We addressed this research gap using the jade jumping spider, Siler semiglaucus, whose males exhibit remarkable sexually selected colour patterns and whose females show preferences for males with low abdomen pattern contrast (pattern contrast is defined as the spatial feature of the relative abundance of two adjacent colour patches). By manipulating the dorsal abdomen colour patterns of S. semiglaucus males, we created males with varying abdomen pattern contrasts. We then assessed female preference for males that varied in both absolute and proportional differences in pattern contrast. We found that females preferred males with lower abdomen pattern contrasts and discriminated between males based on both absolute and proportional differences in pattern contrast. While proportional difference alone was not a significant predictor of female mate choice, discrimination based on proportional difference, coupled with absolute difference had a greater influence on female mate preference than absolute difference alone. Hence, our findings suggest that S. semiglaucus female preference for males with lower pattern contrast follows Weber’s law, and female discrimination may have the potential to limit the exaggeration of sexually selected colour patterns.
Female preference for males with lower pattern contrast follows Weber’s law of proportional processing in jumping spiders