Colour polymorphic lures exploit innate preferences for spectral versus luminance cues in dipteran prey

Area of Science:

• Ecology
• Evolutionary Biology
• Animal Behavior

Background:

• Color polymorphism in signaling systems can be maintained by variations in visual context.
• The orb-weaving spider Gasteracantha fornicata exhibits "white" and "yellow" morphs, attracting dipteran prey through conspicuous dorsal signals.
• Dipteran prey may rely on luminance and spectral cues differently for detecting small versus large stimuli.

Purpose of the Study:

• To test if perceptual differences in color vision contribute to maintaining color polymorphism in Gasteracantha fornicata.
• To investigate how apparent spider size influences prey attraction to different morphs.

Main Methods:

• Experimental trials using color-naïve Drosophila hydei and Musca domestica in Y-mazes.
• Manipulation of apparent spider model size by altering viewing distance.
• Presentation of morphs against naturalistic and extreme background conditions.

Main Results:

• Flies showed no preference between morphs on typical backgrounds, regardless of model size.
• On extreme backgrounds, flies preferred white morphs at longer ranges (suggesting luminance cue reliance).
• Flies showed no preference between morphs at close range, even on extreme backgrounds.

Conclusions:

• Apparent stimulus size affects relative morph attractiveness, aligning with predictions based on fly visual ecology.
• Gasteracantha fornicata morph signal structure may be tuned to perceptual features exploited by prey.
• This study suggests a mechanism for maintaining deceptive polymorphism through differential exploitation of visual channels by prey.