Beauty is in the eye of the beholder: mate choice in glow-worms depends on perceived, not emitted signals

While the strength of sexual signals is important in mate attraction, the
ability to accurately compare signals may also have a major effect on mate
choice. Large distances between competitors may reduce competition, as
accurate comparison of signals becomes harder. This may be advantageous to
weak signallers and detrimental to stronger signallers. We create a
mathematical model examining optimal distance from stronger competitors
for sexual signallers and test its predictions using the common glow-worm
(Lampyris noctiluca). Female glow-worms are flightless and attract males
by glowing. Males prefer the brightest female if two females are close to
each other. Our model gave different predictions depending on whether
searchers fly or not. The model and experiment showed that weak signallers
should move away from competitors and strong signallers should move closet
to weaker competitors when searchers fly. In contrast, the model predicted
that the distance between competing signallers has no effect when
searchers do not fly. This reveals an unexpected spatial competition
between strong and weak signallers. We conclude that while signal strength
is important in sexual selection, location in relation to others is
similarly important as ornamentation in determining the result of mate
attraction.