Proportional assessment of weapons
by Wei Zhou | Daiqin Li | National University of Singapore | National University of Singapore
Abstract ID: 195
Event: The 3rd AsiaEvo Conference
Topic: The evolution of invertebrate sensory ecology and behaviours
Presenter Name: Wei Zhou

Sexual selection through male contests leads to the evolution of exaggerated weapons enhancing the access of males to potential mates. Perceptual processing may mediate contest behaviors. Weber’s law of proportional perception states that perceptual discrimination between stimuli is based on proportional (not absolute) differences in stimulus magnitude. Proportional perception operates in female mate-choice in some animal taxa, but its role in animal contests remains empirically untested. Studying the ant-mimicking jumping spider, Toxeus maxillosus, where only males have exaggerated chelicerae, which serve as weapons, we staged two males matched for body size with varying chelicera sizes to test whether males assess and compare their chelicera size with that of their opponents and make contest decisions based on proportional differences in chelicera size following Weber’s law. While males armed with longer chelicerae had greater chances of winning contests, contest outcomes were better explained by proportional (not absolute) differences in chelicera size. Furthermore, contest duration was negatively correlated with proportional difference in chelicera width in the assessment stage but this correlation was absent in the combat stage. This suggests that the loser may persist for a shorter time and retreat earlier when proportional difference in chelicera width between two males is larger. Our simulated contest data further provided the diagnosis plots which support the discrimination between mutual assessment with proportional perception and other assessment strategies. Together, our results indicate that proportional perception plays a role in male contests, therefore having the potential to influence the important selective pressure of intrasexual competition and shape the evolution of exaggerated animal weapons.