Appearance matters: multiple functional signals of body colours in a weevil

Abstract

Visual signals in animals are often shaped by sexual selection. For aposematic species, advantages may result from advertising unpalatability to decrease predation and attracting mates to increase reproductive success. On Green Island, Taiwan, most Eupyrgops waltonianus weevils have metallic blue spots on the body; however, some weevils have no conspicuous coloration. The role of coloration in sexual selection and any disadvantages encountered by dull individuals are unknown. To understand whether morphological traits affect mating success in E. waltonianus , we compared different traits between mating and nonmating individuals in the field. A manipulation experiment was also used to test whether coloration affects mating choice and behaviour. The function of colour as an aposematic signal was tested. Results showed that body size and coloration were important indicators of female mating success in field and laboratory experiments, respectively. In the field, males preferred to mate with larger, more conspicuous females, and females preferred to mate with conspicuous males; however, no such preference was shown in the laboratory. Intrasexual competition was stronger in males than in females. Predators avoided colourful weevils. Thus, conspicuous coloration in both sexes is a multifunctional trait and could be an attractive or aposematic signal for different receivers. • The spots on weevils play an important role in survival and reproduction. • Higher spot area ratio was related to a higher mating probability in the field. • Weevils displayed higher levels of male-male than female-female competition. • Weevils' coloration could be attractive or aposematic depending on receiver type.