Abstract
In damselflies, sexual colour dimorphism is commonly explained as a consequence of selection on traits that increase male attractiveness to females. However, while many species in the damselfly family Coenagrionidae (Insecta: Odonata) are sexually dimorphic, the males do not engage in displays, and male competition for mates resembles a “scramble”. An alternative explanation for the sexual differences in coloration within these species is that sexual dimorphism has evolved as a sex-related warning signal, with males signalling their uprofitability as mates to other males, thereby avoiding harassment from conspecifics. We evaluated an underlying assumption of the theory that male-male harassment rate is influenced by colour by comparing harassment of males of the species Nehalennia irene that had been painted to make them appear: (i) similar to an unaltered male (blue), (ii) different from a male (orange) and (iii) more similar to a female (black). When caged together we found that blue-painted males experienced significantly lower harassment than black-painted males. When unpainted males were caged with each type of painted male we found that blue-painted males and the unpainted males housed in the same cages experienced lower rates of harassment than males housed in cages where some males were painted black, suggesting that a single, reliable signal of unprofitability may benefit the individuals that carry it. While our results do not in themselves demonstrate that sexual colour dimorphism originally evolved as an intra-specific warning signal, they do show that harassment is influenced by coloration, and that such selection could conceivably maintain male coloration as a warning signal.
Highlights
Many damselfly species demonstrate sexual colour dimorphism in which males are brightly coloured, while females are more drab [1,2,3]
Conspicuous male coloration has been attributed to premating sexual selection acting on male characters: that is, competition among males to gain access to females, with males actively displaying their quality as mates, either in their physical attributes or in the quality of the resources that they defend [4,5,6,7,8,9,10,11]
All experiments performed comply with the laws for animal handling and field observations for Canada and the province of Ontario. These experiments were performed at localities on the property of Queen’s University Biological Station (QUBS); experimental design and property access were approved by QUBS management
Summary
Many damselfly species demonstrate sexual colour dimorphism in which males are brightly coloured, while females are more drab [1,2,3]. Conspicuous male coloration has been attributed to premating sexual selection acting on male characters: that is, competition among males to gain access to females, with males actively displaying their quality as mates, either in their physical attributes or in the quality of the resources that they defend [4,5,6,7,8,9,10,11]. Among many species in the family Coenagrionidae, males do not defend territories or engage in displays to females [3]. In these species, mating resembles a “scramble” with males searching for mating opportunities and pursuing potential mates aggressively, at times coercing them to mate. Males approach females from above as they prepare to go into tandem with them, and as such, their coloration may not be immediately visible to the female
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call