title: Conspicuous Coloration in Males of the Damselfly Nehalennia irene (Zygoptera: Coenagrionidae): Do Males Signal Their Unprofitability to Other Males?
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.
authors.affiliation: Department of Biology, Santa Clara University, 500 El Camino Real, Santa Clara, CA, 95053-0268, United States of America.|Department of Ecology & Evolutionary Biology, Cornell University, E149 Corson Hall, 215 Tower Road, Ithaca, NY, 08053, United States of America.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Beatty
authors.affiliation: Department of Biology, University of Saskatchewan, Saskatoon, Saskatechewan, S7N 0W0, Canada.
authors.forename: José A
authors.initials: JA
authors.lastname: Andrés
authors.affiliation: Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
authors.forename: Thomas N
authors.initials: TN
authors.lastname: Sherratt
mesh_terms: D000818:Animals; D003116:Color; D005260:Female; D008297:Male; D063191:Odonata / Q000235:genetics / Q000502:physiology*; D010858:Pigmentation / Q000235:genetics*; D012727:Sex Characteristics; D012725:Sexual Behavior / Q000502:physiology*