Available online at www.sciencedirect.com The conspicuousness of colour cues in male pond damselflies depends on ambient light and visual system TOM D. SCHULTZ, CHRISTOPHER N. ANDERSON & LAUREL B. SYMES Department of Biology, Denison University, Granville, Ohio (Received 16 February 2008; initial acceptance 13 March 2008; final acceptance 7 April 2008; published online 12 August 2008; MS. number: A08-00093) The colours of male coenagrionid damselflies have been interpreted by some as intraspecific signals that reduce intrasexual harassment by advertising the unprofitability of pursuing conspecific males as potential mates. As visual cues, male colours should be conspicuous to other males under the specific light environ- ments where males search for females. We tested this prediction by using spectroradiometry and two models of damselfly colour vision to determine the chromatic and achromatic contrast of males from six species of Enallagma damselflies with pond backgrounds under the ambient light conditions when each species was most active. The males of five species were active at the time when their colour was most conspicuous against aquatic vegetation. Three blue species were most active and attained their high- est levels of contrast during midday, while species that became active in late afternoon or evening reflected longer wavelengths and increased in brightness contrast under low sun angles. A sixth species, Enallagma pictum, departed from this pattern. We propose that colour may serve as a signal of both sexual and species identity among males. Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Keywords: colour vision; Enallagma damselflies; sensory drive; sexual signal; spectral reflectance Sexual dichromatism is common among animals and often attributed to sexual selection for characteristics in one sex that reflect light as a conspicuous visual signal to members of the same or opposite sex (Silberglied 1984; Andersson 1994; Irwin 1994; Houde 1997). The utility of colour as a signal depends on the vision of the receiver and the light environment in which the sender and the re- ceiver interact. A conspicuous colour will reflect the ambi- ent light, provide strong contrast with the visual background and exploit the sensory characteristics of the receiver (Endler 1990, 1993). Spectrometry and quantita- tive measurements of colour have been useful in interpret- ing the evolution of sexual signals in vertebrates, their tactical design and their efficacy in the relevant environ- mental context (Endler & The ´ry 1996; Macedonia 2001; Fuller 2002; Gomez & The ´ry 2004; Leal & Fleishman 2004; Uy & Endler 2004; Doucet et al. 2007; Stuart-Fox et al. 2007). In this study, we applied similar techniques and a comparative approach to assess the conspicuousness of insect colours that are presumed to serve as intraspecific signals. Damselflies (Odonata: Zygoptera) have been the subject of numerous studies of mating behaviour (Corbet 1999; Fincke et al. 2005). Research on the signal content of dam- selfly coloration has focused on the territorial and court- ship behaviour of calopterygid damselflies (Grether 1996; Siva-Jothy 1999; Fitzstephens & Getty 2000; Cor- doba-Aguilar et al. 2007) or the evolution of female poly- morphism in coenagrionid damselflies (Cordero & Andre ´s 1996; Sherratt 2001; Van Gossum et al. 2001; Sirot et al. 2003; Fincke 2004; Fincke et al. 2005). Male coenagrionid damselflies practice scramble competition mating behav- iour (e.g. Bick & Bick 1963; Bick & Hornuff 1966; Fincke 1982) and there is no evidence that females exert mate Correspondence and present address: T. D. Schultz, Department of Biology, Denison University, Granville, OH 43023, U.S.A. (email: schultz@denison.edu). C. N. Anderson is now at the Department of Ecology and Evolution, 3205 Life Science Building, University of Cali- fornia, Los Angeles, CA 90095, U.S.A. L. B. Symes is now at the De- partment of Biological Sciences, 113H Centerra Bio Labs, Dartmouth College, Hanover, NH 03755, U.S.A. 1357 0003e 3472/08/$34.00/0 Ó 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2008, 76, 1357e1364 doi:10.1016/j.anbehav.2008.04.024