ORIGINAL PAPER Light environment and mating behavior in Trinidadian guppies (Poecilia reticulata) Gabrielle A. Archard & Innes C. Cuthill & Julian C. Partridge Received: 28 April 2009 / Revised: 1 July 2009 / Accepted: 16 July 2009 / Published online: 5 August 2009 # Springer-Verlag 2009 Abstract Male guppies, Poecilia reticulata, have color patterns that result from a balance between natural selection for crypsis to avoid predators and sexual selection for bright, complex patterns that attract females. Males use displays to show off these patterns to potential mates, but their conspicuousness also depends on the light environ- ment in which they are viewed. We investigated variation in natural underwater guppy light environments in Trinidad, West Indies, and found that mating behavior is correlated with both the ‘quantity’ (total irradiance) and ‘quality’ (spectral composition) of light: light intensity and the proportion of ultraviolet light were negatively related to display rates. Experimental manipulation of light environ- ment to mimic natural daily changes demonstrated that these relationships are causal and are independent of time of day effects. At lower light levels, when guppies are less detectable by visually hunting predators, females had more opportunity for active mate choice, because males dis- played more. However, these light conditions may reduce the ability of females to accurately discriminate between males. Guppy mating behavior is therefore strongly affected by light environment, and this may have important effects on sexual selection. Keywords Guppy . Light environment . Irradiance . Mating behavior . Sexual selection Introduction Visual signals are extremely common in the animal kingdom. The way in which these signals are viewed is strongly affected by the transmission properties of the environment (Lythgoe 1979; Endler 1991, 1992; Fuller 2002) as well as the three-dimensional radiance distribution surrounding the signaler-receiver: i.e., their light environ- ment. Light environments are highly variable, both within and between habitats, and change with time of day, weather, and season (Endler 1993; Lythgoe 1979). Changes in the light environment in which signaling occurs may therefore have large effects on the perception of signals and the behavior of both signalers and receivers (Endler 1991; Endler and Théry 1996). Direct effects of changes in light environment on behavior are distinct from the very common circadian role of light in the control of animal behaviors (e.g., on plankton migrations, Ringelberg (1999); the use by fireflies of self- generated bioluminescent light to attract mates, Buck (1988); and the timing of fish spawning, Reebs (2002). Communicated by C. St. Mary Electronic supplementary material The online version of this article (doi:10.1007/s00265-009-0834-2) contains supplementary material, which is available to authorized users. G. A. Archard : I. C. Cuthill : J. C. Partridge School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK I. C. Cuthill e-mail: I.Cuthill@bristol.ac.uk J. C. Partridge e-mail: J.C.Partridge@bristol.ac.uk Present Address: G. A. Archard (*) School of Forest Resources, The Pennsylvania State University, State College, PA 16802, USA e-mail: gaa11@psu.edu Behav Ecol Sociobiol (2009) 64:169–182 DOI 10.1007/s00265-009-0834-2