SUMMARYSignal reception and production form the basis of animal visual communication, and are largely constrained by environmental light. However, the role of environmental light in producing variation in either signal reception or production has not been fully investigated. To chart the effect of environmental light on visual sensitivity and body colouration throughout ontogeny, we measured spectral sensitivity, lens transmission and body pattern reflectance from juvenile and adult Nile tilapia held under two environmental light treatments. Spectral sensitivity in juveniles reared under a broad-spectrum light treatment and a red-shifted light treatment differed mostly at short wavelengths, where the irradiance of the two light treatments differed the most. In contrast, adults held under the same two light treatments did not differ in spectral sensitivity. Lens transmission in both juveniles and adults did not differ significantly between environmental light treatments, indicating that differences in spectral sensitivity of juveniles originated in the retina. Juveniles and adults held under the two environmental light treatments differed in spectral reflectance, and adults transferred to a third, white light treatment differed in spectral reflectance from their counterparts held under the two original treatments. These results demonstrate that environmental light plays a crucial role in shaping signal reception in juveniles and signal production throughout ontogeny, reinforcing the notion that environmental light has the capacity to influence animal communication, and suggesting that the characteristics of environmental light should be considered in models of ecological speciation.Key words: ontogenetic variation, visual sensitivity, body colouration, sensory drive, animal communication. (Kocher, 2004), and are a growing presence in laboratory research (El-Sayed, 2006). Cichlid fish show variation in signal reception, as visual pigment complements show a great range of natural variation (Carleton and Kocher, 2001;Parry et al., 2005;Sabbah et al., 2010;O'Quin et al., 2010). Additionally, cichlids are notorious for their variation in signal production, showing myriad behaviours (Barlow, 2000) and body colourations (Kornfield and Smith, 2000), many of which are species specific (Hofmann et al., 2009). When these sources of variation are coupled with changes in the spectral quality of available environmental light, which, for example, occur as water depth varies (e.g. Sabbah et al., 2011), the basic requirements for sensory drive are met. However, the role of environmental light in these sources of variation, particularly signal production, remains somewhat elusive.Nile tilapia have been shown to differentially express seven visual pigments throughout ontogeny: SWS1 (360nm), SWS2b (425nm), SWS2a (456nm), Rh2b (472nm), Rh2aβ (518nm), Rh2aα (528nm) and LWS (561nm) (Spady et al., 2006). Juveniles predominantly express SWS2b, SWS2a, Rh2a (a combination of Rh2aβ and Rh2aα, as their maximum absorbance wavelengt...

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Color vision is most beneficial when the visual system is color constant and can correct the excitations of photoreceptors for differences in environmental irradiance. A phenomenon related to color constancy is color induction, where the color of an object shifts away from the color of its surroundings. These two phenomena depend on chromatic spatial integration, which was suggested to originate at the feedback synapse from horizontal cells (HC) to cones. However, the exact retinal site was never determined. Using the electroretinogram and compound action potential recordings, we estimated the spectral sensitivity of the photoresponse of cones, the output of cones, and the optic nerve in rainbow trout. Recordings were performed before and following pharmacological inhibition of HC-cone feedback, and were repeated under two colored backgrounds to estimate the efficiency of color induction. No color induction could be detected in the photoresponse of cones. However, the efficiency of color induction in the cone output and optic nerve was substantial, with the efficiency in the optic nerve being significantly higher than in the cone output. We found that the efficiency of color induction in the cone output and optic nerve decreased significantly with the inhibition of HC-cone feedback. Therefore, our findings suggest not only that color induction originates as a result of HC-cone feedback, but also that this effect of HC-cone feedback is further amplified at downstream retinal elements, possibly through feedback mechanisms at the inner plexiform layer. This study provides evidence for an important role of HC-cone feedback in mediating color induction, and therefore, likely also in mediating color constancy.

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