Age-dependent effect of environmental light on spectral sensitivity and body colouration of Nile tilapia Oreochromis niloticus
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Signal reception and production form the basis of animal communication, and are largely constrained by environmental biophysical factors such as environmental light. However, the role of environmental light in producing variation in either signal reception or production has not been fully investigated. Using two distinct environmental light treatments, as well as a third treatment for a sampling of adults, I recorded corneal electroretinograms, lens transmission, and spectral reflectance of the body pattern of juvenile and adult Nile tilapia to chart the effect of environmental light on visual sensitivity and body colouration throughout ontogeny. Environmental light had an age-dependent effect on spectral sensitivity and an age-independent effect on spectral reflectance. 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 environmental light treatments differed the most. In contrast, adults reared under the two environmental light treatments did not differ in spectral sensitivity. Lens transmission did not differ significantly between environmental light treatments, indicating that differences in spectral sensitivity of juveniles originated in the retina. Both juveniles and adults reared under the two environmental light treatments differed in spectral reflectance, and adults transferred to the third environmental light treatment differed in spectral reflectance from their counterparts reared under the two original treatments. These results demonstrate that environmental light plays a large role in shaping signal reception in juveniles and signal production throughout ontogeny, suggesting that environmental light has the capacity to drive ecological speciation.