Summary Signal 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.
The effects of post-laying egg spottiness on nestling condition and parental provisioning were investigated in a nest box-breeding population of European Starlings (Sturnus vulgaris). Our objectives were to ascertain whether egg spottiness was associated with the nest ectoparasite Carnus hemapterus, and to examine potential relationships between egg spottiness, presence of C. hemapterus, nestling condition, and parental provisioning effort in European Starlings. Spotted-egg clutches were present over all 3 years in our population, but the spots did not reflect C. hemapterus abundance. Nestlings from spotted-egg clutches did not have more C. hemapterus than those from unspotted-egg clutches. However, nestlings from spotted clutches were in better condition than those from unspotted clutches. Nestling condition was not associated with C. hemapterus abundance. Adult male and female provisioning rates to the offspring did not differ between spotted and unspotted clutches. Similarly, the proportion of provisioning visits by males did not differ significantly between spotted and unspotted clutches, indicating that parents in our population of European Starlings do not use egg spots as a cue to altering their provisioning effort. Further research is required to fully understand the cause and consequences of egg spots in European Starlings.
Non-mammalian vertebrates and invertebrates use extraretinal photoreceptors to detect light and perform diverse non-image-forming functions. Compared to well-studied visual systems, the effect of ambient light conditions on photosensory systems of extraretinal photoreceptors is poorly understood. Chromatophores are photosensitive dermal pigment cells that play an important role in the formation of body color patterns to fit the surrounding environment. Here, we used tilapia erythrophores to investigate the relationship between environmental light and chromatophore photoresponses. All erythrophores from three spectral conditions aggregated their pigment granules in UV/short wavelengths and dispersed in middle/long wavelengths. Unlike retinal visual systems, environmental light did not change the usage of the primary opsins responsible for aggregation and dispersion. In addition, short wavelength-rich and red-shifted background conditions led to an inhibitory effect on erythrophore photoresponses. We suggest that, as extraretinal photoreceptors for non-image-forming functions, chromatophores directly adjust their photoresponse sensitivity via changes in opsin expression levels rather than opsin types when environmental light changes.
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