Modulation of environmental light alters reception and production of visual signals in Nile tilapia

Abstract

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...

Proximate and ultimate causes of variable visual sensitivities: Insights from cichlid fish radiations

“…This agrees with developmental plasticity demonstrated in other fishes such as the black bream (Shand et al 2008). The only study to examine adult plasticity showed that adult tilapia were not plastic to altered lighting environments (Hornsby et al 2013). This lack of adult plasticity is similar to studies of the South American species Aequidens pulcher, which found no shifts in photoreceptor sensitivities when fish were reared under different colored lights in the lab (Wagner and Kroger 2005).…”

Differentiation of visual spectra and nuptial colorations of two Paratanakia himantegus subspecies (Cyprinoidea: Acheilognathidae) in response to the distinct photic conditions of their habitats

“…The light environment is a factor known to drive both the reception and production of visual signals of fishes (Hornsby et al 2013;Hurtado-Gonzales et al 2014;Shin and Choi 2014;Terai et al 2006;Tezuka et al 2014). Indeed, the present study showed that the spectral sensitivities of P. h. himantegus and P. h. chii are distinct: P. h. himantegus is more sensitive than P. h. chii to longer wavelength light, while it is less sensitive than P. h. chii at shorter wavelengths.…”

Functional characterisation of the chromatically antagonistic photosensitive mechanism of erythrophores in the tilapiaOreochromis niloticus

“…The photosensitivity peaks present in the UV (380 nm) and middlewavelength (480 nm) regions were close to the maximum absorbances (λ max ) of the tilapia retinal cone photopigments (SWS1, 360 nm; RH2b, 472 nm) (Spady et al, 2006). To better understand the interaction between photopigments, the visual pigment templates of SWS1 and RH2b were fitted to the erythrophore action spectrum plot (Govardovskii et al, 2000;Sabbah et al, 2012;Hornsby et al, 2013). Because of the opposing effects elicited by these two photopigments, a neutral area of the antagonistic interaction is suggested to be located in the spectral region near 440-460 nm, which is within the overlapping area of the α-bands (the primary absorption peaks) of these two photopigments.…”

“…The spectral characteristics of each pigment have been well-established from absorbance spectra of in vitro reconstituted proteins and from in situ microspectrophotometry (MSP) measurement (Spady et al, 2006;Carleton et al, 2008;Lisney et al, 2010). Based on reported sensitivity peaks of tilapia cone pigments (Spady et al, 2006), absorption templates were used to fit the photosensitivity curve using a least-squares fit as described previously (Govardovskii et al, 2000;Anderson et al, 2010;Hornsby et al, 2013). In the action spectrum curve of tilapia erythrophores, two peaks present at 380 and 480 nm were close to the maximum absorbances (λ max ) of the retinal cone photopigments (SWS1, 360 nm; RH2b, 472 nm; with 11-cisretinal; Spady et al, 2006).…”

“…where the range of a is 0≤α≤1 (Hornsby et al, 2013). In freshwater fish species, A2 chromophore is favoured in retinal photoreceptors (Carleton et al, 2008).…”