School of Biological Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
Department of Biology, Lund University, S-212263 Lund, Sweden.
J Exp Biol. 2022 Jun 1;225(11). doi: 10.1242/jeb.244317. Epub 2022 Jun 13.
Despite lizards using a wide range of colour signals, the limited variation in photoreceptor spectral sensitivities across lizards suggests only weak selection for species-specific, spectral tuning of photoreceptors. Some species, however, have enhanced short-wavelength sensitivity, which probably helps with the detection of signals rich in ultraviolet and short wavelengths. In this study, we examined the visual system of Tiliqua rugosa, which has an ultraviolet/blue tongue, to gain insight into this species' visual ecology. We used electroretinograms, opsin sequencing and immunohistochemical labelling to characterize whole-eye spectral sensitivity and the elements that shape it. Our findings reveal that T. rugosa expresses all five opsins typically found in lizards (SWS1, SWS2, RH1, RH2 and LWS) but possesses greatly enhanced short-wavelength sensitivity compared with other diurnal lizards. This enhanced short-wavelength sensitivity is characterized by a broadening of the spectral sensitivity curve of the eye towards shorter wavelengths while the peak sensitivity of the eye at longer wavelengths (560 nm) remains similar to that of other diurnal lizards. While an increased abundance of SWS1 photoreceptors is thought to mediate elevated ultraviolet sensitivity in a couple of other lizard species, SWS1 photoreceptor abundance remains low in this species. Instead, our findings suggest that short-wavelength sensitivity is driven by multiple factors which include a potentially red-shifted SWS1 photoreceptor and the absence of short-wavelength-absorbing oil droplets. Examining the coincidence of enhanced short-wavelength sensitivity with blue tongues among lizards of this genus will provide further insight into the co-evolution of conspecific signals and whole-eye spectral sensitivity.
尽管蜥蜴使用了广泛的颜色信号，但蜥蜴的感光器光谱敏感度的变化有限，这表明对感光器的物种特异性、光谱调谐的选择较弱。然而，有些物种具有增强的短波长敏感度，这可能有助于检测富含紫外线和短波长的信号。在这项研究中，我们研究了 Tiliqua rugosa 的视觉系统，它具有紫外线/蓝色舌头，以深入了解该物种的视觉生态。我们使用视网膜电图、视蛋白测序和免疫组织化学标记来描述整个眼睛的光谱敏感度及其形成元素。我们的研究结果表明，T. rugosa 表达了通常在蜥蜴中发现的所有五种视蛋白（SWS1、SWS2、RH1、RH2 和 LWS），但与其他昼行蜥蜴相比，它具有增强的短波长敏感度。这种增强的短波长敏感度的特征是眼睛的光谱敏感度曲线向较短波长扩展，而眼睛在较长波长（560nm）处的峰值敏感度与其他昼行蜥蜴相似。虽然认为 SWS1 感光器的增加数量可以介导其他几种蜥蜴的紫外线敏感度升高，但在该物种中，SWS1 感光器的数量仍然较低。相反，我们的研究结果表明，短波长敏感度是由多种因素驱动的，包括潜在的红移 SWS1 感光器和缺乏短波长吸收的油滴。检查该属中具有增强的短波长敏感度的蓝色舌头与同类信号的共同进化将进一步深入了解整个眼睛的光谱敏感度。
