The spectral tuning properties of the whale shark (Rhincodon typus) rod (rhodopsin or Rh1) and long-wavelength-sensitive (LWS) cone visual pigments were examined to determine whether these retinal pigments have adapted to the broadband light spectrum available for surface foraging or to the narrowband blue-shifted light spectrum available at depth. Recently published whale shark genomes have identified orthologous genes for both the whale sharkRh1andLWScone opsins suggesting a duplex retina. Here, the whale shark Rh1 and LWS cone opsin sequences were examined to identify amino acid residues critical for spectral tuning. Surprisingly, the predicted absorbance maximum (λmax) for both the whale shark Rh1 and LWS visual pigments is near 500 nm. Although Rh1λmaxvalues near 500 nm are typical of terrestrial vertebrates, as well as surface foraging fish, it is uncommon for a vertebrate LWS cone pigment to be so greatly blue-shifted. We propose that the spectral tuning properties of both the whale shark Rh1 and LWS cone pigments are most likely adaptations to the broadband light spectrum available at the surface. Whale shark melanopsin (Opn4) deactivation kinetics was examined to better understand the underlying molecular mechanisms of the pupillary light reflex. Results show that the deactivation rate of whale shark Opn4 is similar to the Opn4 deactivation rate from vertebrates possessing duplex retinae and is significantly faster than the Opn4 deactivation rate from an aquatic rod monochromat lacking functional cone photoreceptors. The rapid deactivation rate of whale shark Opn4 is consistent with a functional cone class and would provide the animal with an exponential increase in the number of photons required for photoreceptor signaling when transitioning from photopic to scotopic light conditions, as is the case when diving.

中文翻译：

---

鲸鲨（Rhincodon typus）的视网膜色素及其在视觉觅食生态中的作用

鲸鲨的光谱调谐特性 (犀牛) 视杆细胞（视紫红质或 Rh1）和长波长敏感 (LWS) 视锥细胞进行了检查，以确定这些视网膜色素是否已适应可用于表面觅食的宽带光谱或可用于深度的窄带蓝移光谱. 最近发表的鲸鲨基因组已经确定了鲸鲨的直系同源基因Rh1和LWS锥视蛋白表明双相视网膜。在这里，对鲸鲨 Rh1 和 LWS 视锥蛋白序列进行了检查，以确定对光谱调谐至关重要的氨基酸残基。令人惊讶的是，预测的最大吸光度 (λ最大限度) 对于鲸鲨 Rh1 和 LWS 的视觉色素都接近 500 nm。虽然 Rh1λ最大限度接近 500 nm 的值是陆生脊椎动物和表面觅食鱼类的典型值，脊椎动物 LWS 视锥细胞色素的蓝移如此大是不常见的。我们建议鲸鲨 Rh1 和 LWS 锥色素的光谱调谐特性最有可能适应表面可用的宽带光谱。研究了鲸鲨黑视蛋白 (Opn4) 的失活动力学，以更好地了解瞳孔光反射的潜在分子机制。结果表明，鲸鲨 Opn4 的失活率与拥有双工视网膜的脊椎动物的 Opn4 失活率相似，并且明显快于缺乏功能性视锥细胞的水生杆状单色体的 Opn4 失活率。