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 shark Rh1 and LWS cone 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 Rh1 λmax values 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.

检查了鲸鲨（Rhincodon typus）杆（视紫红质或Rh1）和长波敏感（LWS）视锥视觉色素的光谱调谐特性，以确定这些视网膜色素是否已适应于可用于表面觅食的宽带光谱或在深处可获得窄带蓝移光谱。最近发表的鲸鲨基因组已鉴定出鲸鲨Rh1和LWS视锥蛋白的直系同源基因，暗示了双链视网膜。在这里，对鲸鲨Rh1和LWS视锥蛋白序列进行了检查，以鉴定对光谱调节至关重要的氨基酸残基。令人惊讶地，所预测的最大吸光度（λ最大）对于鲸鲨Rh1和LWS视觉色素都接近500 nm。虽然皂苷Rh1 λ最大500 nm附近的值是陆生脊椎动物以及表面觅食鱼类的典型特征，脊椎动物LWS锥状色素发生如此大的蓝移现象并不常见。我们提出，鲸鲨Rh1和LWS锥状色素的光谱调谐特性最有可能是对表面可用宽带光谱的适应。鲸鲨黑色素（Opn4）失活动力学进行了检查，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的失活速率与拥有双侧视网膜的脊椎动物的Opn4失活速率相似，并且比缺乏功能性锥感光体的水生杆单色体的Opn4失活速率明显更快。