Spatial resolving power and spectral sensitivity of the saltwater crocodile, Crocodylus porosus, and the freshwater crocodile, Crocodylus johnstoni
| Autor: | Nicolas Nagloo, Shaun P. Collin, Nathan S. Hart, Jan M. Hemmi |
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| Rok vydání: | 2016 |
| Předmět: |
Retinal Ganglion Cells
0301 basic medicine Physiology Range (biology) Cell Count Fresh Water Aquatic Science Crocodile Predation 03 medical and health sciences 0302 clinical medicine biology.animal Animals Seawater 14. Life underwater Molecular Biology Vision Ocular Ecology Evolution Behavior and Systematics Ecological niche Alligators and Crocodiles Color Vision biology Saltwater environment Ecology Trichromacy Cell Differentiation biology.organism_classification 6. Clean water Crocodylus 030104 developmental biology Spectral sensitivity Microspectrophotometry Insect Science Animal Science and Zoology 030217 neurology & neurosurgery Photoreceptor Cells Vertebrate |
| Zdroj: | Journal of Experimental Biology. 219:1394-1404 |
| ISSN: | 1477-9145 0022-0949 |
| DOI: | 10.1242/jeb.135673 |
| Popis: | Crocodilians are apex amphibious predators that occupy a range of tropical habitats. In this study, we examined whether their semi-aquatic lifestyle and ambush hunting mode are reflected in specific adaptations in the peripheral visual system. Design-based stereology and microspectrophotometry were used to assess spatial resolving power and spectral sensitivity of saltwater (Crocodylus porosus) and freshwater crocodiles (Crocodylus johnstoni). Both species possess a foveal streak that spans the naso-temporal axis and mediates high spatial acuity across the central visual field. The saltwater crocodile and freshwater crocodile have a peak spatial resolving power of 8.8 and 8.0 cycles deg−1, respectively. Measurement of the outer segment dimensions and spectral absorbance revealed five distinct photoreceptor types consisting of three single cones, one twin cone and a rod. The three single cones (saltwater/freshwater crocodile) are violet (424/426 nm λmax), green (502/510 nm λmax) and red (546/554 nm λmax) sensitive, indicating the potential for trichromatic colour vision. The visual pigments of both members of the twin cones have the same λmax as the red-sensitive single cone and the rod has a λmax at 503/510 nm (saltwater/freshwater). The λmax values of all types of visual pigment occur at longer wavelengths in the freshwater crocodile compared with the saltwater crocodile. Given that there is a greater abundance of long wavelength light in freshwater compared with a saltwater environment, the photoreceptors would be more effective at detecting light in their respective habitats. This suggests that the visual systems of both species are adapted to the photic conditions of their respective ecological niche. |
| Databáze: | OpenAIRE |
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