Spatial resolving power and spectral sensitivity of the saltwater crocodile, Crocodylus porosus, and the freshwater crocodile, Crocodylus johnstoni

Nicolas Nagloo*, Shaun P. Collin, Jan M. Hemmi, Nathan S. Hart

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    19 Citations (Scopus)

    Abstract

    Crocodilians are apex amphibious predators that occupy a range of tropical habitats. In this study, we examined whether their semiaquatic 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.

    Original languageEnglish
    Pages (from-to)1394-1404
    Number of pages11
    JournalJournal of Experimental Biology
    Volume219
    Issue number9
    DOIs
    Publication statusPublished - 1 May 2016

    Keywords

    • Chromophore shift
    • Microspectrophotometry
    • Reptile
    • Retinal topography
    • Visual ecology

    Fingerprint

    Dive into the research topics of 'Spatial resolving power and spectral sensitivity of the saltwater crocodile, <i>Crocodylus porosus</i>, and the freshwater crocodile, <i>Crocodylus johnstoni</i>'. Together they form a unique fingerprint.

    Cite this