Early evolution of vertebrate photoreception: lessons from lampreys and lungfishes.
Level 5 - mechanism / opinion, no new human data
Level 5 by design analogy: non-human comparative biology and narrative review.
PubMed 21392279 · doi:10.1111/j.1749-4877.2008.00138.x
What was done
The authors reviewed anatomical, ultrastructural, and molecular data on the retinal photoreceptors of two phylogenetically informative extant lineages: the southern hemisphere lamprey (*Geotria australis*) and the Australian lungfish (*Neoceratodus forsteri*).
What was found
Both lineages exhibited complex five-receptor visual complements rather than primitive systems: - *Geotria australis* had five distinct cone-like photoreceptor types expressing five opsin genes (*LWS*, *SWS1*, *SWS2*, *RhA*, *RhB*), providing the basis for potential pentachromatic vision. - *Neoceratodus forsteri* had four cone types and one rod type expressing five opsin genes (*LWS*, *SWS1*, *SWS2*, *Rh1*, *Rh2*), providing the basis for potential tetrachromatic vision. No sample sizes, quantitative spectral tuning curves, or behavioral metrics were reported in the abstract.
Why it matters
This work demonstrates that complex, multi-spectral color vision evolved very early in vertebrate history rather than developing incrementally from simpler monochromatic systems.
Limits
Findings rely on descriptive comparative morphology and molecular genetics in non-human animals with no sample sizes reported in the abstract. Visual capacity is inferred from opsin presence and receptor morphology without reported behavioral discrimination testing.
Cited by
- contradicts Color vision exists exclusively in fruit-eating animals.