Cone topography and spectral sensitivity in two potentially trichromatic marsupials, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus).
The potential for trichromacy in mammals, thought to be unique to primates, was recently discovered in two Australian marsupials. Whether the presence of three cone types, sensitive to short- (SWS), medium- (MWS) and long- (LWS) wavelengths, occurs across all marsupials remains unknown. Here, we have investigated the presence, distribution and spectral sensitivity of cone types in two further species, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus). Immunohistochemistry revealed that SWS cones in the quokka are concentrated in dorso-temporal retina, while in the quenda, two peaks were identified in naso-ventral and dorso-temporal retina. In both species, MWS/LWS cone spatial distributions matched those of retinal ganglion cells. Microspectrophotometry (MSP) confirmed that MWS and LWS cones are spectrally distinct, with mean wavelengths of maximum absorbance at 502 and 538 nm in the quokka, and at 509 and 551 nm, in the quenda. Although small SWS cone outer segments precluded MSP measurements, molecular analysis identified substitutions at key sites, accounting for a spectral shift from ultraviolet in the quenda to violet in the quokka. The presence of three cone types, along with previous findings in the fat-tailed dunnart and honey possum, suggests that three spectrally distinct cone types are a feature spanning the marsupials.
Arrese
Catherine A
CA
School of Animal Biology, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia. carrese@cyllene.uwa.edu.au
Oddy
Alison Y
AY
Runham
Philip B
PB
Hart
Nathan S
NS
Shand
Julia
J
Hunt
David M
DM
Beazley
Lyn D
LD
D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D003118:Color Perception / Q000502:physiology*; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D005136:Eye Proteins / Q000235:genetics*; D014644:Genetic Variation; D007150:Immunohistochemistry; D008394:Marsupialia / Q000033:anatomy & histology / Q000502:physiology*; D015591:Microspectrophotometry; D008969:Molecular Sequence Data; D010802:Phylogeny; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology / Q000502:physiology*; D017422:Sequence Analysis, DNA
D017931:DNA Primers; D018076:DNA, Complementary; D005136:Eye Proteins