Studies of color vision in marsupial mammals have been very limited.
Two photoreceptor genes have been characterized from the tammar
wallaby, but a third cone pigment was suggested by
microspectrophotometric measurements on cone photoreceptors in two
other species, including the fat-tailed dunnart, Sminthopsis
crassicaudata. To determine the sequence and infer absorption
maxima of the cone photoreceptor pigments of S. crassicaudata
and the related stripe-faced dunnart (Sminthopsis macroura),
we have used evolutionarily conserved sequences of the cone pigments of
other species, including the tammar wallaby, to design primers to
amplify the S. macroura and S. crassicaudata pigment
sequences by the polymerase chain reaction (PCR) using genomic DNA or
retinal cDNA as a template. These primers will be useful for amplifying
cone opsin coding sequences from a variety of vertebrates. Amplified
products were directly sequenced to determine gene structure and coding
sequences. The inferred amino acid sequences of the cone visual
pigments indicated that both species have middle-wave-sensitive (MWS)
pigments with a predicted absorption maximum (λmax) at
530 nm, and ultraviolet-sensitive (UVS) pigments with a predicted
λmax at 360 nm. The MWS pigments of the two species
differ by two, and UVS by three amino acid positions. No evidence was
obtained for a third cone pigment in either species.