Platycercus elegans: Intraspecific variation in avian vision? (#451)
The Australian parrot Platycercus elegans shows considerable intraspecific plumage colour variation across the species range, with subspecies showing three colour forms: crimson, yellow, and an intermediate adelaidae form. Currently, the factors driving and maintaining this diversity are unknown. However, sensory drive theories predict that differences in an animal’s colour perception and associated vision-dependent behaviours could drive the plumage variation observed within P. elegans, making the species an ideal potential candidate for intraspecific variation in the physiology of vision, hitherto unreported in birds. We studied the potential for short-term environmental variables and long-term evolutionary factors to cause such variation in P. elegans. For environmental factors, we studied the effects of dietary manipulations on the carotenoid-rich retinal oil droplets that strongly influence spectral sensitivity, and found diet caused complex changes in the absorbance of these droplets. For long term factors, we used two approaches: (1) DNA sequencing of the protein opsins of the visual pigments from P. elegans, and (2) in situ measurement, using microspectrophotometry (MSP), of the light sensitivity of the visual pigments expressed in retinal photoreceptors. Through sequencing we discovered the low light sensitive rod visual pigments possessed an opsin extension unknown in any animal, and features of this could increase the acuity of low light vision. Through MSP, we discovered visual pigment sensitivity in all photoreceptor types appears to be longwave shifted in the yellow subspecies when compared to the crimson. These differences in visual pigments could arise from adaptive changes in colour vision and, through sensory drive, lead to a divergence in plumage colour.