Intraspecific geographic variation in rod and cone visual pigment sensitivity of a parrot, Platycercus elegans

Abstract

Variation in wavelength sensitivity among subspecies is unknown among vertebrates. The parrot Platycercus elegans has extreme plumage variation between subspecies ranging from pale yellow to crimson which, with differences in background colour and light environment between subspecies, makes it a good candidate for the evolution of within-species differences in vision. We report differences in visual pigments between populations of P. elegans from two subspecies, providing the first known support for population and subspecies variation in visual pigments within a vertebrate species; it is also the first instance of intraspecific variation in rod sensitivity within any vertebrate species. Differences in wavelength sensitivity of rods and cones corresponded to geographic differences in plumage colour. Between study populations, visual pigments varied but not oil droplets. Adaptive functions for the visual pigment differences are untested but they could cause divergence in behaviours associated with colour as well as in dim light, and provide insights into the role of senses in divergence and speciation.

Figure 1. Visual pigment templates for the mean λmax from all individual cells for P. e. elegans (red) and P. e. flaveolus (yellow) shown separately for each visual pigment type.

Top panel: (L-R) UVS, SWS, MWS, LWS. Bottom panel: Rod.

Figure 2

Left column: Mean visual pigment λ_max for P. e. elegans and P. e. flaveolus for each visual pigment type. Error bars represent ± 1 standard error. Significant results are indicated by a black line and asterisk. Right column: Spread of all individual photoreceptor cell λ_max for each individual bird, grouped by subspecies: Individuals 1–7: P. e. elegans; Individuals 8–12: P. e. flaveolus. Rows: a: LWS; b: MWS; c: SWS; d: UVS; e: Rod.

Figure 3. Eye models for P. e. elegans (red) and P. e. flaveolus (yellow), showing the predicted sensitivity curves for the four single cone photoreceptors based on the visual pigment and oil droplet microspectrophotometry data collected in this study.