Individual Variation in Cone Photoreceptor Density in House Sparrows: Implications for Between-Individual Differences in Visual Resolution and Chromatic Contrast

Abstract

Between-individual variation has been documented in a wide variety of taxa, especially for behavioral characteristics; however, intra-population variation in sensory systems has not received similar attention in wild animals. We measured a key trait of the visual system, the density of retinal cone photoreceptors, in a wild population of house sparrows (Passer domesticus). We tested whether individuals differed from each other in cone densities given within-individual variation across the retina and across eyes. We further tested whether the existing variation could lead to individual differences in two aspects of perception: visual resolution and chromatic contrast. We found consistent between-individual variation in the densities of all five types of avian cones, involved in chromatic and achromatic vision. Using perceptual modeling, we found that this degree of variation translated into significant between-individual differences in visual resolution and the chromatic contrast of a plumage signal that has been associated with mate choice and agonistic interactions. However, there was no evidence for a relationship between individual visual resolution and chromatic contrast. The implication is that some birds may have the sensory potential to perform “better” in certain visual tasks, but not necessarily in both resolution and contrast simultaneously. Overall, our findings (a) highlight the need to consider multiple individuals when characterizing sensory traits of a species, and (b) provide some mechanistic basis for between-individual variation in different behaviors (i.e., animal personalities) and for testing the predictions of several widely accepted hypotheses (e.g., honest signaling).

Assessing Sexual Dicromatism: The Importance of Proper Parameterization in Tetrachromatic Visual Models

“…Differences in photoreceptor densities are likely to have large consequences on among-species ability to discriminate between similar colors and, as for variation in oil droplet absorbance profiles, within-species variation may be of consequence as well. For example, differences in densities among house sparrows ( Passer domesticus Linnaeus) generated chromatic contrast differences of ~16% (> 3 JNDs) when evaluating the perception of the white wing bars against the brown wing background coloration [45]. Even if these plumage patches likely differ more in the achromatic component of the signal, these chromatic differences may still have implications for mate choice and agonistic interactions.…”

“…Studies comparing dicromats to trichromats [37, 38] and trichromats to tetrachromats [39, 40] have quantified how these visual systems differ in their ability to tell apart patches with different spectral properties. Others have tested the effect of different light environments [22, 41–43], photoreceptors sensitivities [22, 44], photoreceptor densities [44, 45], oil droplet characteristics [44, 46–48], ocular media [22], and receptor signal-to-noise ratio [44]. While these studies have been very informative when considered together, the use of different visual system starting points and non-standardized methods of presenting results have made it difficult to compare the relative effect of each parameter within a single context.…”

Mate choice in the eye and ear of the beholder? Female multimodal sensory configuration influences her preferences

“…Enhanced spatial visual resolution should allow for better discrimination of male visual signals such as fine differences in the degree of feather puffing (e.g. [23]).…”

“…We hypothesized that females with higher sensory filtering capacity would have a greater ability to distinguish variation in male signals compared to those with lower sensory filtering capacity [23][24][25]. Differences in sensory filtering, in turn, should affect a female's ability to choose a mate (i.e.…”

Plumage convergence resulting from social mimicry in birds? A tetrachromatic view

“…More 369 definitive tests of the hypothesis that similarities among species of flycatchers with kiskadee-like plumage 370 may deceive their avian predators or putative competitors thus await additional consideration involving 371 the use of visual models developed specifically for predatory species and for the birds we studied. This is 372 because variation among and within species in visual abilities may exist[65,66] and because differences 373 in unstudied traits such as photoreceptor densities may have large consequences on the ability of species374…”