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Individual variation in cone photoreceptor density in house sparrows: implications for between-individual differences in visual resolution and chromatic contrast.

Ensminger AL, Fernández-Juricic E - PLoS ONE (2014)

Bottom Line: 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.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).

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana, United States of America.

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).

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Between-individual variation in absolute densities of double and single cone photoreceptor densities.Each bar represents the mean and standard error for an individual. Light bars are females (n = 13), dark bars are males (n = 13).
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pone-0111854-g002: Between-individual variation in absolute densities of double and single cone photoreceptor densities.Each bar represents the mean and standard error for an individual. Light bars are females (n = 13), dark bars are males (n = 13).

Mentions: These mixed models revealed that individuals differed significantly in the absolute density of cones (Fig. 2; Table 2). This was true for right and left eyes separately, suggesting that individuals were consistently different from one another within each eye, given the variation among sites. The significant positive covariance across eyes suggests that the differences between individuals in each eye were maintained across their eyes (Table 2). The individual with the highest density of all cones had 36% higher density than the individual with the lowest density (Table 1). The absolute density of the LWS cones varied the most (100% from the individual with the lowest to that with the highest density, Appendix S5), but also had the highest repeatabilities (0.38) and covariance correlation (0.74), indicating a high variability in this cone type across individuals, but a low variability in absolute densities within-individuals.


Individual variation in cone photoreceptor density in house sparrows: implications for between-individual differences in visual resolution and chromatic contrast.

Ensminger AL, Fernández-Juricic E - PLoS ONE (2014)

Between-individual variation in absolute densities of double and single cone photoreceptor densities.Each bar represents the mean and standard error for an individual. Light bars are females (n = 13), dark bars are males (n = 13).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4221115&req=5

pone-0111854-g002: Between-individual variation in absolute densities of double and single cone photoreceptor densities.Each bar represents the mean and standard error for an individual. Light bars are females (n = 13), dark bars are males (n = 13).
Mentions: These mixed models revealed that individuals differed significantly in the absolute density of cones (Fig. 2; Table 2). This was true for right and left eyes separately, suggesting that individuals were consistently different from one another within each eye, given the variation among sites. The significant positive covariance across eyes suggests that the differences between individuals in each eye were maintained across their eyes (Table 2). The individual with the highest density of all cones had 36% higher density than the individual with the lowest density (Table 1). The absolute density of the LWS cones varied the most (100% from the individual with the lowest to that with the highest density, Appendix S5), but also had the highest repeatabilities (0.38) and covariance correlation (0.74), indicating a high variability in this cone type across individuals, but a low variability in absolute densities within-individuals.

Bottom Line: 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.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).

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana, United States of America.

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).

Show MeSH