Browsing by Subject "Color vision"

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Color vision variation, feeding behavior, and reproductive output in a group of wild Ateles belzebuth
(2023-08) Rettke, Samantha Paige; Di Fiore, Anthony, Ph. D.
Color vision among primates is remarkably diverse. Catarrhines and howler monkeys have independently acquired routine trichromacy through duplication of the middle-to-long wavelength-sensitive (M/LWS) opsin gene on the X chromosome. Most platyrrhines and some strepsirrhines, however, possess polymorphic color vision due to allelic variation at a single M/LWS locus; heterozygous females are trichromats, while males and homozygous females are dichromats. Four mechanisms – heterozygote (trichromat) advantage, frequency-dependent selection, mutual benefit of association, and niche divergence – have been proposed to explain the maintenance of the opsin polymorphism, yet the selective advantages of individual phenotypes remain unclear. I reviewed the diversity in platyrrhine color vision as well as the studies that have evaluated each hypothesis. Next, I tested two of these hypotheses in one social group of white-bellied spider monkeys (Ateles belzebuth) that has been monitored at Tiputini Biodiversity Station since 2005. Spider monkeys – a genus of large-bodied frugivorous platyrrhines – have two possible opsin alleles determined by a SNP in exon 5 of the M/LWS locus; in reconstituted pigments they have absorption spectra with peaks at 538 and 553 nm, respectively. Using fecal-extracted DNA, I sequenced exon 5 for 44 group members, identifying 14 male dichromats (seven P538, seven P553), 10 female dichromats (two P538, eight P553), and 20 female trichromats (P538/P553). Then, to investigate the possibility of heterozygote advantage, I compared the interbirth intervals and number of offspring produced for dichromat versus trichromat females. There were no differences in these measures of reproductive output, suggesting that the conditional advantages of trichromacy may not translate to higher fitness. To assess niche divergence, I examined the proportion of total feeding time spent by dichromat versus trichromat adult and subadult males and females on each of three major food types – fruits, new leaves, and flowers – plus all three substrates combined. Additionally, I tested for niche divergence within dichromats by comparing the foraging behavior of P538 versus P553 individuals. Analyses revealed no difference in foraging activity budgets between groups in either case. Future work may consider other aspects of fitness and finer-scale niche differentiation to better understand how multiple visual phenotypes have been maintained in this population.
Effects of light environments on the evolution of primate visual systems
(2012-05) Veilleux, Carrie Cecilia; Kirk, E. Christopher, 1974-
Primate habitats differ dramatically in the intensity and spectral quality (color) of ambient light. However, little research has explored the effects of habitat variation in ambient light on primate and mammalian visual systems. An understanding of variation in nocturnal light environments is particularly lacking, considering the significance of nocturnality and vision in primate evolutionary hypotheses. In this dissertation, I explored effects of habitat variation in light environments on primate visual evolution in three studies. First, I examined how variation in ambient light intensity influenced visual morphology in 209 mammals. Second, I analyzed effects of variation in nocturnal light environments on color vision in nocturnal primates and mammals. For this second objective, I first identified factors influencing variation in nocturnal light environments within and between habitats in Madagascar and explored how nocturnal light spectral quality has influenced mammalian visual pigment spectral tuning. I then analyzed selection acting on the SWS1 opsin gene (coding for blue-sensitive cone visual pigments) between nocturnal lemurs from different habitat types to explore whether nocturnal light environments affect selection for dichromatic color vision. The results of all three studies suggest that habitat variation in light environments has had a significant influence on primate and mammalian visual evolution. In the first study, I found that day-active mammals from forested habitats exhibited larger relative cornea size compared to species from open habitats, reflecting an adaptation to increase visual sensitivity in diurnal forests. The results of the second study revealed that forest and woodland habitats share a yellow-green dominant nocturnal light environment and that nocturnal vertebrates exhibit visual pigments tuned to maximize photon absorption in these environments. Additionally, I observed a potential effect of diet on long-wavelength-sensitive cone spectral tuning among nocturnal mammals. In the third study I sequenced the SWS1 opsin gene in 106 nocturnal lemurs (19 species). Both population genetic and phylogenetic analyses identified clear signatures of differential selection on the gene by habitat type, suggesting that nocturnal light environments has influenced selection for nocturnal dichromacy in nocturnal lemurs. Finally, I discussed the implications of these results for nocturnal primate visual ecology and evolution.
Modeling the self-organization of color selectivity in the visual cortex
(2007-12) De Paula, Judah Ben, 1978-; Miikkulainen, Risto; Bednar, James A.
How does the visual cortex represent and process color? Experimental evidence from macaque monkey suggests that cells selective for color are organized into small, spatially separated blobs in V1, and stripes in V2. This organization is strikingly different from that of orientation and ocular dominance maps, which consist of large, spatially contiguous patterns. In this dissertation, a self-organizing model of the early visual cortex is constructed using natural color image input. The modeled V1 develops realistic color-selective receptive fields, ocular dominance stripes, orientation maps, and color-selective regions, while the modeled V2 also creates realistic colorselective and orientation-selective neurons. V1 color-selective regions are generally located in the center of ocular dominance stripes as they are in biological maps; the model predicts that color-selective regions become more widespread in both cortical regions when the amount of color in the training images is increased. The model also predicts that in V1 there are three types of color-selective regions (red-selective, greenselective, and blue-selective), and that a unique cortical activation pattern exists for each of the HSV colors. In both V1 and V2, when regions of different color-selectivity are located nearby, bands of color form with gradually changing color preferences. The model also develops lateral connections between cells that are selective for similar orientations, matching previous experimental results, and predicts that cells selective for color primarily connect to other cells with similar chromatic preferences. Thus the model replicates the known data on the organization of color preferences in V1 and V2, provides a detailed explanation for how this structure develops and functions, and leads to concrete predictions to test in future experiments.