Doctoral Dissertation Improvement: The effects of light level and color vision on the foraging behavior of cathemeral red-bellied lemurs (Eulemur rubriventer)

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Humans and many other primates have trichromatic color vision, which confers the ability to discriminate between long (e.g., red) and middle (e.g., green) wavelength chromaticities. Among placental mammals, this feature is unique to primates, but the underlying genetic basis for trichromacy varies across lineages. Importantly, the selective pressures favoring the evolution of trichromacy are still being discussed.In humans, Old World monkeys and apes, as well as Neotropical howler monkeys, most individuals in a population have the capacity for trichromatic color vision. In contrast, most Neotropical monkeys and Malagasy lemurs maintain a sex-linked polymorphism, which provides only heterozygous females the potential for trichromacy, while all males and homozygous females are red-green color blind (dichromatic). This situation provides a unique opportunity to investigate the potential advantages and disadvantages to having trichromatic and dichromatic color vision. For example, it has long been hypothesized that trichromats have an advantage over dichromats when foraging on red-colored food. Empirical support for trichromatic foraging advantages, however, particularly in wild populations, is limited. Recent studies suggest that trichromats might experience more pronounced foraging advantages under dim light, such as during dawn and dusk, rather than under bright light levels.Research conducted by doctoral student Rachel Jacobs (Stony Brook University), supervised by Dr. Patricia Wright, tests hypotheses that different types of color vision confer foraging advantages under bright or dim light conditions in a wild population of polymorphic and cathemeral (active throughout a 24-hour day) red-bellied lemurs (Eulemur rubriventer) in Ranomafana National Park, Madagascar. These hypotheses are tested using a combination of 1) systematic behavioral data collection, 2) genetic analyses to determine individual color vision status (behavioral observers will be unaware of the status), and 3) color measurements using reflectance spectra of red-bellied lemur food items. This research addresses long-held hypotheses regarding the adaptive significance of trichromatic and polymorphic color vision in primates. On a broader scale, this project provides training for a Malagasy student and local Malagasy villagers, supports multiple national and international collaborations, and is initiating a large-scale research effort on red-bellied lemurs, greatly facilitating future research on this species.