Efficient detection and selection of reddish fruits against green foliage has long been thought to be a major selective pressure favoring the evolution of primate trichromatic color vision. This has recently been questioned by studies of free-ranging primates that fail to show predicted differences in foraging efficiency between dichromats and trichromats. In the present study, we use a unique approach to evaluate the adaptive significance of trichromacy for fruit detection by undertaking a functional substitution model. The color vision phenotypes of neotropical monkeys are simulated for human observers, who use a touch-sensitive computer interface to search for monkey food items in digital images taken under natural conditions. We find an advantage to trichromatic phenotypes - especially the variant with the most spectrally separated visual pigments - for red, yellow and greenish fruits, but not for dark (purple or black) fruits. These results indicate that trichromat advantage is task-specific, and that shape, size and achromatic contrast variation between ripe and unripe fruits cannot completely mitigate the advantage of color vision. Similarities in fruit foraging performance between primates with different phenotypes in the wild likely reflect the behavioral flexibility of dichromats in overcoming a chromatic disadvantage.

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Sex differences in feeding ecology may develop in response to fluctuations in physiological costs to females over their reproductive cycles, or to sexual size dimorphism, or function to minimize feeding competition within a group via resource partitioning. For most mammal species, it is unknown how these factors contribute to sex differences in feeding, or how the development of males and females reflects these intraspecific feeding differences. We show changes in dietary composition, diversity, overlap, and foraging behavior throughout development in ring-tailed lemurs (Lemur catta) and test how the development of sex differences in feeding is related to female costs of reproduction and year-round resource partitioning. Sex differences in dietary composition were only present when females were lactating, but sex differences in other aspects of feeding, including dietary diversity, and relative time spent feeding and foraging, developed at or near the time of weaning. Sex difference in juveniles and subadults, when present, were similar to the differences found in adults. The low year-round dietary overlap and early differences in dietary diversity indicate that some resource partitioning may begin with young individuals and fluctuate throughout development. The major differences between males and females in dietary composition suggest that these larger changes in diet are closely tied to female reproductive state when females must shift their diet to meet energetic and nutritional requirements.Keywords Behavioral development . Diet . Juvenile . Female dominance . Reproduction . Resource partitioning . Lemur catta It is often expected that individuals within a population of different ages, sexes, and sizes, will exploit varying aspects of the species' feeding niche (Schoener 1986; Ebenman 1988). As part of this variation, sex differences in vertebrate feeding can range from temporal and spatial separation of males and females (Ruckstuhl and Neuhaus 2002;Ruckstuhl 2007) to differences in the composition and diversity in diet (CluttonBrock 1977a;Holmes 1986;Clarke et al. 1998;Lewis et al. 2002;Beck et al. 2005;Krüger 2005). For most species, however, little is known about when sex differences appear, how they change throughout development, if early sex differences mimic adult patterns, and if these sex differences function to partition resources or are only apparent with physiological differences between males and females, particularly those related to reproduction.The successful development of ecological competence and adult diet is the primary determinant of whether individuals