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The sense of smell is an important mediator of health and sociality at all stages of life, yet it has received limited attention in our lineage. Olfaction starts in utero and participates in the establishment of social bonds in children, and of romantic and sexual relationships after puberty. Smell further plays a key role in food assessment and danger avoidance; in modern societies, it also guides our consumer behavior. Sensory abilities typically decrease with age and can be impacted by diseases, with repercussions on health and well‐being. Here, we critically review our current understanding of human olfactory communication to refute outdated notions that our sense of smell is of low importance. We provide a summary of the biology of olfaction, give a prospective overview of the importance of the sense of smell throughout the life course, and conclude with an outline of the limitations and future directions in this field. [ABSTRACT FROM AUTHOR]

Studying fruit traits and their interactions with seed dispersers can improve how we interpret patterns of biodiversity, ecosystem function and evolution. Mounting evidence suggests that fruit ethanol is common and variable, and may exert selective pressures on seed dispersers. To test this, we comprehensively assess fruit ethanol content in a wild ecosystem and explore sources of variation. We hypothesize that both phylogeny and seed dispersal syndrome explain variation in ethanol levels, and we predict that fruits with mammalian dispersal traits will contain higher levels of ethanol than those with bird dispersal traits. We measured ripe fruit ethanol content in species with mammal- (n = 16), bird- (n = 14) or mixed-dispersal (n = 7) syndromes in a Costa Rican tropical dry forest. Seventy-eight per cent of fruit species yielded measurable ethanol concentrations. We detected a phylogenetic signal in maximum ethanol levels (Pagel's λ = 0.82). Controlling for phylogeny, we observed greater ethanol concentrations in mammal-dispersed fruits, indicating that dispersal syndrome helps explain variation in ethanol content, and that mammals may be more exposed to ethanol in their diets than birds. Our findings further our understanding of wild fruit ethanol and its potential role as a selective pressure on frugivore sensory systems and metabolism. [ABSTRACT FROM AUTHOR]

Senses form the interface between animals and environments, and provide a window into the ecology of past and present species. However, research on sensory behaviours by wild frugivores is sparse. Here, we examine fruit assessment by three sympatric primates (Alouatta palliata, Ateles geoffroyi and Cebus imitator) to test the hypothesis that dietary and sensory specialization shape foraging behaviours. Ateles and Cebus groups are comprised of dichromats and trichromats, while all Alouatta are trichomats. We use anatomical proxies to examine smell, taste and manual touch, and opsin genotyping to assess colour vision. We find that the frugivorous spider monkeys (Ateles geoffroyi) sniff fruits most often, omnivorous capuchins (Cebus imitator), the species with the highest manual dexterity, use manual touch most often, and that main olfactory bulb volume is a better predictor of sniffing behaviour than nasal turbinate surface area. We also identify an interaction between colour vision phenotype and use of other senses. Controlling for species, dichromats sniff and bite fruits more often than trichromats, and trichromats use manual touch to evaluate cryptic fruits more often than dichromats. Our findings reveal new relationships among dietary specialization, anatomical variation and foraging behaviour, and promote understanding of sensory system evolution. [ABSTRACT FROM AUTHOR]

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Primates possess remarkably variable color vision, and the ecological and social factors shaping this variation remain heavily debated. Here, we test whether central tenants of the folivory hypothesis of routine trichromacy hold for the foraging ecology of howler monkeys. Howler monkeys (genus Alouatta) and paleotropical primates (Parvorder: Catarrhini) have independently acquired routine trichromacy through fixation of distinct mid- to long-wavelength-sensitive ( M/ LWS) opsin genes on the X-chromosome. The presence of routine trichromacy in howlers, while other diurnal neotropical monkeys (Platyrrhini) possess polymorphic trichromacy, is poorly understood. A selective force proposed to explain the evolution of routine trichromacy in catarrhines-reliance on young, red leaves-has received scant attention in howlers, a gap we fill in this study. We recorded diet, sequenced M/ LWS opsin genes in four social groups of Alouatta palliata, and conducted colorimetric analysis of leaves consumed in Sector Santa Rosa, Costa Rica. For a majority of food species, including Ficus trees, an important resource year-round, young leaves were more chromatically conspicuous from mature leaves to trichromatic than to hypothetical dichromatic phenotypes. We found that 18% of opsin genes were MWS/ LWS hybrids; when combined with previous research, the incidence of hybrid M/ LWS opsins in this species is 13%. In visual models of food discrimination ability, the hybrid trichromatic phenotype performed slightly poorer than normal trichromacy, but substantially better than dichromacy. Our results provide support for the folivory hypothesis of routine trichromacy. Similar ecological pressures, that is, the search for young, reddish leaves, may have driven the independent evolution of routine trichromacy in primates on separate continents. We discuss our results in the context of balancing selection acting on New World monkey opsin genes and hypothesize that howlers experience stronger selection against dichromatic phenotypes than other sympatric species, which rely more heavily on cryptic foods. [ABSTRACT FROM AUTHOR]

Debate on the adaptive origins of primates has long focused on the functional ecology of the primate visual system. For example, it is hypothesized that variable expression of short- (SWS1) and middle-to-long-wavelength sensitive (M/LWS) opsins, which confer color vision, can be used to infer ancestral activity patterns and therefore selective ecological pressures. A problem with this approach is that opsin gene variation is incompletely known in the grandorder Euarchonta, that is, the orders Scandentia (treeshrews), Dermoptera (colugos), and Primates. The ancestral state of primate color vision is therefore uncertain. Here, we report on the genes (OPN1SW and OPN1LW) that encode SWS1 and M/LWS opsins in seven species of treeshrew, including the sole nocturnal scandentian Ptilocercus lowii. In addition, we examined the opsin genes of the Central American woolly opossum (Caluromys derbianus), an enduring ecological analogue in the debate on primate origins. Our results indicate: 1) retention of ultraviolet (UV) visual sensitivity in C. derbianus and a shift from UV to blue spectral sensitivities at the base of Euarchonta; 2) ancient pseudogenization of OPN1SW in the ancestors of P. lowii, but a signature of purifying selection in those of C. derbianus; and, 3) the absence of OPN1LW polymorphism among diurnal treeshrews. These findings suggest functional variation in the color vision of nocturnal mammals and a distinctive visual ecology of early primates, perhaps one that demanded greater spatial resolution under light levels that could support cone-mediated color discrimination. [ABSTRACT FROM AUTHOR]

The polymorphic colour vision system of platyrrhine monkeys is a remarkable example of balancing selection. Yet, the underlying mechanism of natural selection remains debated. Here we test the potential for dietary niche differentiation between sensory phenotypes. Monkeys with dichromacy (red-green 'colourblindness') are predicted to eat more camouflaged foods while trichromatic monkeys ('typical' human-like colour vision) are predicted to eat more reddish foods. We studied a population of wild Costa Rican capuchins (Cebus imitator), comparing the diet and nutrition of adult female dichromats and trichromats. We classified the conspicuity of diet items in capuchin visual space and calculated dietary intake, nutritional intake and niche overlap during periods of high and low habitat-wide fruit abundance. Dichromats and trichromats had similar nutritional profiles, but we found evidence of niche differentiation in the invertebrate prey consumed. In support for our prediction regarding cryptic invertebrate prey, dichromats ate more camouflaged surface-dwelling invertebrates, while trichromats ate more extracted ants. Contrary to our prediction regarding reddish foods, dichromats consumed more dark reddish figs than did trichromats. However, these fruits were likely to be conspicuous to both dichromats and trichromats in luminance contrast. Overall, our results suggest that monkeys with different colour vision types achieve similar nutritional intakes in slightly different ways. Behavioural flexibility driven by sensory differences may decrease intragroup feeding competition while meeting species-specific nutritional needs. Our research sheds light on the extent of foraging niche differentiation in a population of wild mammals and its potential contribution to maintaining colour vision polymorphism. • Dichromatic and trichromatic capuchins exhibited modest dietary differences. • Dichromatic and trichromatic capuchins did not differ in nutritional niches. • Food and nutrient intake by capuchins were shaped by fruit abundance. • Dietary niche differentiation may help maintain polymorphic colour vision. [ABSTRACT FROM AUTHOR]