Led by the nose: Olfaction in primate feeding ecology

Olfaction, the sense of smell, was a latecomer to the systematic investigation of primate sensory ecology after long years in which it was considered to be of minor importance. 1 This view shifted with the growing understanding of its role in social behavior 2 and the accumulation of physiological studies demonstrating that the olfactory abilities of some primates are on a par with those of olfactory‐dependent mammals such as dogs and rodents. 3 , 4 Recent years have seen a proliferation of physiological, behavioral, anatomical, and genetic investigations of primate olfaction. These investigations have begun to shed light on the importance of olfaction in the process of food acquisition. However, integration of these works has been limited. It is therefore still difficult to pinpoint large‐scale evolutionary scenarios, namely the functions that the sense of smell fulfills in primates’ feeding ecology and the ecological niches that favor heavier reliance on olfaction. Here, we review available behavioral and physiological studies of primates in the field or captivity and try to elucidate how and when the sense of smell can help them acquire food.     

Ascidian sperm activating and attracting factor: importance of sulfate groups for the activities and implication of its putative receptor

The sperm activating and attracting factor (SAAF) from the eggs of the ascidian Cionaintestinalis was identified as the sulfated polyhydroxysterol,3alpha,4beta,7alpha,26-tetrahydroxy-5alpha-cholestane-3,26-disulfate. We present a functional analysis of SAAF derivatives that reveals the roles of the various SAAF functional groups. Optical isomerism does not affect SAAF activities. Hydrolysis on one side, i.e. at the sulfate groups of SAAF, decreases the sperm-activating and sperm-attracting activities, while hydrolysis on both sides resulted in the loss of both activities. Biotinylated-SAAF lost its sperm-activating ability, but retained sperm-binding and chemotactic abilities. Thus, the sulfate groups of SAAF are responsible for these activities.     

Immune activation decreases sperm viability in both sexes and influences female sperm storage

All animals are under the constant threat of pathogenic infection. However, little is known regarding the influence of acute infection on sperm viability, particularly in female insects. This information is crucial for our understanding of mating and immune system coevolution, considering that females store sperm and serve as the site of sperm competition. Using the fruitfly, Drosophila melanogaster, we examined the influence of infection on sperm viability and storage. Twenty-four hours after haemocoel inoculation with a pathogen mimic (peptidoglycan, PGN) both sexes exhibited reduced sperm viability, indicating that systemic immune activation played a significant role in gamete survival. Surprisingly, sperm death did not appear to result from a reproductive-immune system trade-off, considering that sperm survived 24 h in vitro once removed from their somatic resources. Instead, our results are most consistent with death owing to immune effector collateral damage. We also examined the potential for sexually transmitted pathogens to influence sperm storage. Females mated with 'infected' males (created by dipping genitalia into a PGN solution) exhibited a higher proportion of empty sperm stores 48 h after mating compared to their controls. Remarkably, these data indicate that females may increase their fitness by removing 'infected' ejaculates from storage over time.     

Olfaction in dragonflies: electrophysiological evidence

The problem of olfaction in Paleoptera (Odonata, Ephemeroptera) cannot be considered fully elucidated until now. These insects have been traditionally considered anosmic, because their brain lacks glomerular antennal lobes, typically involved in Neoptera odor perception. In order to understand if the presumed coeloconic olfactory receptors described on the antennal flagellum of adult Odonata are really functioning, we performed an electrophysiological investigation with electroantennogram (EAG) and single cell recordings (SCR), using Libellula depressa L. (Odonata, Libellulidae) as a model species. Odors representing different chemical classes such as (Z)-3-hexenyl acetate (acetate ester), (E)-2-hexenal, octanal (aldehydes), (Z)-3-hexen-1-ol (alcohol), propionic acid, butyric acid (carboxylic acids), and 1,4-diaminobutane (amine) were tested. Most of the tested chemicals elicited depolarizing EAG responses in both male and female antennae; SCR show unambiguously for the first time the presence of olfactory neurons in the antennae of L. depressa and strongly support the olfactory function of the coeloconic sensilla located on the antennal flagellum of this species. Electrophysiological activity may not necessarily indicate behavioral activity, and the biological role of olfactory responses in Odonata must be determined in behavioral bioassays. This study represents a starting point for further behavioral, electrophysiological, neuroanatomical and molecular investigation on Odonata olfaction, a research field particularly interesting owing to the basal position of Paleoptera, also for tracing evolutionary trends in insect olfaction.     

Olfaction and sensory asymmetry

Eighty years ago it was demonstrated that odours presented tothe left side of the nose are much better perceived than odourspresented to the right side. This finding could not be corroboratedin our experiment. Some possible explanations are offered toaccount for the different results. It also turned out that olfactorysensitivity when smelling with both nostrils open is hardlyhigher than with one nostril open. It was furthermore suggestedthat differences between the two sides of the nose might playa role in studies where verbal and emotional processes are involved,as in olfactory recognition, memory and preference.     

Olfaction and neurogenesis in the olfactory epithelium

Anosmia was experimentally produced in strain C57BL/6 laboratory mice by treatment with 1% zinc sulfate solution. Structural and functional changes taking place in the olfactory epithelium were investigated during this process and during reinstatement of olfaction. Isoamyl acetate, butyl acetate, and substances present in murine urine were used as olfactory stimuli. Response to these odorants was found to recover from zinc sulfate action at different rates. The highest (both relative and absolute) daily rise in amplitude response was that induced by isoamyl acetate and butyl acetate and lowest in the case of odors of biological origin. Response to olfactory stimuli recovered most rapidly in the areas of the epithelium where maximum response to the same stimuli had been seen in intact animals."Biopharmautomatica" Combined Research and Production Unit, Gor'kii. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 500–506, July–August, 1990.     

Olfaction and the common chemical sense: some psychophysical contrasts.

Three experiments explored the olfactory and the common chemical attributes of sensations produced by various concentrations of n-butyl alcohol. These two attributes combine in an almost-linear fashion to produce the overall perceived intensity of the stimulus. Common chemical intensity makes only a small contribution to overall magnitude at low concentrations, but its proportional contribution increases with concentration. In like manner, speed of response (i.e., reciprocal of reaction time) to the common chemical attribute increases more rapidly than that to odor. Nevertheless, odor always makes its appearance sooner than the common chemical attribute, even when the two attributes are matched in perceived magnitude. Repeated inhalations cause odor intensity to decrease slightly but cause common chemical intensity to increase dramatically. The results obtained from the normal subjects studied here agree with those obtained from subjects with unilateral destruction of the trigeminal nerve.     

Olfaction and human kin recognition

Humans, like other mammals, are capable of discriminating between kin and non‐kin by olfactory cues alone. Shortly after birth, breastfed infants become familiar with, and respond preferentially to, their mother' unique odor signature. Mothers likewise recognize the characteristic scent of their newborn infant. Close biological relatives share somewhat similar odor signatures (presumably resulting from genetically mediated similarities in bodily biochemistry and metabolism) that could facilitate kin recognition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Olfaction and Taste: Invasive Odours and Disappearing Objects

The metaphorisation of sight and hearing, the objective senses, dominate the founding ideas, or philosophemes, of Western philosophy. The senses of taste and smell are of little relevance in the formation of conceptual knowledge or in classificatory systems; they are, by virtue of their dissolving objects, incapable of giving objective knowledge in Western metaphysics. Derrida and Ulmer developed a metaphorology that exploits the chemical basis of the subjective senses of taste and smell. The anthropology of the senses takes this questioning of metaphysics into issues of how olfaction and taste function in sociality. In the routine practices of everyday life, is olfaction able to create the sense of community that it does in rituals? Or, has the repression of smell in humanity's evolution towards ‘civilisation’ muted the connective ability of multiple odour particles? In a culture and metaphysics that presumes the separability of the self from the other and the self from the object, is there a place for senses that make a nonsense of separation and objectivity through their state of meaningful dissolution? Through philosophy's metaphorisation, has taste been stripped of its sensuousness and made a sense for aesthetics and not flavours and textures? In a metaphorics premised in judgement and discernment, can taste be a sense that founds sociality? In blurring the boundaries between self and other that are necessary to form and maintain the distinction, the dissolvability of smell and taste makes another metaphorics and other socialities possible. Of all the senses, that of smell—which is attracted without objectifying—bears clearest witness to the urge to lose oneself in and become the ‘other’. As perception and the perceived—both are united—smell is more expressive than the other senses (Horkheimer and Adorno 1979:184).     

Olfaction: diverse species, conserved principles

Olfaction is a vitally important sense for all animals. There are striking similarities between species in the organization of the olfactory pathway, from the nature of the odorant receptor proteins, to perireceptor processes, to the organization of the olfactory CNS, through odor-guided behavior and memory. These common features span a phylogenetically broad array of animals, implying that there is an optimal solution to the problem of detecting and discriminating odors.     

Attitudes toward Olfaction: A Cross-regional Study

This study aimed to determine whether there are regional influences on attitudes toward olfaction. A total of 1082 participants aged 21-50 years from 4 different regions (Mexican, Korean, Czech, and German) were asked to rate general attitudes toward olfaction in everyday life. To examine affective attitudes to odors (i.e., pleasantness), participants were also asked to list 3 odors as being the most pleasant or unpleasant, respectively. Next, the mentioned odor names were attributed to 1 of 4 main categories: "Food & Drink," "Social relationship," "Nature," and "Civilization" and the distribution of these categories was compared across regions. Mexicans were significantly different to the other regions in their general attitudes toward olfaction. In addition, in all regions, in comparison with men, women indicated a higher interest in the sense of smell. Moreover, a significant positive correlation was present between individuals' self-rating of olfactory sensitivity and general attitudes toward olfaction. Finally, there were significant cross-regional differences in affective attitudes toward specific categories of odors. In conclusion, our findings support and extend the notion that regions affect attitudes toward the olfactory world.     

Olfaction and olfactory learning in Drosophila: recent progress

The olfactory system of Drosophila resembles that of vertebrates in its overall anatomical organization, but is considerably reduced in terms of cell number, making it an ideal model system to investigate odor processing in a brain [Vosshall LB, Stocker RF: Molecular architecture of smell and taste in Drosophila. Annu Rev Neurosci 2007, 30:505-533]. Recent studies have greatly increased our knowledge about odor representation at different levels of integration, from olfactory receptors to 'higher brain centers'. In addition, Drosophila represents a favourite model system to study the neuronal basis of olfactory learning and memory, and considerable progress during the last years has been made in localizing the structures mediating olfactory learning and memory [Davis RL: Olfactory memory formation in Drosophila: from molecular to systems neuroscience. Annu Rev Neurosci 2005, 28:275-302; Gerber B, Tanimoto H, Heisenberg M: An engram found? Evaluating the evidence from fruit flies. Curr Opin Neurobiol 2004, 14:737-744; Keene AC, Waddell S: Drosophila olfactory memory: single genes to complex neural circuits. Nat Rev Neurosci 2007, 8:341-354]. This review summarizes recent progress in analyzing olfactory processing and olfactory learning in Drosophila.     

Olfaction in infants and children: developmental and functional perspectives

This paper reviews some studies related to the ontogeny of olfactorycompetence in humans from the foetal – neonatal to thepubertal period. Psychophysical and hedonk studies of developingolfactory function demonstrate keen detection and discriminationabilities from birth onwards. Although the sensory parametersof infantile olfaction nearly equal those of mature function,developmental processes seemingly act upon the hedonic integrationof odours. From the first post-natal week, infants rely on thisolfactory competence in social contexts: olfactory cues derivedfrom conspecifics' body chemistry are used to differentiatefamiliar from unfamiliar individuals or kin from non-kin. Additionalstudies are needed, however, to demonstrate an early recognitionof olfactory individuality by young infants. The infants' discriminativeperformance in regard to social odours and the incentive valuethey assign to them are progressively specified in close relationshipwith the earliest social experiences. To date, the salienceof olfactory stimulations has been poorly documented in theinfants' normal life. But clinical evidence underlines theirpotential involvement (i) in the earliest infant–motherbonding processes, (ii) in the infant's emotional homeostasisand (iii) in the child's interactional adjustments.