Josephine Todrank

A taste illusion: Taste sensation localized by touch

Taste sensations appear to come from all over the inner surface of the mouth, yet the taste receptors are restricted to relatively small particular areas of the oral surface. In addition, even if a relatively large (e.g., one half) proportion of the taste field is damaged, subjective taste experience may be unaffected. The touch system contributes to this constancy because taste sensations appear to be localized by touch. If a taste solution is painted from the side of the tongue (an area of low receptor density) past the tip (an area of high receptor density) and on to the second side, the taste sensation begins weak, gets stronger at the tip, and retains much of its intensity. The strong taste from the tip follows the tactile path of the stimulus sweep. This illusion occurs for all four stimuli tested: sucrose, sodium chloride, citric acid, and quinine hydrochloride.

Odor–Genes Covariance and Genetic Relatedness Assessments: Rethinking Odor-Based “Recognition” Mechanisms in Rodents

Publisher Summary This chapter presents the findings that led to the reevaluation of mechanisms underlying differential responses to odors including a description of the methodologies used to collect the data. The chapter suggests new ways of interpreting the terms used in describing discriminative responses to odors and proposes a hypothesis about the origin and evolutionary basis of differential responses based on genetic relatedness assessments. Prospects for future studies that could deepen the understanding of how these mechanisms work are discussed in detail. The chapter presents data based on the responses of rodents to odors and explores the principles in the experiments that apply equally well to other taxa and to sensory modalities other than olfaction, particularly vision and audition. There were two important consequences of the studies for understanding recognition mechanisms: (1) differential responses to odors of familiar and unfamiliar individuals indicated that rodents learn to associate particular individuals with their individual odors and can recognize the odors of familiar individuals irrespective of genetic relatedness, thus “individual recognition” is a mechanism for responding both to kin and nonkin rather than a “kin recognition” process; (2) in conjunction with evidence for self-referencing in graded responses based on degrees of genetic relatedness to odors of kin, populations, and species, the odor–genes covariance findings raised the intriguing possibility that such self-referencing would be the most practical means of assessing degrees of genetic relatedness to any other individual.

Odors can change preferences for people in photographs: A cross-modal evaluative conditioning study with olfactory USs and visual CSs

Evaluative conditioning is a form of Pavlovian conditioning in which the “CR” is a change in preference or liking for the “CS.” It is probably a major cause of development of likes and dislikes in humans. This research introduces a new, cross-modal evaluative conditioning procedure using odors as USs and photographs of people’s faces as CSs. When liked, neutral, and disliked odors that were plausibly connected with people were contingently presented with photographs of neutral people, subjects shifted their preference ratings for the people in the photographs presented subsequently without odors in the direction of their preference ratings for the odors. Subjects who developed personality sketches of someone “who looked and smelled this way” showed similar shifts as those who simply studied the odor-picture combinations. Results also suggest that a plausible connection between odors and people may play a role in the success of this conditioning.

Individual odour similarities across species parallel phylogenetic relationships in the S. ehrenbergi superspecies of mole-rats.

Research using habituation techniques has shown that rodents from the same kin group, population, or species share similarities in their individual odours that covary with shared genetic similarities between them, that is, the closer their genetic relatedness, the more similar their odours. We assessed similarities in individual odours across four sibling species of subterranean mole-rats from the Spalax ehrenbergi superspecies in Israel. Mole-rats were habituated to the urine odour of a same-sex individual from one species then tested with urine odours of individuals from two different species of the superspecies. Subjects treated urine odours of individuals from more closely genetically related species as similar compared with the odours of individuals from a less closely related species, showing that the covariance between odours and genes extends across species. These similarities in odour also paralleled genetic similarities determined by molecular analysis: odours of descendent species were perceived as similar to those of their closest ancestral species, suggesting that some qualities of the odour of the ancestral species persist in the descendent species. It is generally assumed that during speciation incipient species develop species-specific markers, including, for example, odour markers, to facilitate discrimination of conspecifics from close ancestral heterospecifics. Our findings indicate that similarities in odours across species are more salient than species-specific odour markers. Such findings may also have important implications for mechanisms of species recognition. Copyright 2000 The Association for the Study of Animal Behaviour.

Similarity in the qualities of individual odors among kin and species in Turkish (Mesocricetus brandti) and golden (Mesocricetus auratus) hamsters.

In this investigation, the authors used habituation techniques to explore similarities and differences in the qualities of individual odors from hamsters. In Experiment 1, male Turkish hamsters (Mesocricetus brandti) treated flank-gland odors of 2 males from 1 litter as similar compared with the odor of a male from another litter, whether the odor donors were familiar or unfamiliar. At the same time, the Turkish hamsters discriminated between the subtle differences in the individual odors of their familiar brothers. In Experiment 2, male Turkish and golden hamsters (Mesocricetus auratus) treated the flank-gland odors of 2 unfamiliar, unrelated conspecifics as similar compared with the flank odor of a heterospecific individual. The results suggest that similarities in individual odors are related to genetic similarity of the odor donors. These similarities could provide a basis for different types of social recognition, including kin and species recognition.

Seasonal changes in urinary odors and in responses to them by blind subterranean mole rats

Breeding and nonbreeding season male and female mole rats from two chromosomal species of the Spalax ehrenbergi superspecies were tested in a tunnel T-maze to assess their responses to urine collected from breeding- and nonbreeding season male and female conspecific and heterospecific donors. The results indicate that S. ehrenbergi mole rat urine contains species-, sex-, and season-specific chemosensory cues and that male and female mole rats change their responses to these chemosensory cue depending upon the season. During the nonbreeding season, mole rats avoid conspecific and heterospecific urine of both sexes. In contrast, during the breeding season, mole rats do not avoid conspecific urine and males do not avoid heterospecific urine. These changes in responses to the chemosensory cues in urine are adaptive to their seasonal life underground because they could help the animals avoid aggressive encounters during the nonbreeding season and facilitate their approaching potential mates and competitors during the breeding season. The results suggest that chemical communication could play a role in social encounters, reproduction, and species isolation in the S. ehrenbergi superspecies.

Odours underground: subterranean rodents may not forage "blindly"

Abstract. Subterranean rodents were thought to forage underground for edible roots and bulbs without the benefit of any sensory cues. Subterranean rodents representing four genera from three families (East-Mediterranean Spalax, African Cryptomys and Heterocephalus, and South American Spalacopus), tested in T-mazes filled with soil in which edible plants either had or had not been growing, used odours to discriminate between the soils and chose to dig in the soil containing odorous substances (kairomones) released from roots of growing plants. Such discriminations could enable them to orient their digging toward food sources in the field and thus to improve their foraging efficiency. Spalax blind mole-rats also discriminated between the odours from soil in which edible as opposed to poisonous plants had been growing. These species evolved independently on three continents; thus their abilities probably are characteristic of subterranean rodents in general.

Preferences of newborn mice for odours indicating closer genetic relatedness: is experience necessary?

Evidence from studies with adult rodents indicates that individual recognition enables distinctions between familiar individuals irrespective of relatedness (but including close kin) and a separate mechanism enables discriminations based on genetic relatedness without prior familiarity. For example, adult mice could assess the extent of their genetic relatedness to unfamiliar individuals using perceptual similarities between their individual odours. The ontogeny of this genetic relatedness assessment mechanism, however, had not been investigated. Here, in two-choice tests, newborn mice differentially preferred odours of more genetically similar lactating females (paternal aunts to unrelated conspecific and conspecific to heterospecific) even without prior direct exposure to adults with the tested genotypes. The results provide a direct demonstration of genetic relatedness assessment abilities in newborns and show that experience with parental odours is not necessary for genetic relatedness distinctions. Future studies will be necessary to determine whether exposure to odours of other foetuses in the womb or littermates shortly after birth affects this genetic relatedness assessment process.

INDIVIDUAL ODOR SIMILARITIES WITHIN COLONIES AND ACROSS SPECIES OF CRYPTOMYS MOLE RATS

Abstract We studied similarities and differences in the qualities of individual odors across colonies and species of African eusocial mole rats using habituation techniques. Giant mole rats (Cryptomys mechowi) treated anogenital odors of 2 conspecifics from 1 colony as similar to each other and different from the odor of a conspecific from another colony, providing evidence for kinship odors. Subjects also discriminated between the subtle differences in the individual odors of familiar colony members. In another set of tests, mole rats from 3 species (C. mechowi, C. anselli, and C. kafuensis) treated anogenital odors of genetically closer heterospecifics as more similar to odors of conspecifics than to odors of less closely related heterospecifics. Thus, odor similarities paralleled genetic similarities as determined by the analysis of allozymic and karyotypic distances. The results demonstrate that similarities in individual odors covary with genetic similarities within colonies and across species. These similarities could provide a basis for different types of social recognition based on self-referent matching.

Differential aggressiveness between fire salamander (Salamandra infraimmaculata) larvae covaries with their genetic similarity

Responding differentially to kin and non-kin is known to be adaptive in many species. One example is the inclusive fitness benefits of reducing aggression toward closer relatives. Little is known, however, about the ability of animals to assess differential degrees of genetic relatedness and to respond accordingly with differential levels of aggression. In the present study, we tested whether aggressiveness between body mass-matched pairs of fire salamander (Salamandra infraimmaculata) larvae covaried with the genetic similarity between them. We quantified aggressiveness at three levels of genetic similarity by selecting pairs within and across pools from recently genotyped populations. We also assessed aggression between pairs of siblings. Aggression and associated injuries decreased as genetic similarity increased across the groups. These findings suggest that cannibalistic salamanders can assess their degree of genetic relatedness to conspecifics and vary their behavioral responses depending on the degree of similarity between them along a genetic relatedness continuum.