Conspecific Odors Research Articles

The scent of cannibalism: The olfactory basis of cannibalism in hermit crabs

Animals are constantly exposed to sensory cues that provide conflicting information about their environments and must somehow rely on these sensory cues to make appropriate behavioral decisions. For cannibalistic scavengers, the odors of injured conspecifics or heterospecifics can serve as conflicting sensory cues because they could represent either the proximity of a food resource or the proximity of a predator (e.g., a recent predation event). Foraging cannibals must therefore weigh the risk–reward consequences of approaching injured conspecifics and heterospecifics. Previous research has shown that foraging cannibals respond to these conflicting cues by exhibiting caution, showing anti-predation behaviors instead of foraging behaviors. Hermit crabs are cannibalistic animals that rely heavily on olfaction to forage. Here I show for the first time that cannibalistic hermit crabs use the odors of crushed conspecifics and heterospecifics as foraging cues instead of anti-predation cues. Test animals, in general, responded to the odors of crushed conspecifics and heterospecifics with increased foraging responses instead of anti-predation responses, and readily consumed both conspecific and heterospecific animals. However, test animals showed faster approach times and longer feeding times for heterospecifics than conspecifics. These results suggest that hermit crabs are capable of discerning between the odors of conspecifics and heterospecifics, and show greater avoidance towards dead conspecifics than heterospecifics.

Competitive naïveté between a highly successful invader and a functionally similar native species

Naïveté can occur within any novel antagonistic interaction, and competitive forces play a fundamental role in shaping community structure, yet competitive naïveté has received very little attention in the literature to date. Naïveté towards a novel competitor is unlikely to result in immediate mortality, but could potentially affect access to resources and hence population growth and survival. In cases where only one species (either native or alien) remains naïve to the other, the species that recognizes the other will gain advantage, with implications for both the persistence of the native species and the establishment and spread of the invasive. The invasive black rat (Rattus rattus) has spread throughout many coastal areas of Australia, and competes with the native bush rat (Rattus fuscipes) wherever they coexist. As these rats have now been interacting for approximately 200years, and multi-species rodent communities generally maintain their structure through olfactory communication, our aim was to determine whether these two very closely related species recognize one another's odors and use them to mediate their interactions. We used remote-sensing cameras deployed in single- and mixed-species sites to record the behavioral responses of each species to conspecific, heterospecific and control odors. Black rats investigated bush rat odors but not vice versa, suggesting that bush rats may remain naïve towards their new competitor. Highly successful invaders such as black rats may possess traits such as broad recognition templates and rapid learning capabilities that contribute to their ongoing success in invading new environments.

Sex‐specific responses of Asian citrus psyllid to volatiles of conspecific and host‐plant origin

AbstractDiaphorina citri Kuwayama (Hemiptera: Psyllidae) is the primary vector of Candidatus Liberibacter spp. bacteria that cause citrus greening, a disease of worldwide importance. Olfactometry was employed to test responses of D. citri to odours from intact citrus plants (Mexican lime, Citrus aurantifolia, sour orange, Citrus aurantium, Marsh grapefruit, Citrus paradisi and Valencia orange, Citrus sinensis), citrus plants previously infested with D. citri, and odours of conspecifics including nymphs, adult insects of same and opposite sex, and their products (honeydew), both alone and in combination. In contrast to other studies, psyllids of both sexes were attracted to volatiles of undamaged Mexican lime leaves, whereas undamaged grapefruit attracted only females, and leaves of Valencia and sour orange did not attract either sex. All four plant species attracted female psyllids when previously infested, but only Mexican lime and sour orange‐attracted males. Thus, Citrus species appear to vary in the production of both constituitive and induced volatiles that attract adult psyllids. Volatiles emitted by nymphs did not attract either sex, but psyllid honeydew was attractive to males, likely due to female pheromone residues. Males oriented to the odour of females, whereas the reverse was not true, and neither males nor females oriented to same‐sex volatiles. The addition of conspecific cues (adults, nymphs or honeydew) did not increase female attraction to previously infested leaves, but male response was increased by the presence of adults and honeydew, regardless of plant species. Thus, female psyllids appear to orient more strongly to volatiles of plant origin, whereas males respond more strongly to cues emanating from females and conspecific excretions. These results suggest that female psyllids drive the initial colonization of host plants, whereas males orient to females and infested plants. Identification of the specific volatiles involved may permit their use in monitoring and management of this pest.

Horses (Equus caballus) discriminate body odour cues from conspecifics

Knowledge about social recognition and memory in animals can help us to determine appropriate management and husbandry techniques. In this study, we used a habituation-discrimination procedure to investigate the ability of horses (Equus caballus) to distinguish between the body odour samples of unfamiliar conspecifics. To pick up body odour, we rubbed material on the coat of horses and presented these unknown body odours to 16 different conspecifics of the same sex and similar age. The test consisted of two successive two-min presentations of a sample from one individual (e.g. individual 'A') and a simultaneous presentation of samples from individual 'A' and a novel individual (e.g. individual 'B') during a final third presentation. The results showed that horses, regardless of sex, decreased the time they spent investigating conspecific body odour across the initial two presentations-demonstrating habituation. In the final presentation, the results demonstrated successful discrimination of the previously experienced odour because horses investigated the novel olfactory sample ('B') significantly more than the pre-exposed sample ('A'). Taken together, these findings suggest, for the first time, that horses are able to discriminate two stimuli derived from body odours of unfamiliar conspecifics over short period of time.

Uropygial gland volatiles facilitate species recognition between two sympatric sibling bird species

AbstractVisual and acoustic cues in birds have been well documented to play a role in species recognition between closely related bird species. Here, we aimed to test whether chemical cues also play a role in avian species recognition between 2 sympatric sibling species of waxwings, Bombycilla garrulus and Bombycilla japonica. Using gas chromatography–mass spectrometry, we characterized from uropygial gland secretions 38 compounds that were quantitatively divergent between species and exhibited sex differences within species. Nine major compounds, including 6 linear alkanols and 3 carboxylic acids, which accounted for more than 85% of all compounds were used for simulation of the scents. Female B. garrulus exhibited a striking preference for their mirror images scented with either conspecific body odor or its synthetic analogs and avoided the scents of the sibling species B. japonica in a Y-maze olfactometer. Our results suggest that the volatile components of uropygial gland secretions have diverged in composition and these differences contribute to species recognition between sympatric sibling bird species and subsequently affect the likehood of speciation.

Aphid responses to volatile cues from turnip plants (Brassica rapa) infested with phloem-feeding and chewing herbivores

Herbivore-induced plant volatiles provide foraging cues for herbivores and for herbivores’ natural enemies. Aphids induce plant volatile emissions and also utilize plant-derived olfactory volatile cues, but the chemical ecology of aphids and other phloem-feeding insects is less extensively documented than that of chewing insects. Here, we characterize the volatile cues emitted by turnip plants (Brassica rapa) under attack by an aphid (Myzus persicae) or by the chewing lepidopteran larva Heliothis virescens. We also tested the behavioral responses of M. persicae individuals to the odors of undamaged and herbivore-damaged plants presented singly or in combination, as well as to the odor of crushed conspecifics (simulating predation). Gas chromatographic analysis of the volatile blend of infested turnips revealed distinct profiles for both aphid- and caterpillar-induced plants, with induced compounds including green-leaf alcohols, esters, and isothiocyanates. In behavioral trials, aphids exhibited increased activity in the presence of plant odors and positive attraction to undamaged turnip plants. However, aphids exhibited a strong preference for the odors of healthy versus plants subjected to herbivore damage, and neither aphid- or caterpillar-damaged plants were attractive compared to clean-air controls. Reduced aphid attraction to herbivore-infested plants may be mediated by changes in the volatile blend constituent composition, including large amounts of isothiocyanates and green-leaf volatiles or, in the case of aphid-infested plants, of the aphid alarm pheromone, (E)-β-farnesene.

Olfactory Cues Are Subordinate to Visual Stimuli in a Neotropical Generalist Weevil

The tropical root weevil Diaprepes abbreviatus is a major pest of multiple crops in the Caribbean Islands and has become a serious constraint to citrus production in the United States. Recent work has identified host and conspecific volatiles that mediate host- and mate-finding by D. abbreviatus. The interaction of light, color, and odors has not been studied in this species. The responses of male and female D. abbreviatus to narrow bandwidths of visible light emitted by LEDs offered alone and in combination with olfactory stimuli were studied in a specially-designed multiple choice arena combined with a locomotion compensator. Weevils were more attracted to wavelengths close to green and yellow compared with blue or ultraviolet, but preferred red and darkness over green. Additionally, dim green light was preferred over brighter green. Adult weevils were also attracted to the odor of its citrus host + conspecifics. However, the attractiveness of citrus + conspecific odors disappeared in the presence of a green light. Photic stimulation induced males but not females to increase their speed. In the presence of light emitted by LEDs, turning speed decreased and path straightness increased, indicating that weevils tended to walk less tortuously. Diaprepes abbreviatus showed a hierarchy between chemo- and photo-taxis in the series of experiments presented herein, where the presence of the green light abolished upwind anemotaxis elicited by the pheromone + host plant odor. Insight into the strong responses to visual stimuli of chemically stimulated insects may be provided when the amount of information supplied by vision and olfaction is compared, as the information transmission capacity of compound eyes is estimated to be several orders of magnitude higher compared with the olfactory system. Subordination of olfactory responses by photic stimuli should be considered in the design of strategies aimed at management of such insects.

Olfactory responses of Conotrachelus psidii (Coleoptera: Curculionidae) to hosts and conspecific odors

Conotrachelus psidii (Coleoptera: Curculionidae) is one of the most important pests of guava plants, Psidium guajava (Myrtaceae). Guava plant is the natural host of this weevil suggesting that volatile compounds from odor of different parts of the plant may be attractive to this insect. The main goal of this research was to determine if host or conspecific odors can act as attractants to guava weevil. The olfactory responses of the guava weevil were tested with a Y-tube olfactometer. The odors included green and ripened fruits, leaves and flower buds of P. guajava, guava weevils and their feces. Stimuli were tested singly and in combinations. Flower buds odors were attractive to C. psidii males suggesting the presence of host kairomones. Males and females weevil feces attracted both male and female weevils, indicating the existence of aggregation pheromones or allelochemicals (undigested plant compounds) in the feces. Further studies should be made to conclude from the nature of these substances. Identification and synthesis of the semiochemicals that attract the guava weevil would allow developing new strategies for monitoring and controlling this pest.

Carry-over effects of delayed larval metamorphosis on early juvenile performance in the mangrove crab Ucides cordatus (Ucididae)

Competent larvae of most benthic marine invertebrates including brachyuran decapod crustaceans can delay their settlement and metamorphosis in the absence of suitable environmental cues. This however may carry significant costs for the post-larval performance and fitness of early benthic juveniles. In this paper, we examined in the laboratory whether delayed larval metamorphosis affects early juvenile performance of the mangrove crab Ucides cordatus, measured as survival and growth through the first five juvenile crab stages (JI–JV). We further investigated whether ‘carry-over’ effects of an extended larval period vary intraspecifically among juveniles from three different hatches (F1–F3). Ucides megalopae were cultivated in two treatments. In the first one, the control, megalopae were cultivated continuously in exposure to conspecific crab odours (adult-conditioned seawater=ACSW) until moulting to the first juvenile crab stage. In the second, the delay-treatment, settlement-competent megalopae were kept for 20days in pure filtered seawater without metamorphosis-triggering odours. From day 21 onwards, megalopae were transferred to ACSW to induce larval moult. The results showed that delayed metamorphosis affects early juvenile survival and growth of U. cordatus. In the delay-treatment, survival rates of juveniles (JI–JV) from F1–F3 were 11–31% lower and intermoult development periods 1.5–4.2days longer than in the control. Delayed juveniles (F1–F3) exhibited 9.2–14.1% smaller body sizes (carapace width) and 1.4–3.9% lower growth rates mostly in the first two moulting events compared to specimens derived from non-delayed megalopae. Most of the detrimental effects were observed in almost all five crab stages studied, indicating that the costs of delayed metamorphosis may persist throughout early juvenile development. Juvenile morphology, however, was not affected. Our study also showed that carry-over effects of delayed larval moult vary intraspecifically among offspring produced by different females. This plasticity in phenotypic effects could relate to differences in the nutritional state, health or age of the females, to stressful environments during embryogenesis or to genetic differences. The observed carry-over effects of delayed settlement on early juvenile performance may affect the overall recruitment success and population dynamics of U. cordatus. In the field, such a situation would appear when new mangrove areas void of conspecific crabs are colonized or when degraded sites are re-populated by larvae originating from elsewhere populations.

Effect of conspecific and heterospecific urine odors on the foraging behavior of the golden spiny mouse

The common spiny mouse (Acomys cahirinus) inhibits the foraging activity of the golden spiny mouse (A. russatus). These two sympatric species of spiny mice, which are considered habitat competitors, occur in extreme arid environments. To test this theory of competition, the influence of urinary odors of both conspecific and heterospecific mice on the foraging behavior of A. russatus was studied under controlled laboratory conditions. Twenty adult males, born in captivity and unfamiliar to the odors of the donor mice, were tested in 3 experimental conditions choosing between 2 seed patches that were scented with urine of either heterospecifics (A. cahirinus), conspecifics (A. russatus) or controls (odors of the tested individual). Of the 20 males, 12 were also tested with urine of unfamiliar gerbils, bushy-tailed jird, considered as competitors in the field. Both conspecific and heterospecific urine samples from Acomys significantly reduced foraging behavior of A. russatus when compared to the control odor. The inhibitory effect of the Acomys urine does not result from the novelty of chemical stimuli of the urine because no effect was shown with unfamiliar gerbil urine. The findings are in accordance with the general theory that A. cahirinus dominates the foraging activity of A. russatus. We hypothesize that chemical cues in the urine of Acomys spp. might induce a negative effect on the foraging behavior of A. russatus.

Finding paradise: cues directing the migration of the waterfall climbing Hawaiian gobioid Sicyopterus stimpsoni

A series of waterfall-climbing trials were conducted to identify cues that direct the climbing of juvenile Sicyopterus stimpsoni. In the first experiment, whether climbing juveniles preferentially ascend water sources with conspecifics or whether the presence of just stream water is sufficient to attract fish to ascend a climbing path were assessed. In the second experiment, whether climbing juveniles create a trail of mucus that facilitates the ability of conspecifics to follow their lead was determined. The results indicate that juvenile S. stimpsoni are less likely to climb in waters devoid of organic cues but are strongly attracted to stream water with or without the odour of conspecifics. Once climbing, performance did not differ for juveniles climbing in differing water choices, suggesting an all-or-nothing commitment once climbing commences. Climbing S. stimpsoni did produce a mucous trail while climbing that was associated with a mucous gland that dramatically increases in size just prior to juveniles gaining the ability to climb. The trail was not followed closely by subsequent juveniles traversing the same channel, however, suggesting only weak trail-following in waterfall climbing S. stimpsoni. Previous genetic studies suggest that juvenile S. stimpsoni do not home to natal streams in the face of strong near-shore oceanic currents. Instead, these fish appear primarily to rely on cues that suggest the presence of organic growth in streams, a factor that may indicate suitable habitat in an ever-changing stream environment but which may also be vulnerable to interference through human activity.

The Functioning of Species-Specific Olfactory Pheromones in the Biology of a Mosquito-Eating Jumping Spider from East Africa

Having unique, complex eyes and vision based on exceptional spatial acuity, salticid spiders are known for their vision-based predatory and mating strategies. Yet Evarcha culicivora, the salticid we consider here, is known for predatory and mating strategies based strongly on the interplay of vision and olfaction. This unusual East African species feeds indirectly on vertebrate blood by choosing blood-carrying female mosquitoes as preferred prey, which it can identify by sight and by smell. Moreover, E. culicivora’s mating strategy is unusual because, unlike the prevailing general pattern among spiders, where males are more active in courtship and females are more active in mate choice, both roles are characteristic of both sexes of E. culicivora. There is also an unusual relationship between diet and mating in this species, with blood meals making both sexes more attractive as potential mates. However, findings from the present study demonstrate that, regardless of source-spider diet and even when restricted to using chemoreception in the absence of seeing another spider, both sexes can discriminate between opposite-sex conspecifics and opposite-sex heterospecifics. Yet there is no evidence that diet (blood versus no blood) influences the attractiveness of opposite-sex heterospecific individuals to E. culicivora. Evidence that the odor of opposite-sex conspecifics is salient to E. culicivora comes from three different experimental designs (retention testing, choice testing and courtship-initiation testing). The effective odor source can be either the presence of the spider or the presence of the spider’s draglines alone.

Polarotaxis in egg-laying yellow fever mosquitoes Aedes (Stegomyia) aegypti is masked due to infochemicals

Aquatic and water-associated insects need to locate suitable bodies of water to lay their eggs in and allow their aquatic larvae to develop. More than 300 species are known to solve this task by positive polarotaxis, relying primarily on the horizontally polarized light reflected from the water surface. The yellow fever mosquito Aedes (Stegomyia) aegypti has been thought to be an exception, locating its breeding habitats by chemical cues like odour of conspecifics, their eggs, or water vapour. We now demonstrate through dual-choice experiments that horizontally polarized light can also attract ovipositing Ae. aegypti females when the latter are deprived of chemical cues: water-filled transparent egg-trays illuminated by horizontally polarized light from below gained a 94.2% higher total number of eggs than trays exposed to unpolarized light, but only when no chemical substances capable of functioning as cues were present. Ae. aegypti is the first known water-associated insect in which polarotaxis exists, but does not play a dominant role in locating water bodies and can be constrained in the presence of chemical cues.

Are Olfactory Cues Involved in Nest Recognition in Two Social Species of Estrildid Finches?

Reliably recognizing their own nest provides parents with a necessary skill to invest time and resources efficiently in raising their offspring and thereby maximising their own reproductive success. Studies investigating nest recognition in adult birds have focused mainly on visual cues of the nest or the nest site and acoustic cues of the nestlings. To determine whether adult songbirds also use olfaction for nest recognition, we investigated the use of olfactory nest cues for two estrildid finch species, zebra finches (Taeniopygia guttata) and Bengalese finches (Lonchura striata var. domestica) during the nestling and fledgling phase of their offspring. We found similar behavioural responses to nest odours in both songbird species. Females preferred the odour of their own nest over a control and avoided the foreign conspecific nest scent over a control during the nestling phase of their offspring, but when given the own odour and the foreign conspecific odour simultaneously we did not find a preference for the own nest odour. Males of both species did not show any preferences at all. The behavioural reaction to any nest odour decreased after fledging of the offspring. Our results show that only females show a behavioural response to olfactory nest cues, indicating that the use of olfactory cues for nest recognition seems to be sex-specific and dependent on the developmental stage of the offspring. Although estrildid finches are known to use visual and acoustic cues for nest recognition, the similar behavioural pattern of both species indicates that at least females gain additional information by olfactory nest cues during the nestling phase of their offspring. Thus olfactory cues might be important in general, even in situations in which visual and acoustic cues are known to be sufficient.

The influence of predator and conspecific odor on sex differences in path choice in meadow voles

Many terrestrial mammals will choose the path that contains evidence of conspecifics with whom they would like to encounter, such as a potential mate, while avoiding a path that will lead them to encounter a threat, such as a same-sex conspecific or predator. We tested hypotheses about the space use of meadow voles, Microtus pennsylvanicus, in an arena containing a short arm and a long arm that both lead to the bedding of a sexually receptive opposite-sex conspecific. Subjects were tested under three conditions: in an empty arena (experiment 1); in an arena containing the scent mark of a known predator, the mink, Mustela vison (experiment 2); in an arena containing the scent mark of a same-sex conspecific (experiment 3). Male voles placed into an empty arena preferred to take the shorter of two paths to reach the bedding of a sexually receptive female; females did not show a preference in the length of the path to reach the bedding of a sexually receptive male. Male and females showed no preference for the short or the long path to reach the bedding of a potential mate, independent of the placement of the scent mark of a mink in the long or short path. Females and males showed no preference for the short or the long path to reach the bedding of a potential mate, independent of the placement of the scent mark of a same-sex conspecific in the long or short path. Males however, were less likely than females to enter a path if it contained the scent mark of a same-sex conspecific. The paths that male and female voles take to reach an opposite-sex conspecifics may be associated with sex differences their responses to risks of predation and same-sex competition.

Male primer endocrine responses to preovulatory female cyprinids under natural conditions in Sweden

This study investigated two related aspects of male-female reproductive interactions in the family Cyprinidae: (1) whether ovulating female rudd Scardinius erythrophthalmus (subfamily Leuciscinae) induce endocrine and gonadal priming responses in conspecific males, a phenomenon which has been described only in species from the subfamily Cyprininae such as goldfish, Carassius auratus, crucian carp Carassius carassius and common carp, Cyprinus carpio and (2) whether the stimuli mediating these responses are species-specific. Field studies of three sympatric European cyprinids, two leuciscins (S. erythrophthalmus and white bream Blicca bjoerkna) and one cyprinin (C. carassius), were conducted on fishes captured in Sweden in the spawning season and held in net pens under natural conditions. As previously reported in C. carassius, male S. erythrophthalmus increased milt (sperm and seminal fluid) volume and plasma concentrations of the sperm maturation hormone 4-pregnen-17,20β-diol-3-one (17,20β-P) when they were held with female S. erythrophthalmus induced to ovulate by injection of Ovaprim (GnRH analogue plus dopamine antagonist). Male S. erythrophthalmus had larger milt volumes than male C. carassius prior to and following exposure to ovulatory conspecifics, but exhibited a smaller proportional milt increase in response to stimulation, suggesting species differences in sperm allocation at spawning. The presence of female S. erythrophthalmus and B. bjoerkna did not affect milt volumes of C. carassius under two experimental conditions: (1) ovulating S. erythrophthalmus and B. bjoerkna did not increase the milt volumes of C. carassius and (2) S. erythrophthalmus and B. bjoerkna did not interfere with the milt volume increase induced in male C. carassius by ovulating conspecifics. These results suggest that, as in C. auratus, C. carassius and C. carpio (subfamily Cyprininae), female S. erythrophthalmus (subfamily Leuciscinae) release a preovulatory pheromone that exerts priming effects on male hormones and sperm allocation. The findings also indicate that C. carassius discriminate between the reproductive odours of conspecifics and heterospecifics.

Chemically-mediated sexual display postures in pre-ovulatory female topmouth gudgeon, Pseudorasbora parva

While mating systems vary considerably throughout the animal kingdom, smell is increasingly recognised as a common factor in successful copulation. However, the full range of olfactory- induced mating behaviours among animals is undoubtedly underestimated in comparison to visual or contact stimuli, and this underestimation suggests that our understanding of courtship rituals may be incomplete. Here, we use the highly invasive topmouth gudgeon,Pseudorasboraparvaas a biological model to separate and validate the induction of headstands as courtship behaviour in many fish species. Conspecific odour was isolated using solid phase extraction (SPE) and fractionated using high-performance liquid chromatography (HPLC). Active fractions were characterised using nuclear magnetic resonance (NMR). Electrophysiological responses of pre-ovulatory females to conspecific odour were also tested via the electro-olfactogram (EOG). Results revealed that pre-ovulatory females adopted headstand body postures during exposure to nest guarding male odour (4/12) and SPE extract (5/12) but did not display during exposure to any other odour. Fractions from HPLC yielded 1 active fraction that induced headstand body postures in pre-ovulatory females (4/12). The active fraction eluted at 30–35 min and showed no response in the UV. NMR imaging revealed low intensity levels of aliphatic protons: methylene protons (CH2) at around 2 parts per million (ppm) and methin (CH) at around 3 ppm. EOG response amplitudes were approximately double in response to pre-ovulatory female odour than to odour derived from post-ovulatory females (Mann–WhitneyU-test, , ). This study provides evidence of sex-specific chemical cues and responsive, adaptive sexual behaviour inP. parvaand demonstrates that female display postures may be induced by chemical stimuli alone.

Odors from proximal species reverse the stress-decreased neurogenesis via main olfactory processing

Unconditioned foot shock followed by restraint in water was used as a stress regimen to induce decreases in neurogenesis in mouse dentate gyrus (DG). Presence of conspecific odors has been known to reverse the stress-induced decrease in DG neurogenesis. In this study, we found that the conspecific odors did not produce these protective effects in mice whose MOE was impaired by nasal zinc sulfate lavage. Moreover, we observed that the presence of odors from rats, hamsters, and guinea pigs throughout the stress procedure reversed the stress-induced decrease in cell proliferation and neurogenesis in mouse dentate gyrus, while these odors alone did not affect mouse dentate cell proliferation or neurogenesis. In contrast, the presence of rabbit, sugar glider, hedgehog, beetle odors did not affect cell proliferation, neurogenesis, the stress-decreased cell proliferation or neurogenesis in DG. Finally, the presence of fox urine odors decreased mouse dentate cell proliferation and neurogenesis but did not affect the stress-induced decrease in cell proliferation or neurogenesis. Taken together, we conclude that olfactory processing via activation of sensory neurons in MOE is responsible for the conspecific odor-produced protective effect against the stress-decreased cell proliferation and neurogenesis. Phylogenetic distances of the odor-generating species and mice might contribute to the odors’ protective effects against the stress-induced decreases in cell proliferation and neurogenesis.

Electrophysiological responses of rat olfactory tubercle neurons to biologically relevant odours

Biologically relevant odours were used to stimulate olfactory tubercle neurons in anaesthetized male rats. Among 120 recorded neurons, 118 showed spontaneous activity (mean firing rate, 15.0 ± 1.4 spikes/s). Ninety-eight neurons were exposed to at least one of the four following odour sources: an empty vial, or a vial containing food pellets (familiar odour), a sample of oestrous rat faeces (conspecific sexual odour), or a sample of male fox faeces (predator odour). The proportion of neurons responding with a change in activity was significantly linked to the odour applied. Repetition of the stimulation with the same odour elicited the same activity change. Between 50 and 70% of neuronal activity changes were not accompanied by respiration changes. Fifty-six neurons were exposed successively to all four odours, and 38 of them showed an activity change in response to at least one. The response of a neuron to an odour was not affected by its response to the previous one, and no neuron responded in the same manner to all odours. Conversely, no odour elicited a unique response in this population of neurons. However, the proportions of excited, inhibited and insensitive neurons depended significantly on the odour applied, suggesting that the recruitment of olfactory tubercle neurons is directly dependent on the biological significance of the odour.

Recognition memory for social and non-social odors: Differential effects of neurotoxic lesions to the hippocampus and perirhinal cortex

The contributions of the hippocampus (HC) and perirhinal cortex (PER) to recognition memory are currently topics of debate in neuroscience. Here we used a rapidly-learned (seconds) spontaneous novel odor recognition paradigm to assess the effects of pre-training N-methyl-D-aspartate lesions to the HC or PER on odor recognition memory. We tested memory for both social and non-social odor stimuli. Social odors were acquired from conspecifics, while non-social odors were household spices. Conspecific odor stimuli are ethologically-relevant and have a high degree of overlapping features compared to non-social household spices. Various retention intervals (5min, 20min, 1h, 24h, or 48h) were used between study and test phases, each with a unique odor pair, to assess changes in novelty preference over time. Consistent with findings in other paradigms, modalities, and species, we found that HC lesions yielded no significant recognition memory deficits. In contrast, PER lesions caused significant deficits for social odor recognition memory at long retention intervals, demonstrating a critical role for PER in long-term memory for social odors. PER lesions had no effect on memory for non-social odors. The results are consistent with a general role for PER in long-term recognition memory for stimuli that have a high degree of overlapping features, which must be distinguished by conjunctive representations.