Male Odors Research Articles

Absence of Female-Typical Pheromone-Induced Hypothalamic Neural Responses and Kisspeptin Neuronal Activity in α-Fetoprotein Knockout Female Mice.

Pheromones induce sexually dimorphic neuroendocrine responses, such as LH secretion. However, the neuronal network by which pheromones are converted into signals that will initiate and modulate endocrine changes remains unclear. We asked whether 2 sexually dimorphic populations in the anteroventral periventricular and periventricular nuclei that express kisspeptin and tyrosine hydroxylase (TH) are potential candidates that will transduce the olfactory signal to the neuroendocrine system. Furthermore, we assessed whether this transduction is sensitive to perinatal actions of estradiol by using female mice deficient in α-fetoprotein (AfpKO), which lack the protective actions of Afp against maternal estradiol. Wild-type (WT) and AfpKO male and female mice were exposed to same- versus opposite-sex odors and the expression of Fos (the protein product of the immediate early gene c-Fos) was analyzed along the olfactory projection pathways as well as whether kisspeptin, TH, and GnRH neurons are responsive to opposite-sex odors. Male odors induced a female-typical Fos expression in target forebrain sites of olfactory inputs involved in reproduction in WT, but not in AfpKO females, whereas female odors induced a male-typical Fos expression in males of both genotypes. In WT females, opposite-sex odors induced Fos in kisspeptin and TH neurons, whereas in AfpKO females and WT males, only a lower, but still significant, Fos expression was observed in TH but not in kisspeptin neurons. Finally, opposite-sex odors did not induce any significant Fos expression in GnRH neurons of both sexes or genotypes. Our results strongly suggest a role for fetal estrogen in the sexual differentiation of neural responses to sex-related olfactory cues.

The "ram effect": new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions.

Reproduction in mammals is controlled by the hypothalamo-pituitary-gonadal (HPG) axis under the influence of external and internal factors such as photoperiod, stress, nutrition, and social interactions. Sheep are seasonal breeders and stop mating when day length is increasing (anestrus). However, interactions with a sexually active ram during this period can override the steroid negative feedback responsible for the anoestrus state, stimulate luteinizing hormone (LH) secretion and eventually reinstate cyclicity. This is known as the “ram effect” and research into the mechanisms underlying it is shedding new light on HPG axis regulation. The first step in the ram effect is increased LH pulsatile secretion in anestrus ewes exposed to a sexually active male or only to its fleece, the latter finding indicating a “pheromone-like” effect. Estradiol secretion increases in all ewes and this eventually induces a LH surge and ovulation, just as during the breeding season. An exception is a minority of ewes that exhibit a precocious LH surge (within 4 h) with no prior increase in estradiol. The main olfactory system and the cortical nucleus of the amygdala are critical brain structures in mediating the ram effect since it is blocked by their inactivation. Sexual experience is also important since activation (increased c-fos expression) in these and other regions is greatly reduced in sexually naïve ewes. In adult ewes kisspeptin neurons in both arcuate and preoptic regions and some preoptic GnRH neurons are activated 2 h after exposure to a ram. Exposure to rams also activates noradrenergic neurons in the locus coeruleus and A1 nucleus and increased noradrenalin release occurs in the posterior preoptic area. Pharmacological modulation of this system modifies LH secretion in response to the male or his odor. Together these results show that the ram effect can be a fruitful model to promote both a better understanding of the neural and hormonal regulation of the HPG axis in general and also the specific mechanisms by which male cues can overcome negative steroid feedback and trigger LH release and ovulatory cycles.

Peripubertal exposure to male chemosignals accelerates vaginal opening and induces male-directed odor preference in female mice

Reproductive physiology in female mouse is profoundly affected by male odor. A well-known effect of male odor is the acceleration of puberty onset in prepubertal female mice exposed to male urine. Whether peripubertal exposure to male odor also influences female sexual behavior in adulthood is poorly known. Recently, we reported that female mice exposed to male-soiled bedding showed advanced vaginal opening associated with early expression of male-directed odor preference in adulthood. The aim of the present study is to determine whether peripubertal exposure to male urinary chemosignals affects both occurrence of vaginal opening and attraction to male odor at older age in female mice. Therefore, we exposed female mice to (1R, 5S, 7R)-3,4-dehydro-exo-brevicomin (DHB), 6-hydroxy-6-methyl-3-heptanone (HMH) and (S)-2-sec-butyl-4,5-dihydrothiazole (SBT), individually or in mixture, from postnatal day (PD) 21 to PD38 and monitored the occurrence of vaginal opening. We measured then the time that the female mice spent sniffing male and female mouse urinary volatiles at PD45. As expected, peripubertal exposure to DHB, HMH or SBT accelerated vaginal opening in female mice. In addition, we showed that exposure to a mixture of these three compounds induced expression of male-directed odor preference at PD45, contrary to the single exposure to each of these molecules. In conclusion, the volatile compounds DHB, HMH and SBT in urine of male mice influence both occurrence of vaginal opening and adult expression of male-directed odor preference in female mice.

Mapping axillary microbiota responsible for body odours using a culture-independent approach.

BackgroundHuman axillary odour is commonly attributed to the bacterial degradation of precursors in sweat secretions. To assess the role of bacterial communities in the formation of body odours, we used a culture-independent approach to study axillary skin microbiota and correlated these data with olfactory analysis.ResultsTwenty-four Caucasian male and female volunteers and four assessors showed that the underarms of non-antiperspirant (non-AP) users have significantly higher global sweat odour intensities and harboured on average about 50 times more bacteria than those of AP users. Global sweat odour and odour descriptors sulfury-cat urine and acid-spicy generally increased from the morning to the afternoon sessions. Among non-AP users, male underarm odours were judged higher in intensity with higher fatty and acid-spicy odours and higher bacterial loads. Although the content of odour precursors in underarm secretions varied widely among individuals, males had a higher acid: sulfur precursor ratio than females did. No direct correlations were found between measured precursor concentration and sweat odours. High-throughput sequencing targeting the 16S rRNA genes of underarm bacteria collected from 11 non-AP users (six females and five males) confirmed the strong dominance of the phyla Firmicutes and Actinobacteria, with 96% of sequences assigned to the genera Staphylococcus, Corynebacterium and Propionibacterium. The proportion of several bacterial taxa showed significant variation between males and females. The genera Anaerococcus and Peptoniphilus and the operational taxonomic units (OTUs) from Staphylococcus haemolyticus and the genus Corynebacterium were more represented in males than in females. The genera Corynebacterium and Propionibacterium were correlated and anti-correlated, respectively, with body odours. Within the genus Staphylococcus, different OTUs were either positively or negatively correlated with axillary odour. The relative abundance of five OTUs (three assigned to S. hominis and one each to Corynebacterium tuberculostearicum and Anaerococcus) were positively correlated with at least one underarm olfactory descriptor.ConclusionsPositive and negative correlations between bacterial taxa found at the phylum, genus and OTU levels suggest the existence of mutualism and competition among skin bacteria. Such interactions, and the types and quantities of underarm bacteria, affect the formation of body odours. These findings open the possibility of developing new solutions for odour control.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-014-0064-3) contains supplementary material, which is available to authorized users.

An alien in the group: eusocial male bees sharing nonspecific reproductive aggregations.

Sexual selection predicts that individuals competing for access to sexual partners should maximize their chances of mating by looking for sites where the chances of finding partners are more likely to occur. However, males of stingless bees have been observed sharing nonspecific reproductive aggregations. This uncommon behavior appears to confer no obvious increase of individual fitness. It has been suggested that this reproductive strategy is due to the similarity between male odors common to different stingless bee species. Cuticular hydrocarbons (CHCs) are candidate odors of interest because their nonvolatile pheromone nature allows them to play an important role in sexual behavior and species recognition. Here, we review the literature to evaluate whether any phylogenetic patterns exist among male stingless bees that aggregate with closely or distantly related species. We also compared the CHC profiles of males of Neotropical stingless bee species (Plebeia sp. Schwarz, Trigona spinipes (F.), Tetragona clavipes (F.), Nannotrigona testaceicornis (Lepeletier), Scaptotrigona aff. depilis (Moure), Tetragonisca angustula (Latreille), and Melipona subnitida (Ducke) to reveal any chemical similarities among their male odors. We found males of 21 stingless bee species involved in interspecific interactions mainly from Neotropical and Indo-Malayan/Australasian regions. Alien males did not necessarily visit host aggregations of closely related species. Furthermore, the CHC profiles of different studied species were very distinct from each other and do not overlapped at all. It is unclear yet why this apparently nonadaptive behavior carried out by some stingless bee males.

The role of odors and ultrasonic vocalizations in female rat (Rattus norvegicus) partner choice.

Intrasexual competition for access to a female mate is believed to be unusual in wild male rats, which suggests that female choosiness could be more important. It has been shown that females spend more time with one male than with others when tested in a multiple partner paradigm. The male of first entry is visited most. The role of ultrasonic vocalizations (USVs) and male odors in the female rat's initial choice to approach one male instead of another are studied in these experiments. In Experiment 1, female rats were allowed to choose between 3 different intact males, whereas in Experiment 2, females could choose between a devocalized male and 2 intact males. Both experiments started with a 15-min period with inaccessible males followed by a 15-min period with accessible males in which the female could copulate with the males of her choice. The results showed that female rats spent more time with the male of first entry over the males visited subsequently. No differences were found in USV subtype patterns emitted by the different males or the time spent sniffing the different males in the period preceding the choice. In addition, the results of Experiment 2 showed that females visited the silent males as much as the vocalizing males. Thus, the present experiments did not offer any evidence suggesting that USVs or individual differences in male odors play any role in female mate choice. Other factors that were not investigated in this study might be involved in female rat mate selection, but it should also be considered that mate selection could be random.

A male pheromone-mediated trade-off between female preferences for genetic compatibility and sexual attractiveness in rats

IntroductionChemosensory signals play a vital role in socio-sexual interactions of rodents. Females rely heavily on chemosensory signals to evaluate genetic similarity and quality of potential mates, but their olfactory preferences for these criteria often conflict in mate choice.ResultsUsing two inbred strains of rats, Brown Norway (BB) and Lewis (LL) and their F1 reciprocal hybrids (BL, BB♀ breed with LL♂; LB, LL♀ breed with BB♀) as genetic models, we found that the chemosensory preferences of BB and LL females between these 4 strains of rats could be predicted on the basis of genetic compatibility benefits, except that LL females exhibited incestuous preferences for male urine odor of LL rats over that of the BB strain and the F1 hybrids. Seven ketone components of major urine volatiles proved to be potential male pheromones and were enriched in LL males compared to BB males or the F1 hybrid males. We hypothesize that these ketones produced an extravagant male trait that attracts LL females, overriding compatibility traits. This conclusion was corroborated by adding three synthetic pheromone analogues, 4-heptanone, 2-heptanone and 9-hydroxy-2-nonanone of these 7 components, which resulted in equalization of the sexual attractiveness of BB male urine and LL male urine. Additionally, in the genetically diverse F2 hybrids (BL♀ breed with BL♂), the pheromones-enriched males could consistently attract the F2 females.ConclusionsWe suggest that the exaggerated male pheromones serve as a “sexual chemical ornament” to attract females, independent of genetic compatibility, whereas genetic dissimilarity could influence the preferences only when male pheromones varied on a small scale.

Female attraction to male scent and associative learning: the house mouse as a mammalian model

Many territorial mammals invest heavily in competitive scent marks that advertise their location, identity and current social and physiological status. Here we review the behavioural and molecular components of scent marking in house mice, Mus musculus domesticus , that influence female attraction to males and discuss how pheromone-induced learning among females and differential scent investment among males both influence female attraction to specific scent owners. Although mouse urine scents contain numerous sex-specific and individual-specific components, female attraction to spend more time near urine from males depends on contact with an involatile protein pheromone, darcin. This is an atypical major urinary protein (MUP) expressed only by males. On contact, this pheromone acts as a highly potent stimulus for associative learning, such that females learn similar attraction to the individual male's airborne odour associated with darcin; they also learn attraction to spatial cues where the pheromone was encountered. This targets female attraction to both the odour and location of individual male scent mark owners. However, the concentration and quality of airborne volatiles emitted from scent marks influence approach and contact with male scents. Under competitive pressure, males invest heavily in refreshment of scent marks at a high rate and deposit a high concentration of MUPs that bind urinary volatiles and extend the duration of volatile release. Females also gain information from airborne volatiles, including the social and infection status of the owner, which can alter their attraction to contact his scent. The ability of females to learn about individual males from their scent marks means that most decisions about preferred males are likely to be made before females are ready to mate. We are just starting to understand how different information in male scents is integrated in making these decisions.

Pathogen threat and unfamiliar males rapidly bias the social responses of female mice

There is mounting evidence that pathogen threat affects social preferences and responses. In humans, the presence of strangers also elicits heightened sensitivity to pathogen threat, promoting ‘in-group’ bias and ‘out-group’ avoidance. Whether or not a similar effect of social context on responses to pathogen threat occurs in nonhuman animals is unclear. Here we show that the responses of female laboratory mice, Mus muculus, to males are also rapidly affected by the presence of unfamiliar or infected males. In female mice, where odour cues drive appetitive and aversive social responses, brief (1 min) exposure to the urinary odours of an unfamiliar male led to females subsequently discriminating more strongly against the odours of males subclinically infected with the murine nematode parasite, Heligmosomoides polygyrus. Likewise, brief exposure to the odours of infected males attenuated the responses of females to the odours of the normally preferred unfamiliar males and enhanced their preferences for familiar males. These findings are consistent with the concept of ‘assortative’ sociality, whereby the presence of pathogen threat and unfamiliar individuals biases female preferences for uninfected and familiar individuals (‘in-group’ preference and, in human terms, ‘ethnocentrism’) and leads to the avoidance of unfamiliar individuals (‘out-group’ avoidance and ‘xenophobia’). Hence, as in humans, social information associated with infection can rapidly bias the social preferences of female mice. These rapid shifts in social preferences can have implications for our understanding of the evolution of social interactions and group composition.

P.6.c.019 Persistent microglia activation contributes to the depressive/psychotic-like phenotype induced by adolescent THC exposure in rats

Rodents rely upon their olfactory modality to perceive opposite-sex pheromonal odors needed to motivate courtship behaviors. Volatile and nonvolatile components of pheromonal odors are processed by the main (MOS) and accessory olfactory system (AOS), respectively, with inputs converging in the medial amygdala (Me). The Me in turn targets the mesolimbic dopamine system, including the nucleus accumbens core (AcbC) and shell (AcbSh), the ventral pallidum (VP), medial olfactory tubercle (mOT) and ventral tegmental area (VTA). We hypothesized that pheromone-induced dopamine (DA) release in the ventral striatum (particularly in the mAcb and mOT) may mediate the normal preference of female mice to investigate male pheromones. We made bilateral 6-OHDA lesions of DA fibers innervating either the mAcb alone or the mAcb + mOT in female mice and tested estrous females’ preference for opposite-sex urinary odors. We found that 6-OHDA lesions of either the mAcb alone or the mAcb + mOT significantly reduced the preference of sexually naïve female mice to investigate breeding male urinary odors (volatiles as well as volatiles + nonvolatiles) vs. estrous female urinary odors. These same neurotoxic lesions had no effect on subjects’ ability to discriminate between these two urinary odors, on their locomotor activity, or on their preference for consuming sucrose. The integrity of the dopaminergic innervation of the mAcb and mOT is required for female mice to prefer investigating male pheromones.

Sex pheromones are not always attractive: changes induced by learning and illness in mice

A male-specific major urinary protein named darcin is attractive to female mice, Mus musculus, stimulates a learned attraction to volatile components of a male's urinary odour and induces spatial learning. In this article we show that darcin also induces learned attraction for a previously neutral olfactory stimulus (the odorant isoamyl acetate), acquired by repeated presentation of both stimuli together. We hypothesize that this is a case of olfactory–vomeronasal associative learning, in which darcin acts as the unconditioned reinforcer. However, the presence of darcin is not always attractive to adult female mice. Urine from males parasitized by the nematode Aspiculuris tetraptera has no attractive value for females, despite apparently normal presence of darcin. The loss of attractive value may be due to unknown infection-derived chemicals whose detection overrides the attraction induced by darcin, or prevents detection of darcin by other (unknown) mechanisms. Other cases in which male urine (and thus the presence of darcin) does not induce attraction are discussed, namely in lactating females, which respond with aggression towards intruder males, and in prepubertal females, which show aversive responses towards unfamiliar male urine. Thus, although the darcin sex pheromone induces attraction in adult female mice that does not need to be learned, such innate pheromonal responses can be modulated by the physiological or health status of the sender and receiver. This provides a degree of flexibility in response to pheromonal signals, but such that individuals of the same class or status still share consistent predictable responses to improve their reproductive fitness. Further, by readily inducing the same response towards other odorants through associative learning, pheromones can also target responses flexibly towards odour signatures at an individual-specific level.

6-Hydroxydopamine lesions of the anteromedial ventral striatum impair opposite-sex urinary odor preference in female mice

Rodents rely upon their olfactory modality to perceive opposite-sex pheromonal odors needed to motivate courtship behaviors. Volatile and nonvolatile components of pheromonal odors are processed by the main (MOS) and accessory olfactory system (AOS), respectively, with inputs converging in the medial amygdala (Me). The Me in turn targets the mesolimbic dopamine system, including the nucleus accumbens core (AcbC) and shell (AcbSh), the ventral pallidum (VP), medial olfactory tubercle (mOT) and ventral tegmental area (VTA). We hypothesized that pheromone-induced dopamine (DA) release in the ventral striatum (particularly in the mAcb and mOT) may mediate the normal preference of female mice to investigate male pheromones. We made bilateral 6-OHDA lesions of DA fibers innervating either the mAcb alone or the mAcb+mOT in female mice and tested estrous females’ preference for opposite-sex urinary odors. We found that 6-OHDA lesions of either the mAcb alone or the mAcb+mOT significantly reduced the preference of sexually naïve female mice to investigate breeding male urinary odors (volatiles as well as volatiles+nonvolatiles) vs. estrous female urinary odors. These same neurotoxic lesions had no effect on subjects’ ability to discriminate between these two urinary odors, on their locomotor activity, or on their preference for consuming sucrose. The integrity of the dopaminergic innervation of the mAcb and mOT is required for female mice to prefer investigating male pheromones.

Identification of the aggregation pheromone of the melon thrips, Thrips palmi.

The objective of this study was to identify the aggregation pheromone of the melon thrips Thrips palmi, a major pest of vegetable and ornamental plants around the world. The species causes damage both through feeding activities and as a vector of tospoviruses, and is a threat to world trade and European horticulture. Improved methods of detecting and controlling this species are needed and the identification of an aggregation pheromone will contribute to this requirement. Bioassays with a Y-tube olfactometer showed that virgin female T. palmi were attracted to the odour of live males, but not to that of live females, and that mixed-age adults of both sexes were attracted to the odour of live males, indicating the presence of a male-produced aggregation pheromone. Examination of the headspace volatiles of adult male T. palmi revealed only one compound that was not found in adult females. It was identified by comparison of its mass spectrum and chromatographic details with those of similar compounds. This compound had a structure like that of the previously identified male-produced aggregation pheromone of the western flower thrips Frankliniella occidentalis. The compound was synthesised and tested in eggplant crops infested with T. palmi in Japan. Significantly greater numbers of both males and females were attracted to traps baited with the putative aggregation pheromone compared to unbaited traps. The aggregation pheromone of T. palmi is thus identified as (R)-lavandulyl 3-methyl-3-butenoate by spectroscopic, chromatographic and behavioural analysis.

Responses by wild house mice (Mus musculus) to various stimuli in a novel environment

House mice (Mus musculus) pose a threat to the native flora and fauna on islands, and can cause significant damage wherever they have been introduced. Methods used to eradicate invasive rodents, like house mice, at high population densities may not be appropriate for intercepting them at lower densities. A better understanding of the immediate behavior of house mice when first introduced to a novel environment would help managers develop effective biosecurity techniques to protect against new invasions. To address this problem, we conducted a controlled laboratory experiment that simulated an invasion by wild house mice into a novel environment. We quantified and compared the immediate behaviors of wild house mice (n=40) by testing various odors and other attractants, including odors (e.g., foods and conspecific), shelter, water, and a control. There was a significant difference in mouse responses to these treatments (P≤0.0001). We found that the most common immediate reaction of invading mice was to seek shelter in a den box (μ=47.7 box entries) rather than responding to the other potential attractants presented. Secondarily, the mice were interested in some food scents, particularly bacon grease (μ=18.3 box entries), peanut butter (μ=17.0 box entries), and cheese (μ=14.5 box entries). The sex of the mouse did not influence their responses to odors and attractants (P≥0.243), however, we noted that females visited male feces and urine odors (μ=17 visits) more than males visited female feces and urine odors (μ=11 visits). Fewest visits were to the empty box (μ=8.0 box entries) and the water box (μ=5.1 box entries) Based on our findings, we surmise that a secure den box which included certain food odors might entice and hold mice in a restricted area for a short duration in a novel environment. If done properly, this arrangement could be utilized for early detection and response to newly-invading house mice.

Female puberty acceleration by male odour in mice: neural pathway and behavioural consequences.

In female mice, exposure to male chemosignals results in early puberty onset characterized by advanced vaginal opening and higher uterine weight. Evidence suggests that the male chemosignals responsible for acceleration of female puberty are androgen-dependent, but not all of the compounds that contribute to puberty acceleration have been identified. The male chemosignals are primarily detected and processed by the vomeronasal system including the vomeronasal organ, the accessory olfactory bulb and the medial amygdala. By contrast, the mechanism by which this olfactory information is integrated in the hypothalamus is poorly understood. In this context, the recent identification of the neuropeptide kisspeptin as a gatekeeper of puberty onset may provide a good candidate neuropeptide system for the transmission of chemosensory information to the gonadotrope axis.

Activation of the olfactory system in response to male odors in female prepubertal mice

Exposure to male odors during the prepubertal period accelerates puberty, a phenomenon known as the Vandenbergh effect. This experiment identifies the parts of the olfactory pathway that respond to male odors in prepubertal female mice. Female mice were kept in a room free of adult male odors from birth until odor exposure. At post-natal day 21, 24 or 28, (ages representing time points early, intermediate, and late in the prepubertal period) mice were exposed to clean bedding, soiled bedding from castrated males, or soiled bedding from intact males. Each group was exposed to odor in separate rooms to prevent cross contamination. Ninety minutes after odor exposure, mice were sacrificed, the brains removed and prepared for c-Fos immunohistochemistry. The numbers of neurons expressing c-Fos were counted in a defined area of the following nuclei: AOB mitral layer, AOB granular layer, MOB, MEPV, MEPD, Aco, BNST, MPOA, and VMH. There was a significant effect of age on c-Fos-expression in the MEPV, MEPD, Aco, MPOA, BNST and piriform cortex. There was a significant effect of odor on c-Fos-expression in the MEPV, MEPD, Aco, MPOA, and VMH, showing that these areas are differentially sensitive to intact male odors vs. clean bedding and that these brain areas may be responsible for communicating odor information that drives puberty acceleration.

Variation in female guppy preference for male olfactory and visual traits

Abstract Animals often use different sensory systems to assess different sexually selected signals from potential mates. However, the relative importance of different signals on mate choice is not well understood in many animal species. In this study, we examined the relative importance of male olfactory and visual cues on female preference in the guppy Poecilia reticulata. We used digitally modified male images to standardize visual stimuli. We found that, regardless of whether females were presented without male visual stimuli or with identical male visual stimuli, they preferred stimuli with the odor of males to those without. However, when females were allowed to choose between dull male visual stimuli with male odor, and brightly colored male visual stimuli without male odor, there was no clear preference for either. Some females preferred the dull male visual stimuli with male odor, whereas some other females preferred the brightly colored male visual stimuli without male odor. These results indicate that the relative importance of olfactory and visual cues in female mate preference varied between individuals.

Pheromones: The Scent of a Male

There has been an enduring fascination with discovering biological odours which can evoke behavioral and physiological responses in mammals. New findings in goats have now identified a key molecule involved in the effect male odours have on female reproductive cycles.

Male mealworm beetles increase resting metabolic rate under terminal investment

Harmful parasite infestation can cause energetically costly behavioural and immunological responses, with the potential to reduce host fitness and survival. It has been hypothesized that the energetic costs of infection cause resting metabolic rate (RMR) to increase. Furthermore, under terminal investment theory, individuals exposed to pathogens should allocate resources to current reproduction when life expectancy is reduced, instead of concentrating resources on an immune defence. In this study, we activated the immune system of Tenebrio molitor males via insertion of nylon monofilament, conducted female preference tests to estimate attractiveness of male odours and assessed RMR and mortality. We found that attractiveness of males coincided with significant down-regulation of their encapsulation response against a parasite-like intruder. Activation of the immune system increased RMR only in males with heightened odour attractiveness and that later suffered higher mortality rates. The results suggest a link between high RMR and mortality and support terminal investment theory in T. molitor.

Sex differences and the modulating effects of gonadal hormones on basal and the stressor-decreased newly proliferative cells and neuroblasts in dentate gyrus

This study was undertaken to assess sex differences and the modulating effects of gonad intactness and the estrous phase on basal and the stressor-decreased cell proliferation and early differentiation in Balb/C mouse dentate gyrus (DG). Besides, we compared the stress-reversing effects exerted by the presence of male and female Balb/C mouse odors in stressed male and female mouse DG in this regard. Female mice had lower baselines in the number of newly proliferated cells and neuroblasts than male mice. Although the stressor induced decreases in the number of newly proliferative cells and neuroblasts in both male and female DG, an obvious decrease in neuronal lineage commitment was observed in female DG. Moreover, ovariectomy induced decreases in baselines in the number of proliferative cells and neuroblasts but did not affect the stressor-induced decrease in neuronal lineage commitment in female DG. Interestingly, pro-estrous mice exhibited the stressor-decreased neuronal lineage commitment, while estrous and diestrous mice did not display such a decrease. Furthermore, orchidectomy did not affect basal or the stressor-decreased newly proliferative cells or neuroblasts in male DG. Finally, male odors were less effective than female odors in abolishing the stressor-decreased neuronal lineage commitment in female mice, while male and female odors were comparable in reversing the stressor-decreased newly proliferated cells and neuroblasts in male mice. The protective effects of mouse odors' company in the stressed male mouse DG were associated with local BDNF and NGF replenishment. Taken together, sexual differences in baselines in the number of newly proliferative cells, neuroblasts, and the sensitivity to stress-altered neuronal lineage commitment in the DG could be, in part, due to gonadal hormone differences between the two sexes. Mouse odors may reverse stressor-decreased newly proliferative cells and neuroblasts in male, but not in female, mouse DG by restoring BDNF and NGF levels.