Sensory cues and the suppression of reproduction in subordinate female marmoset monkeys, Callithrix jacchus

A tale of two hierarchies: Hormonal and behavioral factors underlying sex differences in social dominance in cooperative breeding callitrichids

Callitrichid primates are recognized for high levels of sociality in small groups, their great behavioral flexibility, and single-female dominant hierarchies. Previous work has highlighted that dominant, breeding callitrichids engage in behavioral and hormonal reproductive suppression of related and unrelated subordinates by both producing more offspring, having higher levels of ovulatory hormones, and accessing more sociosexual opportunities. This suppression constitutes a nexus of changes in pituitary responsiveness, ovarian cyclicity, sexual behavior, affiliation, and aggression. In this review, I will highlight important features that characterize callitrichid social hierarchies across broad social contexts. Dominant females sometimes exert reproductive suppression on subordinate nonbreeding females, but this suppression varies across callitrichids based on social stability and changes in group composition, particularly related to the number, experience, and age of nonbreeding subordinates. Meanwhile, dominant males may induce suppression of reproduction in subordinate males, but these effects occur by different behavioral and endocrine mechanisms and to a much lesser extent than their female counterparts; While dominant female callitrichids usually show higher levels of aggression relative to their male counterparts, callitrichids show a general absence of intersexual dominance, likely as an effort of maintaining a cohesive breeding pair within a stable social group and social cooperation. Future efforts are needed to identify precise neuroendocrine mechanisms underlying the presence of sex differences in callitrichid behavior separate from peripheral reproductive function. This is especially important with regard to parental experience, social relationships, development and aging, with larger implications toward understanding sex differences in overall health and wellbeing.

Molecular identification of an androgen receptor and the influence of long-term aggressive interaction on hypothalamic genes expression in black rockfish (Sebastes schlegelii)

This study aims to explore the mechanism on how aggressive interaction alters reproductive physiology by testing whether aggressive interaction can activate the reproductive neuroendocrine function via the hypothalamus-pituitary-gonadal (HPG) axis in black rockfish (Sebastes schlegelii). The expressions of the androgen receptor gene (ar) and gonadotropin-releasing hormone genes (gnrhs), the concentration of plasma androgens, and GSI (the ratio of testes mass to body mass) were compared between the interaction group (dominant males or subordinate males) and the isolation group in male black rockfish after 3 weeks. A full-length cDNA encoding an androgen receptor (AR) of 766 amino acids was isolated. Transcripts encoding this AR were detected at a high relative abundance in the liver, kidney, testis, ovary, muscle, and intestine tissue. Further evaluation of brain genes transcripts abundance revealed that the mRNA levels of gnrh I and ar genes were significantly different between the interaction group and the isolation group in the hypothalamus. However, no significant difference was detected in testosterone, 11-keto-testosterone, and GSI between these two groups. This study indicates that a long-term aggressive interaction affect the expression of hypothalamic gnrh I and ar but may not change the physiological function of the HPG axis in an all-male condition.

Female-Based Patterns and Social Function in Avian Chemical Communication

Much of the growing interest in avian chemical signals has focused on the role of kin recognition or mate attraction, often with an emphasis on males, with uropygial gland secretions perhaps providing information about an individual's identity and quality. Yet, data collected to date suggest sexual dimorphism in uropygial glands and secretions are often emphasized in female, rather than in male birds. That is, when a sexual difference occurs (often during the breeding season only), it is the female that typically exhibits one of three patterns: (1) a larger uropygial gland, (2) a greater abundance of volatile or semi-volatile preen oil compounds and/or (3) greater diversity of preen oil compounds or associated microbes. These patterns fit a majority of birds studied to date (23 of 30 chemically dimorphic species exhibit a female emphasis). Multiple species that do not fit are confounded by a lack of data for seasonal effects or proper quantitative measures of chemical compounds. We propose several social functions for these secretions in female-based patterns, similar to those reported in mammals, but which are largely unstudied in birds. These include: (1) intersexual advertisement of female receptivity or quality, including priming effects on male physiology, (2) intrasexual competition, including scent marking and reproductive suppression or (3) parental behaviors, such as parent-offspring recognition and chemical protection of eggs and nestlings. Revisiting the gaps of chemical studies to quantify the existence of female social chemosignals and any fitness benefit(s) during breeding are potentially fruitful but overlooked areas of future research.

Female Chemical Signalling Underlying Reproduction in Mammals

Chemical communication plays many key roles in mammalian reproduction, although attention has focused particularly on male scent signalling. Here, we review evidence that female chemical signals also play important roles in sexual attraction, in mediating reproductive competition and cooperation between females, and in maternal care, all central to female reproductive success. Female odours function not only to advertise sexual receptivity and location, they can also have important physiological priming effects on male development and sperm production. However, the extent to which female scents are used to assess the quality of females as potential mates has received little attention. Female investment in scent signalling is strongly influenced by the social structure and breeding system of the species. Although investment is typically male-biased, high competition between females can lead to a reversed pattern of female- biased investment. As among males, scent marking and counter-marking are often used to advertise territory defence and high social rank. Female odours have been implicated in the reproductive suppression of young or subordinate females across a range of social systems, with females of lower competitive ability potentially benefiting by delaying reproduction until conditions are more favourable. Further, the ability to recognise individuals, group members and kin through scent underpins group cohesion and cooperation in many social species, as well as playing an important role in mother-offspring recognition. However, despite the diversity of female scent signals, chemical communication in female mammals remains relatively understudied and poorly understood. We highlight several key areas of future research that are worthy of further investigation.

Olfactory Bulbectomy Modifies Photic Entrainment and Circadian Rhythms of Body Temperature and Locomotor Activity in a Nocturnal Primate

Studies on rodents have emphasized that removal of the olfactory bulbs modulates circadian rhythmicity. Using telemetric recordings of both body temperature (Tb) and locomotor activity (LA) in a male nocturnal primate, the gray mouse lemur, the authors investigated the effects of olfactory bulbectomy on (1) the circadian periods of Tb and LA in constant dim light condition, and (2) photic reentrainment rates of circadian rhythms following 6-h phase shifts of entrained light-dark cycle (LD 12:12). Under free-running condition, bulb-ectomized males had significantly shorter circadian periods of Tb and LA rhythms than those of control males. However, the profiles of Tb rhythms, characterized by a phase of hypothermia at the beginning of the subjective day, and Tb parameters were not modified by olfactory bulbectomy. Under a light-dark cycle, olfactory bulbectomy significantly modified the expression of daily hypothermia, especially by an increase in the latency to reach minimal daily Tb, suggesting a delayed response to induction of daily hypothermia by light onset. Re-entrainment rates following both a 6-h phase advance and a 6-h phase delay of entrained LD were also delayed in bulbectomized males. Olfactory bulbectomy led to significant fragmentation of locomotor activity and increased locomotor activity levels during the resting period. The shortening of circadian periods in bulbectomized males could partly explain the delayed responses to photic stimuli since in control males, the longer the circadian period, the better the response to light entrainment. This experiment shows for the 1st time that olfactory bulbs can markedly modify the circadian system in a primate.

Contextual modulation of social and endocrine correlates of fitness: insights from the life history of a sex changing fish

Steroid hormones are critical regulators of reproductive life history, and the steroid sensitive traits (morphology, behavior, physiology) associated with particular life history stages can have substantial fitness consequences for an organism. Hormones, behavior and fitness are reciprocally associated and can be used in an integrative fashion to understand how the environment impacts organismal function. To address the fitness component, we highlight the importance of using reliable proxies of reproductive success when studying proximate regulation of reproductive phenotypes. To understand the mechanisms by which the endocrine system regulates phenotype, we discuss the use of particular endocrine proxies and the need for appropriate functional interpretation of each. Lastly, in any experimental paradigm, the responses of animals vary based on the subtle differences in environmental and social context and this must also be considered. We explore these different levels of analyses by focusing on the fascinating life history transitions exhibited by the bi-directionally hermaphroditic fish, Lythrypnus dalli. Sex changing fish are excellent models for providing a deeper understanding of the fitness consequences associated with behavioral and endocrine variation. We close by proposing that local regulation of steroids is one potential mechanism that allows for the expression of novel phenotypes that can be characteristic of specific life history stages. A comparative species approach will facilitate progress in understanding the diversity of mechanisms underlying the contextual regulation of phenotypes and their associated fitness correlates.

D'scent of man: a comparative survey of primate chemosignaling in relation to sex

This article is part of a Special Issue (Chemosignals and Reproduction). As highly visual animals, primates, in general, and Old World species (including humans), in particular, are not immediately recognized for reliance in their daily interactions on olfactory communication. Nevertheless, views on primate olfactory acuity and the pervasiveness of their scent signaling are changing, with increased appreciation for the important role of body odors in primate social and sexual behavior. All major taxonomic groups, from lemurs to humans, are endowed with scent-producing organs, and either deposit or exude a wealth of volatile compounds, many of which are known semiochemicals. This review takes a comparative perspective to illustrate the reproductive context of primate signaling, the relevant information content of their signals, the sexually differentiated investigative responses generated, and the behavioral or physiological consequences of message transmission to both signaler and receiver. Throughout, humans are placed alongside their relatives to illustrate the evolutionary continuum in the sexual selection of primate chemosignals. This ever-growing body of evidence points to a critical role of scent in guiding the social behavior and reproductive function throughout the primate order.

Simultaneous courtship and parenting in males and sex role reversal in females of the haremic bluebanded goby, Lythrypnus dalli

While males typically compete for females, species with female biased sex ratios and/or large male investment in offspring care often exhibit reversed sex roles. Here we investigated, in a haremic fish species, the bluebanded goby, Lythrypnus dalli, the impact of male and female courtship behaviour on male reproductive success, measured as the total number of eggs in the nest and total number of developed eggs. Reproductive success was not associated with rates of male behaviour, such as parenting, approaching and courtship, but was associated with rates of female courtship. Consistent with predictions for a role-reversed reproductive strategy, only males demonstrated nest care and females exhibited high rates of courtship and intrasexual competition, such that alpha females interrupted courtship solicitations by beta females. Overall, these data are consistent with sex role reversal in L. dalli and show that the expression of male courtship behaviour does not interfere with paternal care.

The vomeronasal organ of Lemur catta

The vomeronasal organ (VNO), also known as the Jacobson's organ, is a bilateral chemosensory organ found at the base of the nasal cavity specialized for the detection of higher-molecular weight (non-volatile) chemostimuli. It has been linked to pheromone detection. The VNO has been well studied in nocturnal lemurs and lorises, but poorly studied in diurnal/cathemeral species despite the large repertoire of olfactory behaviors noted in species such as Lemur catta. Here, the VNO and associated structures were studied microanatomically in one adult female and one adult male L. catta. Traditional and immunohistochemical procedures demonstrate the VNO epithelium consists of multiple rows of sensory neurons. Immunoreactivity to Growth-associated protein 43 (GAP43) indicates the VNO is postnatally neurogenic. In volume, the VNO neuroepithelium scales similarly to palatal length compared to nocturnal strepsirrhines. Numerous taste buds present at the oral opening to the nasopalatine duct, with which the VNO communicates, provide an additional (or alternative) explanation for the flehmen behavior that has been observed in this species. The VNO of L. catta is shown to be microanatomically comparable to that of nocturnal strepsirrhines. Like nocturnal strepsirrhines, the VNO of L. catta may be functional in the reception of high-molecular weight secretions.

Resolving social conflict among females without overt aggression

Members of animal societies compete over resources and reproduction, but the extent to which such conflicts of interest are resolved peacefully (without recourse to costly or wasteful acts of aggression) varies widely. Here, we describe two theoretical mechanisms that can help to understand variation in the incidence of overt behavioural conflict: (i) destruction competition and (ii) the use of threats. The two mechanisms make different assumptions about the degree to which competitors are socially sensitive (responsive to real-time changes in the behaviour of their social partners). In each case, we discuss how the model assumptions relate to biological reality and highlight the genetic, ecological and informational factors that are likely to promote peaceful conflict resolution, drawing on empirical examples. We suggest that, relative to males, reproductive conflict among females may be more frequently resolved peacefully through threats of punishment, rather than overt acts of punishment, because (i) offspring are more costly to produce for females and (ii) reproduction is more difficult to conceal. The main need now is for empirical work to test whether the mechanisms described here can indeed explain how social conflict can be resolved without overt aggression.

Maternal care associates with play dominance rank among adult female rats

Variations in maternal care influence important life history traits that determine reproductive fitness. The adult female offspring of mothers that show reduced levels of pup licking/grooming (LG; i.e., low-LG mothers) show increased defensive responses to stress, accelerated pubertal development, and greater sexual receptivity than the female offspring of high-LG mothers. Amongst several species an accelerated pattern of reproductive development is associated with increased dominance-related behaviors and higher social rank. We hypothesize that rats from low-LG dams may thus also secure higher social rank as a means to compete for limited resources with conspecifics. In this study, social interactions were observed in triads of adult female rats aged p90 that received low, mid, and high levels of pup LG over the first week of life. Low- and mid-LG females had the highest pinning scores and high-LG rats the lowest, showing that low- and mid-LG adult females engage in greater play dominance-related behavior. Likewise, low- and mid-LG rats spent significantly more time drinking following 24 hr of water deprivation in a water competition test thus allowing them to secure a limited resource more easily than high-LG rats. Interestingly, pinning by play dominant females was increased when subordinates were sexually receptive (proestrus/estrus), suggestive of a process of reproductive suppression. Some evidence suggests that low-LG and mid-LG rats also show greater fecundity than high-LG rats. Variations in maternal care may thus have a long-term influence on the development of play dominance and possibly social rank in the female rat, which might contribute to reproductive success within a competitive environment.

The vomeronasal organ of New World monkeys (platyrrhini)

Although all platyrrhine primates possess a vomeronasal organ (VNO), few species have been studied in detail. Here, we revisit the microanatomy of the VNO and related features in serially sectioned samples from 41 platyrrhine cadavers (14 species) of mixed age. Procedures to identify terminally differentiated vomeronasal sensory neurons (VSNs) via immunolabeling of olfactory marker protein (OMP) were used on selected specimens. The VNO varies from an elongated epithelial tube (e.g., Ateles fusciceps) to a dorsoventrally expanded sac (e.g., Saguinus spp.). The cartilage that surrounds the VNO is J-shaped or U-shaped in most species, and articulates with a groove on the bony palate. Preliminary results indicate a significant correlation between the length of this groove and length of the VNO neuroepithelium, indicating this feature may serve as a skeletal correlate. The VNO neuroepithelium could be identified in all adult primates except Alouatta, in which poor preservation prevented determination. The VNO of Ateles, described in detail for the first time, had several rows of VSNs and nerves in the surrounding lamina propria. Patterns of OMP-reactivity in the VNO of perinatal platyrrhines indicate that few or no terminally differentiated VSNs are present at birth, thus supporting the hypothesis that some platyrrhines may have delayed maturation of the VNO. From a functional perspective, all platyrrhines studied possess structures required for chemoreception (VSNs, vomeronasal nerves). However, some microanatomical findings, such as limited reactivity to OMP in some species, indicate that some lineages of New World monkeys may have a reduced or vestigial vomeronasal system.

Does nonnutritive tree gouging in a rainforest-dwelling lemur convey resource ownership as does loud calling in a dry forest-dwelling lemur?

Nonhuman primates may defend crucial resources using acoustic or chemical signals. When essential resources are limited, ownership display for a resource may be enhanced. Defending resources may depend on population density and habitat characteristics. Using the Milne Edwards' sportive lemurs (Lepilemur edwardsi) and weasel sportive lemurs (L. mustelinus) as models, we tested whether two cryptic nocturnal lemur species differing in population density and habitat show differences in their vocal and chemical communication for signaling ownership of resources. L. edwardsi inhabits a western dry deciduous forest in a high-density population, whereas L. mustelinus is found in an eastern rainforest in low density. We followed ten L. edwardsi (six males and four females) and nine L. mustelinus (four males and five females) for 215 hr during the early evening (06:00-10:00 p.m.) and the early morning (02:00-05:00 a.m.) and recorded their behavior using focal animal sampling. We found that both species differed in their vocal and chemical communication. L. edwardsi was highly vocal and displayed loud calling in the mornings and evenings while feeding or in the vicinity of resting places. In contrast, L. mustelinus never vocalized during observations, but displayed tree-gouging behavior that was never observed in L. edwardsi. Tree gouging occurred more often during early evening sessions than early morning sessions. Subjects gouged trees after leaving their sleeping hole and before moving around. We suggest that, in weasel sportive lemurs, non-nutritive tree gouging is used as a scent-marking behavior in order to display ownership of sleeping sites. Altogether, our findings provide first empirical evidence on the evolution of different communication systems in two cryptic nocturnal primate species contrasting in habitat quality and population density. Further investigations are needed to provide more insight into the underlying mechanisms.

Reproductive skew in female common marmosets: what can proximate mechanisms tell us about ultimate causes?

Common marmosets are cooperatively breeding monkeys that exhibit high reproductive skew: most subordinate females fail to reproduce, while others attempt to breed but produce very few surviving infants. An extensive dataset on the mechanisms limiting reproduction in laboratory-housed and free living subordinate females provides unique insights into the causes of reproductive skew. Non-breeding adult females undergo suppression of ovulation and inhibition of sexual behaviour; however, they receive little or no aggression or mating interference by dominants and do not exhibit behavioural or physiological signs of stress. Breeding subordinate females receive comparable amounts of aggression to non-breeding females but are able to conceive, gestate and lactate normally. In groups containing two breeding females,however, both dominant and subordinate breeders kill one another's infants. These findings suggest that preconception reproductive suppression is not imposed on subordinate females by dominants, at a proximate level, but is instead self-imposed by most subordinates, consistent with restraint models of reproductive skew. In contrast to restraint models, however, this self-suppression probably evolved not in response to the threat of eviction by dominant females but in response to the threat of infanticide. Thus,reproductive skew in this species appears to be generated predominantly by subordinate self-restraint, in a proximate sense, but ultimately by dominant control over subordinates' reproductive attempts.

Physiological Constraints and Latitudinal Breeding Season in the Canidae

Physiological strategies that maximize reproductive success may be phylogenetically constrained or might have a plastic response to different environmental conditions. Among mammals, Canidae lend themselves to the study of these two influences on reproductive physiology because all the species studied to date have been characterized as monestrous (i.e., a single ovulatory event per breeding season), suggesting a phylogenetic effect. Greater flexibility could be associated with environments that are less seasonal, such as the tropics; however, little is known for many of the species from this region. To compensate for this lack of data, two regressions were done on the length of the reproductive season relative to the latitudinal distribution of a species: one with raw data and another with phylogenetically independent contrasts. There was a significant negative relationship, independent of phylogeny, with canids that have longer breeding seasons occurring at lower latitudes. In contrast, the pervasiveness of monestrus within Canidae appears to be phylogenetically constrained by their pairing/packing life and is most likely associated with monogamy. The persistence of the monestrous condition is supported by a captive study where a tropical canid, the fennec fox, Vulpes zerda, never exhibited polyestrous cycles despite a constant photoperiod (12L : 12D).

Social dominance and breeding activity in Spanish ibex (Capra pyrenaica) maintained in captivity

The relationship between ovulatory activity and social dominance was determined in 10 Spanish ibex females by recording their plasma progesterone and plasma cortisol levels. In a second experiment, the influence of dominance status on the establishment of pregnancy after introduction to males during late anoestrous (late October) was evaluated in another nine females. Dominance hierarchies were established in both groups by noting agonistic interactions between the individual females. Six high-ranking females of the 10 ibexes without male contact showed ovulatory activity with 1–3 progesterone cycles. The first progesterone cycle appeared in December (18 December ± 4 days). Dominance status correlated with age (R = 0.86, P < 0.01), bodyweight (R = 0.96, P < 0.001) and the number of progesterone cycles (R = 0.82, P < 0.01). Cortisol differences were associated with differences in reproductive function rather than social status per se. Introduction to males during late anoestrous brought forward the initiation of ovulatory activity (14 November ± 5 days) and resulted in three pregnancies in females with higher dominance ranks. The results suggest that social interactions are important in the control of ovulatory activity in the Spanish ibex.

Seasonal Endocrine Changes and Breeding Activity in Mediterranean Wild Ruminants

The methods of assisted reproduction commonly used in domestic animals are currently being applied to non-domestic species. This is because of the limitation of maintaining the genetic variability in the wild, as it occurs in wild ruminants of the Mediterranean Basin. Despite the apparent progress of the technology, success of the offspring to grow and become healthy adult individuals has remained low in wild species. Difficulties usually arise from insufficient information about basic reproductive biology, such as the seasonal changes in ovarian and testicular activity. Directional adaptive evolution involves development of speciespecific physiological reproductive patterns to cope with various environmental factors. Thus, species originating and living at the same latitude display different reproductive strategies to entrain the breeding activity at an optimal time of the year. The aim of this paper was to present current knowledge on reproductive physiology of Mediterranean wild ruminants as a basic prerequisite for the successful use of assisted reproduction methods. Special emphasis is given to seasonal endocrine changes, ovarian cycles and testicular activity of Iberian wild ruminants, together with the role of social interactions on the regulation of these events.

Accessory chemosignaling mechanisms in primates

Accessory olfaction is defined as the chemoreceptive system that employs the vomeronasal complex (VNC) and its distinct central projections to the accessory olfactory bulb (AOB) and limbic/cortical systems. Comparisons of the structural and functional features of primate accessory olfaction can now be made at many levels. Advances in the understanding of molecular mechanisms of odorant transfer and detection, physiological analyses of signal processing, and appreciation of ontogenetic timetables have clarified the contribution of accessory chemoreception to the sensory map. Two principal functions dominate: the decoding of social information through the uptake of signals (often fluid-borne), and the provision of an essential pathway for the "migration" of presumptive neurocrine (GnRH) cells from the olfactory placode to the hypothalamus. VN "smelling" (vomerolfaction) is now seen to overlap with primary olfaction. Both systems detect signal compounds along the spectrum of volatility/molecular weight, and neither is an exclusive sensor. Both main and accessory chemoreception seem to require collaborative molecular devices to assist in odorant transfer (binding proteins) and (for the VNO) signal recognition (MHC1 proteins). Most adaptive-selective features of primate chemocommunication variously resemble those of other terrestrial mammals. VN function, along with its genome, has been maintained within the Strepsirrhines and tarsiers, reduced in Platyrrhines, and nearly extinguished at the Catarrhine up to hominin levels. It persists as an intriguing ancient sense that retains key features of past evolutionary events.

Genetic basis of olfactory communication in primates

The genes involved in olfactory communication in mammals via the vomeronasal system are summarized, and studies investigating these genes in primates are reviewed. Only five potentially functional vomeronasal receptor genes (V1RL s) have been found in humans, and only one of these (V1RL1) has been studied in other primates. V1RL1 has become a pseudogene repeatedly during primate evolution, but patterns of natural selection on primate V1RL genes demonstrate that this gene family diverged under natural selection throughout at least part of primate evolution. Evolution of the TRP2 gene, which encodes for an ion channel that is important in vomeronasal organ (VNO) signalling, strongly suggests that this signalling function was lost in ancestral Catarrhines. Overall, much work remains to be done to elucidate the repertoire of genes that are involved in pheromonal communication, particularly in Strepsirhines. Such studies promise unique insights into the evolution of this modality.

Individual olfactory signatures in common marmosets (Callithrix jacchus)

Individual discrimination is likely a prerequisite for most primate social interactions. Olfactory cues are one set of stimuli used by primates to discriminate between individuals. Despite the importance of these olfactory signatures, there is little published research assessing the existence or function of individually unique odors among primates. This review systematically assesses behavioral and biochemical aspects of individual odors in a New World primate, the common marmoset (Callithrix jacchus). There are three objectives to this review: First, behavioral evidence for odors unique to the individual is evaluated in the context of results demonstrating that marmosets are able to discriminate between the scents from a familiar and a novel individual conspecific in behavioral bioassays under a variety of conditions. Second, biochemical evidence for individual scent signatures is debated with reference to studies examining qualitative and quantitative differences between the chemical compositions of scent-mark pools from adult females. A combined gas chromatography (GC) and mass spectrometry (MS) analysis demonstrated that each female had a unique ratio of highly volatile chemicals in the scent mark that could affect individual discrimination. Finally, the possible adaptive significance of individual odors in marmosets is debated. Individual odors may play a key role in regulating both female intrasexual competition and intersexual communication by providing a basis for the assessment of individual quality.

Expression of neuron-specific markers by the vomeronasal neuroepithelium in six species of primates

Vomeronasal organ (VNO) morphology varies markedly across primate taxa. Old World monkeys display no postnatal VNO. Humans and at least some apes retain a vestigial VNO during postnatal life, whereas the strepsirrhines and New World Monkeys present a morphologically well-defined VNO that, in many species, is presumed to function as an olfactory organ. Available microanatomical and behavioral studies suggest that VNO function in these species does not precisely duplicate that described in other mammalian taxa. The questions of which species retain a functional VNO and what functions they serve require inquiry along diverse lines but, to be functional, the vomeronasal epithelium must be neuronal and olfactory. We used immunohistochemistry to establish these criteria in six primate species. We compared the expression of two neuronal markers, neuron-specific beta-tubulin (BT) and protein gene product 9.5, and olfactory marker protein (OMP), a marker of mature olfactory sensory neurons, in paraffin-embedded VNO sections from two strepsirrhine and four haplorhine species, all of which retain morphologically well-defined VNOs during postnatal life. The infant Eulemur mongoz, adult Otolemur crassicaudatus, neonatal Leontopithicus rosalia, and adult Callithrix jacchus express all three proteins in their well-defined vomeronasal neuroepithelia. The infant Tarsius syrichta showed some BT and OMP immunoreactivity. We establish that two strepsirrhine species and at least some New World haplorhines have mature sensory neurons in the VNO. In contrast, at all ages examined, Saguinus geoffroyi VNO expresses these markers in only a few cells.

Changes in olfactory inputs modify the energy balance response to short days in male gray mouse lemurs

The role of olfaction/olfactory cues on photoperiodic responses was assessed in Malagasy primate, the gray mouse lemur. When exposed to short photoperiod (SP), this primate demonstrates rapid changes in energy balance as adaptive anticipatory response for winter survival. To follow early changes induced by SP exposure, body mass, food intake, resting metabolism (RMR) and free thyroxin levels in plasma (T4) were measured in males abruptly transferred to SP: six intact males (controls), eight males that underwent bilateral olfactory removal (BOX) and eight males exposed to male urinary cues (U-exposed). To assess the effect of SP exposure, two other groups were maintained for 6 weeks under LP: six controls and six BOX males. Whereas all studied parameters remained constant in controls and BOX males maintained under LP, exposure to SP led to different responses according to groups. In controls, SP exposure led to a regular increase in body mass and after 4 weeks under SP, plasma T4 levels, food consumption and RMR significantly decreased. Even if BOX males demonstrated hyperphagic patterns regardless of the photoperiod, an increase in body mass was also induced by SP exposure but without changes in RMR or food intake that were body mass-dependent. In U-exposed males, body mass gain was significantly reduced while food intake and RMR remained high. In both BOX and U-exposed males, SP exposure led to a transient but high increase in T4 levels compared to controls. These results suggest that olfaction/olfactory cues may delay the SP-mediated changes in energy balance.

Ontogenetic observations on the vomeronasal organ in two species of tamarins using neuron-specific beta-tubulin III

Callitrichid primates (tamarins, marmosets) have extreme variation in the vomeronasal organ (VNO), including ontogenetic differences in the neuroepithelium and vomeronasal duct (VND) patency at birth. Such differences render the timing and extent of VNO maturation debatable in callitrichids, but no studies have used neuron-specific immunohistochemical markers to address this question. The present study compared the number of VNO epithelial cells that express immunoreactivity to neuron-specific beta-tubulin III (BT), VNO length, and VNO cross-sectional area between two species of tamarins (Leontopithecus rosalia and Saguinus geoffroyi) that differed in perinatal VND patency. Neonatal lemurs and adult marmosets and bushbabies were also examined for a comparison to species previously shown to have a relatively large amount of VNO neuroepithelium and patent VNDs. The head of each specimen was serially sectioned in the coronal plane. Based on known rostrocaudal start/stop points of the VNO, selected unstained sections were used for BT protocols and area measurement at three percentiles (25th, 50th, 75th) in each specimen. Each section was photographed and enlarged for cell counts and measurement of cross-sectional epithelial area. In each specimen, the number of BT(+) cells in the VNO was counted at each percentile and expressed as a number per mm(2). Results indicated that lemur VNOs had a dense population of BT(+) cells at birth, but the VNO was more varied in the tamarin species. S. geoffroyi had few or no BT(+) cells in VNOs of neonates, which had fused VNDs, but had an increased BT(+) population by 1 and 2 months postnatal age, when the VND was patent. Of the species with patent VNDs at birth, neonatal L. rosalia had a denser population of BT(+) cells compared to S. geoffroyi, though not to the degree seen in neonatal lemurs or adult marmosets and bushbabies. These findings show that BT immunohistochemistry is a useful comparative method for the study of VNOs in subadult primates. Since the quantity of nonsensory VNO epithelium varies substantially between species, epithelial area measurements may be misleading, and BT(+) cell counts appeared to be the best quantitative method for comparing receptor neuron numbers among primates. It is suggested that the greater BT(+) cell population in L. rosalia at all subadult stages examined reveals an earlier maturation of the neuroepithelium compared to S. geoffroyi. Further investigation should consider whether this may relate to a comparatively brief subadult ontogeny and early onset of adult behaviors in L. rosalia compared to other tamarins studied to date.

Ontogenetic characteristics of the vomeronasal organ in Saguinus geoffroyi and Leontopithecus rosalia, with comparisons to other primates

It has been suggested that the variability of the primate vomeronasal organ (VNO) may be greater than previously thought, especially among New World monkeys. It is not clear to what extent VNO variation reflects ontogenetic, functional, or phylogenetic differences among primates. The present study investigated VNO anatomy in an ontogenetic series of two genera of callitrichid primates, in order to assess recent attempts to develop VNO character states and to examine the evidence for VNO functionality at different life stages. A sample of six Leontopithecus rosalia, one L. chrysomelas, and six Saguinus geoffroyi was serially sectioned and stained using various methods. Two adult Callithrix jacchus were also sectioned for comparative purposes. The VNO of each primate was examined by light microscopy along its entire rostrocaudal extent. VNOs of the tamarins were described to determine whether they fit into 1 of 3 character states recently attributed to various New World monkeys. At birth, the two species of tamarins differed in the nature of communication between the VNO and nasopalatine duct (NPD). Two of 3 neonatal S. geoffroyi exhibited a fused VNO duct in a more dorsal position (adjacent to the nasal cavity) compared to that of L. rosalia. The VNO duct communicated with the NPD and was patent in neonatal L. rosalia. Both species appeared to have an age-related increase in the amount of sensory epithelium in the VNO. Subadult L. rosalia had caudal regions of the VNO that were exceptionally well-developed, similar to those of strepsirhine primates. Compared to subadults, all adult callitrichids appeared to have more ventral communications of the VNO duct directly into the NPD. Adult S. geoffroyi and L. chrysomelas both had VNO sensory epithelium separated by multiple patches of nonsensory epithelium. This contrasted with the VNOs of C. jacchus, which had a nearly continuous distribution of receptors on all surfaces of the VNO. The findings indicate that tamarins have delayed maturation of the VNO epithelium, and that some species have little or no perinatal function. These results also suggest that ontogenetic changes in craniofacial form may alter the position of the VNO in tamarins. The present study supports the use of at least two character states to categorize the VNO of various callitrichids, but it is suggested that one of these, previously called "reduced sensory epithelium" should be instead termed "interrupted sensory epithelium." The distribution of VNO sensory epithelium does not appear to reflect phylogenetic influences; it is more likely a functional characteristic that varies throughout postnatal life. Therefore, this chemosensory system has a high degree of plasticity relating to age and function, which in some instances can confound the use of characteristics as phylogenetic traits. Further study is needed to quantify VNO receptors in various species to determine if functional differences exist and if some species have more precocious VNO function than others.

Matrilineal genetic structure within and among populations of the cooperatively breeding common marmoset, Callithrix jacchus

Common marmosets are members of the family Callitrichidae, South American primates characterized by highly social group living and cooperative breeding. In this study we analysed 1112 base pairs (bp) of the mitochondrial control region in 59 Callithrix jacchus individuals, sampled mainly from two geographically distinct field sites in N.E. Brazil. Analysis of molecular variation revealed a highly significant genetic structuring of haplotypes between social groups and between populations. Examination of matrilineal genetic structure within social groups revealed that seven of nine recorded breeding pairs were from different maternal lineages, indicating assortative mating and outbreeding. In addition to the breeders, at least six of 10 groups contained adult individuals from different matrilines, with five haplotypes present in one social group of nine animals. Groups of mixed lineages raise questions about potential reproductive conflicts of interest, and the extent of kin-selected altruism in the evolution and maintenance of cooperative breeding in this species.

Relaxed selective pressure on an essential component of pheromone transduction in primate evolution

The vomeronasal organ (VNO) detects pheromones in many vertebrate species but is likely to be vestigial in humans. TRPC2(TRP2), a gene that is essential for VNO function in the mouse, is a pseudogene in humans. Because TRPC2 is expressed only in the VNO, the loss of selective pressure on this gene can serve as a molecular marker for the time at which the VNO became vestigial. By analyzing sequence data from the TRPC2 gene of 15 extant primate species, we provide evidence that the VNO was most likely functional in the common ancestor of New World monkeys and Old World monkeys and apes, but then became vestigial in the common ancestor of Old World monkeys and apes. We propose that, at this point in evolution, other modalities, notably the development of color vision, may have largely replaced signaling by pheromones.

Sexual motivation in relation to social rank in pair-housed sows

The influence of social subordination on sexual motivation during oestrus was studied using 36 sows of which 24 treatment sows were housed in pairs and 12 control sows were housed individually in 12 and 6 m(2) pens, respectively. Video recordings were made from 07:00 h to 19:00 h during the first 2 days after grouping, which took place 3 days after weaning of the piglets. Based on the aggressive interactions between the pair-housed sows, their rank was determined. From day 4 after weaning, a test for sexual proceptive behaviour was carried out twice daily and back-pressure test was carried out four times daily in order to detect standing oestrus. When standing oestrus had occurred, transrectal ultrasonographical scans were also carried out in order to determine if ovulation took place. The proceptivity test took place in a T-maze with a 2 m x 10 m runway ending in two 1.5 m x 1.5 m goal boxes each adjacent to a stimulus compartment. One compartment contained an adult sexually experienced boar and the other was empty. Latency to and duration of time spent close to the boar and time spent presenting were recorded during the 10-min test period. On the first day that standing oestrus had been detected, a test for sexual receptivity was also carried out by introducing the sow to a mature boar in his home pen (9 m(2)). Sexual- and fear-related behaviour of sow and boar were recorded until mating was terminated or the sow had spent 5 min in the pen without mating being initiated. During oestrus the proceptivity test showed a significant increase (P < 0.05) in the time spent standing close to the boar and in presenting for single-housed sows and for pair-housed dominant sows, but not for subordinate sows. During oestrus subordinate sows spent significantly less time standing close to the boar than the dominant sows (P = 0.01) and the same tended to be the case for presenting (P = 0.07). In the receptivity test more subordinate sows than dominant sows fled (40% versus 0%, P = 0.001) and more subordinate sows than dominant sows squealed (58% versus 15%, P = 0.02) as a response to boar stimulation. In both tests, the single-housed sows differed neither from the dominant nor the subordinate sows. There was however no difference between the groups in the weaning to oestrous interval, duration of oestrus and number of piglet born. In addition, all the sows ovulated. The results indicate that social subordination can have significant consequences for sexual motivation in sows. Subordinate sows showed fear-related behaviour in response to boar stimulation even when they were in standing oestrus. Thus, both heat detection and mating may be impaired in subordinate sows. The results emphasise the importance to alleviate the social stress experienced by subordinates as well as the need for stock people to pay special attention to these animals when they are to be mated or inseminated.

Social regulation of gonadotropin-releasing hormone

Behavioral interactions among social animals can regulate both reproductive behavior and fertility. A prime example of socially regulated reproduction occurs in the cichlid fish Haplochromis burtoni, in which interactions between males dynamically regulate gonadal function throughout life. This plasticity is mediated by the brain, where neurons that contain the key reproductive regulatory peptide gonadotropin-releasing hormone (GnRH)change size reversibly depending on male social status. To understand how behavior controls the brain, we manipulated the social system of these fish,quantified their behavior and then assessed neural and physiological changes in the reproductive and stress axes. GnRH gene expression was assessed using molecular probes specific for the three GnRH forms in the brain of H. burtoni. We found that perception of social opportunity to increase status by a male leads to heightened aggressiveness, to increased expression of only one of the three GnRH forms and to increases in size of GnRH-containing neurons and of the gonads. The biological changes characteristic of social ascent happen faster than changes following social descent. Interestingly, behavioral changes show the reverse pattern:aggressive behaviors emerge more slowly in ascending animals than they disappear in descending animals. Although the gonads and GnRH neurons undergo similar changes in female H. burtoni, regulation occurs viaendogenous rather than exogenous social signals. Our data show that recognition of social signals by males alters stress levels, which may contribute to the alteration in GnRH gene expression in particular neurons essential for the animal to perform in its new social status.

Reappraisal of the vomeronasal system of catarrhine primates: ontogeny, morphology, functionality, and persisting questions

The vomeronasal organ (VNO) is a chemosensory organ that functions in sociosexual communication in many vertebrates. In strepsirhine primates and New World monkeys, the bilateral VNOs are traditionally understood to exist as a well-developed chemosensory epithelial unit. In contrast, the VNOs of catarrhine primates are thought to be absent or exist only as reduced epithelial tubes of uncertain function. However, the VNO of New World monkeys shows substantial variation in the extent of sensory epithelium. Recent findings that the chimpanzee (Pan troglodytes) possesses a VNO similar to humans suggest the variability of the VNO among haplorhine primates may be more extensive than previously thought, and perhaps more at par with that observed in chiropterans. The atypical histologic structure and location of the human/chimpanzee VNO suggest accessory glandular secretion and transport functions. Other catarrhine primates (e.g., Macaca spp.), may truly be characterized by VNO absence. Unique aspects of facial growth and development in catarrhine primates may influence the position or even presence of the VNO in adults. These recent findings demonstrate that previous investigations on some catarrhine primates may have missed the VNO and underestimated the extent of variability. As an understanding of this variation increases, our view of VNO functionality and associated terminology is changing. Further investigations are needed to consider phylogenetic implications of VNO variability and the association of craniofacial form and VNO anatomic position in primates.

Behavioral discrimination between circumgenital odor from peri-ovulatory dominant and anovulatory female common marmosets (Callithrix jacchus)

Social peer groups of callitrichid monkeys [marmosets and tamarins] exhibit intrasexual dominance hierarchies in captivity. This laboratory study employed two-choice behavioral discrimination bioassys to test the hypothesis that scent from female common marmosets contains chemical cues that permit discrimination between dominant females in the periovulatory versus luteal phase of the ovarian cycle and females holding dominant versus subordinate status. When scent from only dominant females was presented, marmosets directed significantly greater amounts of investigatory behavior toward peri-ovulatory scent versus scent collected during the luteal phase of the ovarian cycle. Animals of both sexes demonstrated significant discriminatory behavior between scent deposited by dominant versus subordinate females, but only when the dominant female was in the peri-ovulatory phase of the ovarian cycle. Test animals directed equal amounts of investigative behavior toward scent from luteal-phase dominant females and subordinate females. Female test subjects deposited significantly more scent marks over presented scents than did male subjects, particularly when the scent had been donated by a peri-ovulatory female. Chemical odors specific to the periovulatory and luteal phases of the ovarian cycle may play a role in mediating behavioral interactions among marmosets.

Adaptations to subordinate status in female marmoset monkeys

In singular cooperatively breeding mammals, social status is a key determinant of female reproductive success. Usually only one dominant female breeds in a social group. In the common marmoset (Callithrix jacchus), a cooperatively breeding primate, adaptations to nonbreeding subordinate status appear to parallel those found in social insect societies which demonstrate similar skew to the marmoset in female reproductive success. Female marmosets exhibit rank-related polyethism in behavior, reproductive neuroendocrinology and non-reproductive physiology, and subordinates participate in alloparental care and territory defense. Olfactory, visual and behavioral cues from dominant female marmosets provide important proximate cues regulating ovarian inhibition in female subordinates. Cooperatively breeding marmosets, therefore, appear to have developed specific neural and neuroendocrine adaptations to subordinate social status analogous to those found in social insects such as the lower wasps, bees and termites. Such parallel developments probably reflect the outcome of repeated convergent evolutionary attempts at adapting to environmental conditions not readily conducive to dispersal and independent breeding.

Behavioural suppression of female pine voles after replacement of the breeding male

Examination of the mechanism of reproductive suppression includes determining which cues are involved and the context in which they occur. We studied groups of pine voles, Microtus pinetorum, that were disrupted by the replacement of the breeding male and compared them with intact family groups. If reproductive suppression is mediated by chemical cues, then soiled bedding should be sufficient to prevent production of litters by daughters. If reproductive suppression involves a behavioural component, we should observe aggressive behaviours or those indicative of dominance interactions directed from the mother towards the daughter or the replacement male. If replacement of the breeding male leads to conflict between the breeding female and her daughter, then more aggression or dominance interactions would be expected in disrupted than in intact families. The presence of the mother decreased reproduction by daughters, but chemical cues alone were not sufficient to prevent the daughter from mating with the replacement male. Rather, this decrease in reproduction seemed to be mediated by behavioural interactions. We propose that the mother's tugging on the daughter may lead to subordination of the daughter. The mother's presence may also alter the behaviour patterns of the male and daughter, which could delay reproductive activation of the daughter, prevent the formation of pair bonds or inhibit sexual behaviour. These behavioural interactions appear to depend on the presence of an unfamiliar male, because tugging, for example, was less frequent in intact family groups. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

Combined olfactory contact with the parent colony and direct contact with nonbreeding animals does not maintain suppression of ovulation in female naked mole-rats (Heterocephalus glaber)

The study investigated the role of odor cues from two naked mole-rat colonies, in conjunction with behavioral cues from nonbreeding colony members, in maintaining suppression of ovulation in subordinate female naked mole-rats isolated from the two parent colonies. Four high ranking nonbreeding female naked mole-rats were removed from their respective parent colonies and singly housed in separate burrow systems. For a 64-day period, the removed females were maintained in daily odor contact with their parent colony by daily rotating soiled bedding material between the parent colony and the burrow systems of removed females. In addition, subsets of nonbreeding animals from the respective parent colony were regularly moved into the burrow systems of removed females for 2-day periods during this 64-day period. Removed females were therefore in continual social contact with subsets of parent colony animals except for the breeding pair. All four removed females exhibited raised levels of urinary progesterone (< 2 ng/mg Cr) indicative of the onset of ovarian function within 3 days of being separated from the parent colony. Removed females exhibited a normal ovulatory cycle with levels of progesterone remaining elevated for 25-35 days (mean concentration of progesterone +/- SEM; 16.2 +/- 2 ng/mg Cr). Initiation of aggression and sexual behavior by removed females increased significantly when they were isolated from the parent colony. The results demonstrated that odor cues from the complete colony in conjunction with behavioral/tactile/vocal cues from the nonbreeding colony members were not the major cues maintaining reproductive suppression in nonbreeding female naked mole-rats. Instead, our results suggest that female reproductive suppression in naked mole-rats is caused by a dominance-related behavioral mechanism requiring direct contact with the breeding female.

Social and developmental influences on reproductive function in female Wied's black tufted-ear marmosets (Callithrix kuhli)

Although marmoset social groups may contain multiple adult females, reproduction is typically limited to one breeding female. A variety of endocrine and behavioral mechanisms have been identified that regulate fertility among female marmosets. In the present study, we assessed the mechanism(s) by which fertility is regulated in female black tufted-ear marmosets, Callithrix kuhli. The reproductive status of 10 daughters aged 2-24 months was evaluated by measuring concentrations of urinary pregnane-diol 3 alpha glucuronide (PdG) and luteinizing hormone (LH). Concentrations of the two hormones were typically low in daughters less than 12 months of age, and the profiles suggested anovulation (mean PdG < 2 micrograms/mg Cr and mean LH < 6 ng/mg Cr). Concentrations of PdG rose dramatically in females older than 12 months. Eight subadult daughters commenced ovulatory function while still living with their family, and the remaining two failed to ovulate. The onset of ovarian function coincided with a change in the social environment in two females, but the remaining six females commenced spontaneous ovarian activity that was not associated with any social or environmental factor (mean age: 15.6 +/- 1.6 months). Ovulatory function was monitored in five daughters while housed in their natal family group, while removed from the natal family group and housed singly, and while paired with an unrelated and unfamiliar male. The ovarian cycles of these females housed in the natal group were characterized by significantly shorter luteal phases and reduced PdG concentrations, relative to when the females were housed on their own, and relative to adult breeding females (n = 6). Stimulatory cues from unfamiliar males were not necessary to trigger regular ovarian function in females. In this species, the regulation of fertility in daughters is a complex combination of behavioral and endocrine factors.

Seasonality in squirrel monkeys (Saimiri sciureus): social facilitation by females

The extent to which social living arrangements influenced seasonal changes in physiology and behavior was examined in adult squirrel monkeys (Saimiri sciureus). Data were collected over 20 months (encompassing two breeding seasons) from animals that were housed in three mixed-sex social configurations that varied in the number of heterosexual and isosexual social partners. For both sexes, the presence of multiple females was found to facilitate reproduction. Females housed with other females were more likely to exhibit seasonal ovarian cyclicity and tended to have higher conception rates. Social facilitation of reproduction was particularly prominent for subordinate females. The presence of same-sex companions also resulted in reduced adrenocortical output in females during the first nonbreeding season. In males, the availability of multiple females increased plasma testosterone levels, except in the presence of more dominant males. Seasonal increases in male weight coincided with increased cortisol levels and were most prominent in social groups containing multiple females. The influence of multiple females on male seasonality occurred despite the finding that male-female interactions were infrequent and, in fact, occurred less frequently when isosexual partners were available. Unexpectedly, affiliative social interactions between same-sex and opposite-sex partners occurred less frequently during the breeding season. As expected, behaviors associated with sex tended to increase during the breeding season. Very little agonism was observed during the course of the study and there was no evidence of interanimal competition for mates.