Fishy Aroma of Social Status: Urinary Chemo-Signalling of Territoriality in Male Fathead Minnows (Pimephales promelas)

Chemical structures of several urinary reproductive pheromones in fish have been identified, and their role in the chemical communication of reproductive condition is well characterized. On the contrary, the role of chemical communication in signalling of social/territorial status in fish is poorly understood. Fathead minnows are an example of a fish species whose life history traits appear conducive to evolution of chemical communication systems that confer information about social/territorial status. Male reproduction in this species is dependent upon their ability to acquire and defend a high quality nesting territory, and to attract a female to the nest. We hypothesized that fathead minnow males use visual and urine-derived chemical cues to signal territorial status. To test this hypothesis, effects of territorial acquisition on male-specific secondary sex characteristics (SSCs) and urine volumes were first assessed. Second, frequencies of male urination in varying social contexts were examined. Finally, nuclear magnetic resonance-based metabolomics was used to identify urinary metabolites that were differentially excreted in the urine of territorial versus non-territorial males. The expression of SSCs, sperm, and urine volumes increased with territory acquisition, and either remained unchanged or decreased in non-territorial males. Frequency of male urination increased significantly in the presence of females (but not males), suggesting that females are the main target of the urinary signals. Territorial and non-territorial males had distinct urinary metabolomic profiles. An unforeseen finding was that one could discern future territorial status of males, based on their initial metabolomic profiles. Bile acids and volatile amines were identified as potential chemical signals of social status in the fathead minnow. The finding that trimethylamine (a fishy smelling volatile amine) may be a social cue is particularly interesting, because it is known to bind trace amine-associated receptors, indicating that these receptors may play role in chemical signalling of social status in fish.     

Modulation of behavior in zebrafish,Danio rerio,according to female reproductive status and visual and chemical cues

Zebrafish, Danio rerio, is one of the most studied vertebrate models. However, there are still many aspects of its reproductive behavior to be elucidated. The aim of this work was to clarify whether males and females of this species display different behaviors according to sexual status, and the kind of cues they were exposed to (visual and/or chemical). Females in two different sexual status, pre- (PreS) or post-spawning (PostS), were exposed to single males cues (visual or chemical) or complementary cues (visual and chemical together). PreS females spent more time near the male’s compartment than PostS when they were exposed to complementary cues, but no differences were found when only one cue was present. Males showed a higher proximity to females when they were exposed to visual, and both cues together, but no difference was found according to females’ reproductive status. When no barrier was present, males and PreS females spent more time swimming together than males with PostS females. These results showed that females’ reproductive status, and the kind of cues to which females and males are exposed to, can modulate behaviors related to reproduction. Particularly, both cues together (visual and chemical) are necessary to trigger different behaviors in females according to their reproductive status.     

The ability of the amphipod Corophium volutator (Pallas) to follow chemical signals from con-specifics

The amphipod Corophium volutator (Pallas) is a tube-dwelling species that only occasionally leaves its burrow. Animals that do crawl on the sediment are mainly males, apparently in search of females. This study was designed to determine whether C. volutator males and females release chemical signals that attract con-specifics, and if so, whether these signals are gender specific. Laboratory experiments were conducted on the over-wintering generation during their reproductive season, using a Y-maze choice test apparatus. The results show that C. volutator females release chemical signals that attract males. In the field, the attractant may guide males in search of burrowed females. In addition, male odour tends to attract males, while females do not follow chemical signals from con-specifics. We thereby show on gender-specific chemical attraction of this species.     

Mating Signals Indicating Sexual Receptiveness Induce Unique Spatio-Temporal EEG Theta Patterns in an Anuran Species

Female mate choice is of importance for individual fitness as well as a determining factor in genetic diversity and speciation. Nevertheless relatively little is known about how females process information acquired from males during mate selection. In the Emei music frog, Babina daunchina, males normally call from hidden burrows and females in the reproductive stage prefer male calls produced from inside burrows compared with ones from outside burrows. The present study evaluated changes in electroencephalogram (EEG) power output in four frequency bands induced by male courtship vocalizations on both sides of the telencephalon and mesencephalon in females. The results show that (1) both the values of left hemispheric theta relative power and global lateralization in the theta band are modulated by the sexual attractiveness of the acoustic stimulus in the reproductive stage, suggesting the theta oscillation is closely correlated with processing information associated with mate choice; (2) mean relative power in the beta band is significantly greater in the mesencephalon than the left telencephalon, regardless of reproductive status or the biological significance of signals, indicating it is associated with processing acoustic features and (3) relative power in the delta and alpha bands are not affected by reproductive status or acoustic stimuli. The results imply that EEG power in the theta and beta bands reflect different information processing mechanisms related to vocal recognition and auditory perception in anurans.     

Surface Chemicals Inform about Sex and Breeding Status in the Biparental Burying Beetle Nicrophorus vespilloides

The multicomponent nature of chemical cues and signals are not very well understood. One reason for the often found complexity of chemical blends might be that they provide multiple messages. Burying beetles which use vertebrate carcasses as food for their larvae and defend these carcasses against inter- and intraspecific competitors are able to recognise the sex and breeding status of conspecifics. Studies have shown that the chemical composition of cuticular lipids is correlated with sex and breeding status, but there is no definitive evidence that these chemicals function in recognition. In the present study, we performed behavioural bioassays to directly asses the role of chemical cues in the recognition system of the burying beetle Nicrophorus vespilloides . After finding a carcass, females were more tolerant of dead males than of females. The behaviour was reversed when a solvent extract from the opposite sex was applied. An earlier experiment had shown that females breeding on a carcass treat non-breeding males more aggressively than breeding ones. In the present study, we could trigger the same dichotomous behaviours by presenting a single elytron from a breeding and a non-breeding beetle. In an additional experiment, females tolerated the elytra of non-breeding beetles if we had first applied an extract from a breeding beetle to these elytra. Our study is the first behavioural proof that female burying beetles obtain multiple information from chemical cues.     

Variation in cuticular hydrocarbon signatures, hormonal correlates and establishment of reproductive dominance in a polistine wasp

In many social insects the relationship between reproductive dominance and physiological correlates is poorly understood. Recent evidence now strongly suggests that cuticular hydrocarbons are important in reproductive differentiation in these societies where they are used as signals of ovarian activity in reproductive females. In this study we investigated the relationship between reproductive dominance, size of the corpora allata (CA, producer of Juvenile Hormone, JH) and the proportions of cuticular hydrocarbons present on the cuticle in overwintering foundresses and both associative (polygynous) and solitary (monogynous) pre-emergence colonies of the social wasp Polistes dominulus. Size of the CA was positively correlated with ovarian development in polygynous colonies. In contrast, solitary foundresses possessed significantly smaller CAs than dominant foundresses from polygynous nests, yet ovarian activity was similar for both female types. CA size variation was associated with variation in cuticular hydrocarbon proportions. Overwintering, solitary, dominant and subordinate (from associative nests) females all possessed distinctive cuticular chemical profiles revealed by multivariate discriminant analyses. Our data indicate that the social environment strongly affects reproductive physiology in this wasp, and we discuss the role of cuticular hydrocarbons in reproductive signaling in P. dominulus and other social insects.     

Chemical recognition of conspecifics in a neotropical lizard, <Emphasis Type="Italic">Liolaemus pacha</Emphasis> (Iguania: Liolaemidae): relation to visual displays,season and sex

Chemical cues play an important role in sexual recognition in several lizard species. Here, we investigated whether the neotropical lizard, Liolaemus pacha (Iguania: Liolaemidae) can discriminate between chemical information obtained from males or females. In addition, we also considered the effect of season (reproductive vs. post-reproductive) and the sex of the tested individual. We experimentally tested scent discrimination, using a terrarium previously occupied by a male, a female, and an untreated terrarium as control as sources of different chemical scents. We counted the number of tongue flicks, a measure of chemical exploratory behavior, and the visual displays triggered by these scents for 10 min. Males performed significantly more tongue flicks when female scent was present than when male and control scents were present, indicating sexual recognition. However, females did not show a significant difference in those same conditions, indicating a lack of sexual recognition. For visual displays, males showed significantly higher rates to female and male scents than to control, whereas females did not show any difference. During the reproductive season, the number of tongue flicks and visual displays were higher than during the post-reproductive season. Our results suggest that for male L. pacha, chemical cues play an important role in mate recognition. We discuss the apparent lack of recognition in females. We suggest that the observed seasonal behavioral differences might be associated with physiological changes related mainly to reproduction.     

Intraspecific communication through chemical signals in female mice: reinforcing properties of involatile male sexual pheromones

In rodents, social and reproductive behaviors critically depend on chemical signals, including sexual pheromones that have been suggested (but not demonstrated) to be rewarding. In this work, we analyze this issue by studying the chemoinvestigatory behavior of adult female mice (without experience with male-derived chemicals) toward 1) the synthetic odorant citralva, 2) bedding soiled by different conspecifics (females, males, and castrated males), and 3) volatiles derived from bedding soiled by males and castrated males (confronted in 2-choice tests). We also study whether these chemical signals are able to induce conditioned place preference, a reliable test for rewarding properties of stimuli. The results show that involatile, male-derived chemicals elicit an intense and sustained chemoinvestigation and, more importantly, are the only tested chemical signals that induce conditioned place preference. In contrast, volatile, male-derived chemicals are not significantly chemoinvestigated. Bedding soiled by castrated males induces a transient chemoinvestigation, likely directed to steroid-independent, biologically relevant chemical signals, whereas the intense chemoinvestigation of female-soiled bedding shows a slow habituation. Finally, females did not explore significantly citralva-odorized bedding. The present work constitutes the first demonstration of the unconditioned reinforcing properties of involatile (likely detected by the vomeronasal organ) steroid-dependent chemical signals in mammals.     

Queen reproduction, chemical signalling and worker behaviour in polygyne colonies of the ant Formica fusca

Potential reproductive conflicts are common in social insects and may occur between and within castes. In multiqueen (polygyne) colonies of ants, reproductive conflicts among coexisting queens may be resolved by aggressive interactions and/or by pheromonal signalling. Pheromonal signals may be directed at workers, which may adjust the reproductive shares of queens behaviourally. Workers are expected to favour a queen that is more likely to be their mother and to produce offspring of close kin to them. We used microsatellite markers to study reproductive partitioning between cobreeding Formica fusca queens in a laboratory experiment where workers received a choice between two queens. We expected queens of this species to communicate their reproductive status by chemical communication, because no aggressive interactions between queens have been observed. We found that queens of different reproductive status (with majority, minority or no production) differed in their cuticular hydrocarbon (CHC) profiles. The fecundity of a queen was associated with worker behaviour; the higher a queen's fecundity, the more attention she received from workers. Our results suggest that a queen fecundity signal is encoded in her CHC profile and acts as a pheromone for workers, which respond to the signal by discriminating between queens. Copyright 2002 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour     

Female and male visually based mate preferences are consistent with reproductive isolation between populations of the Lake Malawi endemic Labeotropheus fuelleborni

Sexual selection via female mate choice is thought to have played a key role in the speciation of haplochromine cichlids, but a dominant role for visual signals in such processes has lately been called into question. In addition, the possible role of male mating preferences in haplochromine speciation has been little studied. We studied patterns of both female and male mate choice, based exclusively on visual signals, in order to evaluate potential reproductive isolation between two populations of the Lake Malawi haplochromine Labeotropheus fuelleborni. In the first experiment, females were allowed to choose between two males, one from the same population and the other allopatric with respect to the female. Females in this experiment responded more frequently to males from their own population. Similarly, the males in these trials displayed more frequently when presented with females of their own population. In the second experiment, a female was allowed to choose between two males, either both from her own population or both allopatric. In these trials, both males and females from the Katale population interacted significantly more frequently in settings in which all three individuals were from the same population ("same-population trios"), and those from the Chipoka population showed a similar trend. Thus, patterns in both male and female courtship behavior suggest that visual signals contribute to at least incipient reproductive isolation between populations of L. fuelleborni [Current Zoology 56 (1): 65-72 2010].     

Ontogeny of cephalic volatile patterns in queens and mating biology of the neotropical stingless bee,Scaptotrigona postica

Summary

Chemical communication is an ancient yet still immensely important part of reproduction. Amongst all invertebrates, the most sophisticated “chemical languages” are used by social insects. Here the sex- and caste-specific pheromonal messages consist of multicomponent mixtures. In the neotropical stingless bee Scaptotrigona postica, an inhabitant of dense tropical rain forests, the cephalic volatiles of a queen transmit information on her reproductive status to males. A distinct ontogenetic pattern of the queen pheromone composition allows drones to discriminate receptive virgins which are then chased during the short nuptial flight through the forest understorey. By means of gas chromatographic/mass spectroscopic analyses, the numerous volatile compounds found in pentane extracts of individual bee heads could be identified. Qualitative as well as quantitative changes of these volatiles in the course of imaginal development could be determined, and bioassays with synthetic compounds were undertaken in order to decode the chemical signals used during the short encounter of a young queen and her mate.     

Detection of female mating status using chemical signals and cues

Males of many species choose their mate according to the female's reproductive status, and there is now increasing evidence that male fitness can depend on this discrimination. However, females will also aim to regulate their mating activity so as to maximize their own fitness. As such, both sexes may attempt to dictate the frequency and timing of female mating, reflecting the potentially different costs of female signaling to both sexes. Here, I review evidence that chemical cues and signals are used widely by males to discriminate between mated and unmated females, and explore the mechanisms by which female odour changes post‐mating. There is substantial empirical evidence that mated and unmated females differ in their chemical profile, and that this variation provides males with information on a female's mating status. Although there appears to be large variation among species regarding the mechanisms by which female odour is altered post‐mating, the transfer of male substances to females during or subsequent to copulation appear to play a major role. This transfer of substances by males may be part of their strategy to suppress reproduction by competing males, particularly in species where females mate more than once.     

Costly major histocompatibility complex signals produced only by reproductively active males,but not females,must be validated by a ‘maleness signal’ in three-spined sticklebacks

Olfactory information about individual major histocompatibility complex (MHC) immune genotypes is important for mate choice in several species. For example, during the mate choice decisions of three-spined sticklebacks, females assess males on the basis of odour cues that convey information about their MHC diversity. Here, we show that an additional ‘maleness’ signal is needed to validate the MHC signal. Furthermore, using interaction between natural odour of sticklebacks and synthetic MHC-ligand peptides, we show that MHC signals are conditional on the reproductive state in males. By contrast, we find that gravid females do not produce such signals. Since MHC olfactory signals relevant to mate choice decisions are conditional upon gender and reproductive state, we suggest that their manufacture is likely to be costly to senders, and therefore, potentially conditional on the health/parasitization status of the sender. We hypothesize that shedding of peptide–MHC complexes compromises immune function, selecting against unconditional use of these signals.     

Condition-dependent chemosignals in reproductive behavior of lizards

This article is part of a Special Issue “Chemosignals and Reproduction”.Many lizards have diverse glands that produce chemosignals used in intraspecific communication and that can have reproductive consequences. For example, information in chemosignals of male lizards can be used in intrasexual competition to identify and assess the fighting potential or dominance status of rival males either indirectly through territorial scent-marks or during agonistic encounters. Moreover, females of several lizard species “prefer” to establish or spend more time on areas scent-marked by males with compounds signaling a better health or body condition or a higher genetic compatibility, which can have consequences for their mating success and inter-sexual selection processes. We review here recent studies that suggest that the information content of chemosignals of lizards may be reliable because several physiological and endocrine processes would regulate the proportions of chemical compounds available for gland secretions. Because chemosignals are produced by the organism or come from the diet, they should reflect physiological changes, such as different hormonal levels (e.g. testosterone or corticosterone) or different health states (e.g. parasitic infections, immune response), and reflect the quality of the diet of an individual. More importantly, some compounds that may function as chemosignals also have other important functions in the organism (e.g. as antioxidants or regulating the immune system), so there could be trade-offs between allocating these compounds to attending physiological needs or to produce costly sexual “chemical ornaments”. All these factors may contribute to maintain chemosignals as condition-dependent sexual signals, which can inform conspecifics on the characteristics and state of the sender and allow making behavioral decisions with reproductive consequences. To understand the evolution of chemical secretions of lizards as sexual signals and their relevance in reproduction, future studies should examine what information the signals are carrying, the physiological processes that can maintain the reliability of the message and how diverse behavioral responses to chemosignals may influence reproductive success.     

Male mate choice based on chemical cues in the cricket Acheta domesticus (Orthoptera: Gryllidae)

1. Males in many animal species exercise mate choice to maximise their reproductive success, assessing females by characteristics related to reproductive potential, such as mating status, body size, and age. The sensory modalities involved in mate choice are often not firmly demonstrated, but only inferred. This is especially true for chemical cues and signals. 2. The present study tests whether males of the cricket Acheta domesticus are able to choose among females based only on chemosensory cues. In A. domesticus, as in many crickets, males call to attract females or roam the habitat silently to search for females. In three‐way choice trials, males were presented with two filter papers that had been placed with females for 24 h prior to the trials and one blank control. Females were either mated or virgin and starved or well‐fed. It was predicted that males would prefer virgin over mated females and those in good condition over starved ones. 3. Males were more likely to contact filters that had been exposed to females. They spent more time examining filter papers from virgin females than those from mated ones, while the condition of the females had no effect. 4. We conclude that males can detect chemical cues from females on substrate and distinguish virgin females from mated ones. Being able to assess sperm competition risk prior to mating or even before further pursuing a trail with chemical cues should confer a considerable benefit to males.     

Mothers matter! Maternal support,dominance status and mating success in male bonobos (Pan paniscus)

Variation in male mating success is often related to rank differences. Males who are unable to monopolize oestrous females alone may engage in coalitions, thus enhancing their mating success. While studies on chimpanzees and dolphins suggest that coalitions are independent of kinship, information from female philopatric species shows the importance of kin support, especially from mothers, on the reproductive success of females. Therefore, one might expect a similar effect on sons in male philopatric species. We evaluate mating success determinants in male bonobos using data from nine male individuals from a wild population. Results reveal a steep, linear male dominance hierarchy and a positive correlation between dominance status and mating success. In addition to rank, the presence of mothers enhances the mating success of sons and reduces the proportion of matings by the highest ranking male. Mothers and sons have high association rates and mothers provide agonistic aid to sons in conflicts with other males. As bonobos are male-philopatric and adult females occupy high dominance status, maternal support extends into adulthood and females have the leverage to intervene in male conflicts. The absence of female support to unrelated males suggests that mothers gain indirect fitness benefits by supporting their sons.     

Environmental and social determinants of sexual function in the male lesser mouse lemur (Microcebus murinus).

Environmental factors that regulate the sexual activity of male lesser mouse lemurs have been studied experimentally with more than 60 captive animals over an 8-year period. In this nocturnal Malagasy prosimian, variation in day length is the primary factor controlling seasonal sexual activity. Plasma testosterone concentrations were low (= 9 ng/ml) during short days and reached 60 ng/ml during long days (> 12-hour day). This cyclic pattern persists unchanged when artificial photoperiodic rhythms are applied and is not altered by ageing. The timing of puberty is also regulated by photoperiodic changes. Nevertheless, the sexual activity of the male lesser mouse lemur can be dramatically modified by the social environment. In heterosexual groups, behavioural and physiological components of sexual activity are depressed in all males except the dominant one, whose aggressive interactions are always successful. Intermale sexual inhibition was shown to be mediated by chemical cues present in the urine of dominant or isolated males but not in urine of subordinate individuals. The inhibitory signals possess lipophilic properties and are not contingent on the gonadal activity of the urine donor but are linked to adrenocortical activity. By contrast, chemical signals stimulating the reproductive function of all males are found in the urine of females, the presence of which is required for the establishment of clear dominance among grouped males. Endocrine mechanisms underlying intermale sexual inhibition by chemical cues were analysed. Variations in prolactin strongly suggest that olfaction interacts with the photoperiodic regulation of reproductive function, leading to changes in the sensitivity of the negative feedback effect of testosterone on gonadotrophin secretion. Inhibitory or stimulatory effects of chemical signals are discussed in the context of their functional significance for wild populations.     

Preference for Male Traits Differ in Two Female Morphs of the Tree Lizard,Urosaurus ornatus

Non-random female mating preferences may contribute to the maintenance of phenotypic variation in color polymorphic species. However, the effect of female preference depends on the types of male traits used as signals by receptive females. If preference signals derive from discrete male traits (i.e., morph-specific), female preferences may rapidly fix to a morph. However, female preference signals may also include condition-dependent male traits. In this scenario, female preference may differ depending on the social context (i.e., male morph availability). Male tree lizards (Urosaurus ornatus) exhibit a dewlap color polymorphism that covaries with mating behavior. Blue morph males are aggressive and defend territories, yellow males are less aggressive and defend smaller territories, and orange males are typically nomadic. Female U. ornatus are also polymorphic in dewlap color, but the covariation between dewlap color and female behavior is unknown. We performed an experiment to determine how female mate choice depends on the visual and chemical signals produced by males. We also tested whether female morphs differ in their preferences for these signals. Female preferences involved both male dewlap color and size of the ventral color patch. However, the female morphs responded to these signals differently and depended on the choice between the types of male morphs. Our experiment revealed that females may be capable of distinguishing among the male morphs using chemical signals alone. Yellow females exhibit preferences based on both chemical and visual signals, which may be a strategy to avoid ultra-dominant males. In contrast, orange females may prefer dominant males. We conclude that female U. ornatus morphs differ in mating behavior. Our findings also provide evidence for a chemical polymorphism among male lizards in femoral pore secretions.     

A chemical signal of offspring quality affects maternal care in a social insect

Begging signals of offspring are condition-dependent cues that are usually predicted to display information about the short-term need (i.e. hunger) to which parents respond by allocating more food. However, recent models and experiments have revealed that parents, depending on the species and context, may respond to signals of quality (i.e. offspring reproductive value) rather than need. Despite the critical importance of this distinction for life history and conflict resolution theory, there is still limited knowledge of alternative functions of offspring signals. In this study, we investigated the communication between offspring and caring females of the common earwig, Forficula auricularia, hypothesizing that offspring chemical cues display information about nutritional condition to which females respond in terms of maternal food provisioning. Consistent with the prediction for a signal of quality we found that mothers exposed to chemical cues from well-fed nymphs foraged significantly more and allocated food to more nymphs compared with females exposed to solvent (control) or chemical cues from poorly fed nymphs. Chemical analysis revealed significant differences in the relative quantities of specific cuticular hydrocarbon compounds between treatments. To our knowledge, this study demonstrates for the first time that an offspring chemical signal reflects nutritional quality and influences maternal care.     

Familiarity affects the assessment of female facial signals of fertility by free-ranging male rhesus macaques

Animals signal their reproductive status in a range of sensory modalities. Highly social animals, such as primates, have access not only to such signals, but also to prior experience of other group members. Whether this experience affects how animals interpret reproductive signals is unknown. Here, we explore whether familiarity with a specific female affects a male's ability to assess that female's reproductive signals. We used a preferential looking procedure to assess signal discrimination in free-ranging rhesus macaques, a species in which female facial luminance covaries with reproductive status. We collected images of female faces throughout the reproductive cycle, and using faecal hormone analysis to determine ovulation, categorized images as coming from a female's pre-fertile, ovulating, or post-fertile period. We printed colour-calibrated stimuli of these faces, reproducing stimuli perceptually the same in colour and luminance to the original appearance of females. These images were presented to males who were either unfamiliar or familiar with stimuli females. Overall, males distinguished ovulatory from pre-ovulatory faces. However, a significant proportion of males did so only among males familiar with stimuli females. These experiments demonstrate that familiarity may increase a receiver's ability to use a social partner's signals to discern their reproductive status.