Vocal signaling is one of many behaviors that animals perform during social interactions. Vocalizations produced by both sexes before mating can communicate sex, identity and condition of the caller. Adult golden hamsters produce ultrasonic vocalizations (USV) after intersexual contact. To determine whether these vocalizations are sexually dimorphic, we analyzed the vocal repertoire for sex differences in: 1) calling rates, 2) composition (structural complexity, call types and nonlinear phenomena) and 3) acoustic structure. In addition, we examined it for individual variation in the calls. The vocal repertoire was mainly composed of 1-note simple calls and at least half of them presented some degree of deterministic chaos. The prevalence of this nonlinear phenomenon was confirmed by low values of harmonic-to-noise ratio for most calls. We found modest sexual differences between repertoires. Males were more likely than females to produce tonal and less chaotic calls, as well as call types with frequency jumps. Multivariate analysis of the acoustic features of 1-note simple calls revealed significant sex differences in the second axis represented mostly by entropy and bandwidth parameters. Male calls showed lower entropy and inter-quartile bandwidth than female calls. Because the variation of acoustic structure within individuals was higher than among individuals, USV could not be reliably assigned to the correct individual. Interestingly, however, this high variability, augmented by the prevalence of chaos and frequency jumps, could be the result of increased vocal effort. Hamsters motivated to produce high calling rates also produced longer calls of broader bandwidth. Thus, the sex differences found could be the result of different sex preferences but also of a sex difference in calling motivation or condition. We suggest that variable and complex USV may have been selected to increase responsiveness of a potential mate by communicating sexual arousal and preventing habituation to the caller.

Why some females choose to mate with a 'preferred' male, whereas others choose to mate with an 'inferior' male is not always clear. Generally, the choosiness of females is thought to decline with advanced age, but relatively few studies have investigated this concept, and reports of this phenomenon in mammals are lacking. To address this deficiency, young and old female golden hamsters were evaluated for their preference for dominant vs. subordinate males. Females observed male dyads as a dominance relationship was established. Dominant and subordinate males were then placed within enclosures at the opposite ends of a Y-maze, and the first approach, scent marking, and time spent near each male were evaluated in young and old females during pro-oestrus-a time when females solicit visits by prospective mates by leaving vaginal and flank scent marks. Whereas the proportion of time spent near the dominant male was significantly greater than random for both young and old females, the proportions of vaginal and flank scent marks left for the dominant male were significantly greater than random for young females, but not for old females. Overall, these results are consistent with a decline in the preference for dominant males by old female hamsters.

Reproductive interference includes any interspecific interaction that reduces the fitness of one or both species involved. There are several types of reproductive interference, but they normally involve the direct cost of interacting or mating with heterospecifics. An indirect cost of interacting with heterospecific individuals is a consequent reduction in successful interactions with conspecifics. We tested the hypothesis that being aggressive towards a heterospecific individual will diminish sexual responses towards conspecifics in later encounters. We used two species of Mesocricetus hamsters (Syrian and Turkish hamsters), whose interspecific interactions have previously been determined. We exposed or both exposed and paired Syrian hamster females with a conspecific or a heterospecific male. Five minutes later, we paired all females with a conspecific male and measured the latency to lordosis, the duration of lordosis and any incidence of aggression. We found that (1) interactions with heterospecific males did not affect how females responded to conspecific males in later encounters and (2) previous pairing of female subjects with either conspecific or heterospecific males promoted a faster sexual response by females in subsequent interactions with conspecific males. Thus, aggressive interactions of Syrian hamster females with heterospecific males, contrary to our initial hypothesis, had a positive effect on subsequent interactions with conspecific males.

Interspecific mating normally decreases female fitness. In many species, females avoid heterospecific males innately or by imprinting on their parents. Alternatively, adult females could learn to discriminate against heterospecific males after exposure to such males. For example, Syrian hamster (Mesocricetus auratus) females learn to discriminate between conspecific males and Turkish hamster (M. brandti) males during adulthood by exposure to males of both species. Adult females not previously exposed to Turkish hamster males will mate similarly with conspecific and heterospecific males. However, in a previous study we showed that exposure to a heterospecific male and a conspecific male for 8 days led to mating avoidance and aggression towards the heterospecific male. Here we conducted two experiments to investigate how much exposure to the heterospecific male was required for females to avoid mating with the heterospecific male (Experiment 1) and how long that avoidance lasted in the absence of continuous exposure to heterospecific stimuli (Experiment 2). Fast and durable learning would indicate the evolution of an efficient avoidance response. In Experiment 1, females were exposed to a heterospecific male for 1, 4 h, 4 or 8 days and then paired with that male. We found more avoidance of interspecific mating after 4 or 8 days of exposure than after 1 or 4 h of exposure. In Experiment 2, females were exposed to a heterospecific male for 8 days and then paired with that male either 10 min later or 8 days later. We found that after an 8-day delay females were highly sexually receptive to the heterospecific male. Additionally, a comparison between the current experiments and a previous study indicates that female Syrian hamsters do not require concurrent exposure to a conspecific male and a heterospecific male to learn to avoid interspecific mating; exposure to a heterospecific male is sufficient.

Adult Syrian hamster females (Mesocricetus auratus) learn to discriminate against familiar heterospecific males (Turkish hamster, M. brandti). We investigated whether females learn to avoid any heterospecific male after exposure to just one heterospecific male. We predicted that, after being exposed to one heterospecific male, a female would avoid mating not only with that familiar male but also with any unfamiliar heterospecific male. We exposed females to a heterospecific male across a wire-mesh barrier for 8 days and then paired the female with (a) that same heterospecific male or (b) an unfamiliar heterospecific male. Females exhibited lordosis faster and for a longer duration toward the unfamiliar than toward the familiar heterospecific male. However, females were similarly aggressive toward familiar and unfamiliar heterospecific males. Perhaps exposure to stimuli from several heterospecific males (a likely scenario in the wild) would result in females behaving similarly toward familiar and unfamiliar heterospecific males.

Testosterone has long been implicated in aggression. However, evidence for its role is contentious. This study examined the influence of testosterone on aggression but also aimed to further explore the effect of previous social stimuli on the outcome of malemale fights. Experimental males were exposed to animal stimuli (males, diestrus females, or estrous females) through a mesh barrier, and then testosterone levels were measured. The following day, control males with no prior exposure fought experimental males, and fighting behavior was recorded. It was hypothesized that exposure to social stimuli, especially exposure to estrous females, would induce testosterone surges in males. These surges would increase aggression in fights, thereby improving fighting ability in males with prior exposure. It was predicted that higher aggression would translate into experimental males winning significantly more fights than their control counterparts. However, results were rather ambiguous. A significant testosterone surge in males was only found after exposure to diestrus females. Males exposed to estrous females exhibited nearly significant testosterone surges, whereas males exposed to other males showed no significant changes in testosterone. The significant testosterone rise in males exposed to diestrus females did seem to increase aggression during fights compared to males with only male exposure. However, this did not predict the outcomes of the fights as expected.

In many species, agonistic interactions result in social relationships that are stable over time. In Syrian hamsters, two unfamiliar males that are placed together will fight vigorously and a clear winner/loser relationship is usually established. In sub- sequent interactions, the loser will flee soon after detecting the familiar winner. Here we tested the hypothesis that losing a fight with a conspecific will affect future agonistic interactions not only toward that individual (i.e., the familiar winner) but also to- ward unfamiliar conspecifics. To test this hypothesis we paired two Syrian hamster males in three trials on one day in which the loser had the opportunity to escape the winner. The next day the loser was paired with an unfamiliar male, also for three trials. If he lost again, he was tested on a third day with a third unfamiliar male. Subjects were those males that were losers on all three days. The latency to escape on the first trial on Days 2 and 3 was significantly shorter than on the first trial on Day 1, indicating that losing against the first male affected the response toward unfamiliar males. However, the latency to escape on the first trial on Days 2 and 3 was significantly longer than that on the third trial on the preceding day, indicating that a loser treats unfamiliar males differently than a familiar winner. These results suggest that a defeat during an interaction with one male affects later ago- nistic behavior towards other, unfamiliar males (Current Zoology 57 (4): 449-452, 2011).

Foraging theory posits that animals should maximize energy gains while minimizing risks, the largest of which is usually predation. For small burrowing mammals the best measure of risk avoidance may be the time spent in the burrow, although this measure is rarely examined. During the spring of 2005 and 2006 we recorded the foraging behavior of female golden hamsters in their natural habitat in southern Turkey. Data were collected with a data logger and by direct observations. Female golden hamsters averaged 64 min per day above ground in a series of foraging trips with a mean duration of 5.5 min. Two nursing females increased their time out of the burrow by a factor of 6–8 times over the course of 16 days by increasing both the number of trips and the length of each trip. These results show that hamsters spend little time out of the burrow, thus minimizing risk, but they also show that time spent out of the burrow is related to the energy needs of the hamsters; lactating females with high energy needs exposed themselves to much greater risk than did non-lactating females.

In many species, young males are the dispersers, leaving their natal area after weaning to establish a breeding area of their own. As young males disperse, however, they are bound to encounter unfamiliar adult males with established territories. Such interactions between an adult male and a young male may always be agonistic. Alternatively, there may be an age threshold below which aggression is not elicited and above which the adult male is aggressive toward the juvenile male. To test these two alternative hypotheses, we paired 47 young Syrian hamster (Mesocricetus auratus) males ranging from 24 to 65 days of age with 47 adult male hamsters and measured aggressive and investigatory behavior for 5 min. We observed no aggression by the adult toward young males between 24 and 47 days of age or toward the single male that was 49 days of age. Young males that were 50 days of age or older, however, elicited significant levels of aggression from the adults. These results indicate that in Syrian hamsters, young males are less vulnerable to adult aggression up to an age threshold and are more vulnerable to adult aggression beyond that threshold. This pattern may facilitate the establishment of territories by dispersing young males below that age threshold.

Im Band 37, Heft 2, Seite 213, soll der erste Satz des Abstract wie folgt verbessert werden: 8 male golden hamsters were observed two at a time in a plexiglas cage (area roughly 11 sg. ft.) subdivided into 47 connected compartments. 8 malexj golden hamsters were observed two at a time in a plexiglas cage (area roughly 11 sp. ft.) subdivided into 47 connected compartments. Each pair spent 2–3 weeks in this cage, observations lasting 1–2 weeks. Dominance relationships, food hoarding and marking behaviour in this situation are described.

In a recent study we showed that female Syrian hamsters (Mesocricetus auratus) from a laboratory stock readily mated with male Turkish hamsters (M. brandti). We hypothesized that captivity and/or unconscious selection of the most receptive females by researchers or animal caretakers results in heightened female sexual receptivity and reduces the tendency to reject heterospecific males. To test this hypothesis, we decided to decrease female receptivity by injection of fluoxetine, which increases the levels of serotonin in a number of brain loci, including areas involved in mediating sexual behavior, and determine whether such a decrease in receptivity would result in better discrimination of heterospecific males and rejection of such males as mates. We treated estrous female Syrian hamsters with 20mg/kg fluoxetine or vehicle and paired them with both a conspecific and a heterospecific male (Turkish hamster) in two sequential tests. All females showed similar behavior — they exhibited lordosis toward both conspecific and heterospecific males. We did not observe any sign of aggression. Latency to display lordosis and the duration of lordosis were not affected by fluoxetine. Fluoxetine thus did not have an effect on the behavior of females toward conspecific or heterospecific males. Independent of treatment (fluoxetine or vehicle injection), females did display lordosis significantly faster and for a longer duration in the presence of a conspecific male, even though these differences were small.

When females mate with a heterospecific male, they do not usually produce viable offspring. Thus, there is a selective pressure for females to avoid interspecific mating. In many species, females innately avoid heterospecific males; females can also imprint on their parents to avoid later sexual interactions with heterospecific males. However, it was previously unknown whether adult females can learn to discriminate against heterospecific males. We tested the hypothesis that adult females previously unable to avoid interspecific mating learn to avoid such mating after being exposed to heterospecific males. Syrian hamster (Mesocricetus auratus) females not previously exposed to Turkish hamster (Mesocricetus brandti) males can discriminate between odors of conspecific and heterospecific males, but they mate with either type of male. However, when we exposed adult females to both a conspecific male and a heterospecific male through wire-mesh barriers for 8 days, and then paired them sequentially with the two males, females were more receptive to conspecific males and more aggressive to heterospecific males. When females were paired with the heterospecific male first and the conspecific male second, no female was receptive and all were aggressive to heterospecific males. When females were paired with the conspecific male first, only 43% of females were then aggressive toward the heterospecific male. That is, interactions with conspecific males may decrease a female’s ability to properly avoid heterospecific males. Our study clearly shows for the first time that females can learn during adulthood to avoid interspecific mating just by being exposed to stimuli from heterospecific males.

Golden hamsters (Mesocricetus auratus) use olfactory cues to assess traits of conspecifics such as kinship, individual identity, and reproductive status. The environment, however, is full of a wide variety of other olfactory information such as signals emitted by some of the hamster’s primary predators. Given this, we hypothesized that hamsters use odors from predators as an indirect sign of increased predation risk in the environment. In addition, based on data that show that wild hamsters are diurnal while laboratory hamsters are nocturnal, we hypothesized that if golden hamsters did respond to the predator odors, perceived predator risk might influence daily activity patterns in hamsters. We tested male and female hamsters over 5 d with scent gland secretion from domestic ferrets (Mustela putorius furo) and compared their behavior to that observed when they were exposed to a clean arena. In response to the predator odor, subjects significantly decreased the amount of time active outside of their burrow, returned to their burrow more quickly, and spent less time near the predator odor than the clean control stimulus. These results strongly support our hypothesis that hamsters, like other species of small mammals, avoid predator odors. The results did not, however, support our second hypothesis that exposure to predator odors during the dark phase of the light cycle would elicit a switch to a more diurnal pattern of activity. More work is needed to understand how environmental cues and internal mechanisms interact to shape activity patterns.

8 malexj golden hamsters were observed two at a time in a plexiglas cage (area roughly 11 sp.ft) subdivided into 47 connected compartments. Each pair spent 2--3 weeks in this cage, observations lasting 1--2 weeks. Dominance relationships, food hoarding and marking behaviour in this situation are described.

Efficient discrimination between individuals of closely related species is important to maximize reproductive potential. Some studies using males as subjects have indicated that the medial amygdala (MeA) is involved in discrimination between odors of conspecific females and females from distantly related species. The authors investigated the involvement of the MeA in discrimination by females between odors of conspecific males and odors of males of a closely related species. The authors exposed estrous or diestrous female hamsters (Mesocricetus auratus) to saline, conspecific male odors, or heterospecific (M. brandti) male odors and quantified the expression of c-fos-related antigens in the anterior and posterior MeA. They found that estrous (but not diestrous) females investigated conspecific male odors longer than heterospecific male odors. Neural activity in both the anterior and the posterior MeA was higher in estrous than in diestrous females. In the anterior MeA, there were no significant differences in response to odors of conspecific and heterospecific males. In the posterior MeA, however, neural activity was higher when estrous females were exposed to conspecific odors than when they were exposed to heterospecific odors. No such difference was observed in diestrous females.

This chapter, which has a focus on vertebrates, starts with a discussion on terminology, especially the term pheromone. A major part of the chapter addresses the discrimination and recognition of individuals, and categories of individuals, by chemical cues and the roles that such recognition has in regulating social behavior. We discuss topics such as individual and kin recognition, interactions between males and females, intrasexual competition, the role of odors in the formation and maintenance of status relationships, the role of odors in sperm competition, the interactions between odors and aggression, and different aspects of scent marking, such as functions and causation of scent marking, counter-marking, allomarking, hormonal control of scent marking, and the costs of scent marking. The roles of odors in modulating hormones in vertebrates are also discussed. Finally, the roles, in communication and social behavior, of the olfactory and vomeronasal systems are detailed. Also included is a description of the structure of these systems, as well as how they are involved in hormonal and behavioral responses to odors, with specific sections on their roles in nipple search and attachment, and sexual behavior and motivation.

In two closely related species, females generally prefer conspecific males over heterospecific males. We found that estrous (but not diestrous) female Syrian hamsters Mesocricetus auratus prefer the odors of conspecific males to odors of Turkish hamsters Mesocricetus brandti. However, female Syrian hamsters are not aggressive toward male Turkish hamsters and will readily mate with them. We hypothesize that many generations in captivity led to a reduction in females' ability to avoid inter-species mating, possibly related to the heightened sexual receptivity observed in Mesocricetus hamsters in captivity. To test this hypothesis, we replicated a study carried out with female Turkish hamsters soon after the current laboratory stock of this species was established. In that study, female Turkish hamsters showed lordosis toward male Syrian hamsters in only 20% of interactions and attacked heterospecific males in 80% of the pairings. Using animals descended from that original colony (after many generations in captivity and certain episodes of inbreeding), 100% of female Turkish hamsters mated with heterospecific males and none showed aggression toward heterospecific males. Thus female avoidance of inter-specific mating may be affected by captive rearing conditions.

It is clear that male hamsters discriminate between the odors of individual, conspecific females, as shown by using habituation-dishabituation methods. However, it is not clear from past research whether male hamsters are able to discriminate between the odors of estrous and non-estrous females. A series of habituation-dishabituation experiments was conducted to determine whether males discriminated between different estrous cycle states using two female secretions, those from flank-glands and vaginal secretions. We found that, when habituated to a female flank-gland secretion, males discriminated between this female and a second female on the test trial, whether both were in estrus, both were in diestrus, or one was in estrus and the other in diestrus. There was no difference, however, in the magnitude of their dishabituation response toward flank-gland odors of females in estrus and diestrus. These results suggest that males use flank-gland odors to gain information primarily about individuals. When tested with vaginal secretions in habituation-dishabituation tests, males only showed differences in investigation when the second female was in estrus, indicating that males use vaginal secretions to gain information primarily about reproductive state.