Peripubertal exposure to male odors influences female puberty and adult expression of male-directed odor preference in mice

Testosterone-dependent olfactory signals emitted by male are well known to accelerate female puberty in mice (Vandenbergh effect). However, it remains unclear whether these chemosignals also influence adult expression of male-directed odor preference. Therefore, we exposed female mice to intact or castrated male bedding (vs clean bedding as control) during the peripubertal period (postnatal day (PD) 21–38) and measured male-directed odor preference in adulthood. At PD45 or PD60, females exposed to intact male odors, and thus showing puberty acceleration, preferred to investigate odors from intact males over females or castrated males. Females exposed to castrated male odors did not show puberty acceleration but preferred male (intact or castrated) over female odors. Finally, control females did not show any odor preference when tested at PD45, although a preference for male odors emerged later (PD60). In a second experiment, females that were exposed to intact male odors after pubertal transition (PD36–53) also preferred intact male over castrated male odors. In conclusion, our results indicate that peripubertal exposure to male odors induced early expression of male-directed odor preference regardless of puberty-accelerating effect and that induction of male-directed odor preference is not specific to the peripubertal period.     

Preference for conspecifics evolves earlier in males than females in a sexually dimorphic radiation of fishes

Speciation by sexual selection is generally modeled as the coevolution of female preferences and elaborate male ornaments leading to behavioral (sexual) reproductive isolation. One prediction of these models is that female preference for conspecific males should evolve earlier than male preference for conspecific females in sexually dimorphic species with male ornaments. We tested that prediction in darters, a diverse group of freshwater fishes with sexually dimorphic ornamentation. Focusing on the earliest stages of divergence, we tested preference for conspecific mates in males and females of seven closely related species pairs. Contrary to expectation, male preference for conspecific females was significantly greater than female preference for conspecific males. Males in four of the 14 species significantly preferred conspecific females; whereas, females in no species significantly preferred conspecific males. Relationships between the strength of preference for conspecifics and genetic distance revealed no difference in slope between males and females, but a significant difference in intercept, also suggesting that male preference evolves earlier than females’. Our results are consistent with other recent studies in darters and suggest that the coevolution of female preferences and male ornaments may not best explain the earliest stages of behavioral isolation in this lineage.     

Sexual experience interacts with steroid exposure to shape the partner preferences of rats

A three-phase experiment manipulated sexual experience and hormone exposure (perinatally and in adulthood) in female rats housed individually from weaning so as to limit peripubertal social and sexual experience. Noncontact partner preference for a male or estrous female rat was measured both before and after sexual experience, first while rats were under the influence of circulating testosterone propionate (TP) and later after priming them with ovarian hormones (estradiol benzoate and progesterone; EB & P). When implanted with TP capsules and tested while sexually naive, all groups of female rats preferred females to males without differing statistically. However, following three sexual experience sessions with estrous females, differences emerged between the masculinized and control groups in the magnitude of their female-directed preference, with masculinized females demonstrating a significantly greater preference for estrous females. Sexual experience with male rats under EB & P did not result in a significant shift in preference in any group. Histological assessment indicated that the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) was increased by exposure to TP postnatally, and SDN-POA volume correlated positively with partner preference scores but only when rats were both sexually experienced and exposed to circulating TP in adulthood. These results suggest that sexual experience interacts with steroid exposure to shape partner preference.     

Variation in female guppy preference for male olfactory and visual traits

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

Potential contribution of prenatal estrogens to the sexual differentiation of mate preferences in mice

The neural mechanisms controlling sexual behavior are sexually differentiated by perinatal actions of gonadal hormones. We recently observed using female mice deficient in alpha-fetoprotein (AFP-KO) and which lack the protective actions of AFP against maternal estrogens, that exposure to prenatal estrogens completely defeminized their potential to show lordosis behavior in adulthood. Therefore, we determined here whether mate preferences were also affected in female AFP-KO mice. We observed a robust preference for an estrous female over an intact male in female AFP-KO mice, which were ovariectomized in adulthood and subsequently treated with estradiol and progesterone, whereas similarly treated WT females preferred the intact male over the estrous female. Gonadally intact WT males preferred the estrous female over the male, but only when visual cues were blocked by placing stimulus animals behind opaque partitions. Furthermore, when given the choice between an intact male and a castrated male, WT females preferred the intact male, whereas AFP-KO females showed no preference. Finally when given the choice between an estrous female and an ovariectomized female, WT males preferred the estrous female whereas AFP-KO females preferred the ovariectomized female or showed no preference depending on whether they could see the stimulus animals or not. Taken together, when AFP-KO females are tested under estrous conditions, they do not show any male-directed preferences, indicating a reduced sexual motivation to seek out the male in these females. However, they do not completely resemble males in their mate preferences suggesting that the male-typical pattern of mate preferences is not solely organized by prenatal estrogens.     

Prey Habitat Location by the Cassava Mealybug Predator Exochomus flaviventris: Olfactory Responses to Odor of Plant, Mealybug, Plant–Mealybug Complex, and Plant–Mealybug–Natural Enemy Complex

Exochomus flaviventris Mader is considered to be the most active predator of the cassava mealybug Phenacoccus manihoti Matile–Ferrero in Central Africa. The response of experienced gravid female coccinellids to the odor of cassava plant (var. Zanaga), unparasitized mealybugs, plant–mealybug complex with or without feeding prey (parasitized or not), and plant–mealybug complex with or without conspecific coccinellids was investigated in a Y-tube olfactometer. The odor of uninfested cassava plants was not more attractive than clean air. Dual-choice tests revealed that mealybug-infested plants were preferred to mealybugs alone and mealybug-damaged plants and were the major sources of volatiles that attract females coccinellids to the microhabitat of its prey. The emission of volatile chemicals did not appear to be limited to the infested parts of the plant but did occur systemically throughout the plant. The presence of conspecific coccinellid larvae or adult males did not modify the attractiveness of the mealybug-infested plants. However, when an infested plant with conspecific predator females (alone or with conspecific males) was compared to an infested plant or infested plant with conspecific males, E. flaviventris females showed a preference for the last two sources of odor. The uninfested plant with conspecific males was also preferred to the uninfested plant with conspecific females. In addition, the odor of conspecific males was preferred over that of conspecific females. Female predators preferred the plant infested with unparasitized mealybugs over the plant infested with mealybugs previously parasitized. These results showed that E. flaviventris females use herbivore-induced plant volatiles during foraging and can detect via olfaction the presence of conspecific gravid females and parasitized prey, thus assessing patch suitability from a distance.     

光周期对雄性布氏田鼠种内个体气味辨别的影响

本文研究了成年雄性布氏田鼠对不同光照周期下(长光照: LD; 短光照: SD) 的陌生雌鼠和陌生雄鼠气味的行为表现。实验发现: 所有被试雄鼠对LD 雄鼠、雌鼠气味比SD 雄鼠、雌鼠气味有更多的社会探究行为。LD 雄鼠比SD 雄鼠对同性或异性陌生个体气味的嗅闻和挖掘行为要多, 而且差异显著。在探究LD 动情雌鼠气味源时, LD 雄鼠比SD 雄鼠表现出更多的嗅闻和挖掘行为; 在探究SD 动情雌鼠气味源时, LD 和SD 雄鼠的行为反应没有明显差别。所有被试雄鼠在LD 雄鼠气味源箱中的停留时间都显著多于在SD 雄鼠气味源箱中的停留时间。LD 雄鼠在LD 雌鼠气味源箱中的停留时间显著多于在SD 雌鼠气味源箱中的停留时间; 而SD 雄鼠在LD 和SD 雌鼠气味源箱中的进入频次和停留时间没有明显差别。同时, LD 雄鼠对LD 动情雌鼠的气味在嗅闻频次和嗅闻时间上多于非动情LD 雌鼠, 而对SD 动情和非动情雌鼠的气味没有表现出明显的偏好; SD 雄鼠对LD 和SD 动情雌鼠的嗅闻行为仅在频次上显著多于对非动情雌鼠的嗅闻, 而在时间上没有显著差别。结果表明: 布氏田鼠嗅觉通讯中的个体气味及其对气味进行辨别过程中的行为反应都随着光照周期的不同而发生变化。动物的个体气味带有季节性信息, 来源于长光照下的气味比短光照下的气味更具有性吸引; 短光照在一定程度上可能抑制了雌鼠的动情和雄鼠的性行为反应。其嗅觉通讯行为的适应意义可能在于: 减少秋季短日照环境下的繁殖活动, 提高雄性个体之间的社会容忍性以利于集群越冬。     

Hormonal regulation of agonistic and affiliative behavior in female mongolian gerbils (Meriones unguiculatus)

Ovarian steroids and oxytocin (OT) have been implicated in the regulation of social behaviors. The purpose of the present study was to examine hormonal substrates of aggression and affiliation in the female Mongolian gerbil (Meriones unguiculatus), a highly social, monogamous rodent. Sexually naive adult females were paired with sexually experienced males for 48 h and their interactions videotaped. Females were gonadally intact and tested during vaginal estrus (INT) or ovariectomized and observed after the following treatments, administered by means of sc injections: EBEB (7 days of estradiol-benzoate); EBP (2 days of EB followed by progesterone), SALEB (saline, days 1-5 then 2 days of EB), OTEB (OT for days 1-5 then 2 days of EB); OTOIL (OT for days 1-5 then 2 days of OIL); or SALOIL (saline days 1-5 then 2 days of OIL). During the first hour of pairing INT females displayed higher levels of affiliation and lower levels of sniffing and agonistic behavior than SALOIL females. All hormonal treatments reduced agonistic behaviors when compared to SALOIL, although none of the hormonal treatments restored affiliation to INT levels. During the 48-h test overt aggression varied by treatment with INT, EBEB, EBP, and OTEB females displaying lower levels than SALOIL, while all groups displayed similar levels of affiliation. The results indicate that OT and E play a significant role in regulating male-directed aggressive behavior in females and that the presence of ovarian hormones as well as OT can increase affiliation during initial contact. Over a sustained period of cohabitation social cues appear to be more important in regulating affiliation than gonadal hormones.     

Sexual incentive motivation, olfactory preference, and activation of the vomeronasal projection pathway by sexually relevant cues in non-copulating and naive male rats

There are some apparently healthy male rats that fail to mate after repeated testing with receptive females. We have previously shown that these "non-copulator (NC)" males show no partner preference for a receptive female when given the opportunity to physically interact with a sexually receptive female or a sexually active male. We also demonstrated that although NC males prefer odors from estrous females to odors from anestrous females, this preference is significantly reduced in comparison to the preference displayed by copulating (C) males. The aim of the present study was to evaluate in NC males sexual incentive motivation, that is, the approach behavior of male rats to either a sexually receptive female or a sexually active male in a test where the subjects can smell, hear, and see the stimulus animal but prevents their physical interaction. In addition, we determined whether NC rats have alterations in their ability to detect odors from conspecifics or odors related to food. In the detection of odors from conspecifics, we determined if these NC males are sexually attracted toward odors from receptive females or sexually active males. For food-related odors, we quantified the time it took the subjects to locate a hidden a piece of apple. Finally, using the induction of Fos-immunoreactivity (Fos-IR) as an index of neuronal activation, we compared the response of the vomeronasal projection pathway (VN pathway) of C and NC male rats exposed to estrous bedding. Males without sexual experience (WSE) were included in all experiments to determine the importance of previous heterosexual experience in the different behavioral tests and in the activity of the VN pathway. In the sexual incentive motivation test, we found that C and WSE male rats have a clear preference for estrous females over sexually active males, whereas NC male rats showed no preference. In odor tests, our results showed that C males had a clear preference for odors from estrous females as opposed to odors from sexually active males. Although NC and WSE male rats showed a preference for estrous female odors, this preference was significantly reduced compared to that shown by C males. No differences were found between WSE, C, and NC males in the detection of stimuli associated with food-related odors. A significant increase in Fos-IR was observed in the mitral cell layer of the accessory olfactory bulb in all groups when exposed to estrous bedding. However, only the C male rats exposed to estrous female bedding showed an increase Fos-IR in all structures of the VN pathway. An increase in Fos-IR was observed in the medial preoptic area (MPOA) of WSE males exposed to estrous bedding. No increases in Fos-IR were detected along the VN pathway in NC male rats. We proposed that NC male rats do not display sexual behavior due to a reduced sexual motivation that could be caused by alterations in the neuronal activity of the VN pathway during the processing of estrous odors.     

Sex differences in olfactory social recognition memory in meadow voles,Microtus pennsylvanicus

Terrestrial mammals, like rodents, use odors, and scent marks to indicate their presence in an area to conspecifics. These odors convey information about the scent donor's genotype, sex, condition, and age. The ability to discriminate among the scent marks of conspecifics and later recollect the identity of the donor is essential for choosing between familiar and unfamiliar mates. We tested the hypothesis that the promiscuous meadow vole (Microtus pennsylvanicus) can recollect the odor of a familiar, opposite-sex conspecific and distinguish it from that of an unfamiliar, opposite-sex conspecific. We also hypothesized that because reproductive success is highly skewed among male meadow voles and competition for mates is intense, males will be more likely than females to recollect the odor of a familiar, opposite-sex conspecific and distinguish it from that of an unfamiliar, opposite-sex conspecific, for a longer period of time. Using a habituation task, we first exposed the voles, 4 times successively, to the anogenital area scent of an opposite-sex conspecific. Then, 1 hr, 24 hrs, 72 hrs, or 96 hrs after the fourth exposure, voles were presented with the odor of the donor from the exposure phase (familiar donor) and that of an unfamiliar, opposite-sex conspecific. Female meadow voles spent similar amounts of time investigating the scent of the familiar male donor and that of an unfamiliar male donor after the 1-hr and 24-hr intervals. Male meadow voles, however, spent more time with the scent of an unfamiliar female donor than that of the familiar female donor after the 1-hr, 24-hr, and 72-hr intervals, suggesting that male voles could recollect the scent mark of a familiar female for at least three days. The implications of these sex differences in social memory may reflect the different strategies male and female meadow voles use in the recognition of previous and potential mates. Recognition of an individual's scents may enhance fitness by allowing animals to direct appropriate behaviors toward those individuals.     

Context alters the ability of clitoral stimulation to induce a sexually-conditioned partner preference in the rat

We have shown previously that clitoral stimulation (CLS) of female rats induces significant conditioned place preference (CPP), indicating that it is rewarding. The present study asked whether CLS could induce a conditioned partner preference. In the first experiment, sexually naïve females received 10 alternating trials of CLS and No-CLS in the presence of a male rat behind a wire-mesh screen. For one group, CLS was made in the presence of the male scented with almond extract. On alternating trials, those females received sham CLS in the presence of an unscented male behind the screen. The order was reversed for the other group. After 5 trials in each condition, females were placed into an open field with two sexually vigorous males, one scented and the other unscented. Contrary to expectation, females displayed a preference for the male associated with sham CLS. The second experiment examined whether a partner preference could be conditioned by associating CLS with the almond odor alone. A new group of sexually naive females received the same CLS-odor, No-CLS-No Odor pairings as above, but with the odor presented on cotton gauze in the chamber. During the final open field test, those females selectively solicited the scented male. We conclude that CLS that induces CPP also induces conditioned partner preference. However, we propose that CLS in the presence of an inaccessible male created a sexual inhibitory state for female rats.     

雄性布氏田鼠对不同熟悉程度和动情状态下雌鼠气味的辨别

通过雄性布氏田鼠（Microtus brandti)对配偶和陌生雌鼠气味的辨别实验发现：（1）雌鼠动情状况对雄鼠气味行为反应的影响,当配偶雌鼠处于动情期时,被试雄鼠对动情陌生雌鼠巢垫物的溴闻和舔舐的持续时间都明显多于对非动情陌生雌鼠巢垫物的嗅闻和舔舐时间,而其他行为没有明显判别当配偶雌鼠处于非动情期时,雄鼠对动情的和非动情的陌生雌鼠的气味行为反应都没有明显判别当陌生雌鼠处于动情期时,被试雄鼠对动情配偶气味的嗅闻时间明显多于对非动情配偶的嗅闻时间,而其他行为反应没有明显差异;当陌生雌鼠处于非动情期时,被试雄鼠对动情配偶雌鼠巢垫物的嗅闻时间,挖掘频次,舔舐频次和时间都明显多于对非动情配偶气味的嗅闻,而且雄鼠在动情配偶气味周围搔扒体侧行为的发生频次和持续时间也多于在非动情配偶气味周围的搔扒行为;（2）熟悉性对雄鼠气味行为反应的影响,当配偶雌鼠和陌生雌鼠都处于动情期或都处于非动情期时,被试雄鼠对陌生雌鼠气味的探究行为（嗅问、挖掘和舔噬）和搔扒体侧行为明显多于对配偶雌鼠气味的探究;雄鼠访问陌生雌鼠气味源箱的频次和在其中的停留时间也都多于访问配偶雌鼠气味源箱的频次和停留时间;当配偶雌鼠处于动情期而陌生雌鼠处于非动情期时,被试雄鼠对配偶气味的嗅闻,挖掘和自身修饰行为明显多于对陌生雌鼠气味的行为反应,进入配偶气味源箱中的访问频次也多于进入陌生雌鼠气味源箱的访问频次。结果说明：雌鼠与被试雄鼠的熟悉程度和雌鼠的动情状况直接影响雄性布氏田鼠的社会探究和气味选择行为,即雄鼠偏好并选择动情雌鼠和陌生雌鼠,雄性布氏田鼠对雌鼠气味的行为反应也表现出田鼠属动物典型的多配制种类特征。     

Male Biases for Male Characteristics in Females in Priapella olmecae and Xiphophorus helleri (Family Poeciliidae)

Preexisting receiver biases can affect the evolution of sexually selected traits once traits favored by such biases arise. Female guayacón olmeca, Priapella olmecae , and green swordtail, Xiphophorus helleri , possess a bias favoring sworded conspecific males, despite phylogenetic evidence that the sexually selected sword expressed by male swordtails arose in Xiphophorus after the divergence of the two genera. In this study, we investigated the state of the bias favoring a sword in male Priapella and Xiphophorus to determine whether males also possess a bias that could operate in an intersexual selection context. Male P. olmecae preferred conspecific females with swords to those without swords. Thus, males and females in this unsworded species appear to share a preexisting bias favoring individuals of the opposite sex with swords. Male X. helleri , however, did not express a bias favoring sworded females; instead, in this species in which the sword is restricted to males, males discriminated against conspecific females with swords. Previous work suggests that female mate choice and male–male competition likely contribute to the maintenance of the sword in X. helleri . The sword may also play a role in sex recognition in swordtails. The absence of a sword preference in male green swordtails could reflect the current function of the sword.     

Medial Preoptic/Anterior Hypothalamic Lesions Induce a Female-Typical Profile of Sexual Partner Preference in Male Ferrets

In T-maze tests given to gonadectomized ferrets treated daily with estradiol benzoate (EB), females consistently prefer to approach and interact sexually with a stud male whereas male subjects, on average, prefer an estrous female. In the present experiment this sexually allomorphic pattern of partner preference was changed in males given lesions of the medial preoptic area/anterior hypothalamus (mPOA/AH). Electrolytic lesions, which caused extensive bilateral damage to the mPOA/AH, including the sexually dimorphic male nucleus (MN) of the POA/AH, led males to shift their mean preference away from the estrous female to the stud male. Their postoperative profile of partner preference more closely resembled that of sham-operated females than that of sham-operated males or of males which sustained either partial or minimal bilateral damage to the mPOA/AH so as to spare the MN-POA/AH in one or both hemispheres. Males with extensive bilateral mPOA/AH lesions, like sham-operated females, showed an even stronger preference to approach the stud male during T-maze tests in which the subjects could smell, see, and hear the stimulus animals without physically interacting with them. After receiving testosterone propionate, male ferrets with either extensive or partial lesions of the mPOA/AH showed significant deficits in neck gripping and mounting performance in tests with either female or male stimulus animals which were sexually receptive after gonadectomy and EB treatment. The present results, coupled with those of a previous study using excitotoxic mPOA/AH lesions, suggest that the male-typical profile of preference for an estrous female depends on the functional integrity of sexually dimorphic mPOA/AH neurons and the reward engendered by coital interaction with such a female. When these neurons either are destroyed experimentally (as in male ferrets with extensive bilateral mPOA/AH lesions) or are absent (as in sham-operated females), subjects are attracted by distal (possibly chemosensory) incentive cues from a stud male.     

The regulation of precopulatory behavior by ovarian hormones in the female Mongolian gerbil

The hormonal regulation of precopulatory behavior in the female Mongolian gerbil was studied using two groups (N = 6) of sexually experienced females. A novel testing procedure was used which involved females living continuously with test males for several days. The test males showed either full sexual behavior (copulating males, C) or only precopulatory behavior (noncopulating males, NC). Experiment 1 investigated changes during the estrous cycle and following ovariectomy in females. Experiment 2 studied the effects of hormonal treatment of these ovariectomized females with 6 micrograms estradiol benzoate (EB) followed by 0.4 mg progesterone (P) or by 0.04 ml arachis oil. When tested with NC males, females displayed a greater range of precopulatory behavior. The patterns could be classified into three groups according to the manner of response to ovariectomy and hormone treatment. Group I patterns (approach, leave, and olfactory investigation of the male's head) were affected by neither ovariectomy nor EB treatment relative to Day 3 levels (Day 3, day preceding estrus; Day 4, estrus), but they were increased to estrous levels by EB and P. Group II patterns (darting, foot-stomping, and the present and piloerection postures) appeared only during estrus, did not appear after ovariectomy, and reappeared only after sequential EB and P treatment. Group III patterns (investigation of the male's anogenital area, allogrooming, ventral gland marking, and sand-rolling) were reduced relative to both estrus and Day 3 levels by ovariectomy and increased above Day 3 levels by EB alone; EB and P treatment further increased Group III patterns to the level of estrus. It is suggested that female precopulatory behavior patterns differ in their responsiveness to ovarian hormones. Estrogen appears to affect those patterns associated with the earliest stages of estrus (Group III).     

Brief Exposure to Female Odors “Emboldens” Male Mice by Reducing Predator-Induced Behavioral and Hormonal Responses

In rodents, where chemical signals play a particularly important role in determining intersexual interactions, various studies have shown that male behavior and physiology is sensitive to female odor cues. Here we examined the effects of brief (1 min) and more prolonged (60 min) preexposure to the odors of a novel estrous female on the behavioral and hormonal responses of sexually experienced and inexperienced male mice, Mus musculus, to subsequent predator (cat and weasel) odor exposure and potential predator risk. Brief, but not prolonged, preexposure to the odors of an estrous female decreased the aversion and avoidance responses of male mice to cat odor in a Y-maze preference test, with the extent of responses being affected by a males prior sexual experience. Similarly, brief, but not prolonged, preexposure to female odors markedly attenuated the analgesic responses elicited in male mice by weasel odor. Brief exposure to a novel estrous female by itself had no significant immediate effects on either corticosterone or testosterone levels in the males. However, brief, but not prolonged, preexposure to the odors of an estrous female attenuated the marked increase in corticosterone and decrease in testosterone that were induced in males by exposure to weasel odor. The decreases in aversive responses to, and effects of, predator odor exposure that are induced by brief exposure to a novel estrous female may reflect a greater risk taking and boldness in males that could directly facilitate access to an immediately, and possibly transiently, available novel sexually receptive female.     

Sexual behavior of female rats in a multiple-partner preference test

In this study, sexually experienced female rats were tested in a multiple-partner preference test (MPPT) in which they were allowed to pace their sexual contacts with four sexually active males. Four cylinders, with a small hole through which only the female could move freely from one cylinder to another, were assembled forming in the center an empty compartment. An intact female was placed in the central compartment and a sexually active male in each cylinder. Female sexual behavior was analyzed throughout the estrus cycle in four consecutive days. Each daily test lasted 15 min. The percentage of exits after intromission or ejaculation was significantly higher than the percentage of exits after each mount. The female spent significantly longer time with one of the males. We designated this male as the preferred male (PM). Although in each of the 4 days studied, females spent significantly longer time with the PM, however, the male selected was not the same throughout the estrus cycle. The number of entries into the compartment of the PM was significantly higher and increased around proestrus. Compared to previous studies, pacing behavior was notably lower in the conditions of the MPPT. No significant differences were observed during the estrous cycle concerning the other parameters recorded. The present results suggest that the MPPT could be a good model to study partner preference in the female rat.     

Olfactory conditioned same-sex partner preference in female rats: Role of ovarian hormones

The dopamine D2-type receptor agonist quinpirole (QNP) facilitates the development of conditioned same-sex partner preference in males during cohabitation, but not in ovariectomized (OVX) females, primed with estradiol benzoate (EB) and progesterone (P). Herein we tested the effects of QNP on OVX, EB-only primed females. Females received a systemic injection (every four days) of either saline (Saline-conditioned) or QNP (QNP-conditioned) and then cohabited for 24 h with lemon-scented stimulus females (CS +), during three trials. In test 1 (female-female) preference was QNP-free, and females chose between the CS + female and a novel female. In test 2 (male-female) they chose between the CS + female and a sexually experienced male. In test 1 Saline-conditioned females displayed more hops & darts towards the novel female, but QNP-conditioned females displayed more sexual solicitations towards the CS + female. In test 2 Saline-conditioned females displayed a clear preference for the male, whereas QNP-conditioned females displayed what we considered a bisexual preference. We discuss the effect of dopamine and ovarian hormones on the development of olfactory conditioned same-sex preference in females.     

Seasonal Differences in Social Behavior among Adult and Juvenile Meadow Voles,Microtus pennsylvanicus

Seasonal differences in behavioral interactions between wild-caught adult and juvenile meadow voles, Microtus pennsylvanicus, were measured in paired encounters in a neutral arena. Seasonal differences existed in the adult-juvenile paired encounters. Early in the breeding season (May—Aug.) paired encounters between adult males and juvenile males were more agonistic than other adultjuvenile pairings. Late in the breeding season (Sep.—Dec.) adult female-juvenile male encounters were more agonistic than other adult-juvenile pairings. Odor preferences of juveniles were determined in a Y-maze olfactometer. Juveniles did not demonstrate seasonal differences in odor preference. Males preferred the odor of adult females to the odor of adult males or their own odor. Females preferred the scent of an adult male to the odor of an adult female, but did not show a preference between their own odor and the odor of an adult male or an adult female. The results are consistent with hypotheses that state in a promiscuous species, females should be philopatric, and males should disperse as a consequence of adult competition. The data suggest that agonistic behavior by adults may regulate juvenile dispersal and recruitment, and define the composition of overwintering groups.     

Sexual Partner Preference in Female Zebra Finches: The Role of Early Hormones and Social Environment

This experiment investigated the effects of early estrogen treatment and sex composition of the social environment on sexual partner preference in female zebra finches, a pair-bonding socially monogamous species. Birds were injected daily with estradiol benzoate (EB) or the steroid vehicle for the first 2 weeks posthatch and then lived in either a unisex (all-female) or a mixed sex group from 40 to 100 days. After 100 days birds were implanted with testosterone propionate and given three kinds of tests: tests with a stimulus female, two-choice mate preference tests with male and female stimuli, and colony tests to assess pairing preference in a more naturalistic context. Both EB and unisex housing independently resulted in a preference for females (masculinized preference) in the two-choice tests, but only females with both EB treatment and unisex living were more likely to pair with females in the colony tests. Sexual partner preference, a key sexually dimorphic component of mate choice, appears to be organized by sex steroids in this pair-bonding species, but in a manner that may be mediated by the social environment.