Patterns of sexual receptivity in the female musk shrew (Suncus murinus)

Female musk shrews (Suncus murinus) were tested daily to examine patterns of sexual receptivity. When only mounting was used as a criterion (to avoid pregnancy), nonpregnant females remained sexually receptive to males every day for 14 consecutive days. When insemination was allowed, most females continued to copulate for the first 5 days of pregnancy. Receptivity declined markedly around Day 10 of gestation, but a few females were receptive even into late pregnancy. Lactating females copulated with males 5 and 10 days after parturition. In general, unlike most mammals studied in the laboratory, the nonpregnant female musk shrew has no behavioral estrous cycle. Musk shrews are ready to mate anytime except in mild to late pregnancy, and even then occasionally mating is found.     

Relation between circulating sex steroid concentrations and sexual behaviour during pregnancy and post partum in the domestic rabbit

Sexual behaviour of 16 female and 12 male rabbits was studied during pregnancy and early post partum. The main behavioural events of the male (nuzzling and mounting) did not differ in the presence of receptive or non-receptive females. When introduced into the cage of the male, receptive and non-receptive females flattened to the floor or circled around. Sexual receptivity to males decreased in early pregnancy and increased to a maximum a few days around parturition; on Days 1 and 6 post partum, all experimental rabbits submitted to mating. Two groups of females were distinguished: one group submitting to mating whatever the stage of pregnancy, the second being receptive only during the few days before parturition or post partum. During pregnancy and early post partum there was no relation between the colour of the vulva and the female sexual behaviour. Does remained sexually receptive even when progesterone concentrations were high. Nevertheless, the number of receptive females was higher when progesterone concentrations decreased around parturition and the mean daily progesterone values were consistently higher in non-receptive than in receptive females. Oestrogen concentrations during pregnancy were very low and were not related to receptive behaviour.     

Urine-marking activity of female mice under the influence of male urine odors

We conducted a study of the urine-marking activity of female mice when simultaneously exposed to urine odors from 2 kinds of males. Females, deposited a greater number of urine spots when presented with urine of normal, rather than castrated, males. Two androgen-dependent compounds known to be present in normal male urine enhanced female urine-marking when mixed with castrated male urine. These results are consistent with previous results concerning odor preference of females. However, females showed no marking preference between normal male urine and preputialectomized male urine, in spite of their preference for the former in our previous odor-preference study. Further experiments with various combinations of male urine revealed that females showed no marking preference when 1 of the 2 presented urine samples was from preputialectomized males, regardless of the other presented stimulus. We concluded that female urine marking is not a simple reflection of sexual preference, but possibly a phenomenon of a complex motivational system.     

Sex differences in scent marking in Propithecus edwardsi of Ranomafana National Park, Madagascar

In this study we compared the scent-marking rates of females with those of males. Specifically, we examined the ability of season, dominance status, and natal status to explain the frequency of scent marking in female sifakas living wild in Ranomafana National Park, Madagascar, and compared the results with those published for males [Pochron et al., American Journal of Primatology, in press]. We also sought to determine whether vulnerability to infanticide affects marking frequency in adults of either sex, and whether female reproductive status affects female marking behavior. We found that males marked at twice the rate of females, and like males, females in single-female groups marked at the highest rates. Dominant females and non-natal females marked at higher rates than did subordinate females and natal females, a pattern also seen in males. This suggests that scent marks may convey important information about status. Neither females nor males varied their marking frequency with the presence of vulnerable infants. Females did not alter marking frequency with reproductive state, and like males, they marked at higher rates in the period prior to the mating season than they did in the mating season itself. This implies that females may use scent marks more for intrasexual aggression or territoriality than for mate attraction.     

Differences in potential reproductive rates of male and female seahorses related to courtship roles

Dwarf seahorses, Hippocampus zosterae (Syngnathidae), are distinguished by extreme morphological specialization for paternal care, the formation of monogamous pair bonds and mating repeatedly over the course of a breeding season. To determine the potential reproductive rates of male and female dwarf seahorses, we measured (1) the maximum number of offspring produced per breeding cycle when sexually receptive mates were unlimited, and (2) the relative time each sex was unavailable for mating ('time out'). We paired sexually isolated males and females with sexually receptive partners and observed them from the day of introduction through to copulation, to determine the length of time it takes each sex to prepare to mate. We conducted additional experiments to determine the length of gestation, which when added to the time needed to prepare to mate and copulate gives an estimate of total reproductive cycle duration, T. We estimated potential reproductive rate by dividing the mean number of offspring produced per breeding cycle by the duration of the breeding cycle (T). We estimated reproductive 'time out' by identifying the period of time males and females were physiologically capable of mating ('time in', S) and subtracting time S from time T. When provided with sexually receptive partners, females took 2 days longer than males to complete courtship and copulation, but neither males nor females remated during gestation. Therefore, males could potentially produce 17% more offspring than females over the course of one breeding season. Females had reproductive 'times out' 1.2 times longer than did males, as they were only capable of mating during the 4 h directly preceding copulation. Thus, H. zosterae males have higher potential reproductive rates and shorter reproductive 'times out' compared with H. zosterae females. These results and previous work indicating that seahorses display traditional courtship roles support the prediction that the sex having the higher potential reproductive rate, or equivalently, the shorter 'time out', will compete more intensely for access to the opposite sex. Copyright 2000 The Association for the Study of Animal Behaviour.     

Do Male Veiled Chameleons,Chamaeleo calyptratus,Adjust their Courtship Displays in Response to Female Reproductive Status?

Variation in male courtship behavior may be due to inherent differences among males or may arise from males adjusting their courtship displays according to female responsiveness. Female veiled chameleons, Chamaeleo calyptratus , exhibit two distinctive suites of body coloration and behavior patterns that vary according to receptive and non-receptive stages of their reproductive cycle. We presented male chameleons with both receptive and non-receptive females, and recorded differences in their mating frequency, courtship intensity and courtship behavior patterns. As expected, males were more likely to court and attempt mating with receptive females. Although fewer males courted non-receptive females, their courtship displays were significantly longer than those directed towards receptive females. Males also adjusted the contents of their displays according to female reproductive condition. Certain behavior patterns were unique to courtship displays directed towards each class of females. Males exhibited the behavior pattern `head roll' only when paired with receptive females, and `chin rub' was displayed only during courtship of non-receptive females. We hypothesize that these differences in male courtship frequency, intensity and content reflect differences in female reproductive value. Although males may benefit from mating with both receptive and non-receptive females, the costs associated with courtship may depend on female responsiveness. Thus, males adjust their courtship tactics accordingly.     

Scent-marking displays provide honest signals of health and infection

Males of many species produce scent marks and other olfactorysignals that function to intimidate rivals and attract females.It has been suggested that scent marks provide an honest, cheat-proofdisplay of an individual's health and condition. Here we reportseveral findings that address this hypothesis in wild-derivedhouse mice (Mus musculus domesticus). (1) We exposed males tofemale odor, which induces an increase in testosterone, andfound that sexual stimulation significantly increased the males'scent-marking and the attractiveness of their scent marks tofemales. (2) We challenged sexually stimulated males with anonreplicating strain of bacteria (Salmonella enterica C5TS)to activate immunity and found that this significantly decreasedthe males' scent-marking and the attractiveness of their scentmarks to females. (3) We collected scent marks from infectedand sham-infected males when they were sexually stimulated ornot, and we found that females could significantly discriminatethe scent marks of infected versus control males, but only whenthe males were sexually stimulated. Taken together, our resultsindicate that male mice modulate their scent-marking displaydepending on their health and perceived mating opportunities.Increased scent marking enhances males' attractiveness to females,scent marks provide an honest indicator of bacterial infection(and perhaps immune activation), and females are able to assessthe health of males more easily when males mark at a high rate.     

Mating Status Effects on Sexual Response of Males and Females in the Parasitoid Wasp <Emphasis Type="Italic">Urolepis rufipes</Emphasis>

Although mate preferences are most commonly examined in females, they are often found in both sexes. In the parasitoid wasp Urolepis rufipes, both female and male mating status affected certain aspects of sexual interactions. Female mating status mattered only in the later stages of mating. Males did not discriminate between virgin and mated females in terms of which they contacted or mounted first. However, once mounted, most virgin females were receptive to copulation, whereas very few mated females were. Whether a male’s mating status affected his own sexual response depended on the female’s ability to respond and the stage of mating. Examining male behavior toward dead females allowed elimination of the role of female behavior in how males responded. Virgin and mated males are both attracted to dead females as evidenced by their fanning their wings at such females. However, mated males were quicker than virgin males to contact and to mount in an experiment with dead females, whereas there was no such differential response in an experiment with live females. This difference is consistent with greater female sexual responsiveness to virgin males. Male mating status also affected female receptivity to copulate. Once mounted, live virgin females were less likely to become receptive to copulation by mated males than to virgin males, but only in a choice experiment, not in a no-choice experiment.     

The Reproductive State of Female Voles Affects their Scent Marking Behavior and the Responses of Male Conspecifics to Such Marks

During the breeding season, the reproductive condition of female mammals changes. Females may or may not be sexually receptive. We conducted a series of experiments to determine whether reproductive condition of female meadow voles affects their scent marking behavior as well as the scent marking behavior of male conspecifics. In expt 1, females in postpartum estrus (PPE females) deposited more scent marks than females that were neither pregnant nor lactating (REF females) or ovariectomized females (OVX females). In expt 2, male voles scent marked more and deposited more over‐marks in areas marked by PPE females than by REF and OVX females. In expt 3, PPE females deposited more scent marks and over‐marks in areas marked by males than did females in the other reproductive states. The results of these experiments showed that male and female voles may vary in the number, type and location of scent marks they deposit in areas scented by particular conspecifics.     

Fetal effects on sexual behavior and aggression in young and old female mice treated with estrogen and testosterone

During fetal life female mice (Mus musculus) that develop between two male fetuses (2M females) have higher blood concentrations of testosterone than do females that do not develop next to a male fetus (0M females). In the first experiment reported here, sexual receptivity and sexual attractiveness to males were examined in young (5 month old) and old (17 month old) ovariectomized, estrogen- and progesterone-treated 0M and 2M female mice that were placed in like-age pairs with a male. Most males inseminated the 0M female prior to inseminating the 2M female regardless of age. In addition, 0M females were more likely to exhibit lordosis when mounted than were 2M females. When the same young females were 9 months of age and the old females were 21 months of age, they were treated with testosterone and again placed together in pairs along with a sexually receptive female. Young 2M females exhibited more aggression toward the testosterone-treated female partner, and also exhibited more mounting of the receptive female, than did young 0M females. But, both old 0M and old 2M females were highly aggressive and exhibited mounting. An increase in sensitivity to the effects of testosterone on behavior thus occurs during aging in 0M females, which are relatively insensitive to testosterone in young adulthood. In contrast, when treated with estrogen and progesterone, 0M females were more attractive to males and were more sexually receptive than 2M females regardless of age.     

Behavioral characterization of non-copulating male mice

Non-copulating (NC) males are those animals that do not mate in spite of repeated testing with sexually receptive females. They have been observed in several species including rats and mice. The present experiment was designed to perform a detailed behavioral characterization of NC male mice. Thus, we evaluated their sexual incentive motivation for a sexually receptive female or a sexually active male, olfactory preference for volatile and non-volatile odors from females or males, and olfactory discrimination between female and male volatile odors and food related odors (milk versus vinegar). We compared the activity of the accessory olfactory system (AOS) in copulating (C) and NC males in response to estrous bedding using the induction of Fos-immunoreactivity (Fos-IR) as a measure of neuronal activation. We also determined if estradiol or dopamine treatment could induce sexual behavior in NC males. Finally, we compared the testis weight and the number of penile spines in C, NC, and gonadectomized males. In the sexual incentive motivation test C males spend significantly more time in the female incentive zone than in the male incentive zone. On the other hand, NC males spend the same amount of time in both incentive zones. In tests of olfactory preference, NC males spent less time investigating estrous odors than C males. As well, NC males discriminate urine from conspecifics but they spend less time smelling these odors than C males. In addition, no increase in Fos expression is observed in NC males when they are exposed to odors from estrous females. Our data also suggest that the deficits observed in NC males are not due to lower circulating levels of gonadal hormones, because estradiol supplementation does not induce sexual behavior in these animals, and their testis weight and the number of penile spines are normal. The results suggest that NC males are not sexually motivated by the receptive females and their odors.     

Female Defensibility in a Small Troops of Japanese Macaques vis-à-vis Nontroop Males and Copulation on the Periphery of the Troop

I provide data compiled over 4 yr on the mating behavior in small troops of wild Japanese macaques on Yakushima Island. The key parameters are the number of sexually receptive females, the number of nontroop males (NTMs), and copulation on the periphery of the troop. I analyzed the following aspects: 1) changes in the proportion of copulation with high-ranking males (HRMs) and NTMs, 2) variations in factors such as fluctuation in the number of sexually receptive females and troop males and their effects on the number of visiting NTMs, 3) the effect of attempted interruption of mounting series by other males, and 4) some aspects of copulation on the periphery of the troop. Throughout the study, 56% of the total number of females mated most frequently with the α-male in a single mating season. However, the relative mating success of HRMs varied over the years and between individuals. The number of visiting NTMs varied depending on the number of receptive females and troop males. Females tended to mate with the NTMs when they appeared around their troops. The direct effect of interruption of the mounting series by other males is equivocal. The females mated with the low-ranking males (LRMs) and NTMs on the periphery of the troop, which increased the possibility of mounting series ending with ejaculation. Females actively sought opportunities for copulation on the periphery of the troop by moving there or initiating close proximity with LRMs and NTMs there. On Yakushima Island, the mating success of HRMs was not always as high as that predicted by the priority of access model. The injury status of the HRM, the number of visiting NTMs, and female choice are all considered to influence a male’s mating success.     

Male southern water skinks (Eulamprus heatwolei) use both visual and chemical cues to detect female sexual receptivity

A wide range of organisms use chemical and visual cues in mate attraction and courtship; however, chemical discrimination relevant to reproduction and the interplay between these two types of communication are poorly understood in reptiles. We experimentally tested the ability of male Eulamprus heatwolei, a scincoid lizard, to discriminate between sexually receptive and non-receptive females in two ways. First, we conducted 155 staged encounters between males and females over 29 days to determine the start and the duration of the female receptive period based on the date of copulations. These data suggest that the receptive period lasted for approximately 7 days in late October under controlled laboratory conditions. We also recorded 6,330 individual male and female behaviours during these trials to evaluate the frequency of female courtship and rejection behaviours and the intensity of male courtship behaviour. Female courtship increased sharply during the receptive period and then diminished. The disparity between female courtship behaviours and female rejection behaviours was greatest during the receptive period. Male courtship intensity increased sharply prior to the receptive period, peaked during the receptive period and thereafter declined rapidly. To determine if males were using visual cues, chemical cues or both from females, we conducted an experiment during and after the receptive period wherein male lizards were presented with a choice of two retreat sites treated either with the odour of large sexually receptive females, odour of small sexually non-receptive females or no odour (control). Males preferred the scent of females over the odourless control, and analysis using a special form of a generalized linear model, the Bradley–Terry model, showed a clear order of retreat site preferences, with large sexually receptive females favoured over small non-receptive females over the odourless control. We speculate that males use vision to find females and then use their chemosensory ability to chemically evaluate female sexual receptivity once the pair are in close proximity.     

Mating does not influence reproductive investment, in a viviparous lizard

Mating is crucial for females that reproduce exclusively sexually and should influence their investment into reproduction. Although reproductive adjustments in response to mate quality have been tested in a wide range of species, the effect of exposure to males and mating per se has seldom been studied. Compensatory mechanisms against the absence of mating may evolve more frequently in viviparous females, which pay higher direct costs of reproduction, due to gestation, than oviparous females. To test the existence of such mechanisms in a viviparous species, we experimentally manipulated the mating opportunity of viviparous female lizard, Lacerta (Zootoca) vivipara. We assessed the effect of mating on ovulation, postpartum body condition and parturition date, as well as on changes in locomotor performances and body temperatures during the breeding cycle. Female lizards ovulated spontaneously and mating had no influence on litter size, locomotor impairment or on selected body temperature. However, offspring production induced a more pronounced locomotor impairment and physical burden than the production of undeveloped eggs. Postpartum body condition and parturition dates were not different among females. This result suggests that gestation length is not determined by an embryonic signal. In the common lizard, viviparity is not associated with facultative ovulation and a control of litter size after ovulation, in response to the absence of mating.     

Regulation of urine marking in male and female mice: effects of sex steroids

Effects of sex steroids on urine-marking activity were studied in male, female, and neonatally androgenized female mice. Urine marking was estimated by suspending ceramic tubes that were connected in a horizontal row with a steel rod into the home cage of an isolated mouse. Intact males showed high marking activity, which was diminished after castration. Both testosterone propionate (TP) and estradiol benzoate (EB) were effective in restoring the marking activity of castrated males, while 5-alpha-dihydrotesterone (DHT) did not have any stimulative effects. Intact normal females showed quite low marking activity and ovariectomy further depressed it. TP and DHT enhanced the marking of ovariectomized females, but EB restored the activity only to the preovariectomy level. In intact females which were neonatally androgenized, the marking activity was much higher than that of normal females. The pattern of the change induced by gonadectomy and hormone treatment in these females resembled that in males. Thus, ovariectomy reduced the activity and both TP and EB restored the level. These results indicate that the sexual dimorphism in the urine marking in mice is primarily determined by hormonal environment during early postnatal age. Hormonal control of scent marking is discussed in relation to the studies in other rodents.     

Reproductive synchrony in the intertidal amphipod Corophium volutator

Following logic of the mate-availability hypothesis, females are expected to show asynchronous reproduction in those species where operational sex ratios are female-biased and under circumstances where an individual female is sexually receptive only for short durations. We show that females of the intertidal amphipod Corophium volutator are receptive to mating only for a few days following their moult and are unable to hasten onset of moulting in the presence of a male. Despite meeting the conditions of the mate-availability hypothesis, reproduction was synchronous for female C. volutator across spatial and temporal scales relevant to mate-searching abilities of males. As such, some females are not expected to mate between moults, which coincide with their ability to mate. However, females do moult frequently (relative to males) which should increase their likelihood of mating over their lifetimes. It is unlikely that seasonal constraints, predation, or competition can account for the high degree of synchrony among breeding female amphipods. We suggest that dispersal of females or their offspring may constrain activity of females, as they moulted almost entirely during spring tides (although not always during the same set of spring tides). Female reproductive synchrony also has implications for reproductive behaviour of males, in particular, the possibility of harem-defence polygyny.     

Scent Marking in Female Prairie Voles: a Test of Alternative Hypotheses

We conducted three experiments with females in different stages of reproductive condition to test alternative hypotheses for the function of scent marking in female prairie voles, Microtus ochrogaster . The three reproductive categories were isolated females prior to sexual stimulation (anoestrous), sexually stimulated (oestrous) and lactating. Females in different reproductive condition were given the opportunity to scent mark clean unmarked substrate or areas that had previously been marked by adult females or adult males. The numbers of scent marks deposited by females did not differ statistically for females in different reproductive condition. However, there was a trend for anoestrous females to mark the most, oestrous females less, and lactating females the least. The lack of scent marking by lactating females might be to reduce conspicuousness to conspecifics or predators. Oestrous females tended to mark the most in the area marked previously by males, although the difference was not statistically significant.
Our results provide some support for a mate-attraction hypothesis and a territorial-defense hypothesis, but were most consistent with a self-advertisement hypothesis. Over marking was uncommon and did not differ by experiment or sex of previous donor. Our results suggest that the number and placement of scent marks by females are highly variable and function primarily to convey individual identity.     

Female sexual behavior displayed by androgenized female rhesus macaques

Adult, prenatally androgenized female rhesus macaques (female pseudohermaphrodites) that had been ovariectomized were treated with estradiol benzoate (20 micrograms/day) and paired with males at weekly intervals for 4 weeks beginning on Day 12 of injection. Their sexual behavior was compared to that of a control group of females. The sexual behavior of the males toward the two groups of genetic females (control females with normal female genitalia and hermaphrodites with well-formed male genitalia) was also observed. Females and hermaphrodites were equally receptive to male invitations to copulate. Although there were some differences in the specific components of proceptive behavior displayed by the two groups, the overall differences were negligible. Earlier studies had shown that infant and juvenile hermaphrodites resemble males in patterns of play and sexual behavior. When treated with testosterone as adults and paired with receptive females, they displayed mounting patterns typical of males--one of seven hermaphrodites achieved intromission and ejaculated. It has now been demonstrated that when treated with estrogen and paired with males, they responded as females. Hence, the capacity to behave sexually as males is not incompatible with the capacity to respond sexually as females under certain hormonal and environmental conditions.