Females In Postpartum Estrus Research Articles

Dopaminergic activity mediates pups' over male preference of postpartum estrous rats

Pups have greater incentive value than males for rats during the postpartum estrus (PPE); a period when females are both maternally and sexually motivated. Mesolimbic dopaminergic system has been proposed as a general motivational circuit; however in the literature it has been more related to the control of the motivational aspects of maternal than sexual motivation of females. Therefore, we aimed to assess the effect of antagonizing dopaminergic neurotransmission of PPE females on their preference for pups over a male. To achieve this objective we tested PPE rats in a Y-maze with three-choice chambers (one containing eight pups, the other a male and the last one no stimulus) after the systemic administration of the dopaminergic antagonist haloperidol (0.0; 0.025 or 0.05 mg/kg). Furthermore, to determine if this dopaminergic antagonist differentially affects maternal and sexual motivations when pups and male are not competing, we evaluated the effect of haloperidol in the preference of females for pups vs. a non-receptive female and for a male vs. a non-receptive female. In the preference test for pups vs. male, both doses of haloperidol decreased the time that females spent in pups' chamber while increased the time that they spent in male's chamber, resulting in a lack of preference between both incentives. Besides, haloperidol reduced the effort -attempts to get access to the stimuli- made by the females to obtain the pups. Conversely, 0.05 mg/kg of haloperidol did not affect the preference for both incentives when they were confronted to a non-receptive female. Together, these results indicate that the dopaminergic activity mediates pups' preference over male during the PPE and point toward a more relevant role of this system in females' behavioral output when incentives are competing.

Previous and recent maternal experiences modulate pups’ incentive value relative to a male without affecting maternal behavior in postpartum estrous rats

This study extends the behavioral analysis of the postpartum estrus (PPE) which represents a unique period in the female rat’s lifetime when maternal and sexual motivations co-exist. The aim of this study was to explore how previous and recent maternal experiences influence the maternal responses to pups when confronted with a male in a preference test or when they are presented independently in the home cage. To achieve this objective, we firstly compared the maternal behavior in the home cage and the preference for pups or a male in a Y-maze of primiparous and multiparous females approximately twelve hours after delivery. No differences were observed in the active and passive components of the maternal behavior of primiparous and multiparous rats; however second-time mothers made more efforts to gain access to the pups and tended to spend more time with them in the Y-maze than maternally inexperienced dams. In a second experiment, we assessed the influence of recent maternal experience with pups on PPE females’ behavior by comparing pups vs. male preference and maternal behavior of females that had experienced continuous or limited (approximately two hours) interaction with their litters after parturition was completed. PPE rats subjected to reduced interaction with their pups preferred the male, while females continuously exposed to pups chose them over the male. This change in females’ preference was not accompanied by significant alterations of maternal performance in the home cage, although anogenital licking tended to decrease in females with limited mother-litter interaction. Together, the results of these experiments indicate that previous and recent maternal experiences influence the motivational responses of PPE females, and that these effects are more evident when both motivations compete.

Food Deprivation and Restriction During late Gestation Affect the Sexual Behavior of Postpartum Female Meadow Voles, Microtus pennsylvanicus

In many species of small mammals, including meadow voles, Microtus pennsylvanicus, females come into postpartum estrus (PPE) within 12-24 h of giving birth, allowing them to mate and become pregnant while raising the current litter. PPE females show increases in attractivity, proceptivity, and receptivity, the three components of sexual behavior, relative to females not in PPE. Several studies have shown that food deprivation and restriction reduce attractivity, proceptivity, and receptivity of females not in PPE. We tested the hypothesis that food deprivation and restriction during late gestation causes deficits and decreases the attractivity, proceptivity, and receptivity of females when they enter PPE. Our data support the hypothesis. On day 1 of lactation, females that were food deprived and food restricted produced scent marks that were significantly less attractive as those produced by control PPE females. Food deprivation but not food restriction caused females to no longer display significant preferences for the scent marks of males over those of females (proceptivity). Food deprivation and food restriction were sufficient to induce females to become significantly less sexually receptive than control females. Eleven of 12 control PPE females mated, 4 of 12 food-restricted females mated, and 3 of 12 food-deprived females mated. Dams facing food deprivation or restriction during late gestation may have to balance the benefits of mating during PPE with the increased costs associated with getting pregnant while they are lactating.

The response of male meadow voles, Microtus pennsylvanicus, to same- and mixed-sex over-marks depends on the reproductive state of the top- and bottom-female scent donors

Many female terrestrial mammals undergo postpartum estrus (PPE), a state of heightened sexual attractiveness to male conspecifics relative to females not in PPE (REF females). PPE and REF females of several species may use over-marks to maintain territories and attract and indicate interest in males as potential mates. In our first two experiments, we determined if the response of male meadow voles, Microtus pennsylvanicus, to the top- and bottom-scent donors of a same-sex over-mark was affected by the reproductive state of the scent donors. We found that after exposure to a same-sex over-mark in which the female scent donors were in the same reproductive state, males spent more time investigating the mark of the top-scent female. Males, however, spent more time investigating the mark of the PPE female to that of a female not in PPE, independent of the position of either female’s scent mark in the over-mark. The third and fourth experiments determined if the response of males to the female scent donor of a mixed-sex over-mark was affected by whether she is the top- or bottom-scent donor. In three of the four comparisons, males spent more time investigating the mark of a novel PPE female (not in the over-mark) to that of the top- or bottom-scent female. In addition, males spent similar amounts of time investigating the mark of a novel female not in PPE and that of a top-scent PPE female. However, males spent more time investigating the novel REF female’s mark compared to that of a bottom-scent PPE female. The results are discussed in terms of the natural history and mating strategies of male meadow voles.

Variable mode of estrus affects female decision for multiple mating

Investigating patterns of variation in mating strategies may shed light on their evolutionary importance as well as their impact on the strength and shape of sexual selection. Multimale mating (polyandry) and mate choice are intensely studied subjects in the area of sexual selection, but little is known about intraspecific patterns of variation that may respond to dynamic cost-benefit balances. In a laboratory study, we investigated the mating behavior of female bank voles (Myodes glareolus) with distinctly different time and energy budgets: They were either in cycling estrus (CE) or postpartum estrus (PPE) shortly after delivery. Postpartum mating is highly constrained by time and energy due to maternal commitments to the newborn litter. All females had a free and simultaneous choice among 4 males that differed in scent-marking frequency (indicator of dominance) and body mass. We show that females in CE engaged significantly more often in multimale mating than females in PPE. Additionally, PPE females mated with males that scent marked more, whereas CE females seemingly mated indiscriminately. We discuss our findings in light of time and energy budgets of females and also consider alternative explanations such as pup protection against infanticidal males or physiological constraints to estrus modes.

Female Meadow Voles, Microtus pennsylvanicus, Experience a Reduction in Copulatory Behavior During Postpartum Estrus

AbstractIn many small mammalian species, females undergo postpartum estrus (PPE), mate, and become pregnant soon after delivering a litter. Mating during PPE implies a trade‐off between attending to the new litter and leaving that litter to mate. We tested the hypothesis that copulatory behavior is faster when a female mates during PPE than when it mates outside of PPE, during male‐induced estrus (MIE), a time when it is not lactating. We compared several variables of copulatory behavior in female meadow vole mating during both PPE and MIE. Females in PPE received significantly fewer intromissions, with shorter intervals between intromissions. Each ejaculatory series was also shorter for females in PPE. As a consequence, the total amount of time devoted to copulation was much shorter for females in PPE than for those in MIE. These data support the hypothesis that female meadow voles are able to reduce their copulatory behavior during PPE.

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

AbstractDuring 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.

Mating behaviour of bank voles (Clethrionomys glareolus) modified by hormonal and social factors

Summary The bank vole is a common European rodent. In a natural population the adult females are territorial, and during the breeding season each female's home range overlaps with the home range of several males. The aim of the present study was to investigate the influence of sexual experiences of females and males on mating behaviour. The results indicate that the activity of the female was modified by her sexual experience and by the experience of the partner. Females were more active in presence of sexually non-experienced than experienced males. Males also showed higher activity in the presence of virgin than in the presence of experienced females. Females in postpartum estrus were more active than virgins and injection of gonadotropins stimulated virgin females. Males tested with gonadotropin-treated virgin females or postpartum estrous females showed similar sexual activity. Sexual experience increased the activity of males; they approached receptive females frequently and exhibited a higher number of mountings than did non-experienced males. The higher activity of an experienced partner can prevent copulation with another male during the same estrus, so that only one male becomes the father of the offspring. The present results indicate that in sexually experienced males bulbectomy but not vomeronasalectomy decreased the sexual activity and only 2 out of 6 lesioned males copulated with receptive females.

Evidence that a novel type of progestational phase control occurs in the corn mouse, a South American murid rodent.

Most Muridae display a short luteal phase that becomes functional as a consequence of the prolactin release induced by the stimulation of copulation and/or lactation. The corn mouse also shows a short luteal phase, and we wanted to know whether copulation and/or lactation would release prolactin and maintain progesterone secretion in this species. Females in postpartum estrus were either allowed to copulate with an intact male or not, and either to lactate their young or not. Afterward, plasma progesterone was elevated over the baseline level only in females that had copulated and were bearing growing embryos (whether or not they were lactating), while prolactin was elevated only in lactating females. In another experiment, endometrial scratching induced decidualization both in females that had copulated with a vasectomized male and in those that had not copulated; sham operations had no effect in either case. Progesterone levels were elevated in decidualized animals as compared with their sham-operated controls. Results indicate that the initiation of the progestational phase in the corn mouse is not dependent on prolactin release. A short luteal phase during which nidation may occur has not yet been described in any other mammal.

Mechanisms of sexual fidelity in the monogamous California mouse, Peromyscus californicus

Peromyscus californicus are exclusively monogamous in the wild. We examined in the laboratory whether established pairs of male and female P. californicus would remain faithful when given the opportunity to mate with an opposite sex stranger, either in the presence or absence of their partner. When the partner was present she or he was tethered and could not intervene. Females in postpartum estrus (day 0 postpartum) preferred to associate with their pairmate rather than the unfamiliar virgin male. Females also preferred to mate with their partner, but 15–20% of the females mated with the unfamiliar male both in the presence and absence of their partner. Paired males were tested with an unfamiliar, sexually inexperienced estrous female on days 4 and 8 postpartum with their partners either absent or present but not in postpartum estrus, and on day 0 in the absence of their partner. Males preferred to associate with their pairmate. Contrary to theoretical expectations, males did not copulate with the estrous female when given the opportunity regardless of whether their partner was present or not. Furthermore, few males (2/13) tested in the absence of their partner mated with a sexually experienced, postpartum estrous female. These results indicate that monogamy in P. californicus is maintained by a strong attraction and preference of pairmates for each other and by self-restraint from mating with others. Male mate guarding may further ensure female faithfulness. Males exhibit apparently more sexual fidelity than females.

Modes of estrus induction as a factor in studies of the reproductive behavior of rodents

The choice of a mode of estrus for use in studies related to reproductive processes often is made arbitrarily. Females may be in hormone-induced estrus (HIE), cycling estrus (CE), male-induced estrus (MIE), or postpartum estrus (PPE). Although mode of estrus affects various aspects of copulatory behavior in different species in different ways, males mating with PPE females generally require more intromissions to reach ejaculation than with females in HIE or CE; males mating with females in CE generally attain more ejaculations than with PPE females. The duration of receptivity generally is shorter in PPE than in CE. Females in CE and PPE have different stimulus thresholds for pregnancy initiation, with the direction of the difference varying with the species. Among the other phenomena affected by mode of estrus are sperm competition, mate choice, and the Bruce effect. Because mode of estrus can be an important determinant of results, selection of a mode of estrus for any experiment should not be simply a matter of convenience. Further study of effects of mode of estrus is warranted.

Hormonal correlates of sexual behavior and ovulation in male-induced and postpartum estrus in female prairie voles

The purpose of the present study was a description of hormonal profiles in female prairie voles (Microtus ochrogaster) in estrus that was induced by male exposure versus postpartum estrus. Hormonal profiles are reported in sexually naive females and in sexually experienced females, as a function of varying amounts of coital stimulation and as a function of time since male exposure. Ovarian estradiol levels, uterine weights and uterine protein levels increased in virgin females after exposure to a male, were highest in females that showed lordosis, declined slowly when estrous females were isolated from males and decreased sharply following mating. Ovarian progesterone levels increased more rapidly following mating in females in male-induced estrus than in females in postpartum estrus. Serum progesterone levels did not increase significantly within 24 hr following mating, but were elevated by 72 hr after mating. These findings are discussed as they relate to the hormonal control of female sexual behavior.

Sperm competition in deer mice (Peromyscus maniculatus bairdi)

Six experiments were conducted to determine the effects of mode of estrus (cycling versus postpartum) and intervals between matings on sperm competition in deer mice. When there was no lengthy interval between matings by different males, sperm competition matings by different males, sperm competition with females in postpartum estrus was the same as that with females in cyclin estrus (i.e., no male order effect). Imposition of 4 h delays between males did not engender a mating advantage when females were in postpartum estrus. When 4 h intervals were imposed with females in cycling estrus and tests were begun relatively early in the dark phase, there was a secondmale advantage with respect to the number of pups sired. When minimal delays were imposed with females in cycling estrus the time of testing within the dark phase did not affect the pattern of sperm competition, but larger litters were born following matings later in the dark phase. When 4 h delays were imposed with the first male mating late in the dark phase a first-male advantage resulted. It is hypothesized that for females in cycling estrus there is a period of peak fertilizability. There is no straight-forward effect of delays between males per se; rather, effects must be analyzed in relation to the period of peak fertilizability. The timing of insemination appears less critical for postpartum females.

Studies of pericopulatory pregnancy blockage and the gestation period in deer mice ( Peromyscus maniculatus)

It has previously been shown that female deer mice in cycling estrus that copulate with or are exposed to more than one male at the time of mating have a lower probability of delivering a litter than when mating with and being exposed to just one male. In the present research the effect of post-mating exposure to the bedding of a strange versus a familiar male was studied in females in postpartum estrus. In four experiments females in postpartum estrus were protected from pericopulatory pregnancy blockage, presumably by suckling-induced elevated prolactin levels. Varying female experience, number of ejaculations, and the presence of suckling pups had no effect on this protection. Thus, both the pericopulatory block and the Bruce effect (a more delayed type of pregnancy blockage) occur in cycling, but not suckling, females. This suggests that the two may have a common mechanism and leads to a new perspective in the search for adaptive significance. In addition, the subsequent gestation periods were prolonged in females nursing young; the length was affected by the number of pups weaned from the previous litter and the number of pups being carried.

Economics of Harem Maintenance by a Neotropical Bat

In theory harem mating systems can evolve only if it is energetically feasible for one male to defend females or some limited resource used by females (Emlen and Oring 1977). In practice quantifying the energetic cost of defense is difficult because many diverse behaviors are usually involved. In the Neotropical fruit bat Artibeus jamaicensis, males maintain harems by defending tree hollows used as day roosts by groups of 3-14 nursing, postpartum estrus females (Morrison 1979). The infrared and radio-telemetry observations reported here indicate that although several different behaviors are involved in defense, all require that the male be in flight. The energetic cost of harem maintenance could therefore be calculated by contrasting the nightly flying times of harem males to those of females and nonharem males.