Estrous state influences on investigative,aggressive, and tail flicking behavior in captive female Asian elephants

Females of species that live in matrilineal hierarchies may compete for temporally limited resources, yet maintain social harmony to facilitate cohesion. The relative degree of aggressive and nonaggressive interactions may depend on the reproductive condition of sender and receiver. Individuals can benefit by clearly signaling and detecting reproductive condition. Asian elephants (Elephas maximus) live in social matrilineal herds. Females have long estrous cycles (14–16 weeks) composed of luteal (8–12 weeks) and follicular (4–8 weeks) phases. In this study, we observed the behavior of four captive Asian elephant females during multiple estrous cycles over 2 years. We evaluated whether investigative, aggressive, and tail flicking behaviors were related to reproductive condition. Investigative trunk tip contacts showed no distinct pattern by senders, but were more prevalent toward female elephants that were in their follicular compared with their luteal phase. The genital area was the most frequently contacted region and may release reproductively related chemosignals. Aggression did not differ significantly with estrus; however, rates of aggression were elevated when senders were approaching ovulation and receivers were in the luteal phase. Females in the follicular phase may honestly advertise their condition. Contacts by conspecifics may serve to assess condition and reduce aggression. A behavior termed “tail flicking” was performed mainly during the mid‐follicular phase when estrogen and luteinizing hormone levels are known to spike. Tail flicking may disperse chemical signals in urine or mucus as well as act as a tonic signal that could provide a means of anticipating forthcoming ovulation by elephants and also for human observers and caretakers. Zoo Biol 27:167–180, 2008. © 2008 Wiley‐Liss, Inc.     

Lactation and interbirth interval in the Senegal galago (Galago senegalensis moholi)

Five years of reproductive data on Galago senegalensis moholi at the Duke University Primate Center were examined to determine the effect of lactation on interbirth interval and its component phases, postpartum anovulatory interval and interval from onset of estrous cycles to conception. Females whose infants died within 3 weeks of birth had significantly shorter interbirth intervals and postpartum anovulatory intervals than did females who raised their infants until weaning.     

Aggression in the female golden hamster: effects of reproductive state and social isolation

To gain information on possible hormonal correlates, the aggressive behavior of intact female hamsters towards males was observed at various times during the estrous cycle, pseudopregnancy, pregnancy, and lactation. For methodological information, estrous cycle females also were tested after varying periods of social isolation. It was found that pregnant and especially lactating hamsters were more aggressive than pseudopregnant or estrous cycling females. Comparisons of days within each reproductive condition showed that aggression tended to be higher on certain days: the day preceding behavioral estrus of the estrous cycle, Day 10 of pregnancy, and the first 5 days of lactation. Except for pseudopregnancy, sexual behavior unaccompanied by aggression occurred at some time during all reproductive conditions, and both sexual behavior and aggression were found to occur together on Day 10 of pregnancy and Day 1 of lactation. The changes in aggressive behavior associated with reproductive states were attributed to increased male interest, inhibition by ovarian hormones, and facilitation by prolactin. Increasing periods of social isolation also were found to be associated with increased aggression. It was suggested that this effect, too. might have been due to increased prolactin levels.     

Impact of photoperiodic exposures during late gestation and lactation periods on the pineal and reproductive physiology of the Indian palm squirrel, Funambulus pennanti

Studies on the maternal transfer of photoperiodic information in mammals indicate that the daily photoperiod perceived by the mother during the gestation-lactation period is communicated to the fetus either through the placenta or via the milk. However, the impact of photoperiodic exposures during gestation and lactation on the maternal pineal and reproductive physiology has not been reported for any tropical rodent. The exposure of pregnant female Indian palm squirrels (Funambulus pennanti) to constant light (24 h light:0 h dark), constant dark (0 h light:24 h dark), long daylength (14 h light:10 h dark) or short daylength (10 h light:14 h dark) during early gestation (< 30 days) resulted in the resorption of pregnancy, while during late gestation (> 30 days), it did not interfere with the maintenance of pregnancy. Alterations in photoperiodic condition during late gestation and lactation altered the postpartum recovery process. Pineal gland activity, as assessed by pineal mass, protein content and plasma melatonin, was lowest during the breeding phase, but increased gradually after parturition until the next breeding phase. During gestation and lactation, constant light, long daylength and short daylength conditions were less effective, while constant dark condition had a profound effect in depressing pineal gland activity, which subsequently advanced postpartum recovery. Hence, lactating females under constant darkness prepare themselves for next mating much earlier than females under natural daylength (12 h light:12 h dark) conditions. Therefore, photoperiodic information, mediated via the pineal gland, may be important for maintaining gestation physiology as well as postpartum recovery in female rodents.     

Experimental litter size reduction reveals costs of gestation and delayed effects on offspring in a viviparous lizard

Experimental studies have often been employed to study costs of reproduction, but rarely to study costs of gestation. Disentangling the relative importance of each stage of the reproductive cycle should help to assess the costs and benefits of different reproductive strategies. To that end, we experimentally reduced litter size during gestation in a viviparous lizard. We measured physiological and behavioural parameters during gestation and shortly after parturition, as well as survival and growth of females and their offspring. This study showed four major results. First, the experimental litter size reduction did not significantly affect the cellular immune response, the metabolism and the survival of adult females. Second, females with reduced litter size decreased their basking time. Third, these females also had an increased postpartum body condition. As postpartum body condition is positively related to future reproduction, this result indicates a gestation cost. Fourth, even though offspring from experimentally reduced litters had similar weight and size at birth as other offspring, their growth rate after birth was significantly increased. This shows the existence of a maternal effect during gestation with delayed consequences. This experimental study demonstrates that there are some costs to gestation, but it also suggests that some classical trade-offs associated with reproduction may not be explained by gestation costs.     

Effect of mother’s physical condition during pregnancy and lactation on postnatal growth and reproductive success of offspring in water vole <Emphasis Type="Italic">Arvicola terrestris</Emphasis>

Postnatal growth, life span, and probability of reproduction in the adult state depended on the mother’s physical condition during pregnancy and lactation in water vole. The white fat weight in the female abdominal cavity was shown to significantly increase in pregnancy and to decrease in late lactation. As an indicators for nutritional state of females, their body weight difference after parturition (or in late lactation) and expected from the regression equation relating individual body weight at the beginning and the end of each reproductive stage were used (physical condition indexes in pregnancy or lactation). The correlation of the physical condition index in pregnancy with the storage fat weight was 0.67. The metabolic resources of the mother’s body proved to favor faster offspring development. The female offspring weight at the age of 3 and 10 weeks as well as adult ones positively correlated with the mother’s nutritional state in pregnancy, while the male offspring weight demonstrated a similar correlation at the age of 3 and 6 weeks. Increased negative energy balance during lactation proved to decrease the offspring weight in both sexes after separation from mother and at the age of 6 weeks. High nutritional state of mother in pregnancy favored both the probability of reproduction and life span of female offspring. The reproduction of male offspring did not depend on the mother’s physical condition. The life span peaked in male offspring of mothers in a nutritional state below average in pregnancy and above average in lactation. Thus, the physical condition of the mother’s body is an important sex-dependent factor of phenotypic variation in the offspring body weight, reproductive competence, and life span.     

Effect of mother's physical condition during pregnancy and lactation on postnatal growth and reproductive success of offspring in water vole Arvicola terrestris L

Postnatal growth, life span, and probability of reproduction in the adult state depended on the mother's physical condition during pregnancy and lactation in water vole. The white fat weight in the female abdominal cavity was shown to significantly increase in pregnancy and to decrease in late lactation. As an indicators for nutritional state of females, their body weight difference after parturition (or in late lactation) and expected from the regression equation relating individual body weight at the beginning and the end of each reproductive stage were used (physical condition indexes in pregnancy or lactation). The correlation of the physical condition index in pregnancy with the storage fat weight was 0.67. The metabolic resources of the mother's body proved to favor faster offspring development. The female offspring weight at the age of 3 and 10 weeks as well as adult ones positively correlated with the mother's nutritional state in pregnancy, while the male offspring weight demonstrated a similar correlation at the age of 3 and 6 weeks. Increased negative energy balance during lactation proved to decrease the offspring weight in both sexes after separation from mother and at the age of 6 weeks. High nutritional state of mother in pregnancy favored both the probability of reproduction and life span of female offspring. The reproduction of male offspring did not depend on the mother's physical condition. The life span peaked in male offspring of mothers in a nutritional state below average in pregnancy and above average in lactation. Thus, the physical condition of the mother's body is an important sex-dependent factor of phenotypic variation in the offspring body weight, reproductive competence, and life span.     

The tradeoff between torpor use and reproduction in little brown bats (Myotis lucifugus)

In mammals, reproduction, especially for females is energetically demanding. Therefore, during the reproductive period females could potentially adjust patterns of thermoregulation and foraging in concert to minimise the energetic constraints associated with pregnancy and lactation. We assessed the influence of pregnancy, lactation, and post-lactation on torpor use and foraging behaviour by female little brown bats, Myotis lucifugus. We measured thermoregulation by recording skin temperature and foraging by tracking bats which carried temperature-sensitive radio-tags. We found that individuals, regardless of reproductive condition, used torpor, but the patterns of torpor use varied significantly between reproductive (pregnant and lactating) females and post-lactating females. As we predicted, reproductive females entered torpor for shorter bouts than post-lactating females. Although all females used torpor frequently, pregnant females spent less time in torpor, and maintained higher skin temperatures than either lactating or post-lactating females. This result suggests that delayed offspring development which has been associated with torpor use during pregnancy, may pose a higher risk to an individual’s reproductive success than reduced milk production during lactation. Conversely, foraging behaviour of radio-tagged bats did not vary with reproductive condition, suggesting that even short, shallow bouts of torpor produce substantial energy savings, likely obviating the need to spend more time foraging. Our data clearly show that torpor use and reproduction are not mutually exclusive and that torpor use (no matter how short or shallow) is an important means of balancing the costs of reproduction for M. lucifugus.     

Life-history correlates of steroid concentrations in wild peripartum baboons

Steroid concentrations during late pregnancy and early lactation may be affected by both a female's reproductive history and her current condition, and may in turn predict subsequent life-history events, such as offspring survival. This study investigated these relationships in a wild primate population through the use of fecal steroid analysis in repeated sampling of peripartum baboons (Papio cynocephalus). Fecal samples were collected from 32 females in five groups within the Amboseli basin during 8 weeks prior to parturition and 13 weeks postpartum. From December 1999 through February 2002, 176 fecal samples were collected from individuals representing 39 peripartum periods. Fecal concentrations of progestins (fP), estrogen metabolites (fE), glucocorticoids (fGC), and testosterone metabolites (fT) were measured by radioimmunoassay. Steroid concentrations declined from late pregnancy to lactation, and the decline was greatest and most precipitous for fE and fP. Primiparous females had significantly higher mean fE concentrations in each of the last 2 months of pregnancy compared to multiparous females. Among multiparous females, fE and fT were significantly higher during late pregnancy in females carrying a male fetus compared to those carrying a female fetus. During early lactation, high fT in young mothers predicted subsequent infant death during the first year of life. These findings illustrate the potential power of repeated fecal-steroid sampling to elucidate mechanisms of life-history variability in natural populations. They also document significant differences in hormone profiles among subgroups, and highlight that such normative subgroup information is essential for interpreting individual variability in hormone-behavior associations.     

Costs and benefits of maternal aggression in lactating female rhesus macaques

Data from over 400 hr of observation of mother-infant rhesus macaques indicate that during the first 12 weeks of lactation infants are at risk from other group members and that mothers use aggression as well as restraining to protect them. Maternal aggression was negatively correlated with infant restraining. High-ranking mothers reacted aggressively to individuals handling their infants more than did middle- and low-ranking mothers. Conversely, middle- and low-ranking mothers restrained their infants more than did high-ranking mothers. Maternal aggression did not vary with infant age. Maternal aggression was directed toward a higher proportion of higher-ranking adult females and their immature offspring and was more likely to be followed by counter-aggression than nonmaternal aggression, i.e. aggression not related to interactions involving the infant. Middle-and low-ranking mothers suffered higher costs in terms of retaliation than high-ranking mothers. It is argued that the occurrence and distribution of maternal aggression among species and individuals should depend on the risk posed to infants by conspecifics as well as on the characteristics of the social structure (e.g. degree of asymmetry of agonistic contests) and of the mother (e.g. her dominance rank) which may affect the probability of retaliation.     

Patterns of progesterone secretion in free-living California ground squirrels (Spermophilus beecheyi)

During a long-term field study of a free-living population of California ground squirrels (Spermophilus beecheyi), blood samples were drawn at regular intervals from marked females via femoral venipuncture, and plasma progesterone (P) and prolactin (PRL) were measured by radioimmunoassay. Marked fluctuations with season and reproductive condition occurred in circulating levels of both hormones, with peak levels occurring during the spring breeding season. Two peaks in P concentrations were observed each spring, the first occurring during pregnancy, and the second during lactation. Peak PRL levels in females were also reached during the lactation interval, midway between the two P peaks. Analysis of repeated measures from individual females showed a marked decline in circulating P around the time of parturition. Juveniles had lower mean P levels than adults, and yearlings had lower peak levels during their initial reproductive episodes than older females did. The observed pattern of P secretion in S. beecheyi differs from that known for most mammals, but resembles those reported for other ground-dwelling sciurid rodents.     

Postpartum aggression in mice: The influence of suckling stimulation

The influence of suckling stimulation upon postpartum aggression was studied by removing the nipples (thelectomy) of female mice at various times during pregnancy and lactation. Prepartum thelectomy, regardless of whether it was performed prior to mating or shortly before parturition, in combination with the fostering of young, prevented the exhibition of aggression. The aggressive behavior of females thelectomized following either 2 or 5 days of suckling experience was similar to that of normal lactating females. However, only 25% of animals thelectomized following 24 hr of suckling experience exhibited aggressive behavior. The results demonstrate that suckling stimulation is important for the initiation of postpartum aggression but is not essential in animals that have had at least 48 hr of suckling experience.     

Social relationships among adult female baboons

Adult female baboons were studied over a 15-month period which included sexual cycling, pregnancy, and lactation. Females could be ranked in a linear dominance hierarchy which accurately predicted the direction, but not the frequency, of agonistic interactions. Females were most attractive to others during lactation, receiving less aggression, more friendly gestures, more grooming, and grooming by more different individuals than females in other reproductive states. In all three reproductive states high-ranking females were more attractive than others. When differences in behaviour related to changes in reproductive state were factored out, individual females groomed animals next to themselves in the dominance hierarchy more than others. A model is presented showing how rank-relaed access and attractiveness may interact to perpetuate this distribution of grooming over time.     

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.     

Effects of ergocornine and prolactin on aggression in the postpartum golden hamster

The effects on aggressive behavior of prolactin (PRL) and ergocornine hydrogen maleate, an inhibitor of PRL secretion, were investigated in the female golden hamster. Because high aggression and PRL levels are associated with lactation in hamsters, postpartum females were used as subjects. In the first experiment, three groups of ovariectomized and hysterectomized females were compared: normally lactating, ergocornine-treated, and ergocornine plus replacement PRL treated. Normally lactating mothers were typically aggressive towards males in an arena, whereas females given ergocornine were not. Females given both ergocornine and PRL showed an intermediate level of aggression. Although ergocornine suppressed aggression towards adult males, attacks on pups increased. A second experiment sought to determine if ergocornine would depress aggression when PRL involvement was unlikely. At least 30 days following pup removal, females from the first experiment were “trained” to attack home-cage intruders consistently. After ergocornine administration, home-cage attacks by these experienced females were not diminished. Since PRL levels were probably low in these animals, it was concluded that the effects of ergocornine on aggression were limited to instances in which PRL was involved, and that PRL probably can facilitate aggression.     

Reproductive Decisions in Female European Ground Squirrels: Factors Affecting Reproductive Output and Maternal Investment

Physiological and behavioural parameters associated with reproductive effort and success were investigated in female European ground squirrels Spermophilus citellus . The proportion of reproductive (lactating) females in the study population was over 90% and was not related to age. Timing of oestrus and ovulation was found to be affected by the female's emergence date and condition. Females with low emergence mass showed delayed oestrus. Differences in ovulation dates were shown to affect reproductive output in terms of litter size and sex ratio. Early litters were larger and male biased. X-ray techniques were used to determine intrauterine litter size in individual females. The results indicated that litter size and sex ratio were fixed prenatally. Lactation costs were reflected in the intensity of mass loss and duration of lactation. Mass loss varied with litter size, in that females with large litters showed a more rapid loss than others. The second parental investment parameter, lactation duration, varied among individual females and was dependent on the timing of reproduction and litter size (except yearlings). Early born litters, which were, in most cases, larger than later ones, were nursed longer. Prolonged lactation periods affected female condition in that they started prehibernation fattening later and entered hibernation with a lower mass than individuals that had shorter lactation periods. Yearling females probably could not afford the energetic costs of long lactation, independent of their offspring number. These results indicated that females with higher reproductive output and higher investment were unable to compensate these costs before hibernation. Consequences for these individuals could therefore be lower over-winter survival or a delayed oestrus in the following season.     

Postpartum aggression in mice: Experiential and environmental factors

Six experiments were conducted to assess the influence of duration of lactation, the presence of young, and the stimulus characteristics of intruder animals upon postpartum aggression of mice. The first experiment showed that postpartum aggression toward conspecifics was highest between Day 3 and Day 8, declined between Day 9 and Day 14, and was present toward males but absent toward females between Day 15 and Day 21 of the lactation period. Experiment 2 showed that lactating mice rarely attacked conspecifics to which they had been previously exposed but would readily attack strangers. Experiment 3 and 4 demonstrated that lactating animals never attacked intruders when tested 5 hr after pup removal. However, placement of young behind a wire partition in the home-cage for 5 hr or replacement of the offspring for as little as 5 min following 5 hr of separation restored postpartum aggression. The fifth experiment showed that 1- and 10-day old intruders were seldom attacked while intense aggression was directed against 14- and 20-day old intruders. Finally, Experiment 6 demonstrated that 14-day old intruders whose hair was removed were rarely attacked.     

The role of the young in the control of the hormonal events during lactation and behavioral weaning in the golden hamster

This study was designed to determine the relationship between the behavioral and physiological changes occurring in the hamster over the course of lactation. Experimental (E) females were given litters of six 3-day-old pups on Day 13 of lactation and allowed to raise them. Control (C) females raised their own litters of six pups. Groups of E and C females were decapitated at 1000 and 1700 hr when their pups were either 8, 18, or 28 days old. Nursing was observed for 1 hr on the 3 days prior to autopsy. Nursing behavior disappeared by Day 28 in C females. E females exhibited nursing behavior at levels equal to those observed in C females until E pups were 28 days old and 38 days had elapsed since parturition. Despite the fact that E mothers continued to nurse pups on day 18 postpartum when pups were 8 days old, E pups showed lower growth rates than did C pups. Prolactin (PRL) levels remained elevated when E pups were 8 days old even though E pups did not grow normally. PRL levels decreased over time in both C and E females and reached baseline by Day 28 although nursing behavior was still elevated in E females. Thus, nursing behavior did not stimulate PRL release during late lactation. Estradiol (E₂) levels in C females remained at baseline until Day 28 when levels increased. LH, FSH, and Progesterone (P) levels in C females showed a dramatic diurnal pattern which disappeared by Day 28, when levels dropped. Levels of E₂, P, LH, and FSH in E females closely paralleled those of C females only when groups were compared with respect to pup age. Thus, behavioral weaning and the return to estrous cyclicity appear to be dependent upon the age of the pups rather than the time elapsed since parturition. However, milk production and PRL release appear to be more closely tied to the number of days postpartum and can be dissociated from the amount of nursing behavior observed.     

Factor affecting body mass of young fat dormics (Glis glis) at weaning and by hibernation

This paper describes the factors affecting body mass at weaning and by hibernation of young fat dormice (Glis glis) We studied a free-living population in 1991 and 1992 in a mixed forest where 100 nest-boxes were placed. In the two years, 128 females used the nest-boxes to give birth and rear their litters and more than 900 dormice have been individually marked. Body mass of young at weaning was positively correlated to body mass of the mother in both years and to birth date in 1991, while litter size was negatively correlated to body mass of the young in 1992 only, when birth took place about two weeks later than in 1991. On the contrary, by the time of hibernation, young born later weighed significantly less than those born earlier in the season, and heavier young at weaning remained heavier by hibernation, while maternal body mass and litter size did not significantly affect body mass of young at this stage. Body mass of the mother was negatively related to the date of parturition and early breeding females lost weight during lactation, while females that bred later did not. It seems, therefore, that early breeding carries a cost that only females in good condition can afford. It appears that females may follow two strategies: those in poor body condition will delay pregnancy so that lactation occurs when environmental feeding conditions are at their best; those in good condition will breed earlier, since they can afford to lose weight during lactation. Their young will have more time to grow before hibernation and the mothers themselves will have a longer period of time for restoring their fat reserves.     

Lactational estrus induction in the Mexican hairless sow

The purpose of this study was to determine the effects on the reproductive performance of the Mexican hairless pig (MHP) while inducing fertile lactational estrus. Lactational estrus was induced on day 8, postpartum, in 20 primiparous sows during two consecutive reproductive cycles. Boar presence and temporary litter withdrawal were used as stimuli. Group I did not receive stimuli (control, C); group II had a 15 min boar stimulus (B); group III had litter withdrawal for 4 h (LW), and group IV received both stimuli (B + LW). Fertile estrus was detected by sow behavior, exfoliative vaginal cytology, and 17 beta-estradiol and progesterone samples. Individual stimuli did not induce fertile lactational estrus; nevertheless, when used together, both stimuli induced 100% of females into estrus, and 80% of them got pregnant while lactating. The partial withdrawal of the litter had a significant and positive effect on the number of live born piglets. Sows pregnant during lactation had shorter reproductive cycles, by not having non-productive days and litter size was greater. Pregnancy induction during lactation allowed the Mexican hairless sow to reduce the period between parturition's without diminishing the lactation length and litter performance.