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PubMed1997

Serum concentrations of steroid hormones during reproduction in the Atlantic stingray, Dasyatis sabina.

The Atlantic stingray, Dasyatis sabina, has a well-defined annual reproductive cycle in Florida. We collected adult specimens over 12 months and evaluated reproductive parameters and serum levels of five steroid hormones, 17beta-estradiol (E2), progesterone (P4), testosterone (T), dihydrotestosterone (DHT), and corticosterone (CS). Female E2 peaked twice, once in mid-March to early April in association with ovulation and again in mid-June to mid-July in association with the enlargement of a second group of ovarian follicles. Female P4 peaked in early March and early April, coincident with the peak in E2. Female DHT was variable but exhibited a pattern not clearly associated with known events in the reproductive cycle. Female T and CS levels did not vary significantly through time. In males, T, DHT, and CS increased progressively through winter and spring, peaking in March when females were ovulating and when copulation probably took place. DHT concentrations were usually at least twice T levels. These three hormones peaked long after the November/December peak in gonadosomatic index. E2 was measurable in males and was highest during the period of testicular development. Male P4 varied in a pattern not clearly associated with known reproductive events.

Animals↗
PubMed1998

Localization of the neuropeptide APGWamide in gastropod molluscs by in situ hybridization and immunocytochemistry.

The amidated tetrapeptide Ala-Pro-Gly-Trp-NH2 (APGWamide) plays a key role in the control of male copulation behavior in the basommatophoran pulmonate freshwater snail Lymnaea stagnalis. The morphological basis for a conserved role of APGWamide in the control of male reproduction in gastropod molluscs is presented. The prosobranch Littorina littorea, the opisthobranch Aplysia californica, the basommatophoran pulmonate Bulinus truncatus, and the stylommatophoran pulmonates Arion ater and Limax maximus have been examined for the presence of APGWamide producing neurons using immunocytochemistry and in situ hybridization. In all species investigated a cluster of APGWamide expressing neurons is present in the anteromedial region of the cerebral ganglia. The asymmetrical distribution which exists in Lymnaea and which coincides with the innervation of the asymmetrically located penial complex is also found in the opisthobranch Aplysia, as well as in the stylommatophoran pulmonate slugs Arion and Limax, in which APGWamide immunoreactive neurons are only found in the mesocerebrum of the right cerebral ganglion. APGWamide immunoreactive varicose fibers innervate muscles of the male accessory sex organs in Bulinus and Aplysia, confirming the hypothesis that APGWamide may be a biochemically and functionally conserved factor in the regulation of gastropod mollusc reproduction.

Animals↗
PubMed1999

Steroid levels and reproductive cycle of the Galápagos tortoise, Geochelone nigra, living under seminatural conditions on Santa Cruz Island (Galápagos).

The Galápagos Islands are home to 11 subspecies of large terrestrial tortoises (Geochelone nigra). All Galápagos tortoises are considered endangered and approximately 12,000 animals still exist. Until now, the reproductive cycle of the Galápagos tortoise has been studied only in captive animals, and no data from free-ranging tortoises have been available. During a one-year period, blood samples were collected from male and female G. nigra living under seminatural conditions on Santa Cruz Island, Galápagos. Plasma steroid hormones were measured by radioimmunoassays (RIAs). In males, plasma testosterone and corticosterone increased a few months before the onset of the mating season. Peak levels were observed while most copulations occurred and environmental temperatures were highest. Both testosterone and corticosterone showed low levels during the cold and dry nesting season and high levels during the hot and rainy mating season. In females, testosterone and corticosterone also rose during the hot and rainy mating season. Both hormones peaked during the second half of the mating season and decreased during the cooler dry season. Female estradiol levels increased at the onset of the mating season, reaching the highest level at the peak of the mating season, which coincided with the highest annual temperatures measured. Estradiol slowly decreased within the next months and rapidly dropped at the onset of the nesting season when temperatures decreased. Progesterone levels were high close to the time of ovulation and showed clearly elevated levels at the beginning of the nesting season after some females had laid their first clutch. Progesterone decreased during the nesting season, when ambient temperatures began to decrease, and reached minimal levels in the postbreeding period shortly before the onset of the next mating season. There were significant annual variations in plasma testosterone in both males and females. Plasma corticosterone was generally higher in males than in females and varied throughout the year in both sexes.

Animals↗
PubMed1993

Testosterone, antiandrogen, and alloparental behavior in bobwhite quail foster fathers.

Vasectomized male Texas bobwhite quail (Colinus virginianus texanus) are used as foster fathers in a program to reintroduce the endangered masked bobwhite quail to its native habitat. Less than half of the Texas bobwhite, however, show appropriate alloparental behavior toward the chicks. They also undergo a significant decline in testosterone (T) after 3 to 4 days exposure to the chicks. Males that do not show alloparental behavior undergo a significant increase in T during the same exposure to chicks. Implants containing the antiandrogen flutamide do not affect the courtship and copulation behavior of mated bobwhite males, but flutamide implants do decrease the tendency of these males to act aggressively in the presence of an intruder into the pen of the pair. Flutamide implants do not, however, increase the probability that the males will exhibit alloparental behavior toward chicks that are not their own. Implants containing a mixture of flutamide and ATD (an aromatization inhibitor) also do not increase alloparental behavior. We conclude that while blocking the behavioral effects of T may be necessary for the expression of parental or alloparental behavior, it is not sufficient, suggesting that some other hormonal change may also be necessary to stimulate parental care of precocial chicks.

Aggression↗
PubMed1995

Hormonal responses of male gerbils to stimuli from their mate and pups.

Following copulation and cohabitation with a pregnant female, male gerbils show high levels of parental behavior toward their pups. The initiation of male parental behavior may be the result of neuroendocrine changes induced by cohabiting with the pregnant female or by pup stimuli. Experiment 1 examines the changes in androgen and prolactin levels in male gerbils cohabiting with females over the reproductive cycle. Gerbils were mated and blood samples taken from males for hormone analysis 1, 10, and 20 days after pairing and 3, 10, and 20 days after pups were born. A group of unmated male gerbils served as controls. Plasma prolactin levels of males were elevated throughout the female's pregnancy and lactation periods, but were only statistically significantly higher than those of unmated males 20 days after pups were born. Androgen levels rose during pregnancy and dropped significantly after the birth of the pups. These hormonal changes are similar to those found in males of monogamous birds and differ from those found in males of polygynous rodents such as the rat. Experiment 2 examined the hormonal responses of male and female gerbils to pup replacement after 4 hr of parent-pup separation. Female gerbils showed a significant elevation of prolactin levels 1 hr after pup replacement, but males did not. Males with pups returned showed no difference in androgen levels from males who did not have pups returned. Thus, male gerbils show neuroendocrine changes following long-term cohabitation with their mate and pups, but do not show acute hormone responses to pup removal and replacement. These results indicate that parental males have neuroendocrine changes associated with parental behavior and these differ from the neuroendocrine changes underlying female parental behavior.

Androgens↗
PubMed1996

Parental care and the prolactin secretion pattern in the King penguin: an endogenously timed mechanism?

The King penguin (Aptenodytes patagonicus) has been studied on Possession Island, Crozet Archipelago (46 degrees 25'S-51 degrees 45'E). It is an offshore feeder, but it breeds on land. Its breeding cycle is unusually long (about 14 months). It starts at the beginning of spring, is interrupted during 5 months of winter, and ends in the next spring. Furthermore, it is characterized by a long parental care period, of about 11 months, including the winter interruption. In fact, care given to the egg and the chick is biparental, which supposes that parental behavior includes both parents. Each parent alternates care given to the egg and to the chick on land and foraging bouts at sea. An incubation bout, or a chick care bout, is called a shift. Prolactin is the hypophyseal hormone known to be correlated with incubation and chick care. We studied the mechanism of the maintenance of prolactin during the parental care period in the King penguin, a period which is unusually long. In many species, prolactin secretion has been shown to be stimulated by the presence of eggs and/or chicks, but in the King penguin, prolactin secretion is observed throughout the entire period of parental care, despite the fact that the birds leave the egg and the chick repeatedly and for extended periods of time to feed. Prolactin levels rise significantly at the beginning of courtship; females have significantly higher prolactin levels than males during courtship, copulation, and the period of waiting for egg laying. In both sexes, prolactin levels remain high during incubation and the first part of chick rearing, before winter. Prolactin concentrations decline somewhat during the winter period of minimal parental care, but remain that level in spring when parental care starts again. The level returns to basal value during molt. Prolactin levels rise during the incubation shifts but not over the course of contact with young. Prolactin values remain high in unsuccessful breeders, possibly preventing the birds from relaying, but remain low in immature birds. These data raise questions about how prolactin secretion is controlled in this species. The hypothesis of a programmed secretion of prolactin is advanced.

Animals↗
PubMed1998

Estradiol increases female sexual initiation independent of male responsiveness in rhesus monkeys.

Copulation and female initiation of sexual behavior vary across the ovarian cycle, suggesting that female hormonal condition influences female sexual motivation in rhesus monkeys. However, the effects of hormones on female sexual motivation are difficult to identify because male behavior also varies with female hormonal condition. During the nonbreeding season, male rhesus monkeys are sexually unresponsive to females; thus the effects of estradiol treatment on female sexual motivation can be examined independent of male behavior. This study administered estradiol to five ovariectomized females living in a large age-graded social group during the nonbreeding season. The behavior of these females with and without estradiol treatment was compared. Data were collected concurrently on five intact, noncycling, nonpregnant females. Estradiol treatment significantly increased sexual initiation by ovariectomized females toward males without any significant changes in male behavior. Estradiol-treated females also displayed greater sexual initiation than nonpregnant, intact females. Both estrogen and progesterone were important predictors of sexual initiation in females, with progesterone having an inhibitory effect. Endogenous progesterone levels in females were negatively correlated with male contact behavior, suggesting that female attractiveness is reduced by progesterone. This study provides further support for estrogen as the critical steroid increasing female sexual motivation in primates.

Animals↗
PubMed1998

Dispersal status influences hormones and behavior in the male spotted hyena.

Male spotted hyenas (Crocuta crocuta) reach puberty at 24 months of age and then invariably emigrate from their natal clans 1 to 38 months later. Thus there are two classes of reproductively mature males in every Crocuta clan: adult natal males born in the clan and adult immigrant males born elsewhere. In one free-living hyena population in Kenya, these two groups of males were compared with respect to measures of aggression, social dominance, sexual behavior, and circulating hormone levels. Adult natal males engaged in higher hourly rates of aggression than did immigrants, won all fights with immigrants, and were socially dominant to immigrants. In addition, adult natal males engaged in far lower hourly rates of sexual behavior with resident females than did immigrants, and natal males were never observed to copulate with natal females. Mean basal plasma cortisol values did not differ between the two groups of adult males, but cortisol concentrations in immigrants were positively correlated with tenure in the clan and with immigrant male social rank. Adult natal males had plasma testosterone levels significantly lower than those of immigrants. Social rank and plasma testosterone values were positively correlated among immigrant males. Thus two different relationships appear to exist between circulating testosterone and social rank in male Crocuta: one apparent in immigrants and the other in natal adult males. Our results suggest that dispersal might disinhibit testosterone secretion in postpubertal male hyenas.

Aggression↗
PubMed1999

Regulation of noncontact erection in rats by gonadal steroids.

Male rats exhibit erections in the presence of inaccessible estrous females, and we investigated which gonadal steroids regulate these noncontact erections (NCEs). Sexually experienced Wistar males (n >/= 8/group) were tested for NCE four times (every 3 days) before castration, after castration, and after receiving subcutaneous implants of 10-mm Silastic capsules that were empty or filled with crystalline testosterone propionate (TP), dihydrotestosterone (DHT), estradiol benzoate (EB), or DHT + EB (10 mm each). Before castration, males responded with NCE in approximately 50% of tests. No males had NCEs after castration, beginning 3 days after surgery. Also, no males responded after treatment with EB or empty capsules. After receiving implants of TP, DHT, or DHT + EB, 50% of males had NCEs, beginning with the first test 3 days after treatment. On every measure of NCE, males treated with DHT or DHT + EB were indistinguishable from each other and from TP-treated males. Among the sexual responses of male rats, NCE appears to be more sensitive than other behaviors to changes in gonadal condition. In its profile of response to gonadal steroids (testosterone+, dihydrotestosterone+, estradiol-), NCE is similar to reflexive erection, for which spinal systems are sufficient, and unlike copulation (T+, DHT-, E+), which depends on discrete areas of the brain. We nonetheless conclude that NCE depends on androgen-sensitive systems in the brain, but androgen-sensitive neurons in the lumbosacral spinal cord may also play a role.

Animals↗
PubMed1999

Endocrine and energetic mediation of play behavior in free-living Belding's ground squirrels.

Many juvenile mammals play, and rates and patterns of play behavior often differ between young males and females. The sexual dimorphisms typical of mammalian play suggest that it might be influenced by gonadal hormones. Moreover, because play competes with growth, physical development, and acquisition of fat reserves for available energy, play behavior should theoretically be influenced by energetic variables. We examined patterns of social play behavior and endocrine and energetic mediation of social play in free-living juvenile Belding's ground squirrels (Spermophilus beldingi). Bouts of social play in young S. beldingi resembled adult copulation and fighting, and young males initiated sexual play but not play fighting at much higher rates than did young females. To elucidate the proximal causes of play, we altered early androgen exposure by treating females with testosterone (T) at birth and used females treated with oil vehicle as controls. We concurrently manipulated energy availability by provisioning with extra food and used unprovisioned squirrels as controls. Hourly rates of play behavior were highest near the time of weaning and declined thereafter among both experimental and control groups of juveniles. Thus, we observed no influence of either T treatment or food provisioning on the temporal patterning of play behavior. Perinatal T treatment had no effect on play fighting, but caused rates of sexual play behavior initiated by young females to increase to near those observed for young males, suggesting that T organizes a masculine tendency to initiate sexual play behavior but not play fighting. Food provisioning increased rates of play among males and females from both T-treated and control litters, suggesting that energy availability limits play behavior.

Aggression↗
PubMed2000

Appetitive and consummatory sexual behaviors of female rats in bilevel chambers. II. Patterns of estrus termination following vaginocervical stimulation.

Copulation with intromission or manual vaginocervical stimulation (VCS) shortens the duration that intact female rats maintain lordosis responding during estrus. The present study examined whether VCS could shorten the duration of both appetitive and consummatory measures of female sexual behavior, and whether these effects occur differentially in time and across different hormone priming intervals. Ovariectomized, sexually experienced female rats were administered subcutaneous injections of estradiol benzoate 48 h and progesterone 4 h, before receiving 50 manual VCSs with a lubricated glass rod distributed over 1 h. Control females received sham VCSs distributed over the same time. The females were then tested for sexual behavior in bilevel chambers with two sexually vigorous males (to one ejaculatory series or 10 min with each male, separated by 5 min) 12, 16, and 20 h after VCS. Prior to the final hormone treatment, different groups of females had been given the same hormone treatment either 28, 14, 7, or 4 days before. In females tested at 28- and 14-day hormone intervals, VCS induced both active and passive rejection responses at 12, 16, and 20 h. In contrast, females that received sham VCS displayed relatively normal sexual behavior at 12 h, although by 16 and 20 h these females displayed active and passive rejection. Females tested at 7- or 4-day intervals displayed normal levels of lordosis at all testing times, regardless of VCS treatment. These data indicate that VCS facilitates rejection responses that precede the decrease in lordosis responsiveness. However, the effects of VCS are dependent on the frequency of hormone priming, suggesting that hormone treatment may block some of the long-term inhibitory effects of VCS on female sexual behavior.

Animals↗
PubMed2000

Progesterone inhibits female courtship behavior in domestic canaries (Serinus canaria).

We studied copulation solicitation display (CSD) responses to playback in photostimulated female canaries given systemic injections of progesterone. Eight females received injections of 0.1 mg of progesterone dissolved in olive oil during their first breeding cycle and were untreated during their second breeding cycle; eight females received only the oil vehicle during their first breeding cycle and received no treatment during their second breeding cycle. The injections were performed every second day during 15 days, after the onset of nest building. Progesterone treatment resulted in a significant increase of plasma progesterone which in turn provoked an inhibition of females' CSDs and decreased the size of the clutch. During the first breeding cycle, progesterone-treated females had lower CSDs and egg-laying scores than did control females. During the second breeding cycle, when females received no treatment, no differences emerged between the two groups. The suppressive effect of progesterone on female sexual responses was observed as soon as 48 h after the beginning of the treatment. We propose that progesterone plays a key role in mediating the transition from active female courtship behavior to sexual refractoriness in this species. Suppressive effects of progesterone on female sexual behavior have been previously described in lizards as well as in rodents. Our data are consistent with the hypothesis of Godwin et al. (J. Godwin, V. Hartman, M. Grammer, and D. Crews, Horm. Behav. 30, 138-144, 1996) which proposed that the decrease in sexual behavior following plasma progesterone increase represents an evolutionarily conserved mechanism in the regulation of female sexual behavior.

Animals↗
PubMed2000

Testosterone, endurance, and Darwinian fitness: natural and sexual selection on the physiological bases of alternative male behaviors in side-blotched lizards.

The mechanistic bases of natural and sexual selection on physiological and behavioral traits were examined in male morphs of three colors of the side-blotched lizard, Uta stansburiana. Orange-throated males are aggressive and defend large territories with many females. Blue-throated males defend smaller territories with fewer females; however, blue-throated males assiduously mate guard females on their territory. Yellow-throated males do not defend a territory, but patrol a large home range. They obtain secretive copulations from females on the territories of dominant males. Males with bright orange throats had higher levels of plasma testosterone (T), endurance, activity, and home range size and concomitantly gained greater control over female home ranges than blue- or yellow-throated males. Experimentally elevating plasma T in yellow- and blue-throated males increased their endurance, activity, home range size, and control over female territories to levels that were seen in unmanipulated orange-throated males that had naturally high plasma T. However, the enhanced performance of orange-throated males is not without costs. Orange-throated males had low survival compared to the other morphs. Finally, some yellow-throated males transformed to a partial blue morphology late in the season and the endurance of these transforming yellow-throated males increased from early to late in the season. In addition, yellow-throated males that transformed to blue also had significantly higher plasma T late in the season compared to the plasma T earlier in the season. T appears to play an important role in the physiological changes that all three color morphs undergo during the process of maturation. In some yellow males, T plays an additional role in plastic changes in behavior and physiology late in the reproductive season. We discuss natural and sexual selection on physiological and behavioral traits that leads to the evolution of steroid regulation in the context of alternative male strategies.

Aggression↗
PubMed2000

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris).

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.

Animals↗
PubMed1999

Sperm competition. II-post-copulatory guarding

A two round sperm competition model is analysed to determine which male strategy is advantageous for fertilization of a given set of eggs; guarding a particular female or searching for another copulation. A guarding male is one who would guard if he mates in the first round (which may not occur) whilst a non-guarding male decides on how much sperm to allocate if given the opportunity to inseminate a female in round one. Guarding behaviour is defined in terms of a probability of preventing a further insemination if challenged by a rival male. Sperm success with a single female obeys the "raffle principle". An evolutionarily stable strategy (ESS) approach is used to ascertain the best non-guarding ejaculation strategy. We show that for each fixed proportion of guarders in the population the strategies are ordered and that only a single guarding strategy need be considered. The model predicts that there will be evolution to either the guarding strategy or a single non-guarding strategy or a polymorphic combination of guarding and some (or all) of the non-guarding strategies. The conditions for coexistence to occur were shown to be rare in comparison to those necessary for a monomorphism. Copyright 1999 Academic Press.

Journal Article↗
PubMed1995

Behavior patterns of the aplysiid gastropod Bursatella leachii in its natural habitat and in the laboratory.

The behavior of the ragged sea hare, Bursatella leachii pleii Rang, was observed in its natural habitat and in captivity. An indication of the seasonal availability of Bursatella in Puerto Rico was obtained by making multiple observations at a single site. The behavior patterns of Bursatella in the field were indicative of a daily rhythm. They tended to be found in groups at sunrise and as isolated individuals in the afternoon. They were observed to assemble following sunset and to disperse in the morning. Certain aspects of this rhythmic pattern of behavior persisted in animals held in the laboratory, where copulation was the most common behavior in the morning and feeding-related activities became more prevalent in the afternoon. Specific behaviors related to autonomic function (respiration and digestion) were also observed and quantified. It is proposed that the rich behavioral repertoire exhibited by B. leachii, and the ease with which these animals are observed in their native habitat, provide favorable systems for studying neuronal mechanisms involved in the organization and evolution of complex behavior.

Animals↗
PubMed1993

Oligonucleotide fingerprinting of free-ranging and captive rhesus macaques from Cayo Santiago: paternity assignment and comparison of heterozygosity.

Multilocus DNA fingerprinting with oligonucleotide probes (GTG)5, (GATA)4, and (CA)8 was applied in order to determine paternity in one birth cohort (15 infants) of social group (S) from the free-ranging colony of rhesus macaques (Macaca mulatta) on Cayo Santiago. While sires could be identified in 11 cases, all males tested (N = 19) could be excluded from paternity for the remaining four infants. Data revealed marked discrepancies between actual paternity and paternity as inferred from the observation of copulation behavior. Thus, a dominant social rank does not appear to be strongly associated with reproductive success. Furthermore, alternative reproductive strategies were found to yield comparable net benefits in reproduction. A second group of animals (M) was translocated from Cayo Santiago to the Sabana Seca Field Station in 1984. They have continuously resided together in a large outdoor enclosure since then. Here paternity assessment was seriously impeded by a reduced number of discriminating bands, i.e. offspring bands which were unequivocally derived from the sires. This was initially held to be indicative of a smaller degree of heterozygosity in Group M, and was attributed to inbreeding due to a lack of male immigration or extra-group fertilizations. However, a comparison of the DNA fingerprint patterns obtained in Group S and Group M lends only partial support to this idea.

Animals↗
PubMed1981

Locomotion of the filiform sperm of littorina (Gastropoda, Prosobranchia).

The filiform sperm of Littorina sitkana swims effectively in sea water and more viscous fluids, overcoming the problems of a non-uniform flagellar beat with an unusual mechanism, which involves three main events: (1) the sperm rotates anti-clockwise (looking from tail to head); then (2) stops rotating and stiffens itself to form a screw-shape, with the tail being held perpendicular to the middle piece, and finally; (3) reverses its rotation and propels itself forward in a clockwise spiral. The average velocity of sperm is approximately 184 micrometer/s with a rotational frequency of 24 revs/s. The mechanism of propulsion may involve two kinetic centers at opposite ends of the sperm, which coordinate their movements to produce anti-clockwise rotation, stationary twisting, or clockwise rotation, in a manner reminiscent of spirochaetes. Littorina sperm also exhibit slower methods of propulsion including swimming backwards (tail first) at 18 micrometer/s, and "gliding" at about 30 micrometer/s. The adaptive significance of the rapid propulsion is not obvious, because Littorina copulate and fertilize internally and at each stage in the transfer there are external aids to sperm transport, such as ciliary action (oviduct) and muscular expulsion (bursa and seminal receptacle). The filiform shape, however, is well-adapted for long-term storage in the female body. These points are discussed.

Animals↗