Oscillatory Electric Potential on the Olfactory Epithelium Observed during the Breeding Migration Period in the Japanese Toad, Bufo japonicus

Japanese toad (Bufo japonicus) tracks the route to and from the breeding sites using the olfactory cues from the migration route and not from the destination (). We recorded a slow extracellular potential change (electro-olfactogram or EOG) evoked on the olfactory epithelium by applying an olfactory stimulus with an air stream. In September toads, only a simple typical EOG that is common in various vertebrate species was observed. Oscillatory potential changes (OSC) superimposed on the typical EOG were observed in the breeding season when studied throughout a year. There were no sexual differences in the occurrence and the amplitude of the OSC. Oscillatory potentials were observed also from the olfactory nerve of the brain. The OSC in the olfactory epithelium remained even after denervation. In addition, it was suggested that there are multiple sites of OSC initiation in the olfactory epithelium. These results suggest an intimate relationship between OSC appearance and the breeding migration in the toad.     

Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: II. Responses to acute stress in the laboratory.

Circulating concentrations of plasma corticosterone and gonadal steroids were measured in intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season.     

Social influences on oestrous cycle length and plasma progesterone concentrations in the female lesser mouse lemur (Microcebus murinus)

Plasma progesterone concentrations were recorded during one breeding season in 19 lesser mouse lemur females living in different social conditions. The oestrous cycle length and the progesterone profile mainly depended on the social environment of the female. For totally isolated females, the oestrous cycle lasted 38 +/- 5.7 days and included a 25-30-days spontaneous luteal phase with a progesterone peak about 100 ng/ml between the 20th and 25th days after oestrus, and a prolonged preovulatory period of 10-15 days which could be considered equivalent to the follicular phase of a menstrual cycle. When females were able to communicate through olfactory, visual and auditory signals, the oestrous cycle was significantly lengthened (53.7 +/- 5.9 days). When females had tactile contacts, the oestrous cycle was further lengthened (62.7 +/- 0.8 days). This lengthening of the oestrous cycle was related to an extension of the luteal phase associated with a decrease in progesterone concentrations during this period. In females maintained with one male (paired) or with males and females (heterosexually grouped), large individual variations were shown in cycle lengths or in progesterone concentrations. In these females, cycle lengths and progesterone concentrations were inversely correlated to plasma cortisol concentrations.     

Effect of an increase in environmental temperature on testicular androgenesis and spermatogenesis in toad (Bufo melanostictus) during hibernating season

Activities of key testicular androgenic enzymes [Δ(5), 3β-hydroxysteroid dehydrogenase (Δ(5), 3β-HSD) and 17β-hydroxysteroid dehydrogenase (17β-HSD)], plasma levels of testosterone, and testicular gametogenic activities were studied in heat-exposed adult male toads during hibernating season for two consecutive years. Exposure of toads to an elevated environmental temperature for 14 and 21 days resulted in significant elevation of testicular Δ(5), 3β-HSD and 17β-HSD activities, along with plasma levels of testosterone. Testicular gametogenic activity, by means of quantity of all stages of spermatogenic cycle, were elevated significantly at the same experimental schedule, but 7 days of heat exposure resulted in significant elevation only in stage IV. The results indicated that environmental temperature is an important modulator of breeding activities of male toads. It also demonstrated that testicular activities in seasonally breeding toads are probably not linked to hibernating cycle.     

Influence of adrenal cortex on testicular activity in the toad during the breeding season

The aim of the present study was to determine the role of adrenals in gonadal activity in the male toad during the breeding season. Exogenous administration of corticosterone or metapyrone for 6 days inhibited adrenal delta5-3beta(delta 5-3 beta) hydroxysteroid (delta5-3beta-HSD) and testicular 17beta (17 beta) hydroxysteroid dehydrogenase (17beta-HSD) activities, decreased the serum levels of testosterone and inhibited spermatogenesis. When toads were treated with corticosterone a significant rise of serum corticosterone was noted while metapyrone treatment appeared to decrease serum corticosterone levels. It is concluded that adrenocortical hormone plays an indirect role in testicular activity in toads during the breeding season.     

Involvement of the corticoadrenal hormones in the pheromonal restoration of reproductive activity in aging rats

The involvement of the adrenal progesterone and corticosterone in the early gonadotropin secretion associated with the pheromonal restoration of ovarian cyclic activity (PRCA) in aging female rats is studied. PRCA is induced by male urinary pheromones and is preceded by an alpha-adrenergic-mediated release of the hypothalamic decapeptide luteinizing hormone-releasing hormone and plasma increases of estradiol, progesterone and the gonadotropins luteinizing hormone and follicle stimulating hormone. Aging reproductive Wistar female rats were used to study the effects of bilateral adrenalectomy and of a subcutaneous injection of the antisteroid RU486 on plasma levels of corticosterone, progesterone and gonadotropins in rats stimulated with nasal spraying of male urine (MU) or saline. The results demonstrate that progesterone and corticosterone released by MU are from adrenal origin, and that these adrenal secretory products are critical for MU-induced increase of gonadotropins. This suggests that olfactory stimulation of ACTH release stimulates adrenal release of progesterone and corticosterone, and both trigger the events that initiate the activation of the hypothalamus-pituitary-ovarian axis that leads to PRCA.     

Orientation behaviour of toads (Bufo bufo) displaced from the breeding site

Summary The sensory basis and spatial range of orientation to the breeding site were studied in the toadBufo bufo, during two breeding seasons. Toads were displaced passively from their breeding pond and fitted with a tracking device to record the path of migration in individuals. The directional choice and the straightness of trails after release were used to quantify the effect of experimental treatments. In both years, control (untreated): toads headed to the breeding site with the same precision at all release sites. The initial orientation of toads blinded by opaque tape over their eyes. did not differ from controls, but the return paths were not as direct. The directional choice of anosmic toads was apparently random, however, individuals followed a straight path in a chosen direction. Anosmic toads also blinded were completely disoriented, moving in cycloid trails. Bar magnets glued to the head caused an increase in dispersion of toads. However, in some individual releases a directional bias without increased dispersion was observed. Sky conditions (clear or overcast) did not influence the initial orientation or the dispersion of toads. Nevertheless, the breeding site component was significantly correlated with wind direction in relation to the breeding site. Wind blowing from the breeding site improved the initial orientation, whereas wind from the opposite direction reduced the breeding site component. The spatial range for the ability to relocate the breeding pond after displacement exceeded 3 km, but the time taken to select the correct direction increased with the displacement distance. The results indicate that after displacement the initial orientation ofB. bufo is based mainly on olfactory and magnetic cues, with visual control of straightness.     

Peripheral plasma progesterone: a marker for determining cyclicity in yaks (Poephagus grunniens L.)

An attempt was made to determine cyclicity in yaks using plasma progesterone during the breeding and non-breeding seasons. Fifteen non-lactating yaks were used in this experiment. During the breeding season (July to November), blood samples were collected from 8 yaks at least twice weekly until estrus was observed and then at 2 days interval for 30 days. During the non-breeding season (February to March), blood samples were collected from the same number of yaks at 2-day interval for 30 days. Progesterone was determined in plasma samples by radioimmunoassay. During the breeding season, plasma progesterone at estrus was basal (< or = 0.2 ng/ml). Concentrations increased thereafter with a sharp increase during the late luteal phase, typically reaching peak levels around day 15. Concentrations then declined rapidly over the following 4 days, reaching basal levels at estrus. A high proportion (66.7%) of potential estrous periods (based on progesterone concentrations) went undetected, indicating that silent or weak estrus was a prominent problem in yak cows. During the non-breeding season, three animals were found to be cycling as determined by the patterns of plasma progesterone. Yet, behavioral symptoms of estrus were not observed in any of these yak cows. We conclude that peripheral plasma progesterone concentrations can be used to monitor cyclicity in yak cows effectively.     

Immunoreactive inhibin levels in peripheral blood during the breeding season in the female Japanese monkey

Serum levels of immunoreactive inhibin as well as FSH, LH, estradiol-17 beta, and progesterone were measured by RIA in four mature female Japanese monkeys (Macaca fuscata fuscata) during the breeding season and subsequent transition into the nonbreeding season. During the breeding season, each monkey showed 2-6 ovulations, which were inferred from underlying endocrine events. The concentrations of serum inhibin increased during the luteal phase, but were low during the follicular phase. Such changes in serum inhibin levels correlated positively with those in serum progesterone levels. Basal levels of serum inhibin also increased during the breeding season, decreased during transition from the breeding season, and were low during the nonbreeding season. The parallel change in serum levels of inhibin and progesterone together with the increased basal levels of serum inhibin during this period suggests that both the CL and antral follicles are sources of circulating inhibin. Decreases in serum FSH levels during the luteal phase suggest that secretion of FSH is controlled by an inhibitory action of ovarian inhibin in addition to steroid hormones.     

Hormonal Correlates of Social Rank in an Asocial Species, the Common Brushtail Possum (Trichosurus vulpecula)

Dominance hierarchies play an important role in access to mates or resources in many species. Rank is sometimes correlated with circulating testosterone levels or morphological traits such as body weight. The relationship of glucocorticoid secretion and rank, however, is less clear. In this study, we investigated the relationship of male rank to body weight, circulating testosterone and cortisol concentrations in captive possum triads (Trichosurus vulpecula). We carried out two experiments to examine hierarchy formation and the effects of castration of the dominant male during the non‐breeding season. A third experiment measured the effects of removal of the dominant male from a stable hierarchy during the breeding season. We found that dominant male rank was significantly correlated with higher circulating testosterone levels during periods of hierarchy formation and during the breeding season but not during periods of hierarchy stability in the non‐breeding season. Lack of correlation between plasma testosterone concentration and rank after male castration suggests that stable social rank is not dependent on hormone level and may be more dependent on behavioural traits. Any biocontrol measures that rely on manipulation of hormone levels may be unreliable when applied to unstable hierarchical situations, including the establishment of territories by subadult males, and the pre‐breeding season when circulating testosterone concentrations peak in males and a period of hierarchy establishment may occur.     

Testosterone,migration distance,and migratory timing in song sparrows Melospiza melodia

In seasonally migratory animals, migration distance often varies substantially within populations such that individuals breeding at the same site may overwinter different distances from the breeding grounds. Shorter migration may allow earlier return to the breeding grounds, which may be particularly advantageous to males competing to acquire a breeding territory. However, little is known about potential mechanisms that may mediate migration distance. We investigated naturally-occurring variation in androgen levels at the time of arrival to the breeding site and its relationship to overwintering latitude in male and female song sparrows (Melospiza melodia). We used stable isotope analysis of hydrogen (δ²H) in winter-grown claw tissue to infer relative overwintering latitude (migration distance), combined with 14 years of capture records from a long-term study population to infer the arrival timing of males versus females. Relative to females, males had higher circulating androgen levels, migrated shorter distances, and were more likely to be caught early in the breeding season. Males that migrate short distances may benefit from early arrival at the breeding grounds, allowing them to establish a breeding territory. Even after controlling for sex and date, androgen levels were highest in individuals that migrated shorter distances. Our findings indicate that androgens and migration distance are correlated traits within and between sexes that may reflect individual variation within an integrated phenotype in which testosterone has correlated effects on behavioral traits such as migration.     

Electroolfactogram study of the unilaterally axotomized frog

Changes of amplitude in the electroolfactogram (EOG) were investigated following unilateral section of the olfactory nerve. A reduction in EOG amplitude was observed during the first two weeks after the operation; electrical activity gradually began to return to normal and reached 80–100% of control level for trial substances by the end of the third week. Complete disappearance of EOG over the entire surface of the olfactory organ was not observed in any of the animals. A reduction in EOG amplitude was also noted on the unoperated side of the olfactory organ. These changes were less pronounced: the decrease in electrical response level began at a later stage, while complete recovery in amplitude was achieved sooner. Findings showed that EOG amplitude changed at different rates in different areas of the olfactory epithelium; it decreased sooner and began to recover at a later stage in the caudal than in the centromedial portion of the olfactory organ.Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii University, Gor'kii. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 603–610, September–October, 1986.     

Seasonal covariation in progesterone and odorant emissions among breeding crested auklets (Aethia cristatella)

Crested auklets emit a citrus-like odorant that is seasonally modulated, suggesting that it is a secondary sexual trait. We hypothesized that expression of the chemical odorant is facilitated by steroid hormones, similar other secondary sexual traits in birds. Therefore we examined variation in concentrations of hormones in blood plasma and odor production during incubation and early chick rearing. A novel method was used to obtain and measure chemical emissions of crested auklets. Blood plasma samples were analyzed by radioimmunoassay. Progesterone was detected in all birds, and it varied during the breeding season. Octanal emissions covaried with progesterone levels in males but not in females. No seasonal patterns were detected in testosterone, estrogen or DHT, and these hormones were not detected in all breeding adults. Covariance of progesterone and octanal emissions in males suggests there could be at least an indirect relationship between odor emissions and steroid hormones in this species. Thus expression of the citrus-like odorant of crested auklets, like other secondary sexual traits in birds, could be regulated by steroid hormones.     

A preliminary study of olfactory behavior of captiveLemur coronatus during the breeding season

The olfactory behavior of a captive population of crowned lemurs (Lemur coronatus)was studied during their annual breeding season in order to investigate its possible role in the fine-tuning of mating synchrony after photoperiodic initiation of reproductive activity. The frequencies of five stereotyped olfactory behavior patterns were recorded in four male-female groups during 315 1-hr observation sessions between October and March. The mean total scent-marking frequency of all males was positively correlated with their mean testicular size. Male anogenital-, head-, and allomarking frequencies decreased during the breeding season, whereas hand-marking frequencies remained constant. Male head-marking increased significantly in the 5 days preceding female vaginal estrus. Furthermore, males responded to many female scents by olfactory investigation and/or overmarking, whereas females never showed an observable behavioral response to male scent marks. The marking frequencies of two females did not change significantly during the breeding season, while those of two others decreased significantly. These results suggest qualitative changes of female scents during estrus and a less important role of male scents in intersexual communication in the context of reproduction than previously thought.     

The effect of winter temperatures on the timing of breeding activity in the common toad Bufo bufo

A 19-year study of a common toad population in south Dorset, UK, was carried out between 1980 and 1998. The daily arrival of sexually mature male and female toads at a breeding pond was recorded each year. The timing of the main arrival of toads at the breeding pond was highly correlated with the mean daily temperatures over the 40 days immediately preceding the main arrival. When the temperatures were higher than average, breeding occurred significantly earlier in the year than if they were either average or lower than average. During the study, the toad breeding seasons were early (2–13 February) in 5 years (1989, 1990, 1993, 1995, 1998), late (16–23 March) in 2 years (1986, 1996) and average (25 February–8 March) during the remaining 12 years. Evidence was found suggesting that common toads have a daylength threshold of about 9 h, below which the migration to the breeding pond does not occur. Evidence was also found indicating that common toads in southern England have a threshold temperature for activity of about 6°C and that the onset of breeding activity is highly correlated with the number of days during the 40 days prior to the main arrival at the breeding pond that were at or above this temperature. Predicting the start of the main breeding migration to a pond in any year may be possible by comparing the pattern of the 40-day running mean daily temperatures from 21 December the preceding year with those from previous years when the start of breeding activity is known. Although all five of the earliest recorded toad breeding years occurred during the last 10 years, and were associated with the occurrence of particularly mild winters, a significant trend towards earlier breeding in recent years compared with previous years was not found. Received: 16 July 1998 / Accepted: 14 September 1998     

Androgen levels and social interactions in breeding males of the peacock blenny

Nest-holder male Salaria pavo have lower circulating concentrations of 11-ketotestosterone (KT) at the beginning of the breeding season than at its peak. At that peak density of nesting males was higher as were the number of visits of sneaker males to nests and of agonistic interactions between nest-holders and sneaker males. There was no difference between the two dates either in the frequency of male-male interactions or in the frequency of courtship episodes. Thus, higher plasma levels in nest-holders might be explained by a more intense sneaking pressure at the peak of the breeding season. At that peak, nest-holders had higher plasma levels of KT and a higher testosterone (T) to KT metabolization index in the gonads than did floater males. Both nest-holders and floaters had higher levels of KT and T in the testicular gland than in the testis. The levels of both androgens in the testicular gland, but not in the testis, were correlated with circulating concentrations of KT. These results suggest that the testicular gland is the major source of circulating KT in blenniids. Nest-holders had higher metabolization indexes than floaters both in the testis and in the testicular gland, which suggests that nest holding status promotes the conversion of T into KT.     

The breeding season duration hypothesis: acute handling stress and total plasma concentrations of corticosterone and androgens in male and female striped plateau lizards (Sceloporus virgatus)

Acute glucocorticoid elevations can be adaptations to short-term stressors. The breeding season hypothesis predicts reduced glucocorticoid responsiveness to acute stressors in populations or species with short breeding seasons. The striped plateau lizard (Sceloporus virgatus) has a short breeding season in Arizona. We measured plasma corticosterone and total androgen levels (dihydrotestosterone and testosterone) following one of the four stress-handling treatments (0, 10, 60, or 180 min). In both sexes, longer handling stress yielded higher corticosterone; females had higher corticosterone than males at all time points. Androgens did not vary with handling duration, in either sex. Combining treatments, plasma androgens correlated positively with corticosterone (CORT) in females but not in males; plasma CORT and body mass residuals were negatively correlated in both sexes, suggesting lizards in poor body condition and/or not investing heavily in reproduction (follicle mass) have higher acute corticosterone. Total plasma androgens and body mass residuals were positively associated in males, but showed no association in females. The maximal CORT elevation after handling stress in this single-clutching species was of comparable magnitude to responses in related multi-clutching lizard species with longer breeding seasons. Using data from studies of multiple populations of three Sceloporus species, we found no relationship between the relative magnitude of the CORT increase and either latitude or elevation, two variables in the literature correlated with duration of the breeding season, and only weak relationships with geographic elevation and actual (not relative) stress-elevated CORT values in this multi-population comparison.     

Failure of glucocorticoid feedback during breeding in the male red-tailed phascogale Phascogale calura (Marsupialia: Dasyuridae)

An investigation was made into the factors which lead to an elevation in plasma free cortisol concentration during the last weeks of life of males in natural populations of the red-tailed phascogale Phascogale calura. The dexamethasone suppression-test was employed to examine the glucocorticoid feedback control of plasma cortisol both before and during the breeding season. In both sexes ACTH alone or in combination with dexamethasone caused an elevation in the plasma concentration of cortisol, corticosterone and free cortisol. Dexamethasone administration in both males and females resulted in significant decreases in the plasma concentration of each of the glucocorticoid groups both before and during the first week of the breeding season (June and early July), however during the last week of breeding (late July) dexamethasone decreased the plasma glucocorticoid concentration of females but not of males. Administration of ACTH caused a significant elevation in the plasma cortisol concentration in all groups. However, the magnitude of this response diminished with time in both sexes. Dexamethasone treatment resulted in a decrease in the plasma testosterone concentration in males before and early in the breeding season however toward the end of breeding this effect was abolished. It is apparent that towards the end of the breeding season and during the last week of life of the males, glucocorticoid feedback control of ACTH is almost abolished. These changes, which occur only in the males late in the breeding season and near the time of their disappearance from the population, are consistent with a condition known as end organ resistance to steroid hormones.     

Context-dependent effects of castration and testosterone treatment on song in male European starlings

Most seasonally breeding songbirds display dramatic seasonal fluctuations in plasma testosterone (T) levels and mate attraction behaviors, including song. However, males of some songbird species, such as the European starling (Sturnus vulgaris), continue to sing at high levels after the breeding season, when T levels are basal. In male starlings song during the breeding season functions mainly to attract mates, whereas song during the nonbreeding season appears unrelated to reproduction. This suggests that song produced in a context unrelated to female courtship, unlike song directed toward females, is not regulated by plasma T. In captive males housed in large outdoor aviaries we explored the relationship between plasma T and song produced during the breeding season within and outside a courtship context. This was achieved by determining the effects of castration and subsequent T treatment on song and mate attraction behaviors in both the presence and the absence of a female. Compared to intact males, castrated males did not show reduced song activity in the absence of a female for at least 6 months after the operation, strongly suggesting that the expression of noncourtship song is not regulated by plasma T. Likewise, we found that experimentally elevating T levels in castrated males did not affect noncourtship song rates. However, control castrated males receiving empty implants tended to show reduced noncourtship song rates after implantation. This may have been due to a suppressive effect caused by the presence of the T-implanted castrated males in the same aviary. In contrast, courtship singing was clearly controlled by plasma T: it was abolished by castration and restored by subsequent T replacement when males were housed both individually and in a group situation. High plasma levels of T also appeared necessary for the activation of three other behavioral traits critical for mate attraction, namely, nesthole occupancy, spending time (singing) in a nesthole, and carrying green nesting material into a nesthole.