Reproductive Inactivity Research Articles

Mother–offspring relationships in donkeys

The social relationship between female domestic donkeys (jennies) and their offspring was explored by observation of their spatial relationship. The donkeys were kept together for life and the ages of the offspring at the beginning of the observation period ranged from a few hours to 13 yr. There was a gradual change in the jenny–foal spatial relationship in the foal's first year reflecting the foal's increasing independence. The offspring's sex made no difference to this relationship. Jennies stayed very close to their newborn foals but thereafter approached them less frequently and had an overall tendency to move away. The foals responded by moving towards their mothers and so maintaining contact. Older foals were less persistent in following their mothers. In this study, jennies moved away most persistently from their 10-month-old foals. In unconfined conditions, this would begin the process of weaning. Since older foals are also often observed to be some distance away from their mothers, this also allows for the possibility that they can become separated by some external event. Under conditions of domestic management, e.g., unlimited resources, confinement and reproductive inactivity, jenny and offspring do not separate at weaning and their spatial relationship reverts to the close relationship seen between jennies and young foals. This is due mainly to a change in the jennies' behaviour from leaving to approaching and, to a lesser extent, to an increased frequency of approach by the offspring. The result is a pair of adult donkeys that stay very close together and are equally active in maintaining contact. This close relationship may provide some benefits. One potential benefit is an immediately available and willing grooming partner. Another is the potential for the pair to develop a coalition for future support, for example, in accessing resources and mutual protection.

Isolation of a goldfish brain cytochrome P450 aromatase cDNA:: mRNA expression during the seasonal cycle and after steroid treatment

To investigate the molecular basis and physiological regulation of exceptionally high levels of aromatase (P450arom) activity in the brain of teleost fish, a 2927 bp P450arom cDNA encoding a 510 amino acid protein was isolated from a goldfish brain cDNA library. The brain-derived cDNA had 53% and 61–62% sequence identity when compared with human placental and fish ovarian P450arom forms, respectively, and higher homologies in conserved functional domains. Goldfish brain poly(A) RNA was translatable in vitro to a 56 kDa P450arom immunoprecipitation product. Northern blot analysis using the brain cDNA revealed a major 3.0 kb transcript of high abundance in brain (FB, forebrain>M/HB, mid/hindbrain), but no signal in ovary, testis or liver. P450arom mRNA varied seasonally in brain, with a peak at the onset of gonadal regrowth (February) that preceded the annual rise in enzyme levels and was 4-fold (FB) or 50-fold (M/HB) higher than during reproductive inactivity (July–December). Known markers of neurogenesis and estrogen action in brain (28S rRNA, β-actin and β-tubulin transcripts) each had unique seasonal patterns which differed from P450arom mRNA. In vivo steroid treatment showed that estrogen and aromatizable androgen increase FB and M/HB levels of P450arom mRNA 8- and 4-fold, respectively. P450arom mRNA in pituitary and retina had a different regulation. Southern analysis provided no evidence for multiple genes encoding the brain derived cDNA or for brain-specific gene amplification. Results imply that high accumulated levels of P450arom mRNA are the major determinant of high measured enzyme activity in goldfish brain, and that physiological regulation of mRNA expression in the natural environment is mediated by aromatization of androgen to estrogen.

Causes of Reproductive Inactivity and Recovery of Reproductive Ability after Diapause in Females of a Multivoltine Bruchid, Kytorhinus sharpianus (Coleoptera: Bruchidae)

A bruchid, Kytorhinus sharpianus Bridwell, shows a multivoltine life cycle on seeds of a leguminous host plant, Sophola flavescens Aiton. Emergent females from overwintered larvae cannot lay eggs without feeding, but first- (August) and secondgeneration (late September) females can. In this study we examined experimentally the causes of this reproductive inactivity and the recovery of reproductive ability. When diapausing larvae experienced low temperature (10°C) and then emerged as adults in the laboratory, these females could not lay eggs before feeding. Similar results were observed in the overwintering generation in the field. However, emergent males could copulate immediately after emergence, and their mated partners that did not experience cooling could lay eggs. Reproductive activity was also recovered with feeding in these females, even if only water was provided. Application of a juvenile hormone analog also caused recovery of reproductive activity in some females.

Regionalization of eccrine and spermiophagic activity in spermathecae of the salamander Eurycea cirrigera (Amphibia: Plethodontidae).

The spermathecae of female Eurycea cirrigera are compound alveolar glands; narrow neck tubules connect the distal bulbs to a common tube that opens onto the roof of the cloaca. The common tube and neck tubules produce apical secretory vacuoles that contain a periodic acid-Schiff (PAS)+ substance for merocrine export into the lumen. This substance is produced throughout the year, although secretory vacuoles are less numerous during the period of reproductive inactivity in the summer. When sperm are present, the product from the secretory vacuoles bathes sperm in the lumen. Sperm are in orderly arrays and never are embedded in the cytoplasm of the common tube or neck tubules. The distal bulbs do not produce PAS+ secretory vacuoles, and are actively spermiophagic as long as sperm are present. Sperm become embedded in the epithelium of the distal bulbs where lysosomes degrade sperm. © 1993 Wiley-Liss, Inc.

The relationship between reproductive state and “sexually” dimorphic brain areas in sexually reproducing and parthenogenetic whiptail lizards

The anterior hypothalamus-preoptic area and ventromedial hypothalamus are sexually dimorphic in the reproductively active whiptail lizard Cnemidophorus inornatus. The anterior hypothalamus-preoptic area, which is involved in the control of male-typical copulatory behaviors, is larger in males, whereas the ventromedial hypothalamus, which is involved in the control of female-typical receptivity, is larger in females. In the parthenogenetic whiptail lizard C. uniparens, which is a direct descendant of C. inornatus and exhibits both male-like and female-like pseudosexual behaviors, both brain areas are comparable in size to those of female C. inornatus. This study was conducted to determine whether these brain areas change in size in either species or sex during a time of year when these animals are reproductively inactive, or after removal of the gonads. In male C. inornatus both brain areas changed during reproductive inactivity (either seasonally or surgically induced) and became equivalent to the size characteristic of reproductively active female C. inornatus. When corrected for brain size, the anterior hypothalamus-preoptic area was significantly smaller in intact hibernating and castrated males than in intact males from the summer breeding season. Conversely, the ventromedial hypothalamus was significantly larger in intact hibernating and castrated males than in intact males from the summer breeding season. The two brain areas were not significantly different among the groups of female C. inornatus or parthenogenetic C. uniparens. These results suggest that 1) the brain of whiptail lizards may differentiate seasonally and 2) the female state may be a neutral one to which the male brain reverts during reproductive inactivity.

Patterns of Leydig cell and LH gonadotroph activity, and plasma testosterone concentrations in the seasonally reproducing Schreibers' long-fingered bat (Miniopterus schreibersii)

Spermatogenesis in Schreibers' long-fingered bat from approximately 33 degrees S in South Africa was seasonal, and occurred in the 3 months (February-April) preceding ovulation. The ultrastructure of the Leydig cells indicated a period of increased steroidogenesis at this time, and plasma testosterone concentrations were elevated from March to May (10.3 ng/ml). The reproductive accessory glands were secretorily active between March and May, and copulation occurred at the end of this period of activity. Changes in LH-beta immunoreactivity suggest that the LH gonadotrophs were secretorily active 1 month before the onset of spermatogenesis and that peak activity coincided with peak plasma testosterone concentrations, spermiogenesis and spermiation. During winter (May-August) there was no reproductive activity and the bats remained active, only entering prolonged periods of torpor during particularly cold spells. A secondary elevation in plasma testosterone concentration, during reproductive inactivity (October; 9.3 ng/ml), was not accompanied by any change in Leydig cell ultrastructure, and the biological significance of this peak is unknown. Such synchronous activity of the pituitary, Leydig cells, seminiferous epithelium and accessory glands is associated with the typical reproductive cycle of long-fingered bats in which copulation and fertilization are restricted to a brief period at the end of summer, and in which neither sperm storage nor a prolonged period of copulation occur.

Changes in brain aromatase and 5 alpha-reductase activities correlate significantly with seasonal reproductive cycles in goldfish (Carassius auratus).

Aromatization and 5 alpha-reduction are known to be required for the full expression of testosterone actions in neuroendocrine tissues. Although aromatase and 5 alpha-reductase activities in brain and pituitary can be experimentally manipulated by castration and steroid replacement, naturally occurring variations during seasonal reproductive cycles have not been examined in any species. Goldfish (Carassius auratus) were selected for study because they exhibit exceptionally high levels of aromatase in both brain and pituitary, although 5 alpha-reductase levels resemble the vertebrate norm. Four animals of each sex were tested monthly through three breeding seasons (2.5 yr). Using previously validated techniques, the enzymes were assayed by product formation from [3H]androstenedione in homogenates of anterior hypothalamus-preoptic area (AHPOA), remaining telencephalon (TEL), whole pituitary, ovary, and testis. Seasonal variations in aromatase were most dramatic in the AHPOA of female fish, exhibiting a peak in April and May that was 6-fold higher than the nadir in July. As judged by changes in the appearance and weight of the gonads, maximal aromatase coincided with the spawning season, whereas low enzyme levels corresponded to reproductive inactivity. Seasonal variations were similar but of a lesser magnitude in the TEL of females and in the AHPOA and TEL of males (2- to 3-fold, peak to nadir). Both ovarian and testicular aromatase showed cyclic changes; however, activity was much lower than that in brain at all times of the year (4.5, 1.2, and 47.0 pmol/mg protein, maximal values in ovaries, testes, and AHPOA, respectively). Pituitary aromatase varied from 5-22 pmol/mg protein, but was not consistently correlated with season. Cyclic changes in 5 alpha-reductase were distinctly different from those in aromatase, with maximal values in both brain and pituitary occurring when fish were reproductively inactive. In general, circulating sex steroids were high when aromatase was high and low when reductase was maximal; however, there was no apparent causal relationship suggested by temporal changes in a given steroid. Variations in testosterone metabolism, by regulating the quantity and quality of active hormone in close proximity to receptor sites, may be responsible for the changes in feedback sensitivity and behavioral responsiveness that are known to occur in seasonal breeders.

Body Weight, Sex Ratio and Seasonal Reproductive Changes in the Indian Mole Rat, Bandicota bengalensis in the Punjab

A study has been made of seasonal changes in the body weights of males and females, and of ovarian and uterine weights, in the Indian mole rat, Bandicota bengalensis, between July 1976 and June 1978, from areas surrounding Ludhiana (30�56'N.,75�52'E.). An attempt has been made to correlate them and peaks in reproductive activity with environmental factors such as daylength, temperature, rainfall and availability of food. During both years of study, the percentage of males was 45.2. The body, ovary and uterus were lighter during winter, and then gained weight, with peaks during April and August-September. Males were generally heavier than females. On the whole, 34.7% of females were either pregnant or lactating. The breeding season extended from mid-February to mid-October. Two peaks in breeding activity (April and August-September), with a decline during June, were separated by a period of reproductive inactivity from November to mid-February. The average litter size was 8.88 (range 5-13). Embryos occurred with almost the same frequency in the left and right uterine horns. The pre-implantation mortality was 9.6% and post-implantation mortality 4.8%; thus the total prenatal mortality was 13.7%. The percentage of embryos found resorbing was 4.1. The results have been discussed in the light of the literature on the reproductive biology of rodents in this region.

Seasonal changes in the testis and epididymis of the American Grey squirrel, Sciurus carolinensis.

The histological changes in the testis and epididymis of the American Grey squirrel, Sciurus carolinensis (Gmelin) during development and the testicular cycle are described. It was observed that male Grey squirrels, as a population, did not undergo a pronounced seasonal reproductive cycle, however, individual males did experience periods of reproductive inactivity which were asynchronous and not related to seasonal changes in the environment. It is suggested that the individual sexual cycles are due to an endogenous rhythm of gonadotrophin secretion by the pituitaries of these animals.

Reproductive Frequency in Malaysian Flying Squirrels, Hylopetes and Pteromyscus

Little is known about the reproductive frequency, seasonality, and population statistics of tropical rainforest mammals. One nocturnal, arboreal form, the flying squirrel, Hylopetes lepidus, seems to have a superannual periodicity in reproductive activity with periods of reproductive inactivity as long as 17 months. Another species of flying squirrel, Pteromyscus pulverulentus, seems to breed more or less continuously, but only a small proportion of potential breeders are involved at any given time. Population turnover in both species appears to be slow. Litter sizes average 2 in Hylopetes and 1.3 in Pteromyscus. Population turnover, as estimated from the frequency of pregnancies, gestation period (estimated), and litter size, is 27 per cent that of forest rats in Hylopetes, and 13 per cent of the rate in rats in Pteromyscus.

The endocrine basis of reproductive inactivity in Monarch butterflies overwintering in central California

Monarch butterflies ( Danaus plexippus) collected during winter in central California are reproductively inactive. Oögenesis is stimulated in such animals by environments simulating summer conditions. Allatectomized or neck-ligatured winter animals do not normally undergo oögenesis when placed in summer conditions, but apparently normal oögenesis occurs if they are injected with juvenile hormone isomers. Injections of such isomers into winter animals held in environments simulating winter also promote oögenesis, even though winter conditions typically inhibit ovarian development. Reproductive dormany in winter Monarchs of central California therefore appears to be due (at least partially) to environmentally induced inactivity of the corpora allata.

Laboratory studies on the locomotor activity of Coryphosima stenoptera and other West African Acrididae (Insecta: Orthoptera)

The activity of nymphs and adults of C. stenoptera (Schaum) and some other Acrididae was tested in an actograph. Sexually mature females were more active than immature; males were intermediate in activity, while nymphs, females with eggs in the oviducts and those in a condition of reproductive inactivity were least active. There was evidence that the activity of females increases with age, and that individuals differ in the mean level of activity. There appears to be little possibility at present of relating these changes to the neurosecretory and endocrine systems.

34. The Menstrual Cycle of the Primates.—Part IV. Observations on the Lactation Period

Summary. A Pig‐tailed Macaque (Macaca nemestrina) gave birth to a female baby after 171 days' gestation. The first menstruation occurred 216 days after parturition. There had been no sexual‐skin swelling in the interval. A nursing Common Macaque (Macaca irus, M. 61) was killed approximately 114 days after parturition. She was wasted, and post‐mortem examination revealed worm‐infestation of the intestines. Her mammary glands, though they still showed marked lactation hypertrophy, were not secreting milk at the time of death. Her ovaries were inactive, and showed a large number of atretic follicles. Her uterine mucous membrane was low, with short and straight glands, and showed signs indicating that involution was still proceeding at the time of her death. A nursing Langur (Pithecus cristata, M. 46) was shot in Borneo at a time that is estimated to have been at least two months after parturition. The ovaries, though small and contracted, contained medium‐sized follicles, the largest having an average diameter of 2·2 mm. There was no sign of a corpus luteum. Each ovary contained a large corpus candicans. The condition of her uterus was much the same as that of the nursing Common Macaque. Four nursing Chacma Baboons (Papio porcarius, M. 20, 21, 28, 37) were shot in South Africa, two at a time estimated to have been two months, a third four months, and the fourth at an unknown time, after parturition. The reproductive organs of all four were in practically the same condition, and showed no signs of recent cyclical activity. The ovaries were small, containing no signs of copora lutea, but only resting follicles. The uteri were small and inactive, with low endometria, and showed signs indicating that involution was still proceeding at the time of death. These data, as well as sexual‐skin observations recorded in Part I. of this series of papers, indicate that sub‐human primates experience a period of uterine and ovarian inactivity after parturition. This fact is of importance in discussions relating to periods of reproductive inactivity in monkeys, e. g., alleged breeding‐and non‐breeding seasons.