Evidence that the seasonally breeding Bennett's wallaby (Macropus rufogriseus rufogriseus) does not exhibit short-day photorefractoriness

Adult female Bennett's wallabies (N = 6) were maintained in artificial winter solstitial daylengths commencing 3 weeks before the winter solstice for 16 or 42 weeks. Such treatment effectively prevented the normal establishment of seasonal reproductive quiescence with animals continuing to exhibit reproductive cycles beyond the time of the normal termination of the breeding season. Animals maintained in natural photoperiods or simulated natural changes in daylength after the winter solstice all entered reproductive quiescence by early February. In the Bennett's wallaby, therefore, the breeding season does not terminate as a result of refractoriness to short daylengths. Our results indicate that the relatively small increases in photoperiod shortly after the winter solstice provide the environmental signal responsible for initiating the onset of seasonal reproductive quiescence which normally occurs 5-8 weeks after the solstice. These results contrast with the effect of fixed artificial summer solstitial daylengths on the onset of the breeding season in which breeding begins spontaneously at the normal time of year as a result of long-day photorefractoriness.     

The onset of seasonal quiescence in the female Bennett's wallaby (Macropus rufogriseus rufogriseus)

The breeding season of the non-lactating Bennett's wallaby terminates when animals enter the state of seasonal quiescence. To examine this transition, pouch young were removed from females at intervals which were 3, 4 or 8 weeks (6, 11 and 8 animals respectively) after the winter solstice. Within 48 days, 3, 1 and 1 females gave birth respectively, indicating that these animals were not in seasonal quiescence when pouch young were removed. Those animals which did not give birth were either in seasonal quiescence or had undergone a non-pregnant cycle. To differentiate between the 2 possibilities, techniques which would ensure the detection of pregnant and non-pregnant cycles were assessed in 8 females during the breeding season. As has been previously reported for the wallaby, changes in peripheral progesterone concentrations and the vaginal smear occurred during pregnant and non-pregnant reproductive cycles. In addition, mating was detected by marking the male with a mixture of coloured crayon and paraffin wax. It was concluded that reproductive cycles in female wallabies could be monitored by collecting blood samples 2 times each week for progesterone determination and daily examination of females for mating marks. These techniques were then used to study the onset of seasonal quiescence in 9 females. All animals continued to show reproductive cycles after the winter solstice and it was not until 10 weeks after the winter solstice that all animals were in seasonal quiescence. This represents an increase in the duration of the breeding season over that previously reported for this species.     

Refractoriness to melatonin and short daylengths in early seasonal quiescence in the Bennett's wallaby (Macropus rufogriseus rufogriseus)

Adult female Bennett's wallabies were treated with reductions in daylength, melatonin implants or injections of melatonin 2 h before dusk in early or mid-seasonal reproductive quiescence. In early reproductive quiescence (5 weeks after the winter solstice) reproductive quiescence did not end in response to 3 or 5 h of reduced daylength or in response to injections (400 ng/kg) or implants (0.5 g in a Silastic rubber envelope) of melatonin. Reductions in daylength at this time of year did, however, result in an extension of the circadian pattern of melatonin secretion. In mid-reproductive quiescence (21 weeks after the winter solstice) treatment with a 5 h reduction in daylength, melatonin injections administered 2 h before dusk or melatonin implants did result in the termination of reproductive quiescence and reactivation of the quiescent corpus luteum within a period of 5 days. The results of these experiments indicate that, in early reproductive quiescence, the Bennett's wallaby is refractory to the influence of reduced daylength or melatonin, although capable of responding to such reduced days in terms of an increased duration of melatonin secretion. Bennett's wallabies therefore exhibit a refractoriness to short days similar to that of some seasonal eutherians although it remains to be established whether this refractory response is the cause of the transition to seasonal reproductive quiescence.     

The reproductive biology of Bennett's wallaby (Macropus rufogriseus rufogriseus) ranging free at Whipsnade Park

Between August 1981 and October 1982, 76 female and 50 male of the estimated 400 Bennett's wallabies at Whipsnade were caught and examined. Sixty-four of the adult females inspected (84%) were carrying pouch young. A small captive breeding colony was established in the laboratory. Weight and growth curves were established for captive born pouch young and these curves were used to determine the approximate age of pouch young examined at Whipsnade. Eighty-four percent of births occurred in August and September, exactly a six month difference from births reported for this species in Tasmania. The mean length of pouch life of wild living wallabies was 247 days with a range of185–284 days. Young wallabies were observed accompanying their mothers for up to 204 days after emerging permanently from the pouch. Sixty-three percent of young vacated the pouch in May. Sixty-three percent of the total (104) pouch young examined in the course of this study, from animals caught or from post mortem records, were male, but teat selection showed a random distribution. The gestation period from removal of pouch young to day of birth was 27·3 days. The Bennett's wallaby showed precise seasonal breeding with embryonic diapause that may extend for up to 11 months.     

Refractoriness to short and long days determines the end and onset of the breeding season in subtropical goats

The objective was to determine whether refractoriness to short and long days were involved in the end and onset of the breeding season, respectively, in goats adapted to subtropical latitudes. Ovariectomized does given a subcutaneous implant constantly releasing estradiol-l7 β (OVX+E) were used in two experiments. Plasma LH concentrations were determined twice weekly. In Experiment 1, the control group remained in an open-shed pen (natural day length and ambient temperature). Two experimental groups were placed in light-proof buildings (with natural temperature variations). One group was exposed to natural simulated increasing days (winter to spring), whereas the other was exposed to a winter solstice photoperiod (10 h of light) from December 21 to April 28. In Experiment 2, the control group remained under natural day length and ambient temperature. One experimental group was exposed to natural simulated decreasing days (summer to autumn), whereas the other group was exposed to a summer solstice photoperiod (14 h of light) from June 21 to October 20. In Experiment 1, the breeding season was not prolonged in does maintained in the winter solstice day length. Mean dates of decrease in LH secretion (end of the breeding season) did not differ significantly between does exposed to natural (February 3 ± 5 d) or natural simulated photoperiod (January 26 ± 14 d) and those exposed to constant short days of winter solstice (February 4 ± 10 d). In Experiment 2, the onset of the breeding season was not delayed in does maintained in the summer solstice day length. Mean dates of increase in LH secretion (onset of the breeding season) did not differ significantly between does exposed to natural (September 7 ± 8 d) or natural simulated photoperiod (September 18 ± 10 d) and those exposed to constant long days photoperiod of summer solstice (September 24 ± 4 d). In goats adapted to a subtropical environment, we concluded that: 1) the end of breeding season was due to refractoriness to short days, and not the inhibitory effect of increasing day length; and 2) the onset of the breeding season was due to refractoriness to long days, and not a stimulatory effect of decreasing day length.     

Melatonin implants prevent the onset of seasonal quiescence and suppress the release of prolactin in response to a dopamine antagonist in the Bennett's wallaby (Macropus rufogriseus rufogriseus)

Three groups of adult female wallabies were maintained out of doors under conditions of natural photoperiod and temperature from late December to mid-August. One group (M1; N = 6) received Silastic elastomer melatonin implants on 14 December, a second group (M2; N = 5) were given implants on 16 February and a third group (C; N = 7) were unimplanted controls. Group C animals had all ceased cycling by 15 March and the subsequent breeding season commenced on 5 July +/- 6.9 days. Group M1 wallabies continued to cycle throughout the experimental period and did not exhibit ovarian quiescence. In Group M2, 2/5 animals continued to undergo repeated oestrous cycles and 3/5 ceased cycling between 14 December and 27 January and began again after the insertion of melatonin implants on 16 February. The prolactin response 30 min after s.c. administration of the dopamine antagonist domperidone was determined approximately every 4 weeks. In Group C, peak responses were high during the period of seasonal quiescence (January-June; mean range 14.2-19.6 ng/ml) and fell significantly (P less than 0.02) at the beginning of the breeding season in early July to 7.4 +/- 3.1 ng/ml. In Group M1, prolactin levels remained low (2.8-8.2 ng/ml) throughout the course of the experiment while in Group M2, response to domperidone fell following the insertion of the implants and subsequently remained at levels similar to those in Group M1. Our data support the hypothesis that photoperiod-induced changes in the secretion of melatonin after the winter solstice drive this species into seasonal quiescence by influencing the dopaminergic control of prolactin secretion.     

Reproductive biology of the Red-necked wallaby (Macropus rufogriseus banksianus) and Bennett's wallaby (M. r. rufogriseus) in captivity

Bennett's wallaby ( Macropus r. rufogriseus ) of Tasmania give birth from late January to early August in marked contrast to the Red-necked wallaby ( M. r. banksianus ) of mainland south-eastern Australia which produced young in all months. Within the breeding season however, the lengths of the oestrous cycle and gestation period are similar in the two forms and did not differ by more than 0.5 days. The gestation period of about 30 days extended to almost the length of the oestrous cycle of approximately 33 days. Birth was closely followed by mating which normally resulted in fertilization and subsequent embryonic diapause. Renewed blastocyst development was initiated by removal or loss of a pouch young and birth followed about 27 days later.
Unlike other macropodids with a similar breeding pattern, birth, as a result of renewed blastocyst development near the end of a large young's pouch life, did not occur within a day or two of the permanent emergence of the young, but followed 16 to 29 days later. In M. r. rufogriseus , young that left the pouch permanently in the non-breeding period were not replaced by new young until the beginning of the next breeding season two to four months later, and blastocysts resulting from mating of females without pouch young at the end of the breeding season remained quiescent until the next breeding season five to eight months later.
Females of both subspecies first mated at an age of about 14 months, and males were producing mature spermatozoa by about 19 months.
Young first left the pouch for short periods at about 230 days of age and permanently at about 280 days.
Observations are also given on reproductive behaviour, interpretation of vaginal smears, sex ratio of young, selection of teat by pouch young, and development of morphological features in known-age young that may be used as an aid in age determination.     

Refractoriness to inhibitory day lengths initiates the breeding season of the Suffolk ewe

Recent evidence indicates that the breeding season of the Suffolk ewe ends because of loss of response to a day length that was previously inductive. This condition of photorefractoriness could potentially also initiate reproduction, as is the case in several long-day breeding rodents. In this study we determined if ewes enter their breeding season because they become refractory to the long ambient photoperiods of late summer. On the summer solstice, 3 groups of ovariectomized ewes (n = 6) bearing s.c. Silastic implants of estradiol (OVX + E) were placed in different day length treatments: 1) natural photoperiod; 2) artificial photoperiod, stimulating natural day lengths; or 3) artificial photoperiod equivalent to that of the summer solstice (16.25L). Entry into the breeding season is associated with a striking (greater than 30-fold) increase in circulating levels of luteinizing hormone (LH). Timing of the onset of the breeding season was not delayed in ewes maintained on the summer solstice photoperiod; LH levels rose simultaneously in all groups. We conclude that ewes normally begin breeding not because they are actively driven to do so by decreasing or short days, but because they become refractory to prevailing long days. Because the pattern of circulating melatonin, which is known to transduce the photoperiodic message, remained entirely appropriate to day length, we believe that the mechanism responsible for photorefractoriness resides in the postpineal processing of the melatonin signal.     

Photoperiod requirements for puberty differ from those for the onset of the adult breeding season in female sheep

Reproductive responses to photoperiod were directly compared in mature ewes and in their spring-born twin female lambs. All females were ovariectomized and treated with oestradiol implants before transfer into artificial photoperiod; serum LH concentrations and pulsatile LH patterns provided an index of neuroendocrine reproductive activity. Mothers were transferred from natural photoperiod to artificial long days (16 h light:8 h dark) at the summer solstice so that no decrease in photoperiod would be experienced. These ewes began reproductive activity synchronously at the expected time in the autumn. One of each pair of twin lambs was treated exactly as the mothers; to determine the normal timing of puberty the remaining twin was maintained in a photoperiod simulating the natural decrease in daylength. In all 6 control lambs experiencing the simulated natural photoperiod, reproductive activity occurred synchronously at 28 +/- 1 weeks of age (2 October +/- 7 days). However, in their twin sisters which did not experience a decrease in photoperiod, only 2 of 6 lambs had begun reproductive activity by the end of the experiment at 52 weeks of age (March), and these were both delayed relative to their twin control lambs exposed to decreasing daylength. Therefore, a decrease in photoperiod is necessary for the normal timing of puberty in the spring-born, female sheep, whereas seasonally anoestrous, mature sheep can enter the breeding season at a normal time in the absence of decreasing photoperiod. We suggest that the requirement for a decreasing photoperiod by the spring-born lamb reflects its limited photoperiodic history as compared to the adult.     

Variation in the timing of the reproductive season among breeds of sheep in relation to differences in photoperiodic synchronization of an endogenous rhythm.

Photoperiod may regulate seasonal reproduction either by providing the primary driving force for the reproductive transitions or by synchronizing an endogenous reproductive rhythm. This study evaluated whether breed differences in timing of the reproductive seasons of Finnish Landrace (Finn) and Galway ewes are due to differences in photoperiodic drive of the reproductive transitions or to differences in photoperiodic synchronization of the endogenous rhythm of reproductive activity. The importance of decreasing photoperiod after the summer solstice in determining the onset and duration of the breeding season was tested by housing ewes from the summer solstice in either a simulated natural photoperiod or a fixed summer-solstice photoperiod (18 h light:6 h dark; summer-solstice hold). Onset of the breeding season within each breed did not differ between these photoperiodic treatments, but Galway ewes began and ended their breeding season earlier than Finn ewes. The duration of the breeding season was shorter in Galway ewes on summer-solstice hold than on simulated natural photoperiod; duration did not differ between photoperiodic treatments in Finn ewes. The requirement for increasing photoperiod after the winter solstice for initiation of anoestrus was tested by exposing ewes from the winter solstice to either a simulated natural photoperiod or a winter-solstice hold photoperiod (8.5 h light:15.5 h dark). Onset of anoestrus within each breed did not differ between these photoperiodic treatments, but the time of this transition differed between breeds. These observations suggest that genetic differences in timing of the breeding season in Galway and Finn ewes do not reflect differences in the extent to which photoperiod drives the reproductive transitions, because neither breed requires shortening days to enter the breeding season or lengthening days to end it at appropriate times. These findings are consistent with the hypothesis that photoperiod synchronizes an endogenous rhythm of reproductive activity in both breeds and that genetic differences in timing of the breeding season reflect differences in photoperiodic synchronization of this rhythm.     

The effect of melatonin on the seasonal embryonic diapause of the Bennett's wallaby (Macropus rufogriseus rufogriseus)

In seasonally breeding mammals, the hormone melatonin, produced at night by the pineal gland, is known to be important in transducing the effect of photoperiod in timing reproduction. In the Bennett's wallaby, an unimplanted unilaminar blastocyst is held in a state of seasonal diapause from mid-winter to mid-summer. Here we show that an implant of the hormone melatonin rapidly terminates seasonal diapause in this species. Blastocyst reactivation is not accompanied by a significant reduction in levels of the hormone prolactin, thereby refuting earlier suggestions that this hormone is responsible for maintaining seasonal embryonic diapause.     

Ultrastructure of the reactivated corpus luteum after embryonic diapause in the marsupial,Macropus rufogriseus banksianus

Summary During embryonic diapause in the red-necked wallaby, M. r. banksianus, both the corpus luteum and uterine blastocyst remain dormant, and are reactivated following removal of the suckling pouch young (RPY). The morphology of dormant and reactivated corpora lutea has been studied throughout the 26.5 days of delayed gestation. Corpora lutea at 0, 2 1/2, 4, 9, 14, 21 and 25 days after RPY were fixed by perfusion. From day 4 to day 14 after RPY there was a progressive increase in the amount of smooth endoplasmic reticulum and the numbers of mitochondria. However there was a decrease in mitochondrial size from 1–2 m in diameter (0 days after RPY) to 0.5–1 m (14 days after RPY). Densely-staining granules (approximately 0.2 m in diameter) were first observed in the luteal cells at 4 days after RPY. The maximum density of granules was observed at 21 days after RPY. Shortly before birth (25 days after RPY) the number of secretory granules had significantly decreased and the features of cellular regression were evident. As with the eutherian mammals, the wallaby luteal cells have all the structural organelles associated with steroid hormone production. The numbers of densely-staining granules are greatest at 21 days after RPY and may reflect the luteal progesterone content since similar granules in the sheep and cow have been shown to be associated with elevated levels of progesterone.     

Intrauterine development after diapause in the marsupial Macropus eugenii

Three-quarters of adult female Macropus eugenii carry a diapausing blastocyst for up to 10 months of the year. For the first half of the year the diapause is due to the presence of a pouch young, but it continues through the subsequent anestrus. Spontaneous resumption occurs 1–15 days after the summer solstice. Development can be initiated experimentally during the first half of the year by removing the pouch young (RPY) and during anestrus by 10 daily injections of 10 mg progesterone.All blastocysts completed development after RPY, but only about half successfully completed intrauterine development after progesterone treatment. After RPY the corpus luteum grew and influenced growth of the endometrium and blastocyst. After day 13, however, the endometrium was further stimulated by the presence of the embryo or fetal membranes, probably the latter. Most of the failure after progesterone treatment occurred during the first 10 days and after the blastocyst had resumed development. It is suggested that these embryos failed to reach the stage where they could stimulate the endometrium directly. The later failure of progesterone-treated animals to give birth to full term fetuses was probably due to lack of stimulation from the anestrous ovaries.     

Reproductive refractoriness in the Welsh Mountain ewe induced by a short photoperiod can be overridden by exposure to a shorter photoperiod

The objectives were to determine if relative lengths of photoperiods that induce reproductive cycles in ewes affect the length of the subsequent breeding season, if duration of the refractoriness that terminates breeding is affected by photoperiod length, and if the resulting refractoriness to an inductive photoperiod is absolute. Groups of Welsh Mountain ewes were exposed to either 12L:12D (n = 12) or 8L:16D (n = 6) photoperiods beginning at the summer solstice when daylengths reach a maximum of 17.5 h at Bristol, England. A control group (n = 10) was exposed to natural daylengths. Ovarian cycles in the controls, as judged by monitored plasma progesterone levels, commenced in early October, about 1 mo later (p less than 0.001 in both cases) than in sheep exposed to 12L:12D or 8L:16D. The advancement in cycle onset was similar under 12L:12D and 8L:16D (69 +/- 2 and 77 +/- 4 days after the summer solstice compared with 102 +/- 2 days in the controls). Duration of the breeding season (100 +/- 4 days) in ewes exposed to 12L:12D was significantly shorter (p less than 0.001 in both cases) than in ewes exposed to natural daylengths or 8L:16D (153 +/- 3 and 133 +/- 5 days, respectively). Approximately 70 days after the ending of ovulatory cycles in the 12L:12D group, half of the animals (n = 6) were transferred to 8L:16D. This treatment greatly (p less than 0.001) reduced the duration of anestrus and cycles began again 62 +/- 4 days after transfer to 8L:16D, or about 90 days earlier than in ewes (n = 6) remaining in 12L:12D.(ABSTRACT TRUNCATED AT 250 WORDS)     

Photoperiodic control of testicular regression and moult in male House Sparrows Passer domesticus

Testis size, bill colour and moult were monitored in male House Sparrows Passer domesticus kept under a natural daylength regime between February and November. On three occasions (at the summer solstice, 25 days later and 39 days later), groups of birds were transferred to a daylength of 18 h of light and 6 h of darkness per day (18L: 6D), the natural daylength at the solstice. In birds under natural daylengths, the testes had regressed significantly by 2 5 days after the solstice. In those transferred to 18L:6D at the solstice, the onset of regression was delayed by about 4 weeks. Transfer to 18L: 6D after the solstice did not cause recrudescence; the testes continued to regress. In birds transferred to 18L: 6D at the solstice, moult was delayed by 4 weeks and progressed more slowly. These results suggest that photoperiodically induced gonadal regression in this species contains elements characteristic of both absolute and relative photorefractoriness.     

Pouch young removal and return to oestrus in wild southern hairy-nosed wombats (Lasiorhinus latifrons)

The southern hairy-nosed wombat (Lasiorhinus latifrons) is a seasonal breeding, burrowing marsupial adapted to a semi-arid environment and the closest relative of the endangered northern hairy-nosed wombat (Lasiorhinus krefftii). Females typically give birth to one to two young every 3 years with young weaned at 360-400 days. This study examined the occurrence of polyoestry in a wild population of southern hairy-nosed wombats, and in particular the ability of this species to produce additional offspring in the same breeding season if a young was prematurely lost or removed. Pouch young were removed during the breeding seasons of 1996/1997 and 2003. No females from the 1996 (n=3)/1997 (n=3) group gave birth to a second pouch young in the same breeding season. However, two females in this group gave birth to young the following season. In contrast, all the 2003 group of females (n=6) produced a second offspring in the same breeding season after removal of pouch young (RPY). The reason for the different response to RPY between the two groups is unknown. These studies confirm that southern hairy-nosed wombats are polyoestrus in the wild and are capable of producing more than one offspring in a single breeding season. Females that failed to return to oestrus in the breeding season that pouch young were removed bred again in the following season. Rapid replacement of southern hairy-nosed wombat pouch young in the same breeding season as RPY suggests that this procedure, linked to either hand-rearing or interspecific cross-fostering, should be seriously considered as a priority conservation action to increase the population size of the critically endangered sister species, the northern hairy-nosed wombat.     

The role of photoperiod on the initiation of the breeding season of the brushtail possum (Trichosurus vulpecula).

The role of photoperiod on the initiation of the breeding season of brushtail possums was investigated in possums housed in three light regimens: a short-day, a natural and a long-day photoperiod. Seven possums were housed in a natural photoperiod. Four possums were transferred to a short-day photoperiod (10 h light, 14 h dark) and eight possums to a long-day photoperiod (14 h light, 10 h dark) on 22 November, when the daylength was 13.34 h. The first rises in plasma progesterone concentrations were observed on 9 January +/- 9 days (n = 4), 11 March +/- 6 days (n = 7) and 6 May +/- 6 days (n = 8), for possums held in short-day, natural or long-day photoperiods respectively. Similarly, births were observed on 12 January and 14 February in the short-day group, from 3 March to 8 May for the natural photoperiod group, and from 5 May to 8 August for the long-day group. These results suggest that photoperiod is important in the timing of the breeding season. However, annual breeding will commence in a nonstimulatory long-day photoperiod. Thus a long-day photoperiod does not prevent breeding activity.     

Evidence that the onset of the breeding season in the ewe may be independent of decreasing plasma prolactin concentrations

Ten ewes of each of two breeds, Dorset Horn (long breeding season) and Welsh Mountain (short breeding season), were given subcutaneous oestradiol-17 beta implants and then ovariectomized. Another 10 ewes of each breed were left intact. On 3 May 1982, all the ewes were housed in an artificial photoperiod of 16L:8D. After 4 weeks, half of the ewes of each breed and physiological state were abruptly exposed to a short-day (8L:16D) photoperiod while the others remained in long days (16L:8D). The time of onset of the breeding season was significantly (P less than 0.05) advanced in ewes switched to short days (12 August +/- 10 days) compared to those maintained in long days (4 September +/- 14 days). Dorset Horn ewes began to cycle (20 July +/- 7 days) significantly (P less than 0.001) earlier than Welsh Mountain ewes (19 September +/- 6 days). Disparities in the time of onset of cyclic activity in ewes of different breeds and daylength groups were echoed in disparities in the time at which plasma LH and FSH concentrations rose in oestrogen-implanted, ovariectomized ewes of the same light treatment group. Prolactin concentrations showed an immediate decrease in ewes switched to short days, but remained elevated in long-day ewes. Since the breeding season started in the presence of high prolactin concentrations in long-day ewes, it seems unlikely that prolactin is an important factor determining the timing of the onset of cyclic activity.     

Diurnal variations in plasma testosterone concentrations in the male lesser mouse lemur (Microcebus murinus)

In 6 isolated adult male lesser mouse lemurs, concentrations of testosterone in plasma were determinated at 6-h intervals over a 24-h period. Blood samples were collected at monthly intervals and for a period of 12 months under natural photoperiod. In this nocturnal prosimian, there were no apparent diurnal changes in testosterone concentrations during the non-breeding season (autumn). During seasonal sexual activity (January-August), diurnal changes in testosterone concentrations were characterized by a significant rise during the light phase. The daily testosterone peak occurred about 8.5 h after sunrise from February to July, but at the beginning (January) or at the end (August) of the breeding season, the daily testosterone peak was displaced to the morning. A circannual testosterone rhythm occurred with the highest testosterone values in May/June and the lowest values 6 months later. The dramatic fall in testosterone concentrations after the summer solstice may be associated with a change in the peripheral metabolism of testosterone.