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.     

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.     

Evidence from plasma progesterone concentrations for male-induced ovulation in the brush-tailed bettong, Bettongia penicillata.

Female brush-tailed bettongs, Bettongia penicillata, were housed with either an intact or vasectomized male or isolated from males in the peripartum period. Development of the quiescent corpus luteum formed at the post partum oestrus was initiated by removing the pouch young. Blood samples for analysis of plasma progesterone were collected from the females 2 days before removal of pouch young, daily for 5 or 6 days and then 2-3 times each week until 19 days after removal of pouch young. Plasma progesterone profiles were similar in pregnant and nonpregnant cycles. There was an early progesterone peak (1206 +/- 121 pg ml-1, mean +/- SEM; n = 16) between days 2 and 5 after removal of pouch young, and a second period of high concentrations (greater than 800 pg ml-1) before birth on day 17.4 +/- 0.2 (n = 16). The interval between the early peak and birth was 14 or 15 days. On five of 34 occasions, no increases in plasma progesterone concentrations occurred after removal of pouch young. On 12 of 15 occasions for 13 females that had been isolated from males post partum, plasma progesterone concentrations also remained low (less than 100 pg ml-1) and did not change after removal of pouch young. Females that showed no increases in plasma progesterone concentration after removal of pouch young had significantly lower (P less than 0.001) plasma progesterone concentrations while lactating than those females that did undergo a cycle after removal of pouch young (60 +/- 4 pg ml-1, n = 17 and 225 +/- 23 pg ml-1, n = 30, respectively). Females isolated from males post partum, and monitored until day 12 after removal of the pouch young, and that showed no increases in progesterone in this period, had ovaries that contained no corpus luteum, only corpora albicantia and numerous atretic or developing follicles. We conclude that brush-tailed bettongs are induced ovulators, a characteristic described for only one other marsupial, Monodelphis domestica, from South America.     

PATTERNS OF PARENTAL CARE AND PARENTAL INVESTMENT IN MARSUPIALS

I. Information on growth, development and care of young has been assembled for 62 species of marsupial. 2. During gestation, development of the marsupial embryo proceeds only so far as to allow the neonate to make its way from the urogenital opening to the mammary area on the abdomen of the female where it attaches to a teat. Specific structural adaptations keep the neonate firmly attached to the teat for at least the first month after birth. 3. Six types of pouch are distinguished ranging from lateral folds of skin, which do not cover the mammary area or enclose the developing young, to a fold of skin that covers the mammary area and forms a deep pouch, completely enclosing the developing young. 4. Although the young is very small at birth and birth is rapid, specific changes in the behaviour of females occur around the time of birth, and a specific birth position is adopted. 5. The time at which marsupial young leave the pouch cannot be equated with birth in eutherians, because of the considerable variations in the type of pouch and in patterns of parental care. From a consideration of the functional development of the young in the pouch, it is suggested that the nearest equivalent to eutherian birth is the time at which the marsupial young achieves homeostasis, when it is well furred and endothermic. 6. Maternal behaviour is influenced by the type of pouch. In all species, the mother keeps the young and the pouch clean by licking, especially when the young are wholly within the pouch or attached to the abdomen. In species with reduced pouches where young are left in a nest at an early stage of development, maternal behaviour includes nest building, defence, and retrieving and carrying the young. These functions are performed by the pouch itself in species with large deep pouches in which the young is carried for a much larger part of its development, and other specific maternal behaviours are infrequent. 7. The patterns of parental care are reviewed over all families of marsupial. Not all members of a family have the same pattern of parental care, which appears to be influenced by many factors including body size, type of pouch, diet, litter size and other aspects of life history strategy. 8. Three patterns of parental care are distinguished: (A) As soon as young begin to release the teat they are no longer carried by the mother, and are left in a nest when still barely furred, ectothermic and before the eyes open. This pattern is found in species with large litter size and a pouch reduced or absent, e.g. some Dasyuridae and some Didelphidae. (B) Young remain in the pouch after they begin to release the teat but are left in a nest, at a later stage of development than in A, when well furred, endothermic and with eyes open. After first pouch exit, there is generally a period when young return to the pouch from time to time. This pattern is found in species with well developed pouches and litters of I or > 1 e.g. Peramelidae, some Didelphidae. (C) Young remain in the pouch after they begin to release the teat. At first pouch exit, the young is well furred and endothermic, and leaves the pouch only for brief periods, gradually spending more time out until permanent pouch exit. It is not usually left in a nest. This pattern is found in species with well developed pouches and litters of one, e.g. Macropodidae. 9. Pattern A is seen particularly in the smaller species in any family, where large litter size means that by the time young release the teat, the litter is about 50% of maternal body weight and a considerable burden. In such species, young are left in a nest as soon as possible. In larger species with patterns B or C, litter size is smaller, and by the time they are no longer carried by the female, the litter is still only 20% of maternal weight. 10. Whatever the pattern of parental care, mortality from birth to permanent pouch exit is not unusually high in marsupials in comparison with eutherians. 11. I suggest that the presence of the pouch and the associated patterns of parental care are important determinants of social organization in marsupials. For much of the period of dependence, the young is small, attached to a teat or in a pouch. The male can make little contribution to parental care, and there is little room for improvement in the care of young in complex social groups. In most species, the female on her own is sufficient caretaker. The male is most likely to increase his own biological fitness by going off to mate again and leaving the female to raise his offspring. 12. Patterns of energy expenditure on offspring by female marsupials were assessed throughout the development of young. Investment before birth was assessed by weight of the neonate, during development by growth rate and the time for which the young was carried (pouch life), and total investment by weight of young at weaning and time from birth to weaning. Regression of measures of investment against maternal body weight allowed comparison of investment in animals of different size. 13. Investment in young before birth is very small. Neonatal marsupials range in size from 0·01 to 1 g, and the largest is less than 0·2 % of the size of the mother. Larger mothers produce larger young which are smaller relative to the mother than are the young of smaller species. Individual young in the family Dasyuridae are particularly small. 14. Growth rates in g/d were calculated over the period from permanent pouch exit to weaning. There is a very close correlation between growth rate and maternal body weight - that of litters increases as the 0·78 power of body weight. During this period the growth rate of individuals is comparable with that of eutherian young during lactation, and in litters it is higher still, suggesting that the difference in patterns of growth are not due to the lower metabolic rate of marsupials. As in eutherians there is considerable individual variation in growth rate; it is very high in litters of small dasyurids, which have individual rates comparable to those of larger species. Young of the family Peramelidae grow and develop rapidly; those of the arboreal folivore Phascolarctos do both slowly. I 5. Pouch life, the period for which the young is carried by the mother, increases with body size; as expected, species with pattern A parental care have shorter pouch lives than species of the same size with patterns B or C, reflecting the early stage of development at which young are left in the nest in pattern A. 16. Time from birth to weaning is also longer in larger species. There is a close relationship of age at weaning with maternal weight, with some significant exceptions. For their size, the family Peramelidae have a very short time from birth to weaning, and the time from pouch exit to weaning is particularly short. Many arboreal species have longer periods of dependence than expected from their size. 17. The weight at weaning of individual young is closely related to MBW^0·71, but the weight of one young relative to maternal body weight shows no trend with size, and ranges from 25–61 %, with a mean of 42 %. 18. Parental Investment, as measured by the function Wt. of litter at weaning × 100/MBW, decreases with increasing size of mother as MBW^0·28. The highest levels of investment are found in very small species. In many small species of the family Dasyuridae, a litter at weaning is > 300% MBW. By contrast, investment in the family Peramelidae is low - at weaning a litter of three is about 50% MBW, comparable with investment in a single young of the family Macropodidae. 19. The evolution of patterns of parental care and investment appears to follow three main lines: (1) Species with large litter size, high levels of investment in litters and in individual young. Investment is directed to growth and not to carrying the young in the pouch, since young are left in a nest at an early stage. Typical of this group is the family Dasyuridae, in which many species make few reproductive attempts per year. (2) Species with litters of more than one, low levels of investment in litters and in individuals, but rapid growth and development of young. Because of the small relative size of young they are carried in the pouch for a large part of the period from birth to weaning. This pattern is shown by the family Peramelidae, and seen as an adaptation to rapid and repeated reproduction in an environment with an extended favourable season. (3) Species with small litter size, lower total investment, but investment in individual young is not low, and investment in carrying young to an advanced stage of development is high. Patterns of this type are found in the Diprotodonta, with extreme development in the Macropodidae. 20. Many of the measures of investment have been expressed as a power function of maternal body weight. The exponents of body weight in these functions are such as to suggest that an important underlying variable is metabolic rate. 21. It has been suggested elsewhere that the marsupial mode of reproduction evolved as an adaptation to environmental uncertainty, in that it allows a reproductive attempt to be abandoned at any time much more readily than in eutherians, thereby increasing the likelihood that a female will survive to reproduce again. I consider this suggestion in the light of patterns of parental investment. For small, short-lived species, any reproductive attempt represents a substantial part of its lifetime reproductive output. Investment in any one reproductive attempt is high, and the cost of replacing an abandoned attempt is so high that it seems unlikely that the desertion of offspring would be an important reproductive strategy in small ancestral marsupials, although it may be an important response to environmental uncertainty in certain large modern macropodids.     

Body mass, age and sexual maturity in short-beaked echidnas, Tachyglossus aculeatus

During the course of this 12 year field study body masses of 11 hatchling echidnas (Tachyglossus aculeatus multiaculeatus) and 25 pouch young between the ages of 5 and 60 days were recorded. Body mass increased from 0.3 to approximately 50 g in the first half of pouch life. It then quadrupled before young were placed in a burrow at 45 to 55 days of age. There was a positive correlation between the body mass of the female and that of her young at weaning. From 33 subadult echidnas located, tagged and radio tracked during this study, body masses of 10 were monitored to sexual maturity, i.e. when first encountered in a courtship train. Minimum age of sexual maturity ranged between 5 and 12 years. As subadults, there was no difference between mean body masses of males and females. At sexual maturity, mean body mass of females was significantly higher. No correlation was found between age at sexual maturity and body mass nor was there a significant difference in age of males and females at sexual maturity.     

Iron metabolism during lactation and suckling in a marsupial, the quokka (Setonix brachyurus)

The iron status and transfer of iron through the milk during lactation were determined in a marsupial, the quokka, Setonix brachyurus. Lactating animals were not anaemic and had similar liver and spleen non-haem iron values to non-lactating female adult animals but about 40% less non-haem iron than male adults. The milk iron concentration was very high during the period of lactation when the young is confined to the pouch, averaging about 20 micrograms/ml (eight times the plasma iron concentration), but fell markedly at the time when the young commence to leave the pouch. Blood haemoglobin concentration increased during pouch life of the young to reach adult levels at about 180 days, and liver non-haem iron concentration increased during the same period to values nearly 20 times greater than in their mothers. After the young left the pouch the non-haem iron concentration fell rapidly to the adult level while haemoglobin concentrations were maintained. It is concluded that milk is an adequate source of iron during pouch life of the quokka and enables the animal to build up iron stores which can be utilized after leaving the pouch.     

Cross-fostering in Macropus eugenii leads to increased weight but not accelerated gastrointestinal maturation

Stomach and small intestine development was characterized in tammar wallaby (Macropus eugenii) pouch young (PY) using both morphological and immunohistological criteria. At birth, the stomach is undeveloped in comparison to the well-developed intestinal mucosa. The stomach maintains a uniform morphology in both the forestomach and hindstomach regions until the specialization of cardiac and gastric glands are seen at PY170. Parietal cells, found throughout the mucosa are downregulated in the forestomach as cardiac glandular stomach is developing prior to the transition of the offspring to a diet that includes herbage. In the small intestine, mature-type villi are present at birth but the muscularis externa is immature and undergoes significant development around PY120 onwards. We investigated the effects of changes in maternal milk on gut development in the tammar wallaby using a cross fostering approach that provided younger pouch young with older stage milk. Younger PY (average age 67 days postpartum, n = 5) were transferred onto teats vacated by older stage PY (average age 100 days postpartum, n = 6) for 34 days before gut development was assessed. In addition milk analysis was performed before and after fostering events. Cross-fostered PY animals receiving older stage milk were found to be 31% heavier than controls. There was no difference between carbohydrate and protein concentrations however, fostered PY milk had a higher concentration of lipid than that of controls that may have contributed to heavier fostered PY. No difference was found in stomach or small intestine development between these groups using the criteria employed in this study.     

Development of endothermy in a tasmanian marsupial, Bettongia gaimardi and its response to cold and noradrenaline

Marsupials at birth are ectothermic and gradually attain the ability to change their metabolic heat production during pouch life. How this process occurs in the bettong has been measured on 13 pouch young from week 1 until 3 weeks after pouch vacation (week 18). Oxygen consumption was measured at 35 °C (pouch temperature) and at 22 °C. The results at 35 °C showed an increase in metabolic rate from week 1 until week 12 when there was a decrease to near adult levels after pouch vacation. At 22 °C young bettongs had a lower metabolic rate (compared with measurements made at 35 °C) until week 9 after which there was an increase above measurements made at 35 °C. Noradrenaline had little effect until week 10 after which the metabolic rate (although measured at 35 °C) paralleled the levels measured at 22 °C. The free thyroxine level was low in early pouch life, increased to a peak at week 12 then decreased. Thermal conductance increased until week 10 after which it decreased, reaching values similar to those of adult bettongs by week 20. The results indicate that non-shivering thermogenesis occurs in this macropodoid marsupial. This phenomenon may be a phylogenetic difference between macropodid and non-macropodid marsupials as also suggested by Nicol et al. (1997). Accepted: 19 February 1998     

Renal slice uptake of organic acid and sugar in pouch young of the marsupial Trichosurus vulpecula

Abstract

Kidney tissue was collected from 14 pouch young of the brushtailed possum Trichosurus vulpecula. The young were aged from 5 to 143 days postpartum. Histological observation of a 6-day mesonephric kidney revealed a well-defined microvillus brushborder lining the lumen of the proximal tubule. Renal slices from all the pouch young tested, including mesonephric and metanephric tissue, accumulated p-aminohippurate and α- methyl-d-glucoside at rates comparable to adult renal cortical slices. Tissue to medium concentration ratios after 1 h of uptake averaged 3.8 for p-aminohippurate and 1.9 for α-methyl-d-glucoside in the young. It was concluded that proximal nephron morphology and the transport systems involved in organic acid secretion and sugar reabsorption by the kidney were well-developed at all stages of pouch life.     

Gestational length in the koala, Phascolarctos cinereus

We report a possible case of extended gestation in the koala, Phascolarctos cinereus. Birth of a pouch young was first observed 127 days after the removal of the male from a multi-female colony at Taronga Zoo. No other males were present at that time or had access to the facility. Head measurements and other growth data collected at the time of detection and over the period of pouch life indicates the time from removal of the male and the date of birth to be between 50 and 77 days. DNA fingerprinting using microsatellite loci unambiguously assigned paternity of the pouch young to this male.

These observations suggest either an extended period of gestation of at least 50 days, or activation of a dormant blastocyst from the previous breeding season, as the female entered the period of seasonal oestrus.     

Domestic queens under natural temperate photoperiod do not manifest seasonal anestrus

Domestic cat seasonality between the tropics and the arctic zones is scarcely described and results are inconsistent. The aim of this study was to describe domestic feline seasonal patterns under a natural temperate photoperiod. A total of 372 estrous cycles were studied in 34 post pubertal cats during 900 days. The queens were housed in a cat colony (31°25' South Latitude, 64°11' West Longitude), acclimated under natural photoperiod and daily observed for reproductive behavior. Vaginal cytology was conducted three times a week. For each cat the number of estrous cycles and days in estrus per month for each year were recorded. The months of the year were grouped in four periods of 3 months each according to day length and photoperiod. Comparisons of estrous days among periods were performed by ANOVA for repeated measures. All the cats had estrous cycles throughout the year without intervals of anestrus. Mean number of estrous days differed among the periods (P<0.01), those of long day length and ascending photoperiod being greater (12.5±0.6) to those of descending photoperiod either with long (8.9±0.7) or short (9.3±0.7) days. When the two periods with ascending day lengths were merged and compared to the two periods with descending day lengths merged, the number of estrous days were greater when day length ascended (P<0.01). Nearly 60% of the estrous cycles occurred during the periods of ascending day length. It is concluded, that domestic cats under natural temperate photoperiod have estrous cycles throughout the year showing peak activity the months with increasing photoperiod.     

Reproduction of the quokka, Setonix brachyurus, in captivity

This study records estimations of the chronology of certain events in the calendar of development of the quokka. One gestation period of between 25 and 26 days was observed and 22 joeys (young) had an average birth weight of 0.3852±0.0436 g. Vacation of the pouch occurred between 185 and 195 days of age. One thousand joeys were found to have a masculinity of 0–453 which is statistically smaller than parity. An estimation was made of the age at which the separate teeth erupt and a method of approximating the ages of juveniles and yearlings proposed by using dental eruption stages. The youngest recorded ages at which males and females became reproductively mature were 389 and 252 days respectively. After attaining reproductive maturity all animals born in captivity bred throughout the year. Animals taken from Bald Island, although showing seasonal breeding in the wild, will breed without periodic anoestrus interruption when taken into captivity. Captive animals may live seven years or longer. Using the chronology of some of the above events a comparison was made of the reproductive potential of the wild and domesticated populations.     

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.     

The development of thermoregulation in the rat kangaroo,Potorous tridactylus

• 1.1. The young were first seen out of the pouch on day 103.2 ±2.0 post-partum, and were permanently out of the pouch on day 119.7 ± 1.6, several days prior to the birth of the next young on day 122.8 ± 2.2.
• 2.2. The average mother's pouch temperature and the young's rectal temperature while in the pouch showed similar ranges—however, further analysis demonstrated that the pouch temperature decreased towards the end of lactation.
• 3.3. The difference in rectal temperature of the young in the pouch from 90–107 days to 108–123 days was 0.01 ± 0.34°C, whereas the mother's pouch temperature decreased 0.68 ± 0.37°C.
• 4.4. The results of this study suggests that curiosity and the need for solid food are the primary reasons for the young leaving the pouch and temperature does not play a primary role in the evacuation of the pouch.

     

Müllerian inhibiting substance production and testicular migration and descent in the pouch young of a marsupial

The ontogeny of Müllerian inhibiting substance (MIS) production by the developing testis of an Australian marsupial, the tammar wallaby (Macropus eugenii), was determined during pouch life using an organ-culture bioassay of mouse fetal urogenital ridge. This information was related to the morphological events during testicular migration and descent. MIS biological activity was found in testes (but not ovaries or liver) of pouch young from 2 to 85 days of age. MIS production had commenced by day 2, which is within a day of the first gross morphological signs of testicular differentiation. Müllerian duct regression occurred between 10 and 30 days, which partly coincided with testicular migration to the inguinal region and enlargement of the gubernacular bulb (15 to 30 days). These observations are consistent with the hypothesis that MIS may be involved in testicular transabdominal migration. The epididymis commenced development and growth only after the testis had descended through the inguinal ring. This provides no support for the suggestion that the epididymis is involved in testicular descent into the scrotum. The basic sequence of events in post-testicular sexual differentiation in the wallaby is sufficiently similar to that seen in eutherian mammals to make it an excellent experimental model for future studies of testicular differentiation, migration and descent.     

Life history adaptations of Gasterosteus aculeatus in a Mediterranean wetland

Synopsis The life cycle of leiurus-type Gasterosteus aculeatus occurring in a Mediterranean coastal wetland is described. Fish have a low number of lateral plates, short spines and marked sexual dimorphism in size. The life cycle is strictly annual, adults dying shortly after breeding. Adult fish migrate into seasonally-flooded freshwater marshes to breed, and the young migrate back to brackish water to pass the summer and autumn. Breeding occurs in March at water temperatures of about 10°C, the season lasting about 50 days. Growth of fish occurs throughout the year, but differs from year to year, resulting in variable adult size. Maximum gonadal investment of male fish is in autumn, whereas that of females is in spring. Gonadal investment of female fish, as measured by gonado-somatic index and fecundity, is higher than in other studied leiurus populations, but the number of clutches produced in a season is probably low. These differences in life history from other studied populations of sticklebacks are seen as adaptations to a mediterranean-type climate (high summer temperatures, seasonality of water bodies) and to heavy predation by fish-eating birds.     

Sex determination in marsupials: evidence for a marsupial-eutherian dichotomy

In this paper, we review briefly the current state of knowledge about sexual differentiation in eutherian mammals, and then describe the situation in detail in two marsupial species: the North American opossum and the tammar wallaby. The conventional explanation for the genesis of all male somatic sexual dimorphisms in mammals is that they are a consequence of the systemic action of testicular hormones. In the absence of testes, the embryo will develop a female phenotype. We present evidence for the tammar wallaby that calls into question the universal applicability of this hormonal theory of mammalian sexual differentiation. We have shown that extensive somatic sexual dimorphisms precede by many days the first morphological evidence of testicular formation, which does not occur until around the third day of pouch life. Male foetuses, and pouch young on the day of birth, already have a well-developed gubernaculum and processus vaginalis, paired scrotal anlagen, and a complete absence of mammary anlagen, whereas female foetuses and newborn pouch young have a poorly developed gubernaculum and processus vaginalis, no scrotal anlagen, and well-developed mammary anlagen. Because it seems unlikely that the male gonad could begin hormone secretion until after the Sertoli and Leydig cells are developed, our results strongly suggest that some sexually dimorphic somatic characteristics develop autonomously, depending on their genotype rather than the hormonal environment to which they are exposed. We have been able to confirm the hormonal independence of the scrotum, pouch and mammary gland by administering testosterone propionate daily by mouth to female pouch young from the day of birth; although the Wolffian duct was hyperstimulated, there was no sign of scrotal development, or pouch or mammary inhibition. When male pouch young were treated with oestradiol benzoate in a similar fashion, there was hyperstimulation of the Müllerian duct and inhibition of testicular migration and development, but no sign of scrotal inhibition or pouch or mammary development. Our results in the tammar wallaby are consistent with the earlier studies on the opossum, whose significance was not appreciated at the time. Further evidence in support of this hormonal independence comes from earlier studies of spontaneously occurring intersexes in several species of marsupial, including the opossum and the tammar wallaby. An XXY individual had intra-abdominal testes and complete masculinization of the male reproductive tract internally, but externally there was a pouch and mammary glands and no scrotum.(ABSTRACT TRUNCATED AT 400 WORDS)     

OBSERVATIONS ON THE LAVA GULL LARUS FVLIGINOSUS

Lava Gulls Larus fuliginosus live as scavengers and unspecialized predators along the shores of the Galapagos Islands. Although they concentrate locally at places where refuse is available, their breeding density is low: eight breeding pairs were found along a stretch of 35 miles of the coast of Indefatigable Island. The total (world) population is likely to be less than 300–400 breeding pairs.
Their low breeding density and small total population is attributed to the fact that they are confined to linear feeding grounds of limited extent, which provide a sparse food supply for much of the year.
Lava Gulls nest solitarily, usually in sheltered places near coastal lagoons; all the nests found were at least two miles from any other known site. The clutch consists of two eggs, incubation (one case) lasts 32–33 days, and the fledging period is about 60 days.
Breeding takes place throughout the year, with no apparent peak. Individual cycles of 9–12 months have been recorded.
Observations are given on behaviour and displays, and on the sequence of plumage change and moult in the first two years of life.     

Growth of opossums (Trichosurus vulpecula) in the Orongorongo Valley,Wellington, New Zealand, 1953–61

The growth of pouch young and juvenile Trichosurus vulpecula to maturity is described, based on animals gin‐trapped in 800 ha of indigenous forest in the Orongorongo Valley, near Wellington. Commencing in March 1953 opossums were trapped continuously for 1 year, and then intermittently until 1961. Four ageing criteria were considered: ossification of limb epiphyses and development of cranial ridges were unreliable; tooth wear and closure of the spheno‐occipital skull sutures were more satisfactory, and were adopted. For the first 180 days the mean growth followed a rectilinear regression when size, expressed as cube root of weight, was plotted against age. Thereafter growth accelerated greatly, but steadied towards the end of the first year; its rate increased after several months, and ceased at 2 to 21/2 years. Though adult males (2.65 kg) and females (2.41 kg) differed significantly in weight, there was no detectable difference during the growth phase. Births occurred throughout the year, but were markedly seasonal, 86% occurring between mid March and the end of May. A secondary birth peak in spring, recorded in other areas, was barely apparent. Most young consequently grew fastest in their first spring and summer. The growth pattern appeared to be mainly dependent on age rather than season_^ since all young reared in captivity conformed, irrespective of the season of birth.