Marsupial Reproduction Research Articles

Pouch bacteria: an understudied and potentially important facet of marsupial reproduction

Australia is home to a rich biodiversity of marsupials that are found nowhere else. Unfortunately, many of these species are currently threatened with extinction due to introduced feral predators and other anthropogenic factors. There is growing recognition that host-associated microorganisms can play important roles for animal health, with billions of dollars currently being invested into human gut microbiome research and the development of microbiome-based therapeutics to improve human health. Can microorganisms also be harnessed to stem the tide of marsupial extinctions? In this review, we provide an overview of some of the challenges facing Australia’s marsupials, and our current understanding of the microbiology of the marsupial pouch. We also propose outstanding research questions pertaining to the marsupial pouch, which, if addressed, may provide actionable knowledge and novel microbial therapies that could help stem the tide of marsupial extinctions in Australia.

How to Get into the Pouch: Solving the Riddle of the Kangaroo Birth (1826–1926)

How does the newborn kangaroo get into the pouch after birth? This question was much discussed by naturalists around the globe between 1826, when Etienne Geoffroy Saint-Hilaire first addressed the issue, and 1926, when Ellis Troughton published a “definite” account of the debate. In its first part, this paper focuses on the investigations conducted at European zoos. The advent of kangaroos made it possible to investigate the riddle through observation. In the early 1830s, Richard Owen enlisted the aid of London Zoo to devise a research programme. He claimed that the mother put the embryo into the pouch using her lips, and naturalists in other Europeans zoos were eager to confirm Owen's hypothesis. In its second part, this paper contrasts the zoo-based investigations with observations made in Australia. Hunters and animal traders claimed that the joey travelled into the pouch without any assistance from the mother. This case study allows us to address a number of overarching questions: Could the zoo live up to its promise to generate knowledge in natural history, challenging the classical method of anatomical dissection? What practical difficulties did naturalists and animal keepers face in their observations? How did the information on the reproduction of marsupials circulate (or not) between metropolitan centres and colonial outposts? The riddle of the kangaroo birth casts light on the potential and the limitations of the zoo as a site for research.

Marsupials the alternative therians – From gametes to birth

Marsupial reproduction shares many common features with the more familiar eutherian mammals but things are often done differently, in alternative ways. Like the eutherians marsupials are placental but the period and degree of development supported in the uterus is much shorter and the long growth phase of development is supported by lactation. But these different ways of achieving often similar outcomes are also seen in gamete formation and function, fertilization and early development. This review presents an overview of marsupial reproductive biology with an emphasis on gamete biology.

Reproductive Science as an Essential Component of Conservation Biology: New Edition.

The previous edition of this book mainly provided a snapshot of the state of the art in terms of species-specific reproductive biology and emerging technologies. The influence of environmental changes on reproductive fitness was introduced but not fully explored. The objectives of this second edition were to (1) emphasize the need for holistic and global efforts to understand and sustain reproduction in a constantly changing environment and (2) provide more knowledge in the reproductive physiology of different taxa. The first section of the book is dedicated to survival and adaptation of species in a changing environment (including chapters on environmental impacts in different taxa, as well as the role of microbiomes). The second section focuses on progress in understanding, assisting or even suppressing reproduction in wild species, keeping in mind the influence of environmental factors as well. It contains chapters from the previous edition that were updated (reproduction in elephants, koalas, marsupials, amphibians, and corals), new chapters on species such as sharks and rays, and contributions about the increasing role of reproductive manipulations, such as assisted reproduction and contraception. While the present book emphasizes the overarching issue of environmental impacts on reproduction (resulting in infertility, subfecundity, or fitness), it also highlights the challenges of maintaining wild species in captivity, including those associated with ensuring good welfare. Captive environments can influence reproduction in a multitude of ways, some unexpected, such as the selection of unwanted genetic traits, an essential dimension to be considered to ensure the success of conservation breeding programs. Lastly, new approaches, such as the use of allostatic load indexes and reproductive microbiome analyses also will be closely examined for the first time in rare and endangered species to address conservation issues.

Comparative anatomy of neonates of the three major mammalian groups (monotremes, marsupials, placentals) and implications for the ancestral mammalian neonate morphotype.

The existing different modes of reproduction in monotremes, marsupials and placentals are the main source for our current understanding of the origin and evolution of the mammalian reproduction. The reproductive strategies and, in particular, the maturity states of the neonates differ remarkably between the three groups. Monotremes, for example, are the only extant mammals that lay eggs and incubate them for the last third of their embryonic development. In contrast, marsupials and placentals are viviparous and rely on intra-uterine development of the neonates via choriovitelline (mainly marsupials) and chorioallantoic (mainly placentals) placentae. The maturity of a newborn is closely linked to the parental care strategy once the neonate is born. The varying developmental degrees of neonates are the main focus of this study. Monotremes and marsupials produce highly altricial and nearly embryonic offspring. Placental mammals always give birth to more developed newborns with the widest range from altricial to precocial. The ability of a newborn to survive and grow in the environment it was born in depends highly on the degree of maturation of vital organs at the time of birth. Here, the anatomy of four neonates of the three major extant mammalian groups is compared. The basis for this study is histological and ultrastructural serial sections of a hatchling of Ornithorhynchus anatinus (Monotremata), and neonates of Monodelphis domestica (Marsupialia), Mesocricetus auratus (altricial Placentalia) and Macroscelides proboscideus (precocial Placentalia). Special attention was given to the developmental stages of the organs skin, lung, liver and kidney, which are considered crucial for the maintenance of vital functions. The state of the organs of newborn monotremes and marsupials are found to be able to support a minimum of vital functions outside the uterus. They are sufficient to survive, but without capacities for additional energetic challenges. The organs of the altricial placental neonate are further developed, able to support the maintenance of vital functions and short-term metabolic increase. The precocial placental newborn shows the most advanced state of organ development, to allow the maintenance of vital functions, stable thermoregulation and high energetic performance. The ancestral condition of a mammalian neonate is interpreted to be similar to the state of organ development found in the newborns of marsupials and monotremes. In comparison, the newborns of altricial and precocial placentals are derived from the ancestral state to a more mature developmental degree associated with advanced organ systems.

Reproduction of the opossums Micoureus paraguayanus and Philander frenata in a fragmented Atlantic Forest landscape in Brazil: Is seasonal reproduction a general rule for Neotropical marsupials?

Reproductive seasonality is one of the most important ways by which an animal adapts to temporal changes in its environment, for example, allowing it to deal with seasonal fluctuations in resource availability. Since Davis (1945) seminal work, the seasonal cycle of reproduction of marsupials in Neotropical forests has been well established; reproduction usually falls within the wet season. Marsupials’ main food resources are insects and fruits (Emmons and Feer 1997), which usually have a higher availability in the wet period (Bergallo and Magnusson 1999). As the lactation is the period with highest energy demands in marsupials (Atramentrowicz 1992), its synchronization with the wet season allows lactating females to have more energy available. In fact, many studies with Neotropical marsupials link the beginning of the reproductive period with the increase in precipitation and the resulting enhancement of food resources (Fleming 1973; TyndaleBiscoe and Mackenzie 1976; O’Connell 1979; Fonseca and Kierulff 1989).

Reproductive endocrinology of the largest dasyurids: Characterization of ovarian cycles by plasma and fecal steroid monitoring. Part I. The Tasmanian devil ( Sarcophilus harrisii)

There is a strong body of knowledge on the reproductive endocrinology of macropods, but little detailed information is available on the hormonal control of reproduction in other marsupials. This study used plasma and fecal sex steroid monitoring to characterize the estrous cycle of the largest extant dasyurid—the Tasmanian devil ( Sarcophilus harrisii). A pro-estrous pulse in plasma progesterone (1.33 ± 0.2 ng/ml) occurred several weeks prior to onset of the luteal phase (LP), resulting in a characteristic biphasic pattern during the estrous cycle. This brief, pro-estrous progesterone pulse was associated with a predominantly cornified vaginal smear, and copulation in females paired with males. Mean luteal progesterone concentrations (5.28 ± 0.8 ng/ml) were sustained and peaked around day 15 from luteal onset; thereafter, concentrations declined precipitously and returned to baseline around day 25. Females that did not produce young returned to estrus after 33.7 ± 5.9 days. Fecal 20α-OH-pregnanes analyzed in a pregnanediol assay (PgD) were excreted in consistently higher levels than 20-oxo-pregnanes, but the pattern was similar for the two metabolites, and significantly correlated with fluctuations in plasma progesterone. Fecal total estrogen concentrations were highest during the follicular phase (FP) and accompanied a pro-estrous pulse in fecal progestagens. The mean duration of the estrous cycle was ∼32 days, with a FP of around 14 days (range 8–23 days), and a luteal phase of around 18 days (range 12–25 days). There were no differences in the length of the LP between mated and non-mated cycles. Gestation length was 17.9 ± 1.0 days (range 14–22 days). Fecal steroid monitoring revealed significant differences between the pattern of progestagens and estrogen concentrations during the pregnant and non-mated estrous cycle, suggesting maternal endocrine recognition of pregnancy in the Tasmanian devil.

Influence of donor age on development of gonadal tissue from pouch young of the tammar wallaby, Macropus eugenii, after cryopreservation and xenografting into mice

Ovaries from a marsupial, the tammar wallaby (Macropus eugenii), were grafted into a eutherian recipient at known stages of development to ascertain whether normal development would occur. Xenografted ovaries from pouch young < 20 days old, before the onset of meiosis, retained few germ cells and developed tubule-like structures reminiscent of seminiferous cords. Ovaries from 50-day-old pouch young, which contain primordial follicles, developed into antral follicles and corpora lutea within the eutherian host, and produced hormones that stimulated the reproductive tract of the host. The timing of onset of antrum formation and the progress of follicle development were advanced relative to the timing of events in ovaries in situ. Frozen-thawed ovaries from 50-day-old donors developed into preantral follicles, but at a reduced rate and number. This finding shows that gonads of a marsupial species can develop as xenografts in a eutherian, forming large antral follicles. Accelerated follicular development in xenografts provides a potentially valuable model for studying the factors that control follicle development. Assisted reproduction of endangered marsupials may also be feasible using follicles from pouch young grown as xenografts in a eutherian host.

Influence of donor age on development of gonadal tissue from pouch young of the tammar wallaby, Macropus eugenii, after cryopreservation and xenografting into mice.

Ovaries from a marsupial, the tammar wallaby (Macropus eugenii), were grafted into a eutherian recipient at known stages of development to ascertain whether normal development would occur. Xenografted ovaries from pouch young < 20 days old, before the onset of meiosis, retained few germ cells and developed tubule-like structures reminiscent of seminiferous cords. Ovaries from 50-day-old pouch young, which contain primordial follicles, developed into antral follicles and corpora lutea within the eutherian host, and produced hormones that stimulated the reproductive tract of the host. The timing of onset of antrum formation and the progress of follicle development were advanced relative to the timing of events in ovaries in situ. Frozen-thawed ovaries from 50-day-old donors developed into preantral follicles, but at a reduced rate and number. This finding shows that gonads of a marsupial species can develop as xenografts in a eutherian, forming large antral follicles. Accelerated follicular development in xenografts provides a potentially valuable model for studying the factors that control follicle development. Assisted reproduction of endangered marsupials may also be feasible using follicles from pouch young grown as xenografts in a eutherian host.

Australasian marsupials--to cherish and to hold.

Considerable interchange of mammals between South America and Australasia occurred during the first half of the Tertiary, including the presence of placental mammals in Australia. This challenges the old assumption that the marsupial radiation in Australia was made possible by the absence of placental competition, and suggests that two properties of marsupial organization may have favoured their survival in the increasingly arid climates that developed after the separation of Australasia from Antarctica. The basal metabolic rates of marsupials are about 70% of equivalent placentals, so their maintenance requirements for energy, nitrogen and water are lower, whereas their field metabolic rates are about the same, which means that they have a greater metabolic scope to call on when active. This may have given marsupials an advantage in semi-arid environments. The lengthy and complex lactation of marsupials enables the female to exploit limited resources over an extended period without compromising the survival of the young. Both these properties of marsupials enabled them to survive the double constraints of low fertility soils and the uncertain climate of Australia throughout the Tertiary. The arrival of people was followed first by the extinction of the large marsupials and, much later, by the wholesale decline or extinction of the small-to-medium sized species. The common factor in both extinctions may have been the constraints of marsupial reproduction.

Population dynamics and reproduction of marsupials and rodents in a Brazilian rural area: a five-year study

A five-year mark-recapture study of small mammals was conducted with sampling every two months in a rural area of Sumidouro, State of Rio de Janeiro, Brazil, from June 1991 to July 1996. Population sizes were estimated through MNKA estimator, survivorship and recruitment rates through Jolly-Seber estimator. Nectomys squamipes and Didelphis aurita were the most abundant species, followed by Akodon cursor, Philander frenata and Oligoryzomys nigripes. Marsupials reproduced from July/August to March, with the highest population sizes and recruitment rates in the end of the rainy periods and beginning of the dry period. Rodents were able to reproduce throughout the year. N. squamipes' population size was correlated with survivorship; peaks and the bulk of reproduction occurred during and after the rainy periods. A. cursor's population size increased in dry periods. These species displayed seasonal patterns of population dynamics related to reproduction, with some variations among years chiefly for the rodents.

Effects of cabergoline on reproduction in three families of Australian marsupials.

The effects of the prolactin inhibiting drug, cabergoline, on pregnant and lactating marsupials were investigated in four species from three diverse families: the tammar wallaby, Macropus eugenii, the quokka, Setonix brachyurus, the brushtail possum, Trichosurus vulpecula, and the fat-tailed dunnart, Sminthopsis crassicaudata. In tammar wallabies, 20 micrograms cabergoline kg-1 injected intramuscularly 1 day before expected birth did not alter the timing of parturition but neonates died within a day of birth, suggesting that the onset of lactation was compromised. During early lactation in tammars (56-69 days post partum), an intramuscular injection transiently retarded growth of the young, although they subsequently survived. This treatment induced reactivation of the quiescent corpus luteum and the blastocyst from diapause, so a new birth occurred 26-27 days later, despite the continued sucking of the young in the pouch. Intramuscular injection during late lactation (166-199 days post partum) apparently suppressed milk secretion since pouch young lost up to 20% of their bodyweight or died within 7 days of treatment. Oral administration of cabergoline had no effect on the growth of the young or on the quiescent corpus luteum and diapausing blastocyst. Quokkas showed similar responses to tammars after treatment in late lactation. Possums and dunnarts were less sensitive to injected cabergoline than the two macropodid species, and possums showed no response to oral administration. The lack of response of these marsupial species to oral cabergoline treatment suggests that accidental ingestion of baits, containing 20 micrograms cabergoline kg-1, used to control introduced eutherian pests such as the red fox, Vulpes vulpes, or the feral cat, Felis cattus, should not affect the reproduction of native marsupials.

Likely targets for immunocontraception in marsupials.

There is a growing need to manage marsupial populations as a means to mitigate economic and environmental damage and resolve animal welfare problems. In Australia, the problems of population management are highly specific and localized. In contrast, in New Zealand the problem is the control of the many millions of widely-distributed brushtail possums which are the country's major vertebrate pest. The needs of the two countries are thus very different but immunocontraception may provide an effective and humane alternative to current lethal control strategies. This paper discusses the features of marsupial reproduction and development that offer potential as targets for immunocontraceptive interference, including: (1) sperm production and maturation in the male; (2) sperm transport and maturation in the female; and (3) sperm and egg antigens and the early embryo. Some of these antigen targets are shared with eutherian mammals but others are likely to be unique to marsupials.

Monotreme and marsupial reproduction.

Marsupials were regarded as curiosities by their early European discoverers, animals to be wondered at. Monotremes were even more surprising; the platypus was such an amalgam of characters that it was thought to be a hoax. They were recognized very early as mammals that could make a major contribution to our understanding of reproductive processes, and work on marsupials at the turn of the century was much in evidence. It is, however, only in the past two decades, and especially in the past few years that marsupial research has regained this position. There is no doubt that future research will strengthen this contribution, but we are faced with serious conservation questions that must be solved if we are to maintain these wonderful animals as a resource for future generations.

Evidence from the oestrous cycle for male-induced ovulation in Bettongia penicillata (Marsupialia).

Female brush-tailed bettongs (Bettongia penicillata) housed in a breeding group of one male and one to three females had an average gestation period of 21.2 days (n = 58) and parturition was followed within 24 h by oestrus and mating. If a young was not born as a result of the mating, oestrus recurred after about 21.7 days (n = 12). From removal of pouch young to birth was 17.5 days, on average (n = 85), in females that had mated post partum, but most females that were isolated from a male before parturition returned to oestrus about 6.6 days after simultaneous removal of pouch young and return to the male (n = 9). Females housed in female-only groups appeared not to come into oestrus or to do so irregularly. These females, when returned to the male, usually came into oestrus within 10 days. These data provide evidence that, in most females of B. penicillata, ovulation does not occur in the absence of a male and that previously isolated females return to oestrus within 10 days of return to the male.

Australian marsupials as models for the developing mammalian visual system.

This article makes two points. First, the diprotodont marsupials, including the kangaroos, wallabies and the Australian possum are not primitive mammals, and their brains make as good a general model of the higher mammals such as monkeys and humans as do those of the more common laboratory mammals such as cats and rats. Second, the peculiarities of marsupial reproduction, which comprises a very short period of intrauterine development, followed by a relatively protracted period of development in the pouch, provide unparalleled advantages for research into mammalian neuroembryology. Examples will be provided of how such research has made a contribution to our understanding of neural development, concentrating primarily on the visual system.

Prospects for the Artificial Manipulation of Marsupial Reproduction and Its Application in Research and Conservation

Techniques to manipulate reproduction and productivity are well established features of the husbandry of domestic animals and the treatment of human infertility. Similar approaches are feasible in marsupials, but little work has been done to apply our considerable basic knowledge of marsupial reproduction to produce practical artificial breeding. If the reproduction and productivity of marsupials could be more effectively controlled it would greatly aid research and profoundly change both current practice in the management of zoo animals, and the strategies employed for the breeding and conservation of rare or endangered species. The present paper sets out the likely agenda, reports progress to date and discusses short and long-term prospects for the artificial breeding of marsupials. Topics discussed include: induced ovulation and superovulation, oocyte and embryo collection, semen collection and the frozen storage of sperm, artificial insemination, in vitro fertilization and embryo transfer, frozen storage of embryos, and the use of surrogate mothers in supporting both pregnancy to term, and the development of young in the pouch.

Sex-Ratio Variation in Marsupials

Many marsupials produce sex ratios biased towards male or female young. In several cases these changes are comfortably accommodated in the existing theory of sex allocation. Local resource competition and the Trivers-Willard hypothesis have been usefully applied to several data sets, and preliminary experimental work has supported the main tenets of theory. By contrast, several data sets lack explanation, and provide challenges to theoreticians. The high frequency of bias in marsupials does not result from data-dredging, as bias is usually reported in descriptive accounts of marsupial reproduction, without recourse to any theoretical or mechanistic explanations. It is not possible to distinguish whether the marsupial mode of reproduction is well suited to manipulate sex allocation, or whether it facilitates measurement of biased sex allocation. As for most eutherians and birds, the mechanism of prenatal sex allocation is unknown for any marsupial. However, the current interest in sex-determining mechanisms in marsupials suggests a profitable avenue for collaboration between geneticists, physiologists and evolutionary ecologists.

Activation of estrus by pheromones in a marsupial: stimulus control and endocrine factors.

Little is known about the effects of social factors or about the hormonal control of social factors on reproduction in marsupials. In previous studies on the gray opossum, a small, Brazilian didelphid, the presence of males was found to activate reproduction in females. In this study, the effects of pheromones produced by intact males, castrated males, and intact females on estrus in female gray opossums was examined. It was found that females housed alone rarely showed spontaneous periods of estrus, that exposure to pheromonal cues provided by intact males reliably induced estrus in 75-100% of the experimental females, and that pheromonal cues provided by castrated males or intact, stimulus females induced estrus in 25% of the experimental females. These findings are discussed with respect to the ecology, social behavior, and reproductive characteristics of the didelphid marsupials.

Body size, duration of parental care, and the intrinsic rate of natural increase in eutherian and metatherian mammals.

The intrinsic rate of natural increase (r m), conception to weaning time (t cw), age of first reproduction (tmat), and components of fecundity were compared between ecologically similar groups of 42 metatherian (=marsupial) and 42 eutherian mammals. Marsupial t cw s average 50% longer than those of eutherians. Small marsupials (<400 g) mature later, and have lower and r ms than eutherians; large marsupials (>10,000 g) do not mature later but also have lower r ms. At body sizes of 1,000-3,500 g, marsupials and eutherians have similar t mat s and t cw s but marsupials have greater r ms. Marsupials compensate for their longer t cw s by a variety of methods including embryonic diapause, larger litter sizes, and short periods between weaning and maturity. Although the greatest similarities in marsupial and eutherian life histories are at body sizes of 1-5 kg, compensation for long t cw may be seen at any marsupial body size. Other ecological factors not withstanding, marsupial reproduction is neither inherently inferior to that of eutherians nor obviously more advantageous in unpredictable environs.