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Hynes EF, Shaw G, Renfree MB, Handasyde KA. Contraception of prepubertal young can increase cost effectiveness of management of overabundant koala populations. WILDLIFE RESEARCH 2019. [DOI: 10.1071/wr18109] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Context
With limited resources for wildlife management and conservation, it is vital that the effectiveness of management programs is maximised and costs reduced. Koala populations need to be reduced in locations where they are locally overabundant and over-browsing their food trees. Subcutaneous contraceptive implants containing levonorgestrel are currently used to control koala fertility to assist in reducing population densities. Dependent young are caught with their mothers, so are also available for contraception.
Aims
The overall aim was to investigate whether the effectiveness of koala contraception programs can be improved by administering levonorgestrel implants to female young along with their mothers. This was achieved by: (1) determining if implanting females before sexual maturation affects their fertility, growth and pouch development; and (2) developing a stage-structured population growth model to compare two management scenarios.
Methods
Juvenile female koalas (11–17 months old) were treated with either a control (n = 5) or 70 mg levonorgestrel implant (n = 5). Koalas were caught every 4 to 6 weeks for 15 months, then every 3 to 12 months for 5 years. Koalas were weighed and head length measured. Pouches were checked for young. Pouch development was assessed as a proxy for sexual maturation. A stage-based population model simulating koala population growth was developed to compare different management scenarios: no treatment; treatment of adults only; and treatment of adults plus their dependent young.
Key results
Levonorgestrel implants prevented births with no effect on growth, survival or timing of sexual maturation. Population growth simulations indicate that treating dependent young with their mothers results in earlier population reduction.
Conclusions
The treatment of prepubertal female koalas with levonorgestrel implants is a safe and effective method that increases the effectiveness of koala contraception programs.
Implications
Development of novel strategies may provide opportunities to increase the efficiency and cost-effectiveness of management programs with constrained resources.
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Hetz JA, Menzies BR, Shaw G, Rao A, Clarke IJ, Renfree MB. Growth axis maturation is linked to nutrition, growth and developmental rate. Mol Cell Endocrinol 2015; 411:38-48. [PMID: 25896544 DOI: 10.1016/j.mce.2015.04.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Revised: 04/09/2015] [Accepted: 04/13/2015] [Indexed: 10/23/2022]
Abstract
Maturation of the mammalian growth axis is thought to be linked to the transition from fetal to post-natal life at birth. However, in an altricial marsupial, the tammar wallaby (Macropus eugenii), this process occurs many months after birth but at a time when the young is at a similar developmental stage to that of neonatal eutherian mammals. Here we manipulate growth rates and demonstrate in slow, normal and fast growing tammar young that nutrition and growth rate affect the time of maturation of the growth axis. Maturation of GH/IGF-I axis components occurred earlier in fast growing young, which had significantly increased hepatic GHR, IGF1 and IGFALS expression, plasma IGF-I concentrations, and significantly decreased plasma GH concentrations compared to age-matched normal young. These data support the hypothesis that the time of maturation of the growth axis depends on the growth rate and maturity of the young, which can be accelerated by changing their nutritional status.
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Affiliation(s)
- Jennifer A Hetz
- School of BioSciences, The University of Melbourne, Vic. 3010, Australia
| | - Brandon R Menzies
- School of BioSciences, The University of Melbourne, Vic. 3010, Australia.
| | - Geoffrey Shaw
- School of BioSciences, The University of Melbourne, Vic. 3010, Australia
| | - Alexandra Rao
- Department of Physiology, Monash University, Vic. 3800, Australia
| | - Iain J Clarke
- Department of Physiology, Monash University, Vic. 3800, Australia
| | - Marilyn B Renfree
- School of BioSciences, The University of Melbourne, Vic. 3010, Australia
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Herbert CA, Eckery DC, Trigg TE, Cooper DW. Chronic treatment of female tammar wallabies with deslorelin implants during pouch life: effects on reproductive maturation. Reprod Fertil Dev 2013; 25:879-89. [DOI: 10.1071/rd12087] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 07/25/2012] [Indexed: 11/23/2022] Open
Abstract
The present study reports on attempts to delay puberty in a model marsupial species using the gonadotrophin-releasing hormone (GnRH) agonist deslorelin. Female tammar wallaby pouch young received deslorelin (5 mg) or placebo implants (n = 8/group) when they were 193 ± 2 days old. Sexual maturity was significantly delayed in deslorelin-treated animals, with the first successful production of offspring in treated and control animals occurring at 813 ± 62 and 430 ± 42 days of age, respectively. This delay was associated with a period of retarded pouch and teat development. Progesterone concentrations remained at basal levels throughout the first breeding season, indicating the absence of luteal cycles in treated females. Recovery and maturation of the hypothalamic–pituitary axis was a gradual process. Treated animals failed to respond to GnRH challenge at 12 months of age and had a reduced LH response at 18 months of age, before attaining full responsiveness by 24 months of age. Despite this apparent pituitary recovery by 24 months of age, as evidenced by complete teat eversion and LH responsiveness to GnRH, the time to first parturition was significantly delayed beyond this time in three females. This suggests that there may be longer-lasting effects at the level of the ovary and/or on FSH secretion. The significant delay in the onset of sexual maturation in response to chronic GnRH agonist treatment in this model marsupial species may be of practical significance to the management of fertility in captive and semi-free range marsupial populations.
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Edwards MJ, Hinds LA, Deane EM, Deakin JE. A review of complementary mechanisms which protect the developing marsupial pouch young. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2012; 37:213-220. [PMID: 22504164 DOI: 10.1016/j.dci.2012.03.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/26/2012] [Accepted: 03/26/2012] [Indexed: 05/31/2023]
Abstract
Marsupials are born without a functioning adaptive immune system, into a non-sterile environment where they continue to develop. This review examines the extent of exposure of pouch young to microorganisms and describes the protective mechanisms that are complementary to adaptive immunity in the developing young. Complementary protective mechanisms include the role of the innate immune system and maternal protection strategies, such as immune compounds in milk, prenatal transfer of immunoglobulins, antimicrobial compounds secreted in the pouch, and chemical or mechanical cleaning of the pouch and pouch young.
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Affiliation(s)
- M J Edwards
- Research School of Biology, The Australian National University, Canberra, ACT, Australia.
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Renfree MB, Pask AJ. Reproductive and developmental manipulation of the marsupial, the tammar wallaby Macropus eugenii. Methods Mol Biol 2011; 770:457-473. [PMID: 21805276 DOI: 10.1007/978-1-61779-210-6_18] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The developing marsupial is an ideal animal for use in biomedical research. Marsupials are mammals that have been separated from eutherian mammals for over 130-140 million years. They all deliver altricial young that complete their growth and development after birth usually in a pouch, but not all marsupials have a pouch. Their lactation changes dynamically throughout the period of pouch life, and the mother controls their growth via the production of milk that is tailor-made for each stage of development. The tammar wallaby, Macropus eugenii, has been the experimental marsupial of choice for over five decades, as it is highly amendable to handling and breeds well in captivity. The tammar is especially interesting because it has both a lactational and a seasonal control of its reproduction and embryonic diapause that normally lasts 11 months. Standard molecular techniques can be used for most manipulations in marsupials. However, there are several special techniques for treating the young for experimental surgery and for organ culture that we detail below.
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Affiliation(s)
- Marilyn B Renfree
- Department of Zoology, The University of Melbourne, Melbourne, VIC 3010, Australia.
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Bradshaw FJ, Bradshaw D. Progesterone and reproduction in marsupials: a review. Gen Comp Endocrinol 2011; 170:18-40. [PMID: 20688062 DOI: 10.1016/j.ygcen.2010.07.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Revised: 07/25/2010] [Accepted: 07/28/2010] [Indexed: 01/26/2023]
Abstract
Progesterone (P4) profiles throughout pregnancy and the oestrous cycle are reviewed in a wide range of marsupial species, representing 12 Families, and focus on the corpus luteum (CL) and its functioning, compared with its eutherian counterpart. Physiologically, P4 subtends the same fundamental processes supporting gestation in marsupials as it does in eutherian mammals, from its role in stimulating the secretory endometrium, effecting nutritional transfer across the placenta and establishing lactogenesis. Before the formation of the CL, however, secretion of P4 is widespread throughout many Families and the dual roles of P4 in the induction of sexual behaviour and ovulation are exposed. In Dasyuridae, raised levels of P4 are linked with the induction of sexual receptivity and are also present around the time of mating in Burramyidae, Petauridae and Tarsipedidae, but their function is unknown. Only in Didelphidae has research established that the pheromonally-induced levels of pro-oestrous P4 trigger ovulation. This is principally the role of oestradiol in the eutherian and may be an important difference between the marsupial and the eutherian. The deposition of the shell coat around the early marsupial embryo is also a function of P4, but perhaps the most striking difference is seen in the time taken to form the CL. This is not always immediate and the maximum secretion of P4 from the granulosa cells may not occur until some 2 weeks after ovulation. The slower development of the CL in some species is linked with delays in the development of the embryo during its unattached phase and results in relatively long gestation periods. A common feature of these, in monovular species, is a short pulse of P4 from the newly-luteinised CL, which is all that is needed for the subsequent development of the embryo to term. Maternal recognition of pregnancy occurs soon after the formation of the blastocyst, with embryo-induced changes in ovarian production of P4 and the uterine endometrium. The embryo, similar to the eutherian, determines the length of the gestation period and initiates its own birth, but in direct contrast, the embryo of some marsupial species shortens the life-span of the CL. The evidence points to a different strategy; one of a reduction, rather than an expansion of the potential ovarian and placental support available during pregnancy. The marsupial mode of reproduction, where all species produce highly altricial young, receiving complex and extensive maternal care, has facilitated the adaptive radiation of this group and avoided the need for precociality.
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Affiliation(s)
- Felicity J Bradshaw
- School of Animal Biology M092, The University of Western Australia, Perth, Western Australia, Australia.
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Hickford D, Frankenberg S, Renfree MB. Surgery on tammar wallaby (Macropus eugenii) pouch young. Cold Spring Harb Protoc 2010; 2009:pdb.prot5334. [PMID: 20150081 DOI: 10.1101/pdb.prot5334] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
INTRODUCTIONTwo features of marsupial young make them ideal for developmental studies: (1) Their immune system, like that of the thyroid and thermoregulation, develops relatively late after birth, and (2) they tolerate xenografts. This late development allows transplants to grow and survive in the recipient for at least 150 d without the use of immunosuppressants. The immaturity of the organ systems and the tiny size of the neonate pose difficulties for anesthesia. However, because the pouch young are completely heterothermic until at least 3 mo of age, cooling can be used as an anesthetic agent. In practice, however, we use hypothermia for neonates and young up to the age of 25-30 d, and injectable anethetics thereafter. Healing is remarkably rapid. This tolerance of xenografts and the ability and ease with which hypothermia can be applied to marsupial young provides a unique approach to understanding developmental processes that normally take place in utero in eutherians. This protocol describes surgical procedures and post-surgical care performed on tammar wallaby (Macropus eugenii) pouch young (PY).
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Affiliation(s)
- Danielle Hickford
- Department of Zoology, The University of Melbourne, Victoria 3010, Australia
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Renfree MB, Fenelon J, Wijiyanti G, Wilson JD, Shaw G. Wolffian duct differentiation by physiological concentrations of androgen delivered systemically. Dev Biol 2009; 334:429-36. [DOI: 10.1016/j.ydbio.2009.07.040] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2009] [Revised: 06/24/2009] [Accepted: 07/30/2009] [Indexed: 10/20/2022]
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Pask A, Renfree MB. Sex determining genes and sexual differentiation in a marsupial. THE JOURNAL OF EXPERIMENTAL ZOOLOGY 2001; 290:586-96. [PMID: 11748607 DOI: 10.1002/jez.1109] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The role of genes in the differentiation of the testis and ovary has been extensively studied in the human and the mouse. Despite over a decade of investigations, the precise roles of genes and their interactions in the pathway of sex determination are still unclear. We have chosen to take a comparative look at sex determination and differentiation to gain insights into the evolution and the conserved functions of these genes. To achieve this, we have examined a wide variety of eutherian sex determining genes in a marsupial, the tammar wallaby, to determine which genes have a conserved and fundamental mammalian sex determining role. These investigations have provided many unique insights. Here, we review the recent molecular and endocrine investigations into sexual development in marsupials, and highlight how these studies have shed light on the roles of genes and hormones in mammalian sex determination and differentiation.
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Affiliation(s)
- A Pask
- Department of Zoology, The University of Melbourne, Victoria, 3010, Australia.
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Abstract
Embryonic diapause, or delayed implantation as it is sometimes known, is said to occur when the conceptus enters a state of suspended animation at the blastocyst stage of development. Blastocysts may either cease cell division so that their size and cell numbers remain constant, or undergo a period of very slow growth with minimal cell division and expansion. Diapause has independently evolved on many occasions. There are almost 100 mammals in seven different mammalian orders that undergo diapause. In some groups, such as rodents, kangaroos, and mustelids, it is widespread, whereas others such as the Artiodactyla have only a single representative (the roe deer). In each family the characteristics of diapause differ, and the specific controls vary widely from lactational to seasonal, from estrogen to progesterone, or from photoperiod to nutritional. Prolactin is a key hormone controlling the endocrine milieu of diapause in many species, but paradoxically it may act either to stimulate or inhibit growth and activity of the corpus luteum. Whatever the species-specific mechanisms, the ecological result of diapause is one of synchronization: It effectively lengthens the active gestation period, which allows mating to occur and young to be born at times of the year optimal for that species.
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Affiliation(s)
- M B Renfree
- Department of Zoology, University of Melbourne, Parkville, Victoria, Australia.
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