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Severe flooding in early 2020 and 2021 necessitated major desedimentation works at the iconic Blue Lake in the Jenolan Karst Conservation Reserve (JKCR). Movements and behaviour of platypuses were monitored before, during and after these works, using direct observations, remote cameras and environmental DNA (eDNA) sampling. Platypuses were observed along a 3 km reach of the Jenolan River, including the areas where works occurred, although in low numbers. In their use of the available waterways, platypuses negotiated artificial barriers, including a 10 m high dam, two smaller weirs and natural waterfalls and cascades. Overland movements were detected through vegetation tunnels, drainage pipes and culverts, and individuals were seen entering the cave system, where eDNA was also detected. Platypuses responded to the works activity by foraging outside the affected areas but also continued to traverse these areas from time to time. We describe movements around and through instream infrastructure and past natural barriers and report on other species detected by remote cameras. These observations could help planning and deployment of bypasses suitable for movement of platypuses around anthropogenic barriers and provide insights into impediments to dispersal and gene flow within stream systems. Because of their cryptic nature and being active predominately at night, movement of wild platypuses is poorly documented. Our studies of their movements in the upper Jenolan River showed them moving around and through natural and artificial instream structures, including across weirs, through culverts, around waterfalls and entering caves. This research is important to the management and conservation of the species in relation to human activities in rivers. Photograph by Anne Musser. [ABSTRACT FROM AUTHOR]

We report on a male platypus (Ornithorhynchus anatinus) who was tagged in November 2000 at the age of 1 year and recaptured in September 2023, when nearly 24 years old, in a small creek system in Melbourne's southeastern suburbs. By comparison, a female platypus recently reached the age of 30 years in captivity, though with signs of ageing that may have precluded her survival if she were living in the wild. Ten other captive individuals have lived to an age of more than 20 years in recent decades. A new platypus longevity record in the wild (nearly 24 years) has been confirmed for a male living in a creek in Melbourne's southeastern suburbs. In captivity, a female platypus recently reached the age of 30 years at Healesville Sanctuary. Photograph by Barry Baker. [ABSTRACT FROM AUTHOR]

The platypus is a challenging species to survey and monitor. We investigated the use of time-lapse cameras to detect platypus activity in a Tasmanian creek by deploying three camera models diurnally at a single site over 6 months, and deploying one model both nocturnally and diurnally at two sites over 12 months. Variation in camera attributes and settings (camera view angle, length of time-lapse intervals) contributed to a 10-fold difference in the mean number of platypus images recorded in a given behavioural sequence (or 'event') and an approximately 50% difference in median event duration among the three models. Results also varied between sites and at diel and bimonthly time scales due to pool topography, day length (affecting site illumination) and likely temporal differences in platypus activity and population size. However, even the least-effective camera model reliably captured ≥1 platypus image within the first 24 h of deployment at the two study sites throughout the year. Time-lapse cameras are a suitable tool to assess platypus occurrence and measure activity, as long as appropriate equipment is selected for the intended purpose and sources of spatial and temporal variation are carefully considered when designing studies and interpreting results. We investigated how equipment-related differences and sources of spatial and temporal variation affected how often platypus activity was recorded by time-lapse camera models along a southern Tasmanian creek. The results confirm that time-lapse cameras can be a useful tool for platypus detection and monitoring. Photograph by Simon Roberts. [ABSTRACT FROM AUTHOR]

Genetic mutations resulting in abnormal colouration occur across all vertebrate groups but are considered rare, especially in mammals. Hypo-pigmentary conditions can be separated into albinism, leucism and piebaldism. The impact of colour variation on an animal's risk of predation and its ability to blend with its surroundings is widely recognised. We report our observations of a white platypus (Ornithorhynchus anatinus) in a tributary of the Gwydir River in the upper reaches of the Murray Darling Basin, New South Wales, Australia. We describe our observations in the context of historical platypus records since 1835. [ABSTRACT FROM AUTHOR]

The platypus's tapered shape and benthic foraging habits predispose it to becoming entangled in encircling rings or loops of plastic, rubber or metal rubbish. Based on 54 cases of litter entanglement recorded in Victorian live-trapping surveys, items may encircle the neck (68%), torso (8%), jaw (2%) or be wrapped bandolier-fashion from in front of a shoulder to behind the opposite foreleg (22%). Entanglement frequency was eight times higher in the greater Melbourne region than in regional Victoria, and was significantly greater in first-year juveniles than in older animals and also in adult/subadult females compared with adult/subadult males. Items recovered from carcasses or from rescued animals that were unlikely to have survived without human intervention included elastic hair-ties, fishing line, a hospital identification wristband, an engine gasket and a plastic ring seal from a food jar; all of these items had cut through skin and (in most cases) deeply into underlying tissue. Up to 1.5% of the platypus residing in the greater Melbourne area and 0.5% of those living in regional Victoria are estimated to be at risk of entanglement-related injuries or death at any point in time. Plastic, rubber and metal rubbish is hazardous to a platypus when it loops around the neck or body and then cuts through skin. The problem increases in urban settings and decreases with size and age: females are entangled more often than males, and juveniles are entangled more often than older animals. Up to 1.5% of the platypus near Melbourne and 0.5% of those in regional Victoria are at risk of rubbish-related injuries or death at any point in time. Photograph by Australian Platypus Conservancy. [ABSTRACT FROM AUTHOR]

Distribution data on platypus populations within the Greater Brisbane region is currently lacking, limiting our understanding of their population status. We report 4 years of platypus environmental DNA data from waterways in this region and compare them to historical observational records from 1990 to 2016 to determine any changes to their distribution. Twenty-one of the 54 eDNA sampled waterways were sampled multiple times and had records of previous platypus presence. Five of these 21 repeatedly sampled waterways (24%) did not have evidence of platypus presence, based on eDNA. This raises the concern that platypuses may no longer inhabit these waterways. We hope this study encourages further investigations on platypus to identify the extent of their decline within the region, along with possible broader state-wide review of their conservation status for future protection. [ABSTRACT FROM AUTHOR]

Maternal care in platypuses has never been rigorously studied due to the difficulty in locating and accessing nesting burrows. Here we describe the maternal behaviour of a captive female platypus and the growth and development of her offspring over 11 breeding seasons. We located a nesting burrow and inserted a camera to record the activity and behaviour of the female and her offspring. We also measured the female's food intake during lactation. The ages of the offspring were assigned to developmental milestones including opening of the eyes and development of pelage. Twins (n = 4) were left alone for periods longer than 24 h by the mother at an earlier age than single nestlings (n = 2). The dietary energy intake of the breeding female was more than double that of non-lactating females in the last month of lactation, indicating the large energy requirements of milk production. The mean age of young at emergence from the burrow was 128 ± 1 days and in 60% of nestlings emergence occurred after weaning. This suggests a rapid transition from a completely milk-based diet to a diet of aquatic macroinvertebrates. The techniques we developed have allowed us to study maternal care in platypuses and the development of nestlings, both of which were previously only poorly understood. This study investigates the maternal care given to platypus nestlings and describes a technique to study animals in a burrow. Platypus nestlings develop quickly over four months. The mother has high energy requirements for lactation, increasing her food intake by double towards the end. Weaning occurred rapidly at the time of emergence. This paper is the first to describe the growth and development of platypus nestlings at known ages. Photograph by Jessica Thomas. [ABSTRACT FROM AUTHOR]

We present data from an 18-year study of a wild population of Tasmanian echidnas, which show that the presence of spurs in an adult are a reliable indicator of sex, and that there is a slight but significant sexual dimorphism in size, with a male to female mass ratio of 1.1. Minimum age at first breeding in the wild for Tasmanian echidnas was 5 years, as has been found on Kangaroo Island, compared with 3 years in captive echidnas. It is often assumed that although the echidna is distributed throughout Australia, New Guinea and off-shore islands that all aspects of its basic biology are the same in all populations, but comparisons of our results with data from other populations suggest that there may be differences in size and sexual dimorphism. [ABSTRACT FROM AUTHOR]

The platypus nesting burrow, where females lay eggs and rear their young, has not been well studied. We have little knowledge of its structure and the process of construction. This study aimed to investigate nesting behaviour of breeding females and to describe the structure and features of the burrow. We used infrared cameras to record behaviour of captive breeding female platypuses during the nest-building period, over nine years. After the young had become independent, we excavated 11 nesting burrows and mapped their structural features. Nesting behaviour was observed 7-15 days after mating and was an indicator of gravidity. Females invested an average of 8 h 18 min over 3.5 nights, gathering and transporting wet nesting material to their burrows. The nests were composed mostly of native mat-rush leaves. Nesting burrows varied in length from 3.2 to 10.4 m. They contained narrow tunnels, 'pugs' of backfilled earth, dead ends, multiple entrances and a chamber at the end that contained the nest. Appropriate nesting sites and nesting materials must be provided to female platypuses for captive breeding programs to succeed. [ABSTRACT FROM AUTHOR]

Anecdotal observations of captive platypuses (Ornithorhynchus anatinus) suggest that they show a seasonal preference for particular foods, but this has never been rigorously measured. This study aimed to determine seasonal food preferences and energy consumption of captive platypuses so that better protocols for maintaining platypuses in captivity can be developed. Seven platypuses were fed an ad libitum diet with all food items weighed in and out of tanks. Food items were analysed for energy, fats, carbohydrates, proteins, vitamins and minerals. Platypuses preferred less mobile prey (mealworms, earthworms and fly pupae) over highly mobile prey (crayfish). There was no significant seasonal change in preference for different dietary items, which is more likely to be driven by prey behaviour. Crayfish contributed the largest percentage (mass) consumed and was highly nutritious. While the relative percentage of items in the diet did not change seasonally, the quantity eaten did. The mean energy intake of platypuses was 921 kJ kg-1 day-1 and varied seasonally, being lowest during the breeding season (810 kJ kg-1 day-1) and highest in the postbreeding season (1007 kJ kg-1 day-1). These changes were associated with preparation and recovery from the breeding season. We conclude that the platypus diet is influenced by nutrition and seasonal factors as well as by prey behaviour. This knowledge will contribute to improving the husbandry and management of platypuses, which are widely recognised as difficult to maintain in captivity. [ABSTRACT FROM AUTHOR]

The platypus (Ornithorhynchus anatinus) occupies a wide range of aquatic habitats, feeding mainly on benthic macroinvertebrates. In this study, we investigated how flow affects platypus reproduction in the unregulated upper Shoalhaven River in rural New South Wales. In a mainly dry period, the population occurred at relatively high density (12.4 animals km-1) and was strongly female-biased (84% of resident animals); mean annual loss and recruitment of resident females were respectively estimated to be 12% and 14%. Percentage lactation was 17-71% (n = 23 years), and annual reproductive success (defined as the mean number of juveniles captured per adult/subadult female from February to April) varied from 0 to 1.5 juveniles female-1 (n = 21 years). A significant positive linear relationship was evident between percentage lactation and antecedent discharge in the five months before breeding (March-July) and a positive curvilinear relationship was evident between percentage lactation and mean litter size. Conversely, reproductive success was compromised by high poststorm discharge in the period when juveniles are confined to a nesting burrow, especially from late November to early January. The relationships identified in our study between flow and reproduction also appear to apply to platypus populations occupying urban streams in Victoria, suggesting that they may be widely relevant to this species. [ABSTRACT FROM AUTHOR]

Body condition is an important aspect of the health of any animal. The current standard method of body condition assessment in the platypus is the tail volume index (TVI). Although the tail is the largest repository of fat in the platypus, the reliability of TVI has not been adequately demonstrated. The aims of this study were, first to assess performance of the TVI, and second, to develop and evaluate performance of new techniques for routine field assessment of platypus body condition. Morphometric data were collected under anaesthesia from 137 adult wild platypuses (74 males, 63 females) captured in north-west Tasmania; ultrasound images of tail fat were also collected from 100 of these individuals (54 males, 46 females). Three new indices for platypus body condition were identified. An objective tail fat index (Relative Tail Fat Volume: RTFVTBL) was developed, based on cross-sectional area measurements taken from detailed ultrasound images compared with total body length (TBL). Two body condition indices intended for routine field use were developed - one based on body mass (mb) and bill width (BW) (Body Condition Index; BCIBW), and the other based on a single linear ultrasonographic measurement of tail fat depth and BW (Relative Fat Depth; RFDBW). Results indicated that RFDBW outperforms TVI as an index of platypus tail fat. Further work, however, is needed to determine the relationship between tail fat and total body fat in the platypus before conclusions can be drawn about the effectiveness of BCIBW as a body condition index. [ABSTRACT FROM AUTHOR]

Little is known of the current status of platypus (Ornithorhynchus anatinus) populations in the Murrumbidgee catchment and other west-flowing rivers in the Murray-Darling Basin. Platypus distribution in the Murrumbidgee catchment was determined from sightings, reports by government departments, the literature and a capture-release study. The platypus was found to be widespread in the catchment, including all subcatchment and elevation categories, but most reports were from the middle and upper subcatchments. Sixty-five captures of 55 individual platypuses were made during 61 trap-nights to 31 study sites in the Murrumbidgee catchment during 2009-10. Only three juveniles (all females) were captured and recapture rates were low, with only nine platypuses captured more than once. Adult males had body weights of 980-2180 g and body lengths of 42-60 cm (n = 32). Adult females weighed 795-1480 g and were 38-52 cm long (n = 20). Tail fat index was significantly affected by season and platypus age, while in comparison, season, platypus length and weight had a significant effect on tail volume index. This study established a baseline that provides a starting point from which the impacts of environmental disturbances or diseases occurring over time can be measured and investigated. [ABSTRACT FROM AUTHOR]

variety of techniques have been used to monitor platypus populations to assess the impacts of the threats they face, but each technique has limitations. In this study we investigated the novel use of in-stream microchip readers, to remotely monitor the movements of microchipped wild platypuses. Over 13 months, we recorded movements of 18 microchipped individuals past nine fixed locations in the Inglis Catchment in northwest Tasmania, using three units of which all were capable of detecting Trovan® unique microchips and two were additionally capable of detecting ISO microchips. Each site was monitored one or two times, for durations of 8-39 days. We undertook direction of movement investigations during two monitoring periods, by placing the antennas from two systems in the same creek within 3 m of each other. In a total of 264 days of monitoring, 528 platypus observations were made from 18 individual platypuses, consisting of 13 of 18 (72%) platypuses captured at the monitoring sites within 16 months prior to monitoring, two platypuses captured at other sites in the same time period, and three of seven (43%) individuals microchipped 3-5 years previously. This number of platypus observations, in combination with the stable number of platypuses observed per day, the range of movement behaviours recorded and the results of the direction of movement investigations, indicates that at appropriate sites, in-stream microchip readers are an effective method of monitoring the movements and survivorship of microchipped wild platypuses. [ABSTRACT FROM AUTHOR]

A variety of techniques have been used to monitor platypus populations to assess the impacts of the threats they face, but each technique has limitations. In this study we investigated the novel use of in-stream microchip readers, to remotely monitor the movements of microchipped wild platypuses. Over 13 months, we recorded movements of 18 microchipped individuals past nine fixed locations in the Inglis Catchment in northwest Tasmania, using three units of which all were capable of detecting Trovan® unique microchips and two were additionally capable of detecting ISO microchips. Each site was monitored one or two times, for durations of 8-39 days. We undertook direction of movement investigations during two monitoring periods, by placing the antennas from two systems in the same creek within 3 m of each other. In a total of 264 days of monitoring, 528 platypus observations were made from 18 individual platypuses, consisting of 13 of 18 (72%) platypuses captured at the monitoring sites within 16 months prior to monitoring, two platypuses captured at other sites in the same time period, and three of seven (43%) individuals microchipped 3-5 years previously. This number of platypus observations, in combination with the stable number of platypuses observed per day, the range of movement behaviours recorded and the results of the direction of movement investigations, indicates that at appropriate sites, in-stream microchip readers are an effective method of monitoring the movements and survivorship of microchipped wild platypuses. [ABSTRACT FROM AUTHOR]

An understanding of animal population dynamics relies on identifying life-history attributes associated with population growth and determining how these are affected by environmental variables. We analysed platypus population processes over a 10-year period through mark-recapture studies conducted in three spatially independent stream systems located in the suburbs of Melbourne, Australia. The three populations were collectively characterised by a slightly male-biased adult sex ratio (1.15 : 1) and relatively low reproductive success (<0.5 juvenile captured annually per adult female). An estimated 16% of core residents disappeared annually and 18% of marked juveniles were recaptured as adults. However, some demographic parameters (reproductive success, frequency of non-core adult captures) varied significantly among populations. Estimates of annual core population size in the three systems varied asynchronously, with different trajectories in population size potentially reflecting habitat differences (amount of urban development, reliability of surface flow) as well as variation in spatial isolation and catchment history (implementation of stream rehabilitation programs, occurrence of severe floods). Across all three populations, significant variability in annual reproductive success was explained by linear relationships with the amount of rainfall recorded in the five months before breeding (positive) and after juveniles emerge from nesting burrows (negative). Platypus population size, sex ratio, reproductive success, juvenile recruitment and longevity are described in three stream systems near Melbourne. Population size varied asynchronously among the systems, which also differed with respect to stream flow, spatial isolation and degree of urbanisation; rainfall patterns accounted for much of the variation in annual reproductive success. [ABSTRACT FROM AUTHOR]

The platypus (Ornithorhynchus anatinus) has a wide distribution in Australia, encompassing the southern island of Tasmania and a broad latitudinal range of the mainland from the temperate south to the tropical north. We used 12 microsatellite markers from 235 individuals sampled from 13 river systems to examine patterns of genetic differentiation and gene flow throughout the species' range. Using a Bayesian approach we identified three large-scale groupings that correspond closely to geographically distinct regions of the species' distribution: the tropical northern mainland, the subtropical and temperate southern mainland, and Tasmania. Six additional clusters were found within the regional groups, three in the northern, two in the southern mainland regions, and the last in Tasmania. These clusters coincided with major river drainages. Genetic differentiation was generally high, with pairwise F[sub st] values ranging from 0.065 to 0.368 for regions and 0.037 to 0.479 for clusters. We found no evidence of contemporary gene flow among the three clusters in the north, but some migration may occur between the larger clusters in the south. Due to the high genetic structuring and lack of gene flow between these three regional populations of the platypus we recommend their treatment as evolutionarily significant units (ESUs) within the platypus species. We have also detailed several smaller management units (MUs) existing within our study area based on subregional clusters and geographically significant features. Using a Bayesian approach, we have identified three evolutionarily significant units (ESUs) in the platypus (Ornithorhynchus anatinus). These ESUs correspond to geographically isolated regions in the platypus' broad distribution. We have also detailed several smaller management units (MUs) existing within our study area based on subregional clusters and geographically significant features. [ABSTRACT FROM AUTHOR]

The article discusses the study that describes the typical course of spur and spur sheath development of the platypus Ornithorhynchus anatinus, and estimates the probability that the wrong age is assigned to unmarked animals on the basis of spur-related attributes. The study revealed that females with only one spur sheath were recorded in most months from February to October, showing the need to carefully check both hind legs when assigning age in females, as the possibility of making a mistake in the identification of juveniles as older individuals based on bilateral sheath loss increases steadily from August onwards. It showed that the use of spur-related attributes is accurate in the identification of juvenile females as first-year animals only up to the age of about nine months.

The article investigates the influence of sex and age on temporal variation in the frequency and direction of platypus, Ornithorhynchus anatinus, captures in fyke nets. Fyke netting surveys conducted in July, the month when the highest frequency of nightly captures was recorded, resulted in almost three times as many adults and subadults entering nets versus those scheduled in April and May. Significant sex-specific variation was evident in relation to monthly capture frequencies. Males were captured most frequently in August, the start of the breeding season, while females were captured most commonly in January, the peak period of lactation. The frequency of platypus captures likewise varied when considered on a nocturnal time scale.

The monotremes (the echidnas and the platypus) display both mammalian and reptilian features. Male monotremes have a bilateral crural gland that is connected via a duct to a spur on each hind limb. Male echidnas appear not to use their spurs as weapons in aggressive acts, but the crural system may have a role in reproductive behaviour because it appears only to be active during the breeding season. The secretions produced by the echidna’s crural gland have not hitherto been biochemically or pharmacologically characterised. We used reverse-phase high-performance liquid chromatography (RP-HPLC) to separate the components of echidna venom and compared the chromatograms with those from platypus venom. The echidna venom appears to contain fewer proteins and peptides than platypus venom; however, it appears to have defensin-like peptides that behave similarly on RP-HPLC to those in platypus venom. Like platypus venom, echidna venom has peptidyl aminoacyl l/d-peptide isomerase activity. An RP-HPLC-based assay showed that the second amino acid residue, of a probe synthetic hexapeptide, was converted into the d-form, when incubated with echidna venom. [ABSTRACT FROM AUTHOR]

Population genetics is a powerful tool to increase the understanding of animals that may otherwise be difficult to study, such as the platypus (Ornithorhynchus anatinus). Focusing on two adjacent river systems in New South Wales, we used 12 polymorphic microsatellite loci to investigate the population dynamics of the platypus. We found that individual river systems acted as discrete population units. Evidence of migration, presumably overland, between systems explains how these units remain connected. This establishes an isolation-by-distance pattern that maintains species continuity across most of the mainland distribution. This improved understanding of population structure will be a valuable contribution to designing accurate management plans for the long-term conservation of this unique Australian animal. [ABSTRACT FROM AUTHOR]

Many infectious agents and parasites have been reported from the platypus (Ornithorhynchus anatinus), but most do not cause serious disease. The fungus, Mucor amphibiorum, is the only disease agent known to cause significant morbidity and mortality in the free-living platypus in Tasmania. Infection has also been reported in free-ranging cane toads and green tree frogs from mainland Australia, but not confirmed in platypuses from the mainland. This paper reviews mucormycosis in the platypus and includes the epidemiology, clinical features, mycology, pathology as well as possible surveillance, treatment and/or control modalities. The emergence and geographical spread of mucormycosis as a disease entity in Tasmanian platypuses from 1982 till 2005 are discussed. The host, agent and environment factors of the traditional epidemiological paradigm are discussed as they contribute to the conditions that lead to the selection or emergence of Mucor amphibiorumas a pathogen in a population of platypuses. [ABSTRACT FROM AUTHOR]

Breeding platypuses (Ornithorhynchus anatinus) in captivity had proved difficult until the last 10 years but with improvements in husbandry and a greater understanding of platypus biology there have been seven successes at two institutions since 1998. This study, using closed circuit video monitoring, took place between 2001 and 2007 at Taronga Zoo and covered three breeding successes with one female in 2002/03, 2004/05 and 2005/06. Results have revealed a consistency of behavioural patterns, which accurately predicted breeding events, mating, burrow construction, subsequent denning period and emergence of young. The female platypus had a receptive period of 4–6 days in the spring of each year, during which her behaviour changed from avoidance to initiating contact with the male. After mating she immediately commenced burrow preparation, ending with a 3–5-day intense period of collecting wet nesting material before retiring to the burrow to lay. The gestation period was estimated at 15–21 days and incubation at less than 12 days. A suckling period of 114–127 days followed, with the frequency of maternal burrow visits and length of stay decreasing as the juveniles grew. Juveniles emerged 133±4 days after retirement. This study provides new and important information about breeding behaviour in this species and will contribute to future breeding success of platypus in captivity. [ABSTRACT FROM AUTHOR]

While the fungal disease mucormycosis has infected Tasmanian platypuses for nearly three decades, its impacts remain largely unknown. This study documents the spatial and temporal distribution of mucormycosis in Tasmanian platypuses as a baseline for assessing its impacts. Over 1800 platypus capture and observation records were collated and mapped, and indicate that between 1982 and 2007 mucormycosis-infected platypuses were present in at least 11, and potentially 22, of Tasmania's 48 river catchments. During 2008–09, live-trapping surveys were undertaken to determine the spread, prevalence and persistence of the disease. Surveys of 75 rivers and creeks across 18 catchments captured 167 individuals, and an additional 12 platypuses were obtained from the public. Only seven of the 179 sampled animals were ulcerated with clinical signs of mucormycosis. All infected individuals were obtained from catchments with prior histories of disease, where platypuses have persisted despite mucormycosis being present for up to 20 years. Detection probabilities were calculated to estimate the probability that the other surveyed catchments are currently disease free. Detection probabilities were generally high (>0.75) per catchment, indicating that sampling effort was adequate to reliably detect diseased animals at historically reported prevalence (which averaged 0.295 from surveys undertaken between 1994 and 2000). Mean disease prevalence in affected catchments sampled during the present study declined to 0.071. This significant four-fold reduction in prevalence makes disease detection more challenging and increased sample sizes are required to confidently assert that some catchments are currently disease free. Reduced disease prevalence suggests that mucormycosis is exerting less impact on Tasmanian platypuses now than it was in the mid to late 1990s; however, the individual consequences of infection are poorly understood and require further investigation. [ABSTRACT FROM AUTHOR]

A common theme in the evolution of sex chromosomes is the massive loss of genes on the sex-specific chromosome (Y or W), leading to a gene imbalance between males (XY) and females (XX) in a male heterogametic species, or between ZZ and ZW in a female heterogametic species. Different mechanisms have evolved to compensate for this difference in dosage of X-borne genes between sexes. In therian mammals, one of the X chromosomes is inactivated, whereas bird dosage compensation is partial and gene-specific. In therian mammals, hallmarks of the inactive X are monoallelic gene expression, late DNA replication and chromatin condensation. Platypuses have five pairs of X chromosomes in females and five X and five Y chromosomes in males. Gene expression analysis suggests a more bird-like partial and gene-specific dosage compensation mechanism. We investigated replication timing and chromosome condensation of three of the five X chromosomes in female platypus. Our data suggest asynchronous replication of X-specific regions on X1, X3and X5but show significantly different condensation between homologues for X3only, and not for X1or X5. We discuss these results in relation to recent gene expression analysis of X-linked genes, which together give us insights into possible mechanisms of dosage compensation in platypus. [ABSTRACT FROM AUTHOR]

Genomic imprinting is widespread in eutherian and marsupial mammals. Although there have been many hypotheses to explain why genomic imprinting evolved in mammals, few have examined how it arose. The host defence hypothesis suggests that imprinting evolved from existing mechanisms within the cell that act to silence foreign DNA elements that insert into the genome. However, the changes to the mammalian genome that accompanied the evolution of imprinting have been hard to define due to the absence of large-scale genomic resources from all extant classes. The recent release of the platypus genome sequence has provided the first opportunity to make comparisons between prototherian (monotreme, which show no signs of imprinting) and therian (marsupial and eutherian, which have imprinting) mammals. We compared the distribution of repeat elements known to attract epigenetic silencing across the genome from monotremes and therian mammals, particularly focusing on the orthologous imprinted regions. Our analyses show that the platypus has significantly fewer repeats of certain classes in the regions of the genome that have become imprinted in therian mammals. The accumulation of repeats, especially long-terminal repeats and DNA elements, in therian imprinted genes and gene clusters therefore appears to be coincident with, and may have been a potential driving force in, the development of mammalian genomic imprinting. Comparative platypus genome analyses of orthologous imprinted regions have provided strong support for the host defence hypothesis to explain the origin of imprinting. [ABSTRACT FROM AUTHOR]

Using a milk-cell cDNA sequencing approach we characterised milk-protein sequences from two monotreme species, platypus (Ornithorhynchus anatinus) and echidna (Tachyglossus aculeatus) and found a full set of caseins and casein variants. The genomic organisation of the platypus casein locus is compared with other mammalian genomes, including the marsupial opossum and several eutherians. Physical linkage of casein genes has been seen in the casein loci of all mammalian genomes examined and we confirm that this is also observed in platypus. However, we show that a recent duplication of β-casein occurred in the monotreme lineage, as opposed to more ancient duplications of α-casein in the eutherian lineage, while marsupials possess only single copies of α- and β-caseins. Despite this variability, the close proximity of the main α- and β-casein genes in an inverted tail–tail orientation and the relative orientation of the more distant kappa-casein genes are similar in all mammalian genome sequences so far available. Overall, the conservation of the genomic organisation of the caseins indicates the early, pre-monotreme development of the fundamental role of caseins during lactation. In contrast, the lineage-specific gene duplications that have occurred within the casein locus of monotremes and eutherians but not marsupials, which may have lost part of the ancestral casein locus, emphasises the independent selection on milk provision strategies to the young, most likely linked to different developmental strategies. The monotremes therefore provide insight into the ancestral drivers for lactation and how these have adapted in different lineages. [ABSTRACT FROM AUTHOR]

One of the most puzzling aspects of monotreme reproductive biology is how they determine sex in the absence of the SRYgene that triggers testis development in most other mammals. Although monotremes share a XX female/XY male sex chromosome system with other mammals, their sex chromosomes show homology to the chicken Z chromosome, including the DMRT1gene, which is a dosage-dependent sex determination gene in birds. In addition, monotremes feature an extraordinary multiple sex chromosome system. However, no sex determination gene has been identified as yet on any of the five X or five Y chromosomes and there is very little knowledge about the conservation and function of other known genes in the monotreme sex determination and differentiation pathway. We have analysed the expression pattern of four evolutionarily conserved genes that are important at different stages of sexual development in therian mammals. DMRT1is a conserved sex-determination gene that is upregulated in the male developing gonad in vertebrates, while DMRT7is a mammal-specific spermatogenesis gene. ATRX, a chromatin remodelling protein, lies on the therian X but there is a testis-expressed Y-copy in marsupials. However, in monotremes, the ATRXorthologue is autosomal. WT1is an evolutionarily conserved gene essential for early gonadal formation in both sexes and later in testis development. We show that these four genes in the adult platypus have the same expression pattern as in other mammals, suggesting that they have a conserved role in sexual development independent of genomic location. [ABSTRACT FROM AUTHOR]

Monotremes are phylogenetically and phenotypically unique animals with an unusually complex sex chromosome system that is composed of ten chromosomes in platypus and nine in echidna. These chromosomes are alternately linked (X1Y1, X2Y2, ...) at meiosis via pseudoautosomal regions and segregate to form spermatozoa containing either X or Y chromosomes. The physical and epigenetic mechanisms involved in pairing and assembly of the complex sex chromosome chain in early meiotic prophase I are completely unknown. We have analysed the pairing dynamics of specific sex chromosome pseudoautosomal regions in platypus spermatocytes during prophase of meiosis I. Our data show a highly coordinated pairing process that begins at the terminal Y5 chromosome and completes with the union of sex chromosomes X1Y1. The consistency of this ordered assembly of the chain is remarkable and raises questions about the mechanisms and factors that regulate the differential pairing of sex chromosomes and how this relates to potential meiotic silencing mechanisms and alternate segregation. [ABSTRACT FROM AUTHOR]

Monotremes feature an extraordinary sex-chromosome system that consists of five X and five Y chromosomes in males. These sex chromosomes share homology with bird sex chromosomes but no homology with the therian X. The genome of a female platypus was recently completed, providing unique insights into sequence and gene content of autosomes and X chromosomes, but no Y-specific sequence has so far been analysed. Here we report the isolation, sequencing and analysis of ~700 kb of sequence of the non-recombining regions of Y2, Y3 and Y5, which revealed differences in base composition and repeat content between autosomes and sex chromosomes, and within the sex chromosomes themselves. This provides the first insights into repeat content of Y chromosomes in platypus, which overall show similar patterns of repeat composition to Y chromosomes in other species. Interestingly, we also observed differences between the various Y chromosomes, and in combination with timing and activity patterns we provide an approach that can be used to examine the evolutionary history of the platypus sex-chromosome chain. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the influence of human-induced habitat modification on platypus affiliations in a Wet Tropics river system in Queensland. The study was conducted in the upper Barron River and its tributaries on the Atherton Tableland, with a tropical climate that featured marked seasonality and very high rainfall during the summer season. Researchers examined a number of habitat variables in order to analyze riparian and in-stream site conditions in the field. Key findings indicated that the presence of platypus in a stream was linked to pool habitats with different levels of intact to low riparian continuity and fine soil substrates present.

It has been suggested that platypuses (Ornithorhynchus anatinus) may avoid nets following capture, compromising abundance estimates using mark-recapture models. Here, we present the first direct evidence of net avoidance behaviour by the platypus. Using acoustic telemetry, we record a platypus bypassing several nets following capture. Understanding variation in capture probabilities will lead to better estimation of platypus abundance, which is currently lacking. [ABSTRACT FROM AUTHOR]