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

An evaluation of DNA sample source and molecular markers to determine gender in the short-beaked echidna (Tachyglossus aculeatus)

The short-beaked echidna is sexually monomorphic such that gender identification without veterinary intervention is challenging. The aim of this study was to evaluate and compare the most optimal noninvasive genetic source by extracting echidna genomic DNA (gDNA) from fecal scats, plucked hair, and quills to perform genetic sex testing using a range of molecular markers. Sex determination of 14 captive short-beaked echidnas was determined by amplifying isolated DNA from noninvasive samples, targeting two Y chromosome (male-specific) genes (mediator complex subunit 26 Y-gametologue [CRSPY] and anti-Müllerian hormone Y-gametologue [AMHY]), in addition to four confirmed sex-specific RADseq markers. Results of noninvasive samples were compared with blood samples and clinical records. Receiver operating characteristic curves were used to assess accuracy of sex determination of markers for each sample type. The gender of the echidnas was successfully identified on 75% of occasions using fecal samples, 90.6% occasions using hair, and 84.6% occasions with quills. Overall, the male-specific RADseq markers accurately identified the sex of echidnas with all sample types for 90% of animals; compared with 81.5% using CRSPY, and 82.0% using AMHY to identify sex. Collection of hair, quills, and feces provides a useful alternative to invasively collected samples, however, the accuracy of results depends on sample type and genetic marker selected. We found gender determination in the short-beaked echidna was most accurate using four male-specific RADseq markers on gDNA isolated from blood and hair. The noninvasive genetic sexing techniques documented here will inform and facilitate husbandry and genetic management of captive echidna populations.

Characterising the Gut Microbiomes in Wild and Captive Short-Beaked Echidnas Reveals Diet-Associated Changes

The gut microbiome plays a vital role in health and wellbeing of animals, and an increasing number of studies are investigating microbiome changes in wild and managed populations to improve conservation and welfare. The short-beaked echidna (Tachyglossus aculeatus) is an iconic Australian species, the most widespread native mammal, and commonly held in zoos. Echidnas are cryptic animals, and much is still unknown about many aspects of their biology. Furthermore, some wild echidna populations are under threat, while echidnas held in captivity can have severe gastric health problems. Here, we used citizen science and zoos to collect echidna scats from across Australia to perform the largest gut microbiome study on any native Australian animal. Using 16S rRNA gene metabarcoding of scat samples, we characterised and compared the gut microbiomes of echidnas in wild (n = 159) and managed (n = 44) populations, which were fed four different diets. Wild echidna samples were highly variable, yet commonly dominated by soil and plant-fermenting bacteria, while echidnas in captivity were dominated by gut commensals and plant-fermenting bacteria, suggesting plant matter may play a significant role in echidna diet. This work demonstrates significant differences between zoo held and wild echidnas, as well as managed animals on different diets, revealing that diet is important in shaping the gut microbiomes in echidnas. This first analysis of echidna gut microbiome highlights extensive microbial diversity in wild echidnas and changes in microbiome composition in managed populations. This is a first step towards using microbiome analysis to better understand diet, gastrointestinal biology, and improve management in these iconic animals.

COVID restrictions impact wildlife monitoring in Australia

The global COVID-19 pandemic has imposed restrictions on people's movement, work and access to places at multiple international, national and sub-national scales. We need a better understanding of how the varied restrictions have impacted wildlife monitoring as gaps in data continuity caused by these disruptions may limit future data use and analysis. To assess the effect of different levels of COVID-19 restrictions on both citizen science and traditional wildlife monitoring, we analyse observational records of a widespread and iconic monotreme, the Australian short-beaked echidna (Tachyglossus aculeatus), in three states of Australia. We compare citizen science to observations from biodiversity data repositories across the three states by analysing numbers of observations, coverage in protected areas, and geographic distribution using an index of remoteness and accessibility. We analyse the effect of restriction levels by comparing these data from each restriction level in 2020 with corresponding periods in 2018-2019. Our results indicate that stricter and longer restrictions reduced numbers of scientific observations while citizen science showed few effects, though there is much variation due to differences in restriction levels in each state. Geographic distribution and coverage of protected and non-protected areas were also reduced for scientific monitoring while citizen science observations were little affected. This study shows that citizen science can continue to record accurate and widely distributed species observational data, despite pandemic restrictions, and thus demonstrates the potential value of citizen science to other researchers who require reliable data during periods of disruption.

EchidnaCSI: Engaging the public in research and conservation of the short-beaked echidna

The short-beaked echidna is an iconic Australian animal and the most-widespread native mammal, inhabiting diverse environments. The cryptic nature of echidnas has limited research into their ecology in most areas; however, from the well-researched and endangered Kangaroo Island echidna population, we understand that the threats include habitat loss, roads, and invasive species. To obtain more information about echidnas Australia-wide, we established the Echidna Conservation Science Initiative (EchidnaCSI) citizen science project. EchidnaCSI calls on members of the public to submit photographs of wild echidnas and learn to identify and collect echidna scats for molecular analysis. To facilitate participation, we developed a smartphone application as well as ongoing social and traditional media activities and community events. In 3 y, more than 9,000 members of the public have downloaded the EchidnaCSI app, collecting 400 scats and submitting over 8,000 sightings of echidnas from across Australia. A subset of submitted scat samples were subjected to DNA extraction and PCR, which validated the approach of using citizen science for scat collection and viability for molecular analysis. To assess the impact of the project through public participation, we surveyed our participants (n = 944) to understand their demographics and motivations for engagement. Survey results also revealed that EchidnaCSI served as a gateway into citizen science more generally for many participants. EchidnaCSI demonstrates the potential for using citizen science approaches to collect high-quality data and material from a cryptic species over a very large geographic area and the considerable engagement value of citizen science research.

Transient role of the middle ear as a lower jaw support across mammals

Mammals articulate their jaws using a novel joint between the dentary and squamosal bones. In eutherian mammals, this joint forms in the embryo, supporting feeding and vocalisation from birth. In contrast, marsupials and monotremes exhibit extreme altriciality and are born before the bones of the novel mammalian jaw joint form. These mammals need to rely on other mechanisms to allow them to feed. Here, we show that this vital function is carried out by the earlier developing, cartilaginous incus of the middle ear, abutting the cranial base to form a cranio-mandibular articulation. The nature of this articulation varies between monotremes and marsupials, with juvenile monotremes retaining a double articulation, similar to that of the fossil mammaliaform Morganucodon, while marsupials use a versican-rich matrix to stabilise the jaw against the cranial base. These findings provide novel insight into the evolution of mammals and the changing relationship between the jaw and ear.

The TMJ Disc Is a Common Ancestral Feature in All Mammals, as Evidenced by the Presence of a Rudimentary Disc During Monotreme Development

The novel mammalian jaw joint, known in humans as the temporomandibular joint or TMJ, is cushioned by a fibrocartilage disc. This disc is secondarily absent in therian mammals that have lost their dentition, such as giant anteaters and some baleen whales. The disc is also absent in all monotremes. However, it is not known if the absence in monotremes is secondary to the loss of dentition, or if it is an ancestral absence. We use museum held platypus and echidna histological sections to demonstrate that the developing monotreme jaw joint forms a disc primordium that fails to mature and become separated from the mandibular condyle. We then show that monotreme developmental anatomy is similar to that observed in transgenic mouse mutants with reduced cranial musculature. We therefore suggest that the absence of the disc on monotremes is a consequence of the changes in jaw musculature associated with the loss of adult teeth. Taken together, these data indicate that the ancestors of extant monotremes likely had a jaw joint disc, and that the disc evolved in the last common ancestor of all mammals.

Tachyglossus aculeatus (Monotremata: Tachyglossidae)

Tachyglossus aculeatus (Shaw, 1792) is a monotreme commonly called the short-beaked echidna. Although considered Australia’s most common native mammal because of its continent-wide distribution, its population numbers everywhere are low. It is easily distinguished from all other native Australian mammals because of its spine-covered body, hairless beak, and unique “rolling” gait. The five subspecies, one of which is found in Papua New Guinea, show variations in fur density, spine diameter, length, and number of grooming claws. The Kangaroo Island short-beaked echidna Tachyglossus aculeatus multiaculeatus is listed as “Endangered” but all other Tachyglossus are listed as “Least Concern” in the 2016 International Union for Conservation of Nature and Natural Resources Red List.

Non-invasive genetic sexing technique for analysis of short-beaked echidna (Tachyglossus aculeatus) populations

Identifying male and female echidnas is challenging due to the lack of external genitalia or any other differing morphological features. This limits studies of wild populations and is a major problem for echidna captive management and breeding. Non-invasive genetic approaches to determine sex minimise the need for handling animals and are used extensively in other mammals. However, currently available approaches cannot be applied to monotremes because their sex chromosomes share no homology with sex chromosomes in other mammals. In this study we used recently identified X and Y chromosome-specific sequences to establish a non-invasive polymerase chain reaction-based technique to determine the sex of echidnas. Genomic DNA was extracted from echidna hair follicles followed by amplification of two Y chromosome (male-specific) genes (mediator complex subunit 26 Y-gametolog (CRSPY) and anti-Müllerian hormone Y-gametolog (AMHY)) and the X chromosome gene (anti-Müllerian hormone X-gametolog (AMHX)). Using this technique, we identified the sex of 10 juvenile echidnas born at Perth Zoo, revealing that eight of the 10 echidnas were female. Future use of the genetic sexing technique in echidnas will inform captive management, continue breeding success and can be used to investigate sex ratios and population dynamics in wild populations.

Spurs, sexual dimorphism and reproductive maturity in Tasmanian echidnas (Tachyglossus aculeatus setosus)

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.

Energy Homeostasis in Monotremes

In 1803, the French anatomist Étienne Geoffroy Saint-Hilaire decided that the newly described echidna and platypus should be placed in a separate order, the monotremes, intermediate between reptiles and mammals. The first physiological observations showed monotremes had low body temperatures and metabolic rates, and the consensus was that they were at a stage of physiological development intermediate between "higher mammals" and "lower vertebrates." Subsequent studies demonstrated that platypuses and echidnas are capable of close thermoregulation in the cold although less so under hot conditions. Because the short-beaked echidna Tachyglossus aculeatus, may show very large daily variations in body temperature, as well as seasonal hibernation, it has been suggested that it may provide a useful model of protoendotherm physiology. Such analysis is complicated by the very significant differences in thermal relations between echidnas from different climates. In all areas female echidnas regulate Tb within 1°C during egg incubation. The lactation period is considered to be the most energetically expensive time for most female mammals but lactating echidnas showed no measurable difference in field metabolic rate from non-lactating females, while the lactation period is more than 200 days for Kangaroo Island echidnas but only 150 days in Tasmania. In areas with mild winters echidnas show reduced activity and shallow torpor in autumn and early winter, but in areas with cold winters echidnas enter true hibernation with Tb falling as low as 4.5°C. Monotremes do not possess brown adipose tissue and maximum rates of rewarming from hibernation in echidnas were only half those of marmots of the same mass. Although echidnas show very large seasonal variations in fat stores associated with hibernation there is no relationship between plasma leptin and adiposity. Leptin levels are lowest during post-reproductive fattening, supporting suggestions that in evolutionary terms the anorectic effects of leptin preceded the adiposity signal. BMR of platypuses is twice that of echidnas although maximum metabolism is similar. High levels of thyroid hormones in platypuses may be driving metabolism limited by low body temperature. Monotremes show a mosaic of plesiomorphic and derived features but can still inform our understanding of the evolution of endothermy.

A Digital Endocranial Cast of the Early Paleocene (Puercan) 'Archaic' Mammal Onychodectes tisonensis (Eutheria: Taeniodonta)

Eutherian mammals-placentals and their closest extinct relatives-underwent a major radiation following the end-Cretaceous extinction, during which they evolved disparate anatomy and established new terrestrial ecosystems. Much about the timing, pace, and causes of this radiation remain unclear, in large part because we still know very little about the anatomy, phylogenetic relationships, and biology of the so-called 'archaic' eutherians that prospered during the ~10 million years after the extinction. We describe the first digital endocranial cast of a taeniodont, a bizarre group of eutherians that flourished in the early Paleogene, reconstructed from a computed tomography (CT) scan of a late Puercan (65.4 million year old) specimen of Onychodectes tisonensis that recovered most of the forebrain and midbrain and portions of the inner ear. Notable features of the endocast include long, broad olfactory bulbs, dorsally-positioned rhinal fissures, and a lissencephalic cerebrum. Comparison with other taxa shows that Onychodectes possessed some of the largest olfactory bulbs (relative to cerebral size) of any known mammal. Statistical analysis of modern mammals shows that relative olfactory bulb dimensions are not strongly correlated with body size or fossorial digging for shelter, but relative bulb width is significantly greater in taxa that habitually dig to forage for food. The anatomical description and statistical results allow us to present an ecological model for Onychodectes and similar taeniodonts, in which they are animals of simple behavior that rely on a strong sense of smell to locate buried food before extracting and processing it with their specialized skeletal anatomy.

Advances in the captive breeding and reproductive biology of the short-beaked echidna (Tachyglossus aculeatus)

Captive breeding of the short-beaked echidna (Tachyglossus aculeatus) has proven a difficult challenge; as recently as 2009, there were fewer than 10 echidnas born in captivity. We present observations of captive reproductive behaviour following video surveillance and measurements of body temperature collected from six captive female echidnas over a six-year period. In the first series of observations (2009–10) we examined the efficacy of artificial burrow boxes as possible aids for reproductive success. Females with access to burrow boxes had significantly higher levels of reproductive activity (P = 0.001), there was coincidental improvement in the production of eggs or pouch young (two eggs, one unhatched and one offspring). During 2009–10, a range of reproductive behaviours (courtship, copulation and postcopulation) were documented and analysed, as were new observations of oestrous cycle activity. Female body temperature was characteristically stable during egg incubation during this study and has the potential to be used as a tool for the assessment of reproductive status. Following initial observations, burrow boxes and infrared lamps were implemented as standard husbandry in our echidna breeding facility and the effects on reproductive success were monitored, albeit less intensively, for a further four years (2011–14). Although no direct causal effect could be ascribed, the use of burrow boxes and heat lamps coincided with a total of 13 young being born to four females in the last four years (2011–14). These female echidnas were found to be receptive at intervals throughout the breeding season, both before and after presumed incubation phases, suggesting that captive animals exhibit polyoestry. In 2012 and 2014, the same female showed evidence of producing two young from one breeding event.

Reproductive parameters and behaviour of captive short-beaked echidna (Tachyglossus aculeatus acanthion) at Perth Zoo

Despite a long history of captive short-beaked echidnas in zoos worldwide, there have been very few successful attempts to breed them. Perth Zoo has been successful in breeding echidnas on five occasions, with young produced over 3 consecutive years. In this paper we document the results of intensive monitoring undertaken before and during these successful breeding seasons. Video camera surveillance was used to monitor activity and reproductive behaviour of adults during the courtship and mating period and to identify the timing and duration of incubation. Temperature data loggers were used to record and compare proximal body temperature with observed behaviours. Echidnas were found to breed in June and July, with courtship lasting a mean 5.75 ± 1.7 days (range 4–9 days, n = 8). Mean duration of gestation was 21.8 ± 2.4 days (range 19–27 days, n = 7). Females incubated their single egg for a mean 11 ± 0.75 days (range 11–13 days, n = 5) in an artificial burrow with increased temperature stability.

Distinct development of the trigeminal sensory nuclei in platypus and echidna

Both lineages of the modern monotremes have been reported to be capable of electroreception using the trigeminal pathways and it has been argued that electroreception arose in an aquatic platypus-like ancestor of both modern monotreme groups. On the other hand, the trigeminal sensory nuclear complex of the platypus is highly modified for processing tactile and electrosensory information from the bill, whereas the trigeminal sensory nuclear complex of the short-beaked echidna (Tachyglossus aculeatus) is not particularly specialized. If the common ancestor for both platypus and echidna were an electroreceptively and trigeminally specialized aquatic feeder, one would expect the early stages of development of the trigeminal sensory nuclei in both species to show evidence of structural specialization from the outset. To determine whether this is the case, we examined the development of the trigeminal sensory nuclei in the platypus and short-beaked echidna using the Hill and Hubrecht embryological collections. We found that the highly specialized features of the platypus trigeminal sensory nuclei (i.e. the large size of the principal nucleus and oral part of the spinal trigeminal nuclear complex, and the presence of a dorsolateral parvicellular segment in the principal nucleus) appear around the time of hatching in the platypus, but are never seen at any stage in the echidna. Our findings support the proposition that the modern echidna and platypus are derived from a common ancestor with only minimal trigeminal specialization and that the peculiar anatomy of the trigeminal sensory nuclei in the modern platypus emerged in the ornithorhynchids after divergence from the tachyglossids.

Development of the hypothalamus and pituitary in platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus)

The living monotremes (platypus and echidnas) are distinguished by the development of their young in a leathery-shelled egg, a low and variable body temperature and a primitive teat-less mammary gland. Their young are hatched in an immature state and must deal with the external environment, with all its challenges of hypothermia and stress, as well as sourcing nutrients from the maternal mammary gland. The Hill and Hubrecht embryological collections have been used to follow the structural development of the monotreme hypothalamus and its connections with the pituitary gland both in the period leading up to hatching and during the lactational phase of development, and to relate this structural maturation to behavioural development. In the incubation phase, development of the hypothalamus proceeds from closure of the anterior neuropore to formation of the lateral hypothalamic zone and putative medial forebrain bundle. Some medial zone hypothalamic nuclei are emerging at the time of hatching, but these are poorly differentiated and periventricular zone nuclei do not appear until the first week of post-hatching life. Differentiation of the pituitary is also incomplete at hatching, epithelial cords do not develop in the pars anterior until the first week, and the hypothalamo-neurohypophyseal tract does not appear until the second week of post-hatching life. In many respects, the structure of the hypothalamus and pituitary of the newly hatched monotreme is similar to that seen in newborn marsupials, suggesting that both groups rely solely on lateral hypothalamic zone nuclei for whatever homeostatic mechanisms they are capable of at birth/hatching.

Development of the spinal cord and peripheral nervous system in platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus)

The modern monotremes (platypus and echidnas) are characterized by development of their young in a leathery egg that is laid into a nest or abdominal pouch. At hatching, the young are externally immature, with forelimbs capable of digitopalmar prehension, but hindlimbs little advanced beyond limb buds. The embryological collections at the Museum für Naturkunde in Berlin were used to examine the development of the spinal cord and early peripheral nervous system in developing monotremes and to correlate this with known behavioural development. Ventral root outgrowth to the bases of both the fore- and hindlimbs occurs at 6.0 mm crown-rump length (CRL), but invasion of both limbs does not happen until about 8.0-8.5 mm CRL. Differentiation of the ventral horn precedes the dorsal horn during incubation and separate medial and lateral motor columns can be distinguished before hatching. Rexed's laminae begin to appear in the dorsal horn in the first week after hatching, and gracile and cuneate fasciculi emerge during the first two post-hatching months. Qualitative and quantitative comparisons of the structure of the cervicothoracic junction spinal cord in the two monotremes with that in a diprotodont marsupial (the brush-tailed possum, Trichosurus vulpecula) of similar size at birth, did not reveal any significant structural differences between the monotremes and the marsupial. The precocious development of motor systems in the monotreme spinal cord is consistent with the behavioural requirements of the peri-hatching period, that is, rupture of embryonic membranes and egg, and digitopalmar prehension to grasp maternal hair or nest material.

Maternal care in the Tasmanian echidna (Tachyglossus aculeatus setosus)

Parental care is central to the differences in reproductive behaviour and energy expenditure between males and females, and it is therefore crucial for understanding animal mating systems. We investigated post-gestation maternal care in a wild population of short-beaked echidnas (Tachyglossus aculeatus) in the Tasmanian midlands using a combination of external temperature loggers and motion-triggered infrared cameras. For the first few weeks of early lactation mothers do not leave their nursery burrow, which they keep at a stable and warm temperature, resulting in a greater rate of maternal mass loss during the period of maternal burrow confinement than during hibernation. However, after lactating mothers recommence feeding, they raise a young to ~1.5 kg on a diet of their milk while increasing their own body mass by a similar amount. Weaning in our population appears not to be abrupt as there is a period where young echidnas begin exploratory foraging while their mother is still lactating. After young are weaned and abandon the nursery burrow, there appear to be no further associations between mothers and young despite young echidnas remaining within their mother’s home range for the first 12 months of their life. Female echidnas time reproductive events with increases in ecosystem productivity, so that young are weaned at a time of maximum food abundance.

Distinct development of peripheral trigeminal pathways in the platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus)

The extant monotremes (platypus and echidnas) are believed to all be capable of electroreception in the trigeminal pathways, although they differ significantly in the number and distribution of electroreceptors. It has been argued by some authors that electroreception was first developed in an aquatic environment and that echidnas are descended from a platypus-like ancestor that invaded an available terrestrial habitat. If this were the case, one would expect the developmental trajectories of the trigeminal pathways to be similar in the early stages of platypus and short-beaked echidna development, with structural divergence occurring later. We examined the development of the peripheral trigeminal pathway from snout skin to trigeminal ganglion in sectioned material in the Hill and Hubrecht collections to test for similarities and differences between the two during the development from egg to adulthood. Each monotreme showed a characteristic and different pattern of distribution of developing epidermal sensory gland specializations (electroreceptor primordia) from the time of hatching. The cross-sectional areas of the trigeminal divisions and the volume of the trigeminal ganglion itself were also very different between the two species at embryonic ages, and remained consistently different throughout post-hatching development. Our findings indicate that the trigeminal pathways in the short-beaked echidna and the platypus follow very different developmental trajectories from the earliest ages. These findings are more consistent with the notion that the platypus and echidna have both diverged from an ancestor with rudimentary electroreception and/or trigeminal specialization, rather than the contention that the echidna is derived from a platypus-like ancestor.

Development of the olfactory pathways in platypus and echidna

The two groups of living monotremes (platypus and echidnas) have remarkably different olfactory structures in the adult. The layers of the main olfactory bulb of the short-beaked echidna are extensively folded, whereas those of the platypus are not. Similarly, the surface area of the piriform cortex of the echidna is large and its lamination complex, whereas in the platypus it is small and simple. It has been argued that the modern echidnas are derived from a platypus-like ancestor, in which case the extensive olfactory specializations of the modern echidnas would have developed relatively recently in monotreme evolution. In this study, the development of the constituent structures of the olfactory pathway was studied in sectioned platypus and echidna embryos and post-hatchlings at the Museum für Naturkunde, Berlin, Germany. The aim was to determine whether the olfactory structures follow a similar maturational path in the two monotremes during embryonic and early post-hatching ages or whether they show very different developmental paths from the outset. The findings indicate that anatomical differences in the central olfactory system between the short-beaked echidna and the platypus begin to develop immediately before hatching, although details of differences in nasal cavity architecture emerge progressively during late post-hatching life. These findings are most consistent with the proposition that the two modern monotreme lineages have followed independent evolutionary paths from a less olfaction-specialized ancestor. The monotreme olfactory pathway does not appear to be sufficiently structurally mature at birth to allow olfaction-mediated behaviour, because central components of both the main and accessory olfactory system have not differentiated at the time of hatching.

Development of the dorsal and ventral thalamus in platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus)

The living monotremes (platypus and echidnas) are distinguished from therians as well as each other in part by the unusual structure of the thalamus in each. In particular, the platypus has an enlarged ventral posterior (VP) nucleus reflecting the great behavioural importance of trigeminosensation and electroreception. The embryological collections of the Museum für Naturkunde in Berlin were used to analyse the development of the dorsal thalamus and ventral thalamus (prethalamus) in both species. Prosomeric organization of the forebrain emerged at 6 mm crown-rump length (CRL), but thalamic neurogenesis did not commence until about 8-9 mm CRL. Distinctive features of the dorsal thalamus in the two species began to emerge after hatching (about 14-15 mm CRL). During the first post-hatching week, dense clusters of granular cells aggregated to form the VP of the platypus, whereas the VP complex of the echidna remained smaller and divided into distinct medial and lateral divisions. At the end of the first post-hatching week, the thalamocortical tract was much larger in the platypus than the echidna. The dorsal thalamus of the platypus is essentially adult-like by the sixth week of post-hatching life. The similar appearance of the dorsal thalamus in the two species until the time of hatching, followed by the rapid expansion of the VP in the platypus, is most consistent with ancestral platypuses having undergone changes in the genetic control of thalamic neurogenesis to produce a large VP for trigeminal electroreception after the divergence of the two lineages of monotreme.

Cool sex? Hibernation and reproduction overlap in the echidna

During hibernation there is a slowing of all metabolic processes, and thus it is normally considered to be incompatible with reproduction. In Tasmania the egg-laying mammal, the echidna (Tachyglossus aculeatus) hibernates for several months before mating in mid-winter, and in previous studies we observed males with females that were still hibernating. We monitored the reproductive activity of radio-tracked echidnas by swabbing the reproductive tract for sperm while external temperature loggers provided information on the timing of hibernation. Additional information was provided by camera traps and ultrasound imaging. More than a third of the females found in mating groups were torpid, and the majority of these had mated. Some females re-entered deep torpor for extended periods after mating. Ultrasound examination showed a developing egg in the uterus of a female that had repeatedly re-entered torpor. The presence of fresh sperm in cloacal swabs taken from this female on three occasions after her presumed date of fertilization indicated she mated several times after being fertilized. The mating of males with torpid females is the result of extreme competition between promiscuous males, while re-entry into hibernation by pregnant females could improve the possibility of mating with a better quality male.

Activity and behaviour of lactating echidnas (Tachyglossus aculeatus multiaculeatus) from hatching of egg to weaning of young

Throughout their Australia-wide distribution, short-beaked echidnas breed during the winter months, i.e. June through early September. Actual duration of the female reproductive cycle, from attracting males and mating until weaning the young, can vary from 7 to 9 months depending on geographic location. Much of this variation is due to length of courtship and age of weaning the young. This paper presents data about the behaviour of free-ranging female echidnas on Kangaroo Island from egg laying through to weaning and compares it with findings from other areas. On Kangaroo Island, behaviour of lactating echidnas falls into two distinct phases: (1) while carrying the young in the pouch; and (2) after the young is placed in a nursery burrow. Females significantly increased both the number of hours active each day as well as the size of area utilised after the young was in the nursery. Although types of nursery burrows are similar throughout Australia, duration of use and frequency visited varies between geographic locations. A major difference is that Kangaroo Island echidnas are often active while carrying either the egg or the young in the pouch and echidnas in other regions remain in a burrow for extended periods.

Reproductive strategies of the short-beaked echidna - a review with new data from a long-term study on the Tasmanian subspecies (Tachyglossus aculeatus setosus)

The short-beaked echidna is the most widely distributed endemic Australian mammal, and echidnas from different geographic areas differ so much in appearance that they have been assigned to several subspecies. In this paper, we present data obtained from free-ranging echidnas in southern Tasmania, and compare this with studies from other parts of Australia. In Tasmania mating occurs between early June and mid-September, and throughout Australia the normal breeding season lies within these limits. In echidnas from the more easterly parts of Australia reproduction closely follows hibernation, with Tasmanian echidnas showing a significant overlap between hibernation and reproduction. There is intense competition between males, and female echidnas from Tasmania show multiple matings. There are significant differences between echidnas from different areas of Australia in the use of nursery burrows and maternal care. One of the most dramatic differences is in duration of lactation: echidnas from Kangaroo Island wean the young at 204–210 days, but in Tasmania weaning occurs at 139–152 days, even though the masses of the young at weaning are comparable.

Seasonal variations in reproductive hormones in free-ranging echidnas (Tachyglossus aculeatus): interaction between reproduction and hibernation

We measured the reproductive steroids testosterone and progesterone in free-ranging adult echidnas over several years. For months other than June-August, the mean progesterone concentration was 0.18+/-0.12 ng ml(-1) (n=14), and all blood samples taken from active female echidnas in June-August had progesterone concentrations above 0.5 ng ml(-1). The highest progesterone value measured was 13.4 ng ml(-1) in a pregnant female several days before egg-laying. For months other than June-August the mean testosterone concentration was 0.09+/-0.05 ng ml(-1) (n=13). During June-August all active sexually mature males had testosterone concentrations in excess of 0.2 ng ml(-1) and were found in mating groups at some time during this period. The highest plasma testosterone concentration measured was 4.62 ng ml(-1).