Sminthopsis Crassicaudata Research Articles

The extension of mammalian pregnancy required taming inflammation: Independent evolution of extended placentation in the tammar wallaby.

In the first live-bearing mammals, pregnancy was likely short and ended with a brief period of inflammatory maternal-fetal interaction. This mode of reproduction has been retained in many marsupials. While inflammation is key to successful implantation in eutherians, a key innovation in eutherians is the ability to switch off this inflammation after it has been initiated. This extended period, in which inflammation is suppressed, likely allowed for an extended period of placentation. Extended placentation has evolved independently in one lineage of marsupials, the macropodids (wallabies and kangaroos), with placentation lasting beyond the 2 to 4 d seen in other marsupial taxa, which allows us to investigate the role of inflammation response after attachment in the extension of placentation in mammals. By comparing gene expression changes at attachment in three marsupial species, the tammar wallaby, opossum, and fat-tailed dunnart, we show that inflammatory attachment is an ancestral feature of marsupial implantation. In contrast to eutherians, where attachment-related (quasi-) inflammatory reaction is even involved in epitheliochorial placentation (e.g., pig), this study found no evidence of a distinct attachment-related reaction in wallabies. Instead, only a small number of inflammatory genes are expressed at distinct points of gestation, including IL6 before attachment, LIF throughout placentation, and prostaglandins before birth. During parturition, a more distinct inflammatory reaction is detectable, likely involved in precipitating the parturition cascade similar to eutherians. We suggest that in wallaby, extended gestation became possible by avoiding an inflammatory attachment reaction, which is a different strategy than seen in eutherians.

Embryology of the fat-tailed dunnart (Sminthopsis crassicaudata): A marsupial model for comparative mammalian developmental and evolutionary biology.

Marsupials are a diverse and unique group of mammals, but remain underutilized in developmental biology studies, hindering our understanding of mammalian diversity. This study focuses on establishing the fat-tailed dunnart (Sminthopsis crassicaudata) as an emerging laboratory model, providing reproductive monitoring methods and a detailed atlas of its embryonic development. We monitored the reproductive cycles of female dunnarts and established methods to confirm pregnancy and generate timed embryos. With this, we characterized dunnart embryo development from cleavage to birth, and provided detailed descriptions of its organogenesis and heterochronic growth patterns. Drawing stage-matched comparisons with other species, we highlight the dunnarts accelerated craniofacial and limb development, characteristic of marsupials. The fat-tailed dunnart is an exceptional marsupial model for developmental studies, where our detailed practices for reproductive monitoring and embryo collection enhance its accessibility in other laboratories. The accelerated developmental patterns observed in the Dunnart provide a valuable system for investigating molecular mechanisms underlying heterochrony. This study not only contributes to our understanding of marsupial development but also equips the scientific community with new resources for addressing biodiversity challenges and developing effective conservation strategies in marsupials.

De novo transcriptome assembly and genome annotation of the fat-tailed dunnart (Sminthopsis crassicaudata).

Marsupials exhibit distinctive modes of reproduction and early development that set them apart from their eutherian counterparts and render them invaluable for comparative studies. However, marsupial genomic resources still lag far behind those of eutherian mammals. We present a series of novel genomic resources for the fat-tailed dunnart (Sminthopsis crassicaudata), a mouse-like marsupial that, due to its ease of husbandry and ex-utero development, is emerging as a laboratory model. We constructed a highly representative multi-tissue de novo transcriptome assembly of dunnart RNA-seq reads spanning 12 tissues. The transcriptome includes 2,093,982 assembled transcripts and has a mammalian transcriptome BUSCO completeness score of 93.3%, the highest amongst currently published marsupial transcriptomes. This global transcriptome, along with ab initio predictions, supported annotation of the existing dunnart genome, revealing 21,622 protein-coding genes. Altogether, these resources will enable wider use of the dunnart as a model marsupial and deepen our understanding of mammalian genome evolution.

Thermal scanners versus spotlighting: New opportunities for monitoring threatened small endotherms

AbstractThreatened species monitoring is challenging for small, cryptic endotherms that are most effectively detected at night. Low detectability is a challenge for monitoring programmes, resulting in low statistical power and sparse or zero‐inflated datasets. To advance conservation management programmes, efforts to address this are required. In recent years thermal scanners have emerged as an effective tool for detecting small endotherms, but the diversity of available thermal tools, focal habitats and target species mean that their applicability in many key scenarios remain untested. We directly compared vehicle‐mounted thermal surveys with vehicle‐based spotlighting targeting small endotherms in Australian native grasslands. Our targets included both common species that occur at high densities, and species that are notoriously difficult to detect with spotlights, which may occur at very low densities. We completed paired surveys of roosting grassland birds, and nocturnally active small mammals at 22 sites, once using thermal scanners and once using spotlights. Ultimately, distance sampling was conducted across 136 km of transects. Thermal scanners facilitated greater detection distances and higher total detections for small endotherms when compared with spotlighting. Species of greatest conservation concern, the Plains‐wanderer (Pedionomus torquatus—Pedionomidae) and Fat‐tailed Dunnart (Sminthopsis crassicaudata—Dasyuridae) were only detected using thermal scanners. Detection distances generated for thermal scanners were reduced by higher vegetation density; however, thermal scanners continued to outperform spotlights under this scenario. Observers also detected more stationary animals and fewer birds were flushed upon detection using thermal scanners when compared with spotlighting. Thermal scanners have the potential to improve the quality of monitoring datasets by increasing detection probabilities for small endotherms. We recommend the adoption of thermal scanners as a best‐practice tool for monitoring small endotherms in open grassland habitats at night, offering new opportunities to monitor endotherms where monitoring has historically been challenging, inadequate or impossible.

Therian origin of INSL3/RXFP2-driven testicular descent in mammals.

Introduction: During early development in most male mammals the testes move from a position near the kidneys through the abdomen to eventually reside in the scrotum. The transabdominal phase of this migration is driven by insulin-like peptide 3 (INSL3) which stimulates growth of the gubernaculum, a key ligament connecting the testes with the abdominal wall. While all marsupials, except the marsupial mole (Notoryctes typhlops), have a scrotum and fully descended testes, it is unclear if INSL3 drives this process in marsupials especially given that marsupials have a different mechanism of scrotum determination and position relative to the phallus compared to eutherian mammals. Methods: To understand if INSL3 plays a role in marsupial testicular descent we have sequenced and curated the INSL3 gene and its receptor (RXFP2) in a range of marsupials representing every order. Furthermore, we looked at single cell RNA-seq and qPCR analysis of INSL3 in the fat-tailed dunnart testis (Sminthopsis crassicaudata) to understand the location and timing of expression during development. Results: These data show a strong phylogenetic similarity between marsupial and eutherian orthologues, but not with monotreme INSL3s which were more similar to the ancestral RLN3 gene. We have also shown the genomic location of INSL3, and surrounding genes is conserved in a range of marsupials and eutherians. Single cell RNA-seq and qPCR data show that INSL3 mRNA is expressed specifically in Leydig cells and expressed at higher levels during the testicular descent phase in developing marsupials. Discussion: Together, these data argue strongly for a therian origin of INSL3 mediated testicular descent in mammals and suggests that a coordinated movement of the testes to the abdominal wall may have preceded externalization in marsupials and therian mammals.

The Rate of Cooling during Torpor Entry Drives Torpor Patterns in a Small Marsupial.

AbstractTo maximize energy savings, entry into torpor should involve a fast reduction of metabolic rate and body temperature (Tb); that is, animals should thermoconform. However, animals often defend against the decrease in Tb via a temporary increase in thermoregulatory heat production, slowing the cooling process. We investigated how thermoregulating or thermoconforming during torpor entry affects temporal and thermoenergetic aspects in relation to body mass and age in juvenile and adult fat-tailed dunnarts (Sminthopsis crassicaudata; Marsupialia: Dasyuridae). During torpor entry, juvenile thermoconformers cooled twice as fast as and used less energy during cooling than juvenile thermoregulators. While both juvenile and adult thermoconformers had a lower minimum Tb, a lower torpor metabolic rate, and longer torpor bouts than thermoregulators, these differences were more pronounced in the juveniles. Rewarming from torpor took approximately twice as long for juvenile thermoconformers, and the costs of rewarming were greater. To determine the difference in average daily metabolic rate between thermoconformers and thermoregulators independent of body mass, we compared juveniles of a similar size (∼13 g) and similarly sized adults (∼17 g). The average daily metabolic rate was 7% (juveniles) and 17% (adults) less in thermoconformers than in thermoregulators, even though thermoconformers were active for longer. Our data suggest that thermoconforming during torpor entry provides an energetic advantage for both juvenile and adult dunnarts and may aid growth for juveniles. While thermoregulation during torpor entry is more costly, it still saves energy, and the higher Tb permits greater alertness and mobility and reduces the energetic cost of endogenous rewarming.

Non-uniform temporal scaling of developmental processes in the mammalian cortex

The time that it takes the brain to develop is highly variable across animals. Although staging systems equate major developmental milestones between mammalian species, it remains unclear how distinct processes of cortical development scale within these timeframes. Here, we compare the timing of cortical development in two mammals of similar size but different developmental pace: eutherian mice and marsupial fat-tailed dunnarts. Our results reveal that the temporal relationship between cell birth and laminar specification aligns to equivalent stages between these species, but that migration and axon extension do not scale uniformly according to the developmental stages, and are relatively more advanced in dunnarts. We identify a lack of basal intermediate progenitor cells in dunnarts that likely contributes in part to this timing difference. These findings demonstrate temporal limitations and differential plasticity of cortical developmental processes between similarly sized Therians and provide insight into subtle temporal changes that may have contributed to the early diversification of the mammalian brain.

Female mate choice in the fat-tailed dunnart (Sminthopsis crassicaudata) influences offspring sex ratio, but not fecundity

Obtaining a suitable mate is an integral part of reproduction, with sexual selection processes such as female mate choice resulting in both direct and/or indirect benefits. Here, we investigated whether olfactory driven female mate choice influenced reproductive success in captive fat-tailed dunnarts (Sminthopsis crassicaudata). Although females spent 67% more time with a preferred male’s scent, reproductive success was not influenced by assigned mate choice. Of the 10 (of 12) litters that survived to weaning, average litter size was higher for non-preferred pairings (3 ± 0.83) compared with preferred pairings (1.6 ± 0.60), with weaning success equal for both pairings. Analyses suggested that offspring sex ratios were influenced by mate choice, with females paired with their preferred mate having more daughters (81%) in comparison to non-preferred pairings (44%) and by paternal body condition, whereby females paired with males in better body condition produced more sons. In this species, altering offspring sex ratios in favour of daughters may be achieved by pairing with preferred males, and towards sons by pairing with males in better body condition. With the increasing need for captive breeding programs, these techniques may provide opportunities to correct sex ratio biases and incorporate natural mating systems into conservation programs.

Marsupials and Multi-Omics: Establishing New Comparative Models of Neural Crest Patterning and Craniofacial Development.

Studies across vertebrates have revealed significant insights into the processes that drive craniofacial morphogenesis, yet we still know little about how distinct facial morphologies are patterned during development. Studies largely point to evolution in GRNs of cranial progenitor cell types such as neural crest cells, as the major driver underlying adaptive cranial shapes. However, this hypothesis requires further validation, particularly within suitable models amenable to manipulation. By utilizing comparative models between related species, we can begin to disentangle complex developmental systems and identify the origin of species-specific patterning. Mammals present excellent evolutionary examples to scrutinize how these differences arise, as sister clades of eutherians and marsupials possess suitable divergence times, conserved cranial anatomies, modular evolutionary patterns, and distinct developmental heterochrony in their NCC behaviours and craniofacial patterning. In this review, I lend perspectives into the current state of mammalian craniofacial biology and discuss the importance of establishing a new marsupial model, the fat-tailed dunnart, for comparative research. Through detailed comparisons with the mouse, we can begin to decipher mammalian conserved, and species-specific processes and their contribution to craniofacial patterning and shape disparity. Recent advances in single-cell multi-omics allow high-resolution investigations into the cellular and molecular basis of key developmental processes. As such, I discuss how comparative evolutionary application of these tools can provide detailed insights into complex cellular behaviours and expression dynamics underlying adaptive craniofacial evolution. Though in its infancy, the field of “comparative evo-devo-omics” presents unparalleled opportunities to precisely uncover how phenotypic differences arise during development.

Strategies for meiotic sex chromosome dynamics and telomeric elongation in Marsupials.

During meiotic prophase I, homologous chromosomes pair, synapse and recombine in a tightly regulated process that ensures the generation of genetically variable haploid gametes. Although the mechanisms underlying meiotic cell division have been well studied in model species, our understanding of the dynamics of meiotic prophase I in non-traditional model mammals remains in its infancy. Here, we reveal key meiotic features in previously uncharacterised marsupial species (the tammar wallaby and the fat-tailed dunnart), plus the fat-tailed mouse opossum, with a focus on sex chromosome pairing strategies, recombination and meiotic telomere homeostasis. We uncovered differences between phylogroups with important functional and evolutionary implications. First, sex chromosomes, which lack a pseudo-autosomal region in marsupials, had species specific pairing and silencing strategies, with implications for sex chromosome evolution. Second, we detected two waves of γH2AX accumulation during prophase I. The first wave was accompanied by low γH2AX levels on autosomes, which correlated with the low recombination rates that distinguish marsupials from eutherian mammals. In the second wave, γH2AX was restricted to sex chromosomes in all three species, which correlated with transcription from the X in tammar wallaby. This suggests non-canonical functions of γH2AX on meiotic sex chromosomes. Finally, we uncover evidence for telomere elongation in primary spermatocytes of the fat-tailed dunnart, a unique strategy within mammals. Our results provide new insights into meiotic progression and telomere homeostasis in marsupials, highlighting the importance of capturing the diversity of meiotic strategies within mammals.

The people behind the paper - Peter Kozulin, Rodrigo Suárez, Qiong-Yi Zhao, Linda Richards and Laura Fenlon.

The neocortex is unique to mammals and so, for evolutionary studies, researchers have compared eutherians and marsupials. A new paper in Development uncovers key differences in the timing of gene expression changes in the cortical development of the mouse and the similarly sized marsupial, the fat-tailed dunnart. We caught up with the authors from The University of Queensland, Australia, to find out more about their research and their future plans.

Morphological events at the time of oocyte maturation and sperm–egg interactions during fertilisation in a dasyurid marsupial

In marsupials there have been several studies on oocyte maturation and sperm–egg interactions at the time of fertilisation, but controversy exists as to when and how some of the processes occur. Here we present a summary of relevant data from a species of dasyurid marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata). The findings show that in oocytes of developing ovarian follicles cortical granules are produced with many of the granules sometimes initially congregating around the cytoplasmic vacuoles before migrating to the proximity of the oocyte cell membrane. During fertilisation the spermatozoon binds to the zona pellucida that surrounds the oocyte with its tail lying parallel to the long axis of the head. As the spermatozoon passes through the zona pellucida it is surrounded by the zona matrix and, when entering the egg cytoplasm, a localised area of elevated ooplasm occurs around the spermatozoon. Also, unlike a recent claim to the contrary, the head of the spermatozoon travels a considerable distance into the egg cytoplasm before chromatin decondensation occurs, an event that probably minimises the chances of chromatin disruption by the sperm tail at the time of its incorporation.

Postnatal development in a marsupial model, the fat-tailed dunnart (Sminthopsis crassicaudata; Dasyuromorphia: Dasyuridae)

Marsupials exhibit unique biological features that provide fascinating insights into many aspects of mammalian development. These include their distinctive mode of reproduction, altricial stage at birth, and the associated heterochrony that is required for their crawl to the pouch and teat attachment. Marsupials are also an invaluable resource for mammalian comparative biology, forming a distinct lineage from the extant placental and egg-laying monotreme mammals. Despite their unique biology, marsupial resources are lagging behind those available for placentals. The fat-tailed dunnart (Sminthopsis crassicaudata) is a laboratory based marsupial model, with simple and robust husbandry requirements and a short reproductive cycle making it amenable to experimental manipulations. Here we present a detailed staging series for the fat-tailed dunnart, focusing on their accelerated development of the forelimbs and jaws. This study provides the first skeletal developmental series on S. crassicaudata and provides a fundamental resource for future studies exploring mammalian diversification, development and evolution.

Fat-tailed dunnarts (

Grasslands are among the most endangered ecosystems, with <1% of Victorian grasslands remaining. Extinctions of many grassland fauna species have occurred since European settlement due to loss of suitable habitat, and dramatic range reductions continue for those that still exist. Fat-tailed dunnarts (Sminthopsis crassicaudata) are the only small ground-dwelling marsupial known to persist in Victorian grassland habitats. The last long-term targeted surveys for this species were conducted in Victoria in the 1970s. Incidental findings from more recent short-term targeted and non-targeted surveys in the same area suggest a decline. We performed direct targeted surveys for fat-tailed dunnarts at the 1970s survey site over a 12-month period in 2019 and found no evidence of fat-tailed dunnart presence. The species is classified as Near Threatened in the state and Least Concern internationally. Our work highlights the importance of targeted surveys to assess the stability of this species across Victoria, and the need for collection of long-term data to better identify population declines.

Preliminary evaluation of urinary cytology and running wheel activity to detect oestrus and the effect of daily handling on breeding success of fat-tailed dunnarts Sminthopsis crassicaudata

Eight recently weaned female fat-tailed dunnarts (Sminthopsis crassicaudata) were divided into two experimental groups: those in Group A (n = 4) received limited handling, whereas those in Group B (n = 4) were handled daily for the collection of urine samples to detect changes in cornified epithelial cells (CEC). Daily faecal output, food consumption, running wheel activity and weekly bodyweight changes were recorded. Faecal corticosterone metabolite (FCM) concentrations were determined over two periods, namely after introduction to either a new enclosure or a male for mating. Although changes in faecal output, food consumption, bodyweight and running wheel activity showed no relationship to oestrus, CEC scoring was a suitable means for detecting oestrus. Overall mean FCM concentrations did not differ significantly (P > 0.05) between the Groups A and B, and pouch young were produced in both (Group A, n = 2; Group B, n = 3), suggesting that daily handling is not a significant factor affecting breeding success. However, females that did not produce young during the study period demonstrated higher baseline FCM concentrations than females that did (mean (±s.e.m.) 79.8 ± 4.0 vs 62.3 ± 3.1 ng g−1). Daily handling for urine collection for CEC scoring appears to have little effect on adrenal output or reproductive success, confirming its utility as a reproductive management tool for this species.

Thermal energetics and behaviour of a small, insectivorous marsupial in response to the interacting risks of starvation and predation.

Central to understanding animal ecology is how prey cope with the interacting risks of starvation and predation. This trade-off is modulated by the energy requirements of prey, yet relatively few studies have incorporated physiological mechanisms for energy savings when considering the behavioural response of prey to predation risk. In our study, we aimed to determine individual variation in behaviour, resting metabolism, body temperature and response to 24-h starvation within a captive population of fat-tailed dunnarts (Sminthopsis crassicaudata; 15-g insectivorous marsupials), and then, using semi-outdoor enclosures, test whether foraging effort and thermal energetics are adjusted in response to manipulation of ground cover, which for small mammals can simulate predation risk. We found that, under the low cover (high predation risk) treatment, dunnarts consumed less food and employed a greater daily reduction in body temperature between their active and rest phase. This result supports the hypothesis that rest-phase thermoregulatory energy savings are employed, even when food is available, if predation risk is perceived to increase the cost of foraging. Individuals exhibited correlated variation along two orthogonal axes incorporating the measured behavioural and metabolic variables, but these differences were not correlated with responses to starvation and predation risk. Our experiment demonstrates that flexibility in daily energy requirements provided by heterothermy can have important consequences for how small mammals respond to both starvation and predation risks. Such challenges are amplified in degraded habitat with introduced predators, making the capacity for heterothermy an even more important mechanism for survival.

Physiological and anatomical investigation of the auditory brainstem in the Fat-tailed dunnart (Sminthopsis crassicaudata).

The fat-tailed dunnart (Sminthopsis crassicaudata) is a small (10–20 g) native marsupial endemic to the south west of Western Australia. Currently little is known about the auditory capabilities of the dunnart, and of marsupials in general. Consequently, this study sought to investigate several electrophysiological and anatomical properties of the dunnart auditory system. Auditory brainstem responses (ABR) were recorded to brief (5 ms) tone pips at a range of frequencies (4–47.5 kHz) and intensities to determine auditory brainstem thresholds. The dunnart ABR displayed multiple distinct peaks at all test frequencies, similar to other mammalian species. ABR showed the dunnart is most sensitive to higher frequencies increasing up to 47.5 kHz. Morphological observations (Nissl stain) revealed that the auditory structures thought to contribute to the first peaks of the ABR were all distinguishable in the dunnart. Structures identified include the dorsal and ventral subdivisions of the cochlear nucleus, including a cochlear nerve root nucleus as well as several distinct nuclei in the superior olivary complex, such as the medial nucleus of the trapezoid body, lateral superior olive and medial superior olive. This study is the first to show functional and anatomical aspects of the lower part of the auditory system in the Fat-tailed dunnart.

Dynamic changes to claudins in the uterine epithelial cells of the marsupial Sminthopsis crassicaudata (Dasyuridae) during pregnancy.

The fluid that surrounds the embryo in the uterus contains important nourishing factors and secretions. To maintain the distinct microenvironment in the uterine lumen, the tight junctions between uterine epithelial cells are remodeled to decrease paracellular movement of molecules and solutes. Modifications to tight junctions between uterine epithelial cells is a common feature of pregnancy in eutherian mammals, regardless of placental type. Here we used immunofluorescence microscopy and western blot analysis to describe distributional changes to tight junctional proteins, claudin-1, -3, -4, and -5, in the uterine epithelial cells of a marsupial species, Sminthopsis crassicaudata. Immunofluorescence microscopy revealed claudin-1, -3, and -5 in the tight junctions of the uterine epithelium of S. crassicaudata during pregnancy. These specific claudins are associated with restricting passive movement of fluid between epithelial cells in eutherians. Hence, their function during pregnancy in S. crassicaudata may be to maintain the uterine luminal content surrounding developing embryos. Claudin-4 disappears from all uterine regions of S. crassicaudata at the time of implantation, in contrast with the distribution of this claudin in some eutherian mammals. We conclude that like eutherian mammals, distributional changes to claudins in the uterine epithelial cells of S. crassicaudata are necessary to support pregnancy. However, the combination of individual claudin isoforms in the tight junctions of the uterine epithelium of S. crassicaudata differs from that of eutherian mammals. Our findings suggest that the precise permeability of the paracellular pathway of the uterine epithelium is species-specific.

Shared and differential features of Robo3 expression pattern in amniotes.

In Bilaterians, commissural neurons project their axons across the midline of the nervous system to target neurons on the opposite side. In mammals, midline crossing at the level of the hindbrain and spinal cord requires the Robo3 receptor which is transiently expressed by all commissural neurons. Unlike other Robo receptors, mammalian Robo3 receptors do not bind Slit ligands and promote midline crossing. Surprisingly, not much is known about Robo3 distribution and mechanism of action in other vertebrate species. Here, we have used whole-mount immunostaining, tissue clearing and light-sheet fluorescent microscopy to study Robo3 expression pattern in embryonic tissue from diverse representatives of amniotes at distinct stages, including squamate (African house snake), birds (chicken, duck, pigeon, ostrich, emu and zebra finch), early postnatal marsupial mammals (fat-tailed dunnart), and eutherian mammals (mouse and human). The analysis of this rich and unique repertoire of amniote specimens reveals conserved features of Robo3 expression in midbrain, hindbrain and spinal cord commissural circuits, which together with subtle but meaningful modifications could account for species-specific evolution of sensory-motor and cognitive capacities. Our results also highlight important differences of precerebellar nuclei development across amniotes.

Sex steroids influence the plasma membrane transformation in the uterus of the fat-tailed dunnart (Sminthopsis crassicaudata, Marsupialia).

The uterine epithelium undergoes remodelling to become receptive to blastocyst implantation during pregnancy in a process known as the plasma membrane transformation. There are commonalities in ultrastructural changes to the epithelium, which, in eutherian, pregnancies are controlled by maternal hormones, progesterone and oestrogens. The aim of this study was to determine the effects that sex steroids have on the uterine epithelium in the fat-tailed dunnart Sminthopsis crassicaudata, the first such study in a marsupial. Females were exposed to exogenous hormones while they were reproductively quiescent, thus not producing physiological concentrations of ovarian hormones. We found that changes to the protein E-cadherin, which forms part of the adherens junction, are controlled by progesterone and that changes to the desmoglein-2 protein, which forms part of desmosomes, are controlled by 17β-oestradiol. Exposure to a combination of progesterone and 17β-oestradiol causes changes to the microvilli on the apical surface and to the ultrastructure of the uterine epithelium. There is a decrease in lateral adhesion when the uterus is exposed to progesterone and 17β-oestradiol that mimics the hormone environment of uterine receptivity. We conclude that uterine receptivity and the plasma membrane transformation in marsupial and eutherian pregnancies are under the same endocrine control and may be an ancestral feature of therian mammals.