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Funding: This project was supported by the National Science Foundation (grant numbers DEB 1838283 and IOS 2032006 to D.M.-S. and Dav.R. and DEB 1838273 and DGE 1633299 to L.D.), National Institutes of Health (grant numbers R01HG002939 and U24HG010136 to J.S., R.H., A.F.A.S., and Je.R.), NHGRI (grant number R01HG008742 to Z.C.), Irish Research Council (grant number IRCLA/ 2017/58 to E.T.), Science Foundation Ireland (grant number 19/FFP/6790 to E.T.), Max Planck Research Group awarded by the Max Planck Gesellschaft to S.V., Human Frontiers Science Program (grant number RGP0058/2016 to S.V.), UK Research and Innovation (grant number MR/T021985/1 to S.V.), and the Swedish Research Council Distinguished Professor Award to K.L.-T. Horizontal transfer of transposable elements (TEs) is an important mechanism contributing to genetic diversity and innovation. Bats (order Chiroptera) have repeatedly been shown to experience horizontal transfer of TEs at what appears to be a high rate compared with other mammals. We investigated the occurrence of horizontally transferred (HT) DNA transposons involving bats. We found over 200 putative HT elements within bats; 16 transposons were shared across distantly related mammalian clades, and 2 other elements were shared with a fish and two lizard species. Our results indicate that bats are a hotspot for horizontal transfer of DNA transposons. These events broadly coincide with the diversification of several bat clades, supporting the hypothesis that DNA transposon invasions have contributed to genetic diversification of bats. Publisher PDF

Horizontal transfer of transposable elements (TEs) is an important mechanism contributing to genetic diversity and innovation. Bats (order Chiroptera) have repeatedly been shown to experience horizontal transfer of TEs at what appears to be a high rate compared with other mammals. We investigated the occurrence of horizontally transferred (HT) DNA transposons involving bats. We found over 200 putative HT elements within bats; 16 transposons were shared across distantly related mammalian clades, and 2 other elements were shared with a fish and two lizard species. Our results indicate that bats are a hotspot for horizontal transfer of DNA transposons. These events broadly coincide with the diversification of several bat clades, supporting the hypothesis that DNA transposon invasions have contributed to genetic diversification of bats.

Globally, urban expansion and climate change interact to threaten stream ecosystems and are accelerating the loss of aquatic biodiversity. Waterway managers urgently need tools to understand the potential combined impacts of urbanisation and climate change, and to identify effective mitigating management interventions for protecting freshwater biota. We address this challenge using the semi-aquatic mammal the platypus (Ornithorhynchus anatinus) as a focal species. We developed high-resolution environmental spatial data for stream networks and spatially-explicit habitat suitability models to explore the impact of threats, and to identify the combination of management actions most likely to maintain or improve habitat suitability over the next 50 years in greater Melbourne, Australia. We developed and evaluated platypus habitat suitability models (males-and-females and females-only) including validation using an independent environmental DNA (eDNA) dataset. Platypus occurred more commonly in larger, cooler streams with greater catchment-weighted discharge, following periods of greater stream flow. They were positively associated with near-stream forest cover and negatively associated with annual air temperature and urban stormwater runoff. Extensive reductions in suitable platypus habitat are predicted to occur under urbanisation and climate change scenarios, with the greatest threat expected from reduced streamflows. This emphasises the importance of maintaining flow regimes as part of conserving platypus in the region, however, substantial additional benefit is predicted by concurrent riparian revegetation and urban stormwater management efforts (that also have the potential to contribute to the streamflow objectives). Provision of adequate streamflows in a future with increasing water demands and water security requirements will likely require creative integrated water management (IWM) solutions. Our high-resolution stream network and habitat suitability models have allowed predictions of potential range-shifts due to urban expansion and climate change impacts at management-relevant scales and at the whole-of-landscape scale. This has enabled systematic strategic planning, priority action planning and target setting in strategic policy development.

Pale chub (

Platypus sinensis (Schedl) * Platypus sinensis Schedl, 1941: 43. New record. Bhutan, W. distr. Thimpu, E. Dochu La, Menshunang, 2400m, 7.vii.1988, C. Holzschuh (2) (NKME). Distribution. Bhutan, China (Fujian). Biology. There is a single record from Castanopsis fargesii (Fagaceae) (RAB unpublished)., Published as part of Beaver, Roger A. & Smith, Sarah M., 2022, The bark and ambrosia beetles of Bhutan (Coleoptera: Curculionidae: Scolytinae and Platypodinae): a synopsis with three new species of Scolytinae, pp. 1-24 in Zootaxa 5174 (1) on page 17, DOI: 10.11646/zootaxa.5174.1.1, http://zenodo.org/record/6972960, {"references":["Schedl, K. E. (1941) Borken- und Ambrosiakafer aus Ostasien. Entomologische Blatter, 37, 42 - 44."]}

Platypus quadriporus (Beeson) Crossotarsus quadriporus Beeson, 1937: 96. Platypus quadriporus (Beeson): Schedl 1962: 209. Recorded from Bhutan by Schedl (1975). New record. Bhutan, W. distr. Thimpu, E. Dochu La, Menshunang, 2400m, 7.vii.1988, C. Holzschuh (5) (NKME). Distribution. Bhutan, China (Fujian), India (West Bengal), Myanmar. Biology. Recorded only from two species of Quercus (Fagaceae) (Beeson 1937)., Published as part of Beaver, Roger A. & Smith, Sarah M., 2022, The bark and ambrosia beetles of Bhutan (Coleoptera: Curculionidae: Scolytinae and Platypodinae): a synopsis with three new species of Scolytinae, pp. 1-24 in Zootaxa 5174 (1) on page 17, DOI: 10.11646/zootaxa.5174.1.1, http://zenodo.org/record/6972960, {"references":["Beeson, C. F. C. (1937) New Crossotarsus (Platypodidae, Col.). Indian Forest Records (New Series), Entomology, 3, 45 - 103.","Schedl, K. E. (1962) Zur Synonymie der Borkenkafer VI. Entomologische Blatter, 58, 201 - 211.","Schedl, K. E. (1975) Ergebnisse der Bhutan-Expedition 1972 des Naturhistorischen Museums in Basel, Coleoptera: Fam: Scolytidae und Platypodidae. Entomologica Basiliensia, 1, 383 - 385."]}

Platypus secretus Sampson Platypus secretus Sampson, 1921: 25. Recorded from Bhutan by Schedl (1975). Distribution. Bangladesh, Bhutan, India (Assam, Sikkim, West Bengal), Laos, Myanmar, Nepal, Thailand, Vietnam. Biology. The species is polyphagous (Beeson 1961)., Published as part of Beaver, Roger A. & Smith, Sarah M., 2022, The bark and ambrosia beetles of Bhutan (Coleoptera: Curculionidae: Scolytinae and Platypodinae): a synopsis with three new species of Scolytinae, pp. 1-24 in Zootaxa 5174 (1) on page 17, DOI: 10.11646/zootaxa.5174.1.1, http://zenodo.org/record/6972960, {"references":["Sampson, F. W. (1921) Further notes on Platypodidae and Scolytidae collected by Mr. G. E. Bryant and others. Annals and Magazine of Natural History, series 9, 7, 25 - 37. https: // doi. org / 10.1080 / 00222932108632486","Schedl, K. E. (1975) Ergebnisse der Bhutan-Expedition 1972 des Naturhistorischen Museums in Basel, Coleoptera: Fam: Scolytidae und Platypodidae. Entomologica Basiliensia, 1, 383 - 385.","Beeson, C. F. C. (1961) The Ecology and Control of the Forest Insects of India and the Neighbouring Countries. (2 nd ed.). Government of India, New Delhi, 767 pp."]}

Fresh light is being shed on the rise of mammals thanks to new clues from one of nature's oddest creatures, finds Ibrahim Sawal

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.

Biofluorescence has been detected in several nocturnal-crepuscular organisms from invertebrates to birds and mammals. Biofluorescence in mammals has been detected across the phylogeny, including the monotreme duck-billed platypus (Ornithorhyncus anatinus), marsupial opossums (Didelphidae), and New World placental flying squirrels (Gluacomys spp.). Here, we document vivid biofluorescence of springhare (Pedetidae) in both museum specimens and captive individuals—the first documented biofluorescence of an Old World placental mammal. We explore the variation in biofluorescence across our sample and characterize its physical and chemical properties. The striking visual patterning and intensity of color shift was unique relative to biofluorescence found in other mammals. We establish that biofluorescence in springhare likely originates within the cuticle of the hair fiber and emanates, at least partially, from several fluorescent porphyrins and potentially one unassigned molecule absent from our standard porphyrin mixture. This discovery further supports the hypothesis that biofluorescence may be ecologically important for nocturnal-crepuscular mammals and suggests that it may be more broadly distributed throughout Mammalia than previously thought.

Monotremes diverged from therian mammal ancestors approximately 184 million years ago and have a number of novel reproductive characteristics. One in particular is their penile morphology. There are differences between echidna and platypus phalluses, but both are somewhat similar in structure to the reptilian phallus. The echidna penis consists of 4 rosette glans, each of which contains a termination of the quadrifurcate urethra, but it appears that only 2 of the 4 glans become erect at any one time. Despite this, only a few historical references describe the structure of the echidna penis and none provides an explanation for the mechanisms of unilateral ejaculation. This study confirmed that the echidna penis contains many of the same overall structures and morphology as other mammalian penises and a number of features homologous with reptiles. The corpus cavernosum is well supplied with blood, extends up to the base of the glans penis and is primarily responsible for erection. However, the echidna possesses 2 distinct corpora spongiosa separated by a septum, each of which surround the urethra only distal to the initial urethral bifurcation in the glans penis. Together with the bifurcation of the main penile artery, this provides a mechanism by which blood flow could be directed to only one corpus spongiosum at a time to maintain an open urethra that supplies 2 of the 4 glans to facilitate unilateral ejaculation.

Since ancient times, people have been fascinated by animals. They are such a close element of the biosphere, that it is not possible for them to go unnoticed. Treating animals as sacred beings is one of the primary elements of totemism – belief in kinship with the class of objects (in this case animals). It is clearly visible in the culture of Australian aborigines. The paper presents, through the scope of mystic relation aborigines-animals, the role of platypus in the culture of indigenous inhabitants of Australia. It is also an attempt to fill the gap in the humanist discourse about animals because to this day platypus haven’t had any monographic study in the field of religious studies, cultural studies or even animal studies. By analyzing the stories from the Dreamtime, the text shows the mythical genesis of this mammal, the origin of its characteristic features, and it functions in the life of a tribe, especially in the light of aquatic symbolism.

Egg-laying mammals (monotremes) are a sister clade of therians (placental mammals and marsupials) and a key clade to understand mammalian evolution. They are classified into platypus and echidna, which exhibit distinct ecological features such as habitats and diet. Chemosensory genes, which encode sensory receptors for taste and smell, are believed to adapt to the individual habitats and diet of each mammal. In this study, we focused on the molecular evolution of bitter taste receptors (TAS2Rs) in monotremes. The sense of bitter taste is important to detect potentially harmful substances. We comprehensively surveyed agonists of all TAS2Rs in platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus) and compared their functions with orthologous TAS2Rs of marsupial and placental mammals (i.e., therians). As results, the agonist screening revealed that the deorphanized monotreme receptors were functionally diversified. Platypus TAS2Rs had broader receptive ranges of agonists than those of echidna TAS2Rs. While platypus consumes a variety of aquatic invertebrates, echidna mainly consumes subterranean social insects (ants and termites) as well as other invertebrates. This result indicates that receptive ranges of TAS2Rs could be associated with feeding habits in monotremes. Furthermore, some orthologous receptors in monotremes and therians responded to β-glucosides, which are feeding deterrents in plants and insects. These results suggest that the ability to detect β-glucosides and other substances might be shared and ancestral among mammals.

XXfemale andXYmale therian mammals equalize X-linked gene expression through the mitotically-stable transcriptional inactivation of one of the two X chromosomes in female somatic cells. Here, we describe an essential function of the X-linked homolog of an ancestral X-Y gene pair,Kdm5c-Kdm5d, in the expression of Xist lncRNA, which is required for stable X-inactivation. Ablation ofKdm5cfunction in females results in a significant reduction in Xist RNA expression.Kdm5cencodes a demethylase that enhancesXistexpression by converting histone H3K4me2/3 modifications into H3K4me1. Ectopic expression of mouse and humanKDM5C, but not the Y-linked homologKDM5D, inducesXistin male mouse embryonic stem cells (mESCs). Similarly, marsupial (opossum)Kdm5cbut notKdm5dalso upregulatesXistin male mESCs, despite marsupials lackingXist, suggesting that the KDM5C function that activatesXistin eutherians is strongly conserved and predates the divergence of eutherian and metatherian mammals. In support, prototherian (platypus)Kdm5calso inducesXistin male mESCs. Together, our data suggest that eutherian mammals co-opted the ancestral demethylase KDM5C during sex chromosome evolution to upregulateXistfor the female-specific induction of X-inactivation.

The evolutionarily unique platypus (Ornithorhynchus anatinus) has experienced major declines and extinctions from a range of historical and recent interacting human-mediated threats. Although spending most of their time in the water, platypuses can move over land. Nevertheless, uncertainties remain whether dams are barriers to movement, thus limiting gene flow and dispersal, essential to evolution and ecology. Here we examined disruption of gene flow between platypus groups below and above five major dams, matched to four adjacent rivers without major dams. Genetic differentiation (F

The passage between keratinization to cornification of the epidermis and skin appendages in vertebrates requires formation of a stratum corneum rich in SS bonds among other cross-linking chemical bonds. A key enzyme, sulfhydryl oxidase (SOXase) catalyzes the oxidation of SH groups present in keratins and in corneous proteins of the epidermis into SS. Presence and distribution of SAXase has been studied by immunohistochemistry in all vertebrates, from fish to mammals. SOXase is immunohistochemically absent in all fish and amphibian species tested with the exception of a thin pre-corneous layer in the epidermis of adult anurans. SOXase is low to absent in corneous appendages such as horny teeth of lamprey or claws and horny beaks of amphibians. Conversely, SOXase is detected in the transitional (pre-corneous) and inner corneous layers of the epidermis of sauropsids and mammals. In lepidosaurian reptiles, SOXase appears in both beta- and alpha-corneous-layers, but is limited to the pre-corneous and corneous layers of the thin soft epidermises of birds and mammals, including the granular layer. SOXase is localized in pre-corneous layers and disappears in external corneous layers of amniote skin appendages such as claws, beaks of turtles and birds, and in developing feathers. This distribution further indicates that the increase activity of epidermal SOXase is/was essential, in addition to other enzymes such as epidermal transglutaminases, for the evolution of the corneous layer and of the different hard skin appendages present in terrestrial vertebrates.

Samples of C. ramosus and D. platypus were collected from Hurgada, the Red Sea during June-August 2018. Samples were transported to the lab at the University of Alexandria, Egypt. This study aims to describe the embryogenesis of C. ramosus inside the capsules and test the effects of signaling factors and neuro-transmitters on the in vitro transformation of larvae of D. platypus and identify some bioactive inducers that increase larval metamorphosis. Capsules of C. ramosus were fixed in 10% saline formaldehyde and capsules of D. platypus were placed in plastic aquaria for immune-histochemical test. The sequence of the embryonic transformations and the duration time of each step of C. ramosus were identified. The importance of the following experiment is to provide a suitable medium for the developing larval stages and improve eugenic manner of the new generations. Undertreated conditions of D. platypus larvae, MF 2.5 mM, C8:0 1 µM, ADMA 2.5 mM, and Acetylcholine 0.5 mM larval transformation from trochophore to veliger to early juvenile stages was accelerated than larvae of control in seawater. Serotonin 10 µg/ml and Acetylcholine 1 mM exerted a negative effect while C8:0 0.1 or 10 µM, MF 300 µM, ADMA 1 mM and 1.5 mM did not affect larval transformation. Atorvastatin (5, 20 and 40 mg), Pravastatin (50 mg and 100 mg), Cetirizine hydrochloride (10 mg), Nebivolol (2.5 mg, 5 mg. and 10 mg), Atenolol (25 mg and 100 mg) and Amlodipine Besylate (2.5 mg, 5.0 mg, and 10 mg) exerted a negative impact on larvae in all stages and mortality predominated.

Aromatase (P450arom, CYP19A1) is the terminal enzyme in the synthesis of the steroid hormone family of estrogens. Not surprisingly, this enzyme has structural similarities between the limited number of species studied thus far. This study examined the structure of aromatases from four diverse Australian species including a marsupial (tammar wallaby; Macropus eugenii), monotreme (platypus; Ornithorhynchus anatinus), ratite (emu; Dromaius novaehollandiae) and lizard (bearded dragon; Pogona vitticeps). We successfully built homology models for each species, using the only crystallographically determined structure available, human aromatase. The amino acid sequences showed high amino acid sequence identity to the human aromatase: wallaby 81%, platypus 73%, emu 75% and bearded dragon at 74%. The overall structure was highly conserved among the five species, although there were non-secondary structures (loops and bends) that were variable and flexible that may result in some differences in catalytic activity. At the N-terminal regions, there were deletions and variations that suggest that functional distinctions may be found. We found that the active sites of all these proteins were identical, except for a slight variation in the emu. The electrostatic potential across the surfaces of these aromatases highlighted likely variations to the protein-protein interactions of these enzymes with both redox partner cytochrome P450 reductase and possibly homodimerization in the case of the platypus, which has been postulated for the human aromatase enzyme. Given the high natural selection pressures on reproductive strategies, the relatively high degree of conservation of aromatase sequence and structure across species suggests that there is biochemically very little scope for changes to have evolved without the loss of enzyme activity.

Platypuses (Ornithorhynchus anatinus) forage for macroinvertebrate prey exclusively in freshwater habitats. Because food material in their faeces is well digested and mostly unidentifiable, previous dietary studies have relied on cheek pouch assessments and stable isotope analysis. Given DNA metabarcoding can identify species composition from only fragments of genetic material, we investigated its effectiveness in analysing the diet of platypuses, and to assess variation across seasons and sexes. Of the 18 orders and 60 families identified, Ephemeroptera and Diptera were the most prevalent orders, detected in 100% of samples, followed by Trichoptera, Pulmonata, and Odonata (86.21% of samples). Caenidae and Chironomidae were the most common families. Diptera had a high average DNA read, suggesting it is an important dietary component that may have been underestimated in previous studies. We found no variation in diet between sexes and only minimal changes between seasons. DNA metabarcoding proved to be a highly useful tool for assessing platypus diet, improving prey identification compared to cheek pouch analysis, which can underestimate soft-bodied organisms, and stable isotope analysis which cannot distinguish all taxa isotopically. This will be a useful tool for investigating how platypus prey diversity is impacted by habitat degradation as a result of anthropogenic stressors.

Genetic diversity at loci concerned with fitness is an important part of the ability of a wild population to adapt to changes in its environment, including climatic events, disease and pollution. Research into the effects of genetic diversity on the impacts of disease on wildlife populations has focussed on genes of the major histocompatibility complex (MHC). This study investigated the genetic diversity at the MHC class II DZB gene, as well as the distribution of alleles of the same gene, for platypuses Ornithorhynchus anatinus in the Seabrook Creek Catchment in northwest Tasmania. This study detected 10 previously identified alleles and two previously unreported alleles at the MHC Class II DZB locus in 18 platypuses from the Seabrook Creek Catchment. An additional sequence isolated from two individuals was consistent with a pseudogene. Alleles were reasonably well distributed geographically through the catchment, but there was evidence of a degree of isolation at one site. Consistent with evidence that smaller wildlife populations have relatively low genetic diversity, and that there is relatively slow gene flow between river catchments, the observed genetic diversity at the MHC Class II locus was lower than those in larger previously studied river catchments but higher than those in two island populations. Consequently, this population of platypuses may have a limited capacity to respond to new infectious challenges, such as the fungal disease mucormycosis.

Most biologists, particularly Australian biologists, are aware that the initial description and attempts to classify the echidna and platypus were surrounded by controversy. Fewer are aware of the important roles played by two eminent scientists, Étienne Geoffroy Saint-Hilaire in Paris and Richard Owen in London, in the debate as to whether the platypus and echidna were really mammals, and whether they laid eggs. Geoffroy argued that they were egg-laying but could not possibly lactate; Owen argued that they lactated but could not possibly lay eggs. Because of these and many other aspects of their biology, monotremes featured prominently in debates about classification of animals and the transmutation of species, and involved many important scientists of the time. These arguments can only be understood in the context of the development of science in the late eighteenth and the nineteenth century, and how that was influenced by the social context. Early ideas of evolution, or transformism, were attractive to radical thinkers, whereas social conservatives were anxious to show that the boundaries between types of animals, just like the boundaries between social classes, were erected by God and could not be crossed.

Microproteins (

Significance Genomes of birds and reptiles, but not mammals, consist of a few large chromosomes and many tiny microchromosomes. Microchromosomes are gene-rich and highly conserved among birds and reptiles and share homology with one or more of the tiny chromosomes of an invertebrate that diverged from the vertebrate lineage 684 Ma. Microchromosomes interact strongly and crowd together at the center of cells, suggesting functional coherence. Many microchromosomes have been lost independently in turtles, snakes, and lizards as they have fused with each other or with larger chromosomes. In mammals they have completely disappeared, yet some chromosomes of the basal platypus line up with several microchromosomes, suggesting that they are the building blocks of the atypically variable chromosomes of mammals., Microchromosomes, once considered unimportant shreds of the chicken genome, are gene-rich elements with a high GC content and few transposable elements. Their origin has been debated for decades. We used cytological and whole-genome sequence comparisons, and chromosome conformation capture, to trace their origin and fate in genomes of reptiles, birds, and mammals. We find that microchromosomes as well as macrochromosomes are highly conserved across birds and share synteny with single small chromosomes of the chordate amphioxus, attesting to their origin as elements of an ancient animal genome. Turtles and squamates (snakes and lizards) share different subsets of ancestral microchromosomes, having independently lost microchromosomes by fusion with other microchromosomes or macrochromosomes. Patterns of fusions were quite different in different lineages. Cytological observations show that microchromosomes in all lineages are spatially separated into a central compartment at interphase and during mitosis and meiosis. This reflects higher interaction between microchromosomes than with macrochromosomes, as observed by chromosome conformation capture, and suggests some functional coherence. In highly rearranged genomes fused microchromosomes retain most ancestral characteristics, but these may erode over evolutionary time; surprisingly, de novo microchromosomes have rapidly adopted high interaction. Some chromosomes of early-branching monotreme mammals align to several bird microchromosomes, suggesting multiple microchromosome fusions in a mammalian ancestor. Subsequently, multiple rearrangements fueled the extraordinary karyotypic diversity of therian mammals. Thus, microchromosomes, far from being aberrant genetic elements, represent fundamental building blocks of amniote chromosomes, and it is mammals, rather than reptiles and birds, that are atypical.

Knowledge of oocyte development and the early differentiation of the germ layers in monotremes stems largely from two articles by J. P. Hill and T. Thomson Flynn. The completeness of their account was due to the large series of echidna ovaries and eggs collected on Tasmania by Flynn, an Australian biologist of whom a brief account is given. A striking finding in the oocyte and early embryo of monotremes was the presence of a latebra connected to the yolk bed beneath the germinal disc as described in birds and several reptiles. A further resemblance was the presence early in vitellogenesis of a striate zone beneath the zona pellucida. Cleavage resulted first in a lens‐shaped blastodisc encircled by cells called vitellocytes that later fused to form a germ‐ring. The blastodisc gave rise to a blastoderm that eventually became unilaminar but comprised two cell types identified as ectoderm and primitive endoderm. Eventually these segregated into two layers and formed a blastula. This sequence resembled that in marsupials except there was no obvious distinction between future embryonic and extra‐embryonic regions. As the blastoderm extended over the surface of the yolk, it was preceded by the germ‐ring that eventually played a role in forming the yolk navel. This was a unique feature of monotreme development. It is shown that Flynn played an important role in analysis of the material as well as in its collection. Knowledge of oocyte development and the early differentiation of the germ layers in monotremes stems largely from two articles by J. P. Hill and T. Thomson Flynn. The completeness of their account was due to the large series of echidna ovaries and eggs collected on Tasmania by Flynn, an Australian biologist of whom a brief account is given. A striking finding in the oocyte and early embryo of monotremes was the presence of a latebra connected to the yolk bed beneath the germinal disc as described in birds and several reptiles. A further resemblance was the presence early in vitellogenesis of a striate zone beneath the zona pellucida. Cleavage resulted first in a lens-shaped blastodisc encircled by cells called vitellocytes that later fused to form a germ-ring. The blastodisc gave rise to a blastoderm that eventually became unilaminar but comprised two cell types identified as ectoderm and primitive endoderm. Eventually these segregated into two layers and formed a blastula. This sequence resembled that in marsupials except there was no obvious distinction between future embryonic and extra-embryonic regions. As the blastoderm extended over the surface of the yolk, it was preceded by the germ-ring that eventually played a role in forming the yolk navel. This was a unique feature of monotreme development. It is shown that Flynn played an important role in analysis of the material as well as in its collection.

High-throughput single-cell sequencing (scSeq) technologies are revolutionizing the ability to molecularly profile B and T lymphocytes by offering the opportunity to simultaneously obtain information on adaptive immune receptor repertoires (VDJ repertoires) and transcriptomes. An integrated quantification of immune repertoire parameters, such as germline gene usage, clonal expansion, somatic hypermutation and transcriptional states opens up new possibilities for the high-resolution analysis of lymphocytes and the inference of antigen-specificity. While multiple tools now exist to investigate gene expression profiles from scSeq of transcriptomes, there is a lack of software dedicated to single-cell immune repertoires. Here, we present Platypus, an open-source software platform providing a user-friendly interface to investigate B-cell receptor and T-cell receptor repertoires from scSeq experiments. Platypus provides a framework to automate and ease the analysis of single-cell immune repertoires while also incorporating transcriptional information involving unsupervised clustering, gene expression and gene ontology. To showcase the capabilities of Platypus, we use it to analyze and visualize single-cell immune repertoires and transcriptomes from B and T cells from convalescent COVID-19 patients, revealing unique insight into the repertoire features and transcriptional profiles of clonally expanded lymphocytes. Platypus will expedite progress by facilitating the analysis of single-cell immune repertoire and transcriptome sequencing.

The occurrence of biofluorescence across Mammalia is an area of active study. We examined three specimens of the platypus (Ornithorhynchus anatinus) from Tasmania and New South Wales, Australia, housed in the Field Museum of Natural History (Chicago, Illinois, USA) and the University of Nebraska State Museum (Lincoln, Nebraska, USA) under visible light and ultraviolet (UV) light. The pelage of the animals appeared uniformly brown under visible light and green or cyan under UV light, due to fluoresced wavelengths that peaked around 500 nm. Our observations are the first report of biofluorescence in a monotreme mammal.

We have used a quantitative statistical approach to compare the pace of development in the cerebellum and precerebellar systems relative to body size in monotremes and metatherians with that in eutherians (rodents and humans). Embryos, fetuses, and early postnatal mammals were scored on whether key structural events had been reached in the development of the cerebellum itself (CC-corpus cerebelli; 10 milestones), or the pontine and inferior olivary precerebellar nuclear groups (PC; 4 milestones). We found that many early cerebellar and precerebellar milestones (e.g., formation of Purkinje cell layer and deep cerebellar nuclei) were reached at a smaller absolute body length in both metatherians and eutherians together, compared to monotremes. Some later milestones (e.g., formation of the external granular layer and primary fissuration) were reached at a smaller body length in metatherians than eutherians. When the analysis was performed with proportional body length expressed as a natural log-transformed ratio of length at birth, milestones were reached at a much smaller proportional body length in rodents and humans than in the metatherians or monotremes. The findings are consistent with the slower pace of metabolic activity and embryonic development in monotremes. They also indicate slightly advanced maturation of some early features of the cerebellum in some metatherians (i.e., early cerebellar development in dasyurids relative to body size), but do not support the notion of an accelerated development of the cerebellum to cope with the demands of early birth. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1998-2013, 2020. © 2019 American Association for Anatomy.

Fruits reaching the floor of tropical forests constitute an attractive resource for a variety of mammals. Study of the characteristics of the frugivory interaction can help to advance in the understanding of the mechanisms favoring animal’s coexistence. However, there are few studies focused on analyzing patterns of activity of mammals feeding on fruits in the forest floor. Camera traps were used to record consumption of Licania platypus and Pouteria sapota fruits by Cuniculus paca, Dasyprocta punctata, Nasua narica, Dycotiles crassus and Tapirella bairdii. Patterns of mammal activity were characterized based on the day, time and tree in which they were recorded. Overlap in daily (delta coefficient) and spatial occurrence (same tree and day, Jaccard, Ochiai indices and V ratio) was assessed. High segregation in the activity of frugivores occurred during the day (mean 0.291 and 0.191 for L. platypus and P. sapota, respectively) and among trees/days (max. Jaccard = 0.14 and 0.19 for L. platypus and P. sapota, respectively). Our results suggest that activity overlap among mammalian frugivores feeding in the forest floor is lower than expected. This likely relates to the fact we conducted our analysis at a finer detail than previous studies (for example those focusing exclusively on dietary overlap). Thus, our study increases our understanding of the possible factor that can favor coexistence of tropical frugivorous mammals.

We have made quantitative volumetric analyses of cerebral cortical (pallial) structures in the brains of three species of monotreme (Ornithorhynchus anatinus, Tachyglossus aculeatus, Zaglossus bruijni) and compared the findings with similar measurements in a range of therian mammals (6 marsupials and 50 placentals). We have found that although the iso- and periallocortical grey matter volume of the monotremes is about what would be expected for their brain size, the proportion of iso- and periallocortical white matter in monotremes is substantially lower than that in the forebrains of therians. This suggests that the forebrains of the three monotremes have fewer association, commissural and/or projection connections than those of similarly sized forebrains of therian mammals. We also found that the iso- and periallocortex of the platypus is relatively smooth-surfaced compared to similarly sized brains of therian mammals, with a distinct caudal shift in the positioning of cortical white matter in the forebrain, consistent with expansion of the posterior thalamic radiation. Central laminated olfactory structures (anterior olfactory nucleus and piriform cortex) are large in the tachyglossid monotremes (Tachyglossus aculeatus and Zaglossus bruijni) and large in xenarthran placental mammals, suggesting convergence of the forebrain structure of monotreme formivores with that of similarly specialized therians like the xenarthrans Myrmecophaga tridactyla and Dasypus novemcinctus. Fil: Ashwell, Ken. University of New South Wales; Australia Fil: Gurovich, Yamila. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Centro de Investigación Esquel de Montaña y Estepa Patagóica. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales - Sede Esquel. Centro de Investigación Esquel de Montaña y Estepa Patagónica; Argentina. University of South Wales; Australia

The platypus (Ornithorhynchus anatinus) is one of the world’s most evolutionarily distinct mammals, one of five extant species of egg-laying mammals, and the only living species within the family Ornithorhynchidae. Modern platypuses are endemic to eastern mainland Australia, Tasmania, and adjacent King Island, with a small introduced population on Kangaroo Island, South Australia, and are widely distributed in permanent river systems from tropical to alpine environments. Accumulating knowledge and technological advancements have provided insights into many aspects of its evolutionary history and biology but have also raised concern about significant knowledge gaps surrounding distribution, population sizes, and trends. The platypus’ distribution coincides with many of Australia’s major threatening processes, including highly regulated and disrupted rivers, intensive habitat destruction, and fragmentation, and they were extensively hunted for their fur until the early 20th century. Emerging evidence of local population declines and extinctions identifies that ecological thresholds have been crossed in some populations and, if threats are not addressed, the species will continue to decline. In 2016, the IUCN Red Listing for the platypus was elevated to “Near Threatened,” but the platypus remains unlisted on threatened species schedules of any Australian state, apart from South Australia, or nationally. In this synthesis, we review the evolutionary history, genetics, biology, and ecology of this extraordinary mammal and highlight prevailing threats. We also outline future research directions and challenges that need to be met to help conserve the species.

The platypus (Ornithorhynchus anatinus) is an egg-laying monotreme mammal whose ancestors diverged ∼166 million years ago from the evolutionary pathway that eventually gave rise to both marsupial and eutherian mammals. Consequently, its genome is an extraordinary amalgam of both ancestral reptilian and derived mammalian features. To gain insight into the evolution of mammalian pluripotency, we have generated induced pluripotent stem cells from the platypus (piPSCs). Deep sequencing of the piPSC transcriptome revealed that piPSCs robustly express the core eutherian pluripotency factors POU5F1/OCT4, SOX2, and NANOG. Given the more extensive role of SOX3 over SOX2 in avian pluripotency, our data indicate that between 315 and 166 million years ago, primitive mammals replaced the role of SOX3 in the vertebrate pluripotency network with SOX2. DAX1/NR0B1 is not expressed in piPSCs and an analysis of the platypus DAX1 promoter revealed the absence of a proximal SOX2-binding DNA motif known to be critical for DAX1 expression in eutherian pluripotent stem cells, suggesting that the acquisition of SOX2 responsiveness by DAX1 has facilitated its recruitment into the pluripotency network of eutherians. Using the RNAseq data, we were also able to demonstrate that in both fibroblasts and piPSCs, the expression ratio of X chromosomes to autosomes (X1-5 X1-5:AA) is approximately equal to 1, indicating that there is no upregulation of X-linked genes. Finally, the RNAseq data also allowed us to explore the process of X-linked gene inactivation in the platypus, where we determined that for any given gene, there is no preference for silencing of the maternal or paternal allele; that is, within a population of cells, the silencing of X-linked genes is not imprinted.

Snakebite envenomation is common in all inhabited continents of the world, with more than 100,000 fatalities occurring every year. Depending on the snake species involved, envenomation includes often disabling intense local tissue damage with inflammation, pain and myonecrosis, caused in part by molecules known as myotoxins. Myotoxins are found in the venoms of several snakes, and their homologs are also found in lizards and mammals (the Platypus). These small peptide toxins show a unique structural/physicochemical resemblance to β-defensins, which are anti-microbial peptides (AMPs) involved in the resistance of epithelial surfaces to microbial colonization. These similarities suggest a possible common phylogenetic and/or functional association among these myotoxic and anti-microbial peptides. These β-defensins seems to play a key role as toxins in the envenomation process by activating the immune system. Crotamine, purified from the venom of the South American Rattlesnake Crotalus durissus terrificus, is one of the first myotoxins to be characterized. In addition to its role in rapid prey incapacitation, several therapeutic applications of myotoxin a like peptides (mainly crotamine), for instance, as antitumor and anti-microbial agents, have been characterized and are listed in this chapter. The several different characterized biological activities exhibited by these myotoxin-like peptides are mostly dependent on their three-dimensional structure and positively charged surface (cationic feature). Herein, we present the main known myotoxins of venoms, introduce some alternatives for neutralizing their effects in snakebite envenomations, and discuss their mechanism of action(s), designated biological functions, and structural/functional similarities with AMPs (β-defensins). This chapter will therefore discuss the structure, biological activities and differences/similarities shared between the toxins with antitumoral/anti-microbial activities (namely, myotoxin-a and crotamine) and the immune effector (defensin-like) polypeptides. Interestingly, toxins and immune effectors share similar evolutionary and structural patterns, and they both seem to have evolved to defend against the threats of potential predators, microbial invasions and/or malignant cells.

Platypus cylindrus (Fabricius, 1792) Records. LUG [Nikulina et al., 2015: 8]., Published as part of Arzanov, Yu. G., Martynov, V. V. & Nikulina, T. V., 2021, A contribution to the fauna of weevil beetles (Coleoptera: Curculionoidea) of the Central Donbass, pp. 5-44 in Caucasian Entomological Bulletin 17 (1) on page 41, DOI: 10.23885/181433262021171-544, http://zenodo.org/record/8145644, {"references":["Nikulina T., Mandelshtam M., Petrov A., Nazarenko V., Yunakov N. 2015. A survey of the weevils of Ukraine. Bark and ambrosia beetles (Coleoptera: Curculionidae: Platypodinae and Scolytinae). Zootaxa. 3912 (1): 1 - 61. DOI: 10.11646 / zootaxa. 3912.1.1"]}

The platypus is a semi-aquatic mammal, endemic to freshwater habitats of eastern Australia. There are gaps in the understanding of platypus movement behaviour within river systems, including spatial and temporal organization of individuals. We tracked movements of 12 platypuses on the regulated Snowy and Mitta Mitta Rivers for up to 12-months, the longest continuous tracking of platypus using acoustic telemetry. Platypuses remained relatively localized, occupying 0.73–8.45 km of river over 12 months, consistent with previous tracking studies over shorter periods. Males moved further than females, and larger males had higher cumulative movements, suggesting a possible relationship to metabolic requirements. Platypuses moved greater distances on the Mitta Mitta River, possibly associated with impacts of altered flow regimes to their macroinvertebrate diet. Increased movements and diurnal activity during winter were primarily driven by males, possibly attributable to breeding behaviours, rather than increased costs of winter foraging. Evidence for relatively small movements has implications for declining populations, given areas of localised declines are unlikely to be supplemented by migrating platypuses, especially when dispersal is restricted by dam walls. Understanding platypus movement behaviour is pertinent for their conservation, as water resource development and habitat modification continue to reduce connectivity between populations across their distribution.

For more than a decade, Josh Griffiths has been trapping the elusive venomous mammals to survey the status of their population. For more than a decade, Josh Griffiths has been trapping the elusive venomous mammals to survey the status of their population.

Genetic differentiation is a vital aspect of population genetics and is a direct consequence of evolutionary forces acting on genetic diversity. By interpreting patterns of genetic differentiation, we can detect, infer and estimate the extent to which natural selection, genetic drift and gene flow affect genetic diversity. In this thesis, estimation of genetic differentiation is used as a tool to answer the following questions, three mainly theoretical, and the other an applied study on platypus conservation. 1. Can a form of linked selection termed associative overdominance (AOD) explain lower levels of genetic differentiation between populations (FST), and higher heterozygosity, than expected under neutrality in experimental populations (Drosophila melanogaster) and in a feral population (Bos taurus)? 2. Under which circumstances does AOD affect FST and heterozygosity? 3. Can AOD be detected in natural populations? 4. Do dams restrict gene flow among platypus groups? AOD is triggered by the occurrence of recessive deleterious mutations that are physically linked and form haplotypes when recombination events are scarce, as in small populations. When haplotypes within an individual contain recessive deleterious mutations at different positions, a heterozygote for two different haplotypes is fitter than either one of the homozygotes. As a result, heterozygosity is higher, and FST lower than expected under neutrality. Here, using feral, experimental and computer- simulated populations, it is demonstrated how AOD might be prevalent in small populations, and a framework for predicting and detecting AOD is provided. The extent to which dams disrupt gene flow among platypus populations is investigated by using four rivers regulated by dams and three unregulated rivers. It was found that: genetic differentiation is significantly correlated with the number of generations since the dams were built; populations and individuals separated by dams are genetically more different than otherwise; and areas of high genetic differentiation coincide with the location of dams. It is suggested that dams jeopardise the long-term viability of platypus populations.

The objective of this study was to biomonitor the effects of potential environmental pollutants in urban-stream waters, on fish health. Pale chub (Zacco platypus), a dominant species in the Korea urban stream waters, was chosen and biomonitoring indicators for the different spatial characteristics were tailored in an urban watershed. Biological responses including biotic-somatic index as well as gonadal development phase and plasma steroids levels, and the biochemical responses, ethoxyresorufin-o-deethylase (EROD) and acetylcholinesterase (AChE) activities, were measured. No significant difference was observed in the length-weight relationship between the up-stream waters and the down-stream waters. However, changes in the gonad-somatic index (GSI) levels, plasma 17β-estradiol (E2) levels, and mature oocyte frequencies in the female fish collected during the spawning season were observed in the down-stream waters at each monitoring site. Moreover, intersex condition (testis-ova) in the male fish in down-stream waters was recorded, even if it was just one fish. Although no significant difference was observed in the EROD and AChE activities between the up-stream waters and the down-stream waters, changes in the reproductive biomarker levels, including the GSI levels, plasma E2 levels, and gonadal maturation, lead to variable biomonitoring endpoints between the spatial different sites. These results imply that exposure to the down-stream waters can cause reproductive impairment in wild Z. platypus, individual variability in the biological responses further indicate the reproductive health was affected more by the down-stream waters than the up-stream waters. The finding from this study can provide the biomonitoring endpoint on the wild fish health in urban watershed that is crucial to the early risk assessment of its biological impacts. More multi-biomarkers studies reflecting the variation in the biological organization of wild fish and, therefore, the effects of urban-stream waters in the fish health are warranted.

Platypuses (Ornithorhynchus anatinus) inhabit the permanent rivers and creeks of eastern Australia, from north Queensland to Tasmania, but are experiencing multiple and synergistic anthropogenic threats. Baseline information of health is vital for effective monitoring of populations but is currently sparse for mainland platypuses. Focusing on seven hematology and serum chemistry metrics as indicators of health and nutrition (packed cell volume (PCV), total protein (TP), albumin, globulin, urea, creatinine, and triglycerides), we investigated their variation across the species’ range and across seasons. We analyzed 249 unique samples collected from platypuses in three river catchments in New South Wales and Victoria. Health metrics significantly varied across the populations’ range, with platypuses from the most northerly catchment, having lower PCV, and concentrations of albumin and triglycerides and higher levels of globulin, potentially reflecting geographic variation or thermal stress. The Snowy River showed significant seasonal patterns which varied between the sexes and coincided with differential reproductive stressors. Male creatinine and triglyceride levels were significantly lower than females, suggesting that reproduction is energetically more taxing on males. Age specific differences were also found, with juvenile PCV and TP levels significantly lower than adults. Additionally, the commonly used body condition index (tail volume index) was only negatively correlated with urea, and triglyceride levels. A meta-analysis of available literature revealed a significant latitudinal relationship with PCV, TP, albumin, and triglycerides but this was confounded by variation in sampling times and restraint methods. We expand understanding of mainland platypuses, providing reference intervals for PCV and six blood chemistry, while highlighting the importance of considering seasonal variation, to guide future assessments of individual and population condition.

Gene-expression programs define shared and species-specific phenotypes, but their evolution remains largely uncharacterized beyond the transcriptome layer 1 . Here we report an analysis of the co-evolution of translatomes and transcriptomes using ribosome-profiling and matched RNA-sequencing data for three organs (brain, liver and testis) in five mammals (human, macaque, mouse, opossum and platypus) and a bird (chicken). Our within-species analyses reveal that translational regulation is widespread in the different organs, in particular across the spermatogenic cell types of the testis. The between-species divergence in gene expression is around 20% lower at the translatome layer than at the transcriptome layer owing to extensive buffering between the expression layers, which especially preserved old, essential and housekeeping genes. Translational upregulation specifically counterbalanced global dosage reductions during the evolution of sex chromosomes and the effects of meiotic sex-chromosome inactivation during spermatogenesis. Despite the overall prevalence of buffering, some genes evolved faster at the translatome layer-potentially indicating adaptive changes in expression; testis tissue shows the highest fraction of such genes. Further analyses incorporating mass spectrometry proteomics data establish that the co-evolution of transcriptomes and translatomes is reflected at the proteome layer. Together, our work uncovers co-evolutionary patterns and associated selective forces across the expression layers, and provides a resource for understanding their interplay in mammalian organs.

Monotremes diverged from therian mammal ancestors approximately 184 million years ago and have a number of novel reproductive characteristics. One in particular is their penile morphology. There are differences between echidna and platypus phalluses, but both are somewhat similar in structure to the reptilian phallus. The echidna penis consists of 4 rosette glans, each of which contains a termination of the quadrifurcate urethra, but it appears that only 2 of the 4 glans become erect at any one time. Despite this, only a few historical references describe the structure of the echidna penis and none provides an explanation for the mechanisms of unilateral ejaculation. This study confirmed that the echidna penis contains many of the same overall structures and morphology as other mammalian penises and a number of features homologous with reptiles. The corpus cavernosum is well supplied with blood, extends up to the base of the glans penis and is primarily responsible for erection. However, the echidna possesses 2 distinct corpora spongiosa separated by a septum, each of which surround the urethra only distal to the initial urethral bifurcation in the glans penis. Together with the bifurcation of the main penile artery, this provides a mechanism by which blood flow could be directed to only one corpus spongiosum at a time to maintain an open urethra that supplies 2 of the 4 glans to facilitate unilateral ejaculation.

Predators can have strong impacts on prey populations, with cascading effects on lower trophic levels. Although such effects are well known in aquatic ecosystems, few studies have explored the influence of predatory aquatic mammals, or whether the same predator has similar effects in contrasting systems. We investigated the effects of platypus (Monotremata: Ornithorhynchus anatinus) on its benthic invertebrate prey, and tested predictions that this voracious forager would more strongly affect invertebrates—and indirectly, epilithic algae—in a mesotrophic lake than in a dynamic stream ecosystem. Hypotheses were tested using novel manipulative experiments involving platypus-exclusion cages. Platypuses had strongly suppressive effects on invertebrate prey populations, especially detritivores and omnivores, but weaker or inconsistent effects on invertebrate taxon richness and composition. Contrary to expectation, predation effects were stronger in the stream than the lake; no effects were found on algae in either ecosystem due to weak effects of platypuses on herbivorous invertebrates. Platypuses did not cause redistribution of sediment via their foraging activities. Platypuses can clearly have both strong and subtle effects on aquatic food webs that may vary widely between ecosystems and locations, but further research is needed to replicate our experiments and understand the contextual drivers of this variation.

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., eLife digest The defining feature of all mammals is how the jaw works. Fish, reptiles and other animals with backbones have a lower jaw made of many bones fused together, one of which connects to the upper jaw. The lower jaw in mammals, however, is made of a single bone that connects with the upper jaw using a completely unique jaw joint. This new joint emerged as the ancestors of all mammals split from the reptiles around 200 million years ago. The bones that formed the original jaw joint ended up in the middle ear in mammals and switched to a role in hearing. Nowadays, there are three types of mammals: the placentals, marsupials and monotremes (the egg laying mammals). In mice, humans and other placental mammals, the skeleton of the adult jaw joint forms in the embryo before birth. However, marsupials (such as kangaroos and opossums) and monotremes (platypuses and echidnas) are born at a much earlier embryonic stage, before the adult jaw joint has formed. It is therefore unclear how newborn marsupials and monotremes are able to move their jaws to feed on milk from their mother. Anthwal et al. compared how the jaw develops in mice, opossums, platypuses and echidnas before and after the adult jaw joint becomes functional. The experiments showed that young echidnas, platypuses and opossums use their middle ear bones to articulate the lower jaw with the head before the adult jaw joint forms. In young opossums, the ear bones form a cushion to support the jaw. In juvenile platypuses a double joint is evident, with the ear bones forming a joint at the same time as the newly formed adult jaw joint, similar to the situation observed in fossils of mammal ancestors. The experiments also indicated that mice and other placental mammals may potentially use their ear bones to support the jaw before birth. These findings shed light on why the ear and jaw have such a close connection in mammals. In humans, the ear and jaw bones are still connected by ligaments, explaining why trauma to the jaw joint can cause dislocation of the ear bones. Similarly, defects in the development of the jaw can impact the ear, such as in Treacher Collins Syndrome, where in some cases the jaw joint fails to form and the ear bones appear to try and take this role. Understanding how the ear and jaw evolved will help us understand why they look like they do and why a defect in one can have knock-on consequences for the other.

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 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 or all mammals.

The newly identified liver-enriched gene 1 (LEG1) encodes a protein with a characteristic domain of unknown function 781 (DUF781/LEG1), constituting a protein family with only one member in mammals. A functional study in zebrafish suggested that LEG1 genes are involved in liver development, while the platypus LEG1 homolog, Monotreme Lactation Protein (MLP), which is enriched in the mammary gland and milk, acts as an antibacterial substance. However, no functional studies on eutherian LEG1s have been published to date. Thus, we here report the first functional prediction study at the cellular level. As previously reported, eutherian LEG1s can be classified into three paralogous groups. Pigs have all three LEG1 genes (pLEG1s), while humans and mice have retained only LEG1a. Hence, pLEG1s might represent an ideal model for studying LEG1 gene functions. RNA-seq was performed by the overexpression of pLEG1s and platypus MLP in HepG2 cells. Enrichment analysis showed that pLEG1a and pLEG1b might exhibit little function in liver cells; however, pLEG1c is probably involved in the endoplasmic reticulum (ER) stress response and protein folding. Additionally, gene set enrichment analysis revealed that platypus MLP shows antibacterial activity, confirming the functional study in platypus. Therefore, our study showed from the transcriptomic perspective that mammalian LEG1s have different functions in liver cells due to the subfunctionalization of paralogous genes.

Atypical TCRδ found in sharks, amphibians, birds, and monotremes and TCRμ found in monotremes and marsupials are TCR chains that use Ig or BCR-like variable domains (VHδ/Vμ) rather than conventional TCR V domains. These unconventional TCR are consistent with a scenario in which TCR and BCR, although having diverged from each other more than 400 million years ago, continue to exchange variable gene segments in generating diversity for Ag recognition. However, the process underlying this exchange and leading to the evolution of these atypical TCR receptor genes remains elusive. In this study, we identified two TCRα/δ gene loci in the Chinese alligator (Alligator sinensis). In total, there were 144 V, 154 Jα, nine Jδ, eight Dδ, two Cα, and five Cδ gene segments in the TCRα/δ loci of the Chinese alligator, representing the most complicated TCRα/δ gene system in both genomic structure and gene content in any tetrapod examined so far. A pool of 32 VHδ genes divided into 18 subfamilies was found to be scattered over the two loci. Phylogenetic analyses revealed that these VHδ genes could be related to bird VHδ genes, VHδ/Vμ genes in platypus or opossum, or alligator VH genes. Based on these findings, a model explaining the evolutionary pattern of atypical TCRδ/TCRμ genes in tetrapods is proposed. This study sheds new light on the evolution of TCR and BCR genes, two of the most essential components of adaptive immunity.