Monotreme Species Research Articles

Applying a modified streamlined disease risk analysis framework to a platypus conservation translocation, with special consideration for the conservation of ecto- and endoparasites

Platypuses are the world's most evolutionarily distinct mammal and have several host-specific ecto- and endoparasites. With platypus populations declining, consideration should also be given to preserving these high conservation priority parasites alongside their charismatic host. A disease risk analysis (DRA) was performed for a platypus conservation translocation, using a modified streamlined methodology that incorporated a parasite conservation framework. DRA frameworks rarely consider parasite conservation. Rather, parasites are typically considered myopically in terms of the potential harm they may cause their host. To address this, a previously proposed parasite conservation framework was incorporated into an existing streamlined DRA methodology. Incorporation of the two frameworks was achieved readily, although there is opportunity for further refinement of this process. This DRA is significant as it is the first performed for any monotreme species, and implements the emerging approach of balancing the health and disease risk of the host with parasite conservation.

A diverse assemblage of monotremes (Monotremata) from the Cenomanian Lightning Ridge fauna of New South Wales, Australia

Six species of monotremes, three newly described here, occur in the Cenomanian fossil fauna from Lightning Ridge in northeastern New South Wales, Australia, making it the most diverse monotreme assemblage on record. Four species are known from a single specimen, suggesting that diversity remains underrepresented. No other mammal lineages are known from the deposit, although the absence of smaller taxa is likely due to sampling biases introduced by the opal mining process. Early-Late Cretaceous monotremes thus clearly diversified in Australia during the absence of other large-bodied mammalian competitors; and subsequently occupied a wider range of ecological niches than at any other time in their evolutionary history. One new taxon described herein represents a previously unknown monotreme family that combines marked elongation and torsion of the dentary with teinolophid character states, including the retention of five molars. Another shares dental features with ornithorhynchids, while the third is a possible diminutive steropodontid and simultaneously represents the smallest-bodied post-Barremian monotreme. Additional material of Steropodon galmani is also documented, confirming that a Meckelian groove is rudimentary or absent in this taxon, thus adding to the morphological understanding of this unusual monotreme. Lastly, we posit that the loss of teeth in ornithorhynchids may have occurred during the Pleistocene as a result of competition with aquatic hydromyin rodents dispersing to Australia from New Guinea. Timothy F. Flannery [tim.fridtjof.flannery@gmail.com] Kristofer M. Helgen [Kris.Helgen@Australian.Museum], and Matthew McCurry [Matthew.McCurry@austmus.gov.au] Australian Museum, 1 William Street Sydney, New South Wales 2000, Australia; Earth and Sustainability Research Centre, School of Biological Earth and Environmental Science, The University of New South Wales, Sydney New South Wales 2052, Australia Thomas H. Rich [trich@museum.vic.gov.au], Museums Victoria, PO Box 666, Melbourne, Victoria 3001, Australia; Patricia Vickers-Rich [pat.rich@monash.edu], School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia; Museums Victoria, PO Box 666, Melbourne, Victoria 3001, Australia; Curtin University, Bentley Street, Perth, Western Australia 6102, Australia Elizabeth T Smith [elizabethtsmith@exemail.com.au ; contact@australianopalcentre.com] Australian Opal Centre, PO Box 229, Lightning Ridge, New South Wales 2834, Australia.

All-a-glow: spectral characteristics confirm widespread fluorescence for mammals.

Mammalian fluorescence has been reported from numerous species of monotreme, marsupial and placental mammal. However, it is unknown how widespread this phenomenon is among mammals, it is unclear for many species if these observations of 'glowing' are true fluorescence and the biological function of fluorescence remains undetermined. We examined a wide range of mammal species held in a museum collection for the presence of apparent fluorescence using UV light, and then analysed a subset of preserved and non-preserved specimens by fluorescent spectroscopy at three different excitation wavelengths to assess whether the observations were fluorescence or optical scatter, and the impact of specimen preservation. We also evaluated if fluorescence was related to biological traits. We found that fluorescence is widespread in mammalian taxa; we identified examples of the phenomena among 125 species representing all 27 living mammalian orders and 79 families. For a number of model species, there was no evidence of a corresponding shift in the emission spectra when the wavelength of excitation was shifted, suggesting that observations of 'glowing' mammals were indeed fluorescence. Preservation method impacted the intensity of fluorescence. Fluorescence was most common and most intense among nocturnal species and those with terrestrial, arboreal and fossorial habits, with more of their body being more fluorescent. It remains unclear if fluorescence has any specific biological role for mammals. It appears to be a ubiquitous property of unpigmented fur and skin but may function to make these areas appear brighter and therefore enhance visual signalling, especially for nocturnal species.

Clade-specific forebrain cytoarchitectures of the extinct Tasmanian tiger

The thylacine, or Tasmanian tiger, is the largest of modern-day carnivorous marsupials and was hunted to extinction by European settlers in Australia. Its physical resemblance to eutherian wolves is a striking example of evolutionary convergence to similar ecological niches. However, whether the neuroanatomical organization of the thylacine brain resembles that of canids and how it compares with other mammals remain unknown due to the scarcity of available samples. Here, we gained access to a century-old hematoxylin-stained histological series of a thylacine brain, digitalized it at high resolution, and compared its forebrain cellular architecture with 34 extant species of monotremes, marsupials, and eutherians. Phylogenetically informed comparisons of cortical folding, regional volumes, and cell sizes and densities across cortical areas and layers provide evidence against brain convergences with canids, instead demonstrating features typical of marsupials, and more specifically Dasyuridae, along with traits that scale similarly with brain size across mammals. Enlarged olfactory, limbic, and neocortical areas suggest a small-prey predator and/or scavenging lifestyle, similar to extant quolls and Tasmanian devils. These findings are consistent with a nonuniformity of trait convergences, with brain traits clustering more with phylogeny and head/body traits with lifestyle. By making this resource publicly available as rapid web-accessible, hierarchically organized, multiresolution images for perpetuity, we anticipate that additional comparative insights might arise from detailed studies of the thylacine brain and encourage researchers and curators to share, annotate, and preserve understudied material of outstanding biological relevance.

Coevolutionary analysis of Forkhead box protein P3 and its physical binary interactors E3 ubiquitin-protein ligase CHIP, Zfp-90, and nuclear receptor ROR-α.

Forkhead box protein P3 (FOXP3) is known to orchestrate the development and maintenance of T regulatory cells, a cell population specialized in immune suppression and peripheral immune tolerance. FOXP3 activity is fine-tuned through its interaction with several protein-binding partners. By using IntAct database, we retrieved three physical binary interactors: E3 ubiquitin-protein ligase CHIP, Zfp-90, and nuclear receptor ROR-α. Coevolution clusters between FOXP3 and its interactors were identified with the use of iBIS2 algorithm, the iterative version of BIS/BIS2. Most of the coevolving pairs came from some species of monotremes and marsupials, as well as from a group of bats, thus suggesting that protein interactions of FOXP3 with its partners may be changed and/or modulated during mammalian speciation. Furthermore, our analysis would suggest the occurrence of a determinant role of FOXP3 in suppressing pregnancy alloreactions in placental mammals. Similarly, FOXP3, through its interaction with different protein interaction mechanisms, would explain the unique control of inflammatory response to infections in bats. By identifying several inter-protein clusters between the different protein pairs, our findings may provide a guide for new therapeutic approaches to modulate T regulatory suppression and/or enhance immune tolerance.

A review of the function and evolution of the cecal appendix.

Since its initial discovery in the 1500s, the cecal appendix has been an anatomical structure of great intrigue, notorious for its inconvenient tendency to become inflamed and often require surgical intervention. Appendicitis is one of the most common indications for emergency abdominal surgery, costing healthcare systems billions of dollars globally and causing tens of thousands of deaths annually. Yet, recent studies have indicated that the appendix may serve important protective functions in fortifying the body's immune response against invading pathogens and re-inoculating the gut with commensal bacteria after periods of gastrointestinal illness. While the cecal appendix was once believed to be a synapomorphy of hominoids (humans and other great apes), recent studies suggested that it is a recurrent trait found in several other species of primates, rodents, lagomorphs, marsupials, and monotremes. Mapping appendiceal and other gastrointestinal traits across a mammalian consensus phylogeny revealed that the cecal appendix has evolved independently numerous times throughout mammalian evolution, significantly more than would be expected due to chance alone, suggesting that the appendix is adaptively advantageous. However, attempts to identify an overarching ecological, behavioral, dietary, or environmental factor driving some species to evolve an appendix have been largely unsuccessful, indicating that the cecal appendix has a complex and diverse evolutionary history. This review discusses the current understanding of the pathophysiology, evolution, and possible functions of the appendix, both within humans and broadly across the class Mammalia.

Species identification of Australian marsupials using collagen fingerprinting

The study of faunal remains from archaeological sites is often complicated by the presence of large numbers of highly fragmented, morphologically unidentifiable bones. In Australia, this is the combined result of harsh preservation conditions and frequent scavenging by marsupial carnivores. The collagen fingerprinting method known as zooarchaeology by mass spectrometry (ZooMS) offers a means to address these challenges and improve identification rates of fragmented bones. Here, we present novel ZooMS peptide markers for 24 extant marsupial and monotreme species that allow for genus-level distinctions between these species. We demonstrate the utility of these new peptide markers by using them to taxonomically identify bone fragments from a nineteenth-century colonial-era pearlshell fishery at Bandicoot Bay, Barrow Island. The suite of peptide biomarkers presented in this study, which focus on a range of ecologically and culturally important species, have the potential to significantly amplify the zooarchaeological and paleontological record of Australia.

Quantitative analysis of cerebellar morphology in monotreme, metatherian and eutherian mammals

To superficial inspection, the mammalian cerebellum appears to be a stereotypical structure that varies little in morphology across mammals. In the present study, the volumes of components of the corpus cerebelli, foliation of the cerebellar cortex and the volumes of the pontine and deep cerebellar nuclei have been measured and compared in three species of monotreme, 90 species of marsupial and 57 species of eutherian mammal. In all three mammalian groups, the volume of the corpus cerebelli scales isometrically with brain volume, and pontine nuclear volume also scales isometrically with cerebellar volume. The ratio of hemisphere to vermal cerebellar cortex is comparable in all mammals at small cerebellar volume, but elaboration of cerebellar hemispheres is largely confined to large cerebella of eutherian mammals. At small cerebellar volumes, diprotodontid metatherians have proportionally large cerebellar hemispheres compared to non-diprotodontid metatherians, and metatherian cerebella in general have a high volume of central white matter for a given cerebellar cortex volume compared to eutherians. The degree of foliation of the cerebellum scales similarly in therian mammals, but is relatively low in the monotremes for the volume of their corpus cerebelli. Among metatherians, cerebellar foliation is stronger among diprotodontid as compared to non-diprotodontids. Although the cerebellum has a similar structure in all mammals, there are subtle differences in structure between different mammal groups with possible functional implications.

Quantitative analysis of forebrain pallial morphology in monotremes and comparison with that in therians

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.

MIR sequences recruit zinc finger protein ZNF768 to expressed genes

Mammalian-wide interspersed repeats (MIRs) are retrotransposed elements of mammalian genomes. Here, we report the specific binding of zinc finger protein ZNF768 to the sequence motif GCTGTGTG (N20) CCTCTCTG in the core region of MIRs. ZNF768 binding is preferentially associated with euchromatin and promoter regions of genes. Binding was observed for genes expressed in a cell type-specific manner in human B cell line Raji and osteosarcoma U2OS cells. Mass spectrometric analysis revealed binding of ZNF768 to Elongator components Elp1, Elp2 and Elp3 and other nuclear factors. The N-terminus of ZNF768 contains a heptad repeat array structurally related to the C-terminal domain (CTD) of RNA polymerase II. This array evolved in placental animals but not marsupials and monotreme species, displays species-specific length variations, and possibly fulfills CTD related functions in gene regulation. We propose that the evolution of MIRs and ZNF768 has extended the repertoire of gene regulatory mechanisms in mammals and that ZNF768 binding is associated with cell type-specific gene expression.

Mammalian development does not recapitulate suspected key transformations in the evolutionary detachment of the mammalian middle ear.

The ectotympanic, malleus and incus of the developing mammalian middle ear (ME) are initially attached to the dentary via Meckel's cartilage, betraying their origins from the primary jaw joint of land vertebrates. This recapitulation has prompted mostly unquantified suggestions that several suspected--but similarly unquantified--key evolutionary transformations leading to the mammalian ME are recapitulated in development, through negative allometry and posterior/medial displacement of ME bones relative to the jaw joint. Here we show, using µCT reconstructions, that neither allometric nor topological change is quantifiable in the pre-detachment ME development of six marsupials and two monotremes. Also, differential ME positioning in the two monotreme species is not recapitulated. This challenges the developmental prerequisites of widely cited evolutionary scenarios of definitive mammalian middle ear (DMME) evolution, highlighting the requirement for further fossil evidence to test these hypotheses. Possible association between rear molar eruption, full ME ossification and ME detachment in marsupials suggests functional divergence between dentary and ME as a trigger for developmental, and possibly also evolutionary, ME detachment. The stable positioning of the dentary and ME supports suggestions that a 'partial mammalian middle ear' as found in many mammaliaforms--probably with a cartilaginous Meckel's cartilage--represents the only developmentally plausible evolutionary DMME precursor.

Trypanosomes of Australian mammals: A review.

Approximately 306 species of terrestrial and arboreal mammals are known to have inhabited the mainland and coastal islands of Australia at the time of European settlement in 1788. The exotic Trypanosoma lewisi was the first mammalian trypanosome identified in Australia in 1888, while the first native species, Trypanosoma pteropi, was taxonomically described in 1913. Since these discoveries, about 22% of the indigenous mammalian fauna have been examined during the surveillance of trypanosome biodiversity in Australia, including 46 species of marsupials, 9 rodents, 9 bats and both monotremes. Of those mammals examined, trypanosomes have been identified from 28 host species, with eight native species of Trypanosoma taxonomically described. These native trypanosomes include T. pteropi, Trypanosoma thylacis, Trypanosoma hipposideri, Trypanosoma binneyi, Trypanosoma irwini, Trypanosoma copemani, Trypanosoma gilletti and Trypanosoma vegrandis. Exotic trypanosomes have also been identified from the introduced mammalian fauna of Australia, and include T. lewisi, Trypanosoma melophagium, Trypanosoma theileri, Trypanosoma nabiasi and Trypanosoma evansi. Fortunately, T. evansi was eradicated soon after its introduction and did not establish in Australia. Of these exotic trypanosomes, T. lewisi is the sole representative that has been reported from indigenous Australian mammals; morphological forms were recorded from two indigenous species of rodents (Hydromys chrysogaster and Rattus fuscipes). Numerous Australian marsupial species are potentially at risk from the native T. copemani, which may be chronically pathogenic, while marsupials, rodents and monotremes appear at risk from exotic species, including T. lewisi, Trypanosoma cruzi and T. evansi. This comprehensive review of trypanosome biodiversity in Australia highlights the negative impact of these parasites upon their mammalian hosts, as well as the threatening biosecurity concerns.

Molecular evolution of a novel marsupial S100 protein (S100A19) which is expressed at specific stages of mammary gland and gut development

S100 proteins are calcium-binding proteins involved in controlling diverse intracellular and extracellular processes such as cell growth, differentiation, and antimicrobial function. We recently identified a S100-like cDNA from the tammar wallaby (Macropus eugenii) stomach. Phylogentic analysis shows wallaby S100A19 forms a new clade with other marsupial and monotreme S100A19, while this group shows similarity to eutherian S100A7 and S100A15 genes. This is also supported by amino acid and domain comparisons. We show S100A19 is developmentally-regulated in the tammar wallaby gut by demonstrating the gene is expressed in the forestomach of young animals at a time when the diet consists of only milk, but is absent in older animals when the diet is supplemented with herbage. During this transition the forestomach phenotype changes from a gastric stomach into a fermentation sac and intestinal flora changes with diet. We also show that S100A19 is expressed in the mammary gland of the tammar wallaby only during specific stages of lactation; the gene is up-regulated during pregnancy and involution and not expressed during the milk production phase of lactation. Comparison of the tammar wallaby S100A19 protein sequence with S100 protein sequences from eutherian, monotreme and other marsupial species suggest the marsupial S100A19 has two functional EF hand domains, and an extended His tail. An evolutionary analysis of S100 family proteins was carried out to gain a better understanding of the relationship between the S100 family member functions. We propose that S100A19 gene/protein is the ancestor of the eutherian S100A7 gene/protein, which has subsequently modified its original function in eutherians. This modified function may have arisen due to differentiation of evolutionary pressures placed on gut and mammary gland developmental during mammal evolution. The highly regulated differential expression patterns of S100A19 in the tammar wallaby suggests that S100A19 may play a role in gut development, which differs between metatherians and eutherians, and/or include a potential antibacterial role in order to establish the correct flora and protect against spiral bacteria in the immature forestomach. In the mammary gland it may protect the tissue from infection at times of vulnerability during the lactation cycle.

Year-Long Presence of Eimeria echidnae and Absence of Eimeria tachyglossi In Captive Short-Beaked Echidnas (Tachyglossus aculeatus)

The short-beaked echidna ( Tachyglossus aculeatus ) is 1 of 5 extant species of monotreme, found only in Australia and Papua New Guinea. The aim of this study was to identify the species of coccidia present and establish a range of subclinical Eimeria spp. (Coccidia: Apicomplexa) oocyst shedding in echidnas from eastern Australia over 18 mo. The coccidia were detected in 89% (49/55) of fecal samples from 12 long-term monitored and healthy captive echidnas, 75% (3/4) of 4 healthy long-term captive echidnas, 83% (5/6) of 6 short-term captive echidnas, and 60% (6/10) of 10 wild echidnas. Echidnas captive for 4 to 23 yr shed 100-46,000 oocysts g(-1) of E. echidnae and remained clinically healthy during this study. Sub-adult and adult wild, and short-term captive, echidnas shed oocysts of both E. echidnae and E. tachyglossi . The lack of coccidia in juvenile short-beaked echidnas suggests these animals are probably non-immune and should not be placed in environments heavily contaminated with oocysts. In addition, no oocysts were found in captive long-beaked echidnas ( Zaglossus bartoni bartoni , n = 2) housed at Taronga Zoo. This study represents an important step in understanding the host-parasite interaction between coccidia and short-beaked echidnas.

Genetic structure and phylogeography of platypuses revealed by mitochondrial DNA

AbstractThe platypus Ornithorhynchus anatinus is an endemic monotreme species with a wide latitudinal distribution in eastern Australia, including Tasmania. Understanding of the phylogeography within this species is very limited at present and represents a gap in the documentation of Australia's unique biodiversity. We analysed mitochondrial DNA sequences (partial control region and complete cytochrome b, including portions of flanking tRNAs) of 74 individuals from across the distribution of the species. Phylogenetic analysis of the concatenated sequences corroborated the primary split within the platypus, showing two major clades: one from mainland Australia and the other from Tasmania/King Island. Estimates of divergence times suggest that these clades last shared a common mitochondrial ancestor ∼0.7–0.94 Ma. Using an extended dataset of partial control region sequences from 284 individuals, we found evidence of genetic structure between river basins, primarily within mainland Australia, as well as an additional divergent lineage in North‐eastern Australia. Overall, few haplotypes were shared between river basins. Analyses of molecular variance of the control region sequences indicated low rates of gene flow and significant divergence, particularly at the river basin and geographical area scales.

Immunome database for marsupials and monotremes

BackgroundTo understand the evolutionary origins of our own immune system, we need to characterise the immune system of our distant relatives, the marsupials and monotremes. The recent sequencing of the genomes of two marsupials (opossum and tammar wallaby) and a monotreme (platypus) provides an opportunity to characterise the immune gene repertoires of these model organisms. This was required as many genes involved in immunity evolve rapidly and fail to be detected by automated gene annotation pipelines.DescriptionWe have developed a database of immune genes from the tammar wallaby, red-necked wallaby, northern brown bandicoot, brush-tail possum, opossum, echidna and platypus. The resource contains 2,235 newly identified sequences and 3,197 sequences which had been described previously. This comprehensive dataset was built from a variety of sources, including EST projects and expert-curated gene predictions generated through a variety of methods including chained-BLAST and sensitive HMMER searches. To facilitate systems-based research we have grouped sequences based on broad Gene Ontology categories as well as by specific functional immune groups. Sequences can be extracted by keyword, gene name, protein domain and organism name. Users can also search the database using BLAST.ConclusionThe Immunome Database for Marsupials and Monotremes (IDMM) is a comprehensive database of all known marsupial and monotreme immune genes. It provides a single point of reference for genomic and transcriptomic datasets. Data from other marsupial and monotreme species will be added to the database as it become available. This resource will be utilized by marsupial and monotreme immunologists as well as researchers interested in the evolution of mammalian immunity.

The development of the olfactory organs in newly hatched monotremes and neonate marsupials.

Olfactory cues are thought to play a crucial role in the detection of the milk source at birth in mammals. It has been shown that a marsupial, the tammar wallaby, can detect olfactory cues from its mother's pouch at birth. This study investigates whether the main olfactory and accessory olfactory system are similarly well developed in other marsupials and monotremes at birth/hatching as in the tammar. Sections of the head of various marsupial and two monotreme species were investigated by light microscopy. Both olfactory systems were less well developed in the kowari and Eastern quoll. No olfactory or vomeronasal or terminal nerves could be observed; the main olfactory bulb (MOB) had only two layers while no accessory olfactory bulb or ganglion terminale were visible. All other investigated marsupials and monotremes showed further developed olfactory systems with olfactory, vomeronasal and terminal nerves, a three-layered MOB, and in the marsupials a prominent ganglion terminale. The main olfactory system was further developed than the accessory olfactory system in all species investigated. The olfactory systems were the least developed in species in which the mother's birth position removed most of the difficulty in reaching the teat, placing the neonate directly in the pouch. In monotremes they were the furthest developed as Bowman glands were found underlying the main olfactory epithelium. This may reflect the need to locate the milk field each time they drink as they cannot permanently attach to it, unlike therian mammals. While it still needs to be determined how an odour signal could be further processed in the brain, this study suggests that marsupials and monotremes possess well enough developed olfactory systems to be able to detect an odour cue from the mammary area at birth/hatching. It is therefore likely that neonate marsupials and newly hatched monotremes find their way to the milk source using olfactory cues, as has been previously suggested for the marsupial tammar wallaby, rabbits, rats and other eutherians.

Computational analyses of mammalian lactate dehydrogenases: Human, mouse, opossum and platypus LDHs

Computational methods were used to predict the amino acid sequences and gene locations for mammalian lactate dehydrogenase ( LDH) genes and proteins using genome sequence databanks. Human LDHA, LDHC and LDH6A genes were located in tandem on chromosome 11, while LDH6B and LDH6C genes were on chromosomes 15 and 12, respectively. Opossum LDHC and LDH6B genes were located in tandem with the opossum LDHA gene on chromosome 5 and contained 7 ( LDHA and LDHC) or 8 ( LDH6B) exons. An amino acid sequence prediction for the opossum LDH6B subunit gave an extended N-terminal sequence, similar to the human and mouse LDH6B sequences, which may support the export of this enzyme into mitochondria. The platypus genome contained at least 3 LDH genes encoding LDHA, LDHB and LDH6B subunits. Phylogenetic studies and sequence analyses indicated that LDHA, LDHB and LDH6B genes are present in all mammalian genomes examined, including a monotreme species (platypus), whereas the LDHC gene may have arisen more recently in marsupial mammals.

Splenic lymphoma in a short‐beaked echidna (Tachyglossus aculeatus)

A 23-year-old, male short-beaked echidna (Tachyglossus aculeatus) housed at a North American zoo was successfully treated for flea-associated anaemia, but subsequently died. Cause of death was presumptive septicaemia secondary to splenic lymphoma. This is only the fifth case of neoplasia reported in this monotreme species, and the first from outside of Australia.

Characterisation of monotreme caseins reveals lineage-specific expansion of an ancestral casein locus in mammals

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