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Journal articles on the topic 'Monotremes'

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Published: 4 June 2021

Last updated: 28 February 2023

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1

Krubitzer, Leah. "What can monotremes tell us about brain evolution?" Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, no. 1372 (July 29, 1998): 1127–46. http://dx.doi.org/10.1098/rstb.1998.0271.

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The present review outlines studies of electrophsyiological organization, cortical architecture and thalmocortical and corticocortical connections in monotremes. Results of these studies indicate that the neocortex of monotremes has many features in common with other mammals. In particular, monotremes have at least two, and in some instances three, sensory fields for each modality, as well as regions of bimodal cortex. The internal organization of cortical fields and thalamocortical projection patterns are also similar to those described for other mammals. However, unlike most mammals investigated, the monotreme neocortex has cortical connections between primary sensory fields, such as SI and VI. The results of this analysis lead us to pose the question of what monotremes can tell us about brain evolution. Monotremes alone can tell us very little about the evolutionary process, or the construction of complex neural networks, as an individual species represents only a single example of what the process is capable of generating. Perhaps a better question is: what can comparative studies tell us about brain evolution? Monotreme brains, when compared with the brains of other animals, can provide some answers to questions about the evolution of the neocortex, the historical precedence of some features over others, and how basic circuits were modified in different lineages. This, in turn, allows us to appreciate how normal circuits function, and to pose very specific questions regarding the development of the neocortex.

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2

Ecroyd, Heath, Brett Nixon, Jean-Louis Dacheux, and Russell C. Jones. "Testicular descent, sperm maturation and capacitation. Lessons from our most distant relatives, the monotremes." Reproduction, Fertility and Development 21, no. 8 (2009): 992. http://dx.doi.org/10.1071/rd09081.

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The present review examines whether monotremes may help to resolve three questions relating to sperm production in mammals: why the testes descend into a scrotum in most mammals, why spermatozoa are infertile when they leave the testes and require a period of maturation in the specific milieu provided by the epididymides, and why ejaculated spermatozoa cannot immediately fertilise an ovum until they undergo capacitation within the female reproductive tract. Comparisons of monotremes with other mammals indicate that there is a need for considerable work on monotremes. It is hypothesised that testicular descent should be related to epididymal differentiation. Spermatozoa and ova from both groups share many of the proteins that are thought to be involved in gamete interaction, and although epididymal sperm maturation is significant it is probably less complex in monotremes than in other mammals. However, the monotreme epididymis is unique in forming spermatozoa into bundles of 100 with greatly enhanced motility compared with individual spermatozoa. Bundle formation involves a highly organised interaction with epididymal proteins, and the bundles persist during incubation in vitro, except in specialised medium, in which spermatozoa separate after 2–3 h incubation. It is suggested that this represents an early form of capacitation.

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3

Temple-Smith, Peter, and Tom Grant. "Uncertain breeding: a short history of reproduction in monotremes." Reproduction, Fertility and Development 13, no. 8 (2001): 487. http://dx.doi.org/10.1071/rd01110.

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Although much is known about the biology of monotremes, many important aspects of their reproduction remain unclear. Studies over the last century have provided valuable information on various aspects of monotreme reproduction including the structure and function of their reproductive system, breeding behaviour, sex determination and seasonality. All three living genera of monotremes have been successfully maintained in captivity, often for long periods, yet breeding has been rare and unpredictable. When breeding has occurred, however, significant gains in knowledge have ensued; for example a more accurate estimate of the gestation period of the platypus and the incubation period for the Tachyglossus egg. One of the great challenges for zoos has been to understand why breeding of monotremes is difficult to achieve. Analysis of breeding successes of platypuses and short-beaked echidnas provides some insights. The evidence suggests that although annual breeding seasons are regionally predictable, individual adult females breed unpredictably, with some showing breeding intervals of many years. The reason for this variation in individual breeding intervals may be resource-dependant, influenced by social factors or may even be genetically induced. Better knowledge of factors that influence breeding intervals may improve the success of monotreme captive breeding programmes. More certainty in captive breeding is also an important issue for enterprises wishing to trade in Australian wildlife since current legislation limits export of Australian fauna for display to at least second-generation captive-bred individuals. Given their unique evolutionary position, knowledge of reproduction in monotremes needs to be gained in advance of any future population declines so that appropriate strategies can be developed to ensure their survival.

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4

Pettigrew, J. D. "Electroreception in monotremes." Journal of Experimental Biology 202, no. 10 (May 15, 1999): 1447–54. http://dx.doi.org/10.1242/jeb.202.10.1447.

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I will briefly review the history of the bill sense of the platypus, a sophisticated combination of electroreception and mechanoreception that coordinates information about aquatic prey provided from the bill skin mechanoreceptors and electroreceptors, and provide an evolutionary account of electroreception in the three extant species of monotreme (and what can be inferred of their ancestors). Electroreception in monotremes is compared and contrasted with the extensive body of work on electric fish, and an account of the central processing of mechanoreceptive and electroreceptive input in the somatosensory neocortex of the platypus, where sophisticated calculations seem to enable a complete three-dimensional fix on prey, is given.

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5

Wong, Emily S. W., Anthony T. Papenfuss, Robert D. Miller, and Katherine Belov. "Hatching time for monotreme immunology." Australian Journal of Zoology 57, no. 4 (2009): 185. http://dx.doi.org/10.1071/zo09042.

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The sequencing of the platypus genome has spurred investigations into the characterisation of the monotreme immune response. As the most divergent of extant mammals, the characterisation of the monotreme immune repertoire allows us to trace the evolutionary history of immunity in mammals and provide insights into the immune gene complement of ancestral mammals. The immune system of monotremes has remained largely uncharacterised due to the lack of specific immunological reagents and limited access to animals for experimentation. Early immunological studies focussed on the anatomy and physiology of the lymphoid system in the platypus. More recent molecular studies have focussed on characterisation of individual immunoglobulin, T-cell receptor and MHC genes in both the platypus and short-beaked echidna. Here, we review the published literature on the monotreme immune gene repertoire and provide new data generated from genome analysis on cytokines, Fc receptors and immunoglobulins. We present an overview of key gene families responsible for innate and adaptive immunity including the cathelicidins, defensins, T-cell receptors and the major histocompatibility complex (MHC) Class I and Class II antigens. We comment on the usefulness of these sequences for future studies into immunity, health and disease in monotremes.

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6

Stannard, Hayley J., Robert D. Miller, and Julie M. Old. "Marsupial and monotreme milk—a review of its nutrient and immune properties." PeerJ 8 (June 23, 2020): e9335. http://dx.doi.org/10.7717/peerj.9335.

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All mammals are characterized by the ability of females to produce milk. Marsupial (metatherian) and monotreme (prototherian) young are born in a highly altricial state and rely on their mother’s milk for the first part of their life. Here we review the role and importance of milk in marsupial and monotreme development. Milk is the primary source of sustenance for young marsupials and monotremes and its composition varies at different stages of development. We applied nutritional geometry techniques to a limited number of species with values available to analyze changes in macronutrient composition of milk at different stages. Macronutrient energy composition of marsupial milk varies between species and changes concentration during the course of lactation. As well as nourishment, marsupial and monotreme milk supplies growth and immune factors. Neonates are unable to mount a specific immune response shortly after birth and therefore rely on immunoglobulins, immunological cells and other immunologically important molecules transferred through milk. Milk is also essential to the development of the maternal-young bond and is achieved through feedback systems and odor preferences in eutherian mammals. However, we have much to learn about the role of milk in marsupial and monotreme mother-young bonding. Further research is warranted in gaining a better understanding of the role of milk as a source of nutrition, developmental factors and immunity, in a broader range of marsupial species, and monotremes.

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7

Tsend-Ayush, Enkhjargal, Shu Ly Lim, Andrew J. Pask, Diana Demiyah Mohd Hamdan, Marilyn B. Renfree, and Frank Grützner. "Characterisation of ATRX, DMRT1, DMRT7 and WT1 in the platypus (Ornithorhynchus anatinus)." Reproduction, Fertility and Development 21, no. 8 (2009): 985. http://dx.doi.org/10.1071/rd09090.

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One of the most puzzling aspects of monotreme reproductive biology is how they determine sex in the absence of the SRY gene that triggers testis development in most other mammals. Although monotremes share a XX female/XY male sex chromosome system with other mammals, their sex chromosomes show homology to the chicken Z chromosome, including the DMRT1 gene, which is a dosage-dependent sex determination gene in birds. In addition, monotremes feature an extraordinary multiple sex chromosome system. However, no sex determination gene has been identified as yet on any of the five X or five Y chromosomes and there is very little knowledge about the conservation and function of other known genes in the monotreme sex determination and differentiation pathway. We have analysed the expression pattern of four evolutionarily conserved genes that are important at different stages of sexual development in therian mammals. DMRT1 is a conserved sex-determination gene that is upregulated in the male developing gonad in vertebrates, while DMRT7 is a mammal-specific spermatogenesis gene. ATRX, a chromatin remodelling protein, lies on the therian X but there is a testis-expressed Y-copy in marsupials. However, in monotremes, the ATRX orthologue is autosomal. WT1 is an evolutionarily conserved gene essential for early gonadal formation in both sexes and later in testis development. We show that these four genes in the adult platypus have the same expression pattern as in other mammals, suggesting that they have a conserved role in sexual development independent of genomic location.

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8

Messer, M., D. C. Shaw, A. S. Weiss, P. Rissmiller, and M. Griffiths. "Estimation of Divergence Dates for Monotremes From Comparisons of A-Lactalbumin Amino Acid Sequences." Australian Mammalogy 20, no. 2 (1998): 310. http://dx.doi.org/10.1071/am98323.

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cx-Lactalbumins were isolated from milk of the platypus (Ornithorhynchus anatinus) and the echidna (Tachyglossus aculeatus). Their amino acid sequences were determined and compared with those of the cx- lactalbumins often eutherian and two marsupial species, using the computer programme ("Distances") to calculate the number of differences (substitutions) between a total of 36 pairs of cx-lactalbumins. As expected, the amino acid sequences of the monotreme cx-lactalbumins were more similar to each other than to those of other mammals, as were the sequences of the marsupial and the eutherian cx-lactalbumins. If one makes the common assumption that marsupials and eutherians diverged from each other 135 Myr ago then simple calculations from the data would suggest that the platypus and echidna lineages diverged 56 ± 8 (SD) Myr ago and that monotremes diverged from the other mammals 152 ± 29 Myr ago. These values are not inconsistent with the little that is known about the palaeontology of the monotremes and are very similar to those derived from previous studies on globin sequences. If, however, monotreme cx-lactalbumins evolved more slowly than the cx-lactalbumins of eutherians and marsupials, these dates could be underestimates.

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9

Choi, Charles Q. "Extreme Monotremes." Scientific American 301, no. 6 (December 2009): 21–22. http://dx.doi.org/10.1038/scientificamerican1209-21.

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10

Kirsch, John A. W., and Gregory C. Mayer. "The platypus is not a rodent: DNA hybridization, amniote phylogeny and the palimpsest theory." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, no. 1372 (July 29, 1998): 1221–37. http://dx.doi.org/10.1098/rstb.1998.0278.

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We present DNA–hybridization data on 21 amniotes and two anurans showing that discrimination is obtained among most of these at the class and lower levels. Trees generated from these data largely agree with conventional views, for example in not associating birds and mammals. However, the sister relationships found here of the monotremes to marsupials, and of turtles to the alligator, are surprising results which are nonetheless consistent with the results of some other studies. The Marsupionta hypothesis of Gregory is reviewed, as are opinions about the placement of chelonians. Anatomical and reproductive data considered by Gregory do not unequivocally preclude a marsupial–monotreme special relationship, and there is other recent evidence for placing turtles within the Diapsida. We conclude that the evidential meaning of the molecular data is as shown in the trees, but that the topologies may be influenced by a base–compositional bias producing a seemingly slow evolutionary rate in monotremes, or by algorithmic artefacts (in the case of turtles as well).

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11

Lefèvre, Christophe M., Julie A. Sharp, and Kevin R. Nicholas. "Characterisation of monotreme caseins reveals lineage-specific expansion of an ancestral casein locus in mammals." Reproduction, Fertility and Development 21, no. 8 (2009): 1015. http://dx.doi.org/10.1071/rd09083.

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

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12

Neff, Ellen P. "Genomes for monotremes." Lab Animal 50, no. 3 (February 25, 2021): 63. http://dx.doi.org/10.1038/s41684-021-00736-9.

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13

Newman, Janet, Julie A. Sharp, Ashwantha Kumar Enjapoori, John Bentley, Kevin R. Nicholas, Timothy E. Adams, and Thomas S. Peat. "Structural characterization of a novel monotreme-specific protein with antimicrobial activity from the milk of the platypus." Acta Crystallographica Section F Structural Biology Communications 74, no. 1 (January 1, 2018): 39–45. http://dx.doi.org/10.1107/s2053230x17017708.

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Monotreme lactation protein (MLP) is a recently identified protein with antimicrobial activity. It is present in the milk of monotremes and is unique to this lineage. To characterize MLP and to gain insight into the potential role of this protein in the evolution of lactation, the crystal structure of duck-billed platypus (Ornithorhynchus anatinus) MLP was determined at 1.82 Å resolution. This is the first structure to be reported for this novel, mammalian antibacterial protein. MLP was expressed as a FLAG epitope-tagged protein in mammalian cells and crystallized readily, with at least three space groups being observed (P1,C2 andP21). A 1.82 Å resolution native data set was collected from a crystal in space groupP1, with unit-cell parametersa= 51.2,b= 59.7,c= 63.1 Å, α = 80.15, β = 82.98, γ = 89.27°. The structure was solved by SAD phasing using a protein crystal derivatized with mercury in space groupC2, with unit-cell parametersa= 92.7,b = 73.2,c= 56.5 Å, β = 90.28°. MLP comprises a monomer of 12 helices and two short β-strands, with much of the N-terminus composed of loop regions. The crystal structure of MLP reveals no three-dimensional similarity to any known structures and reveals a heretofore unseen fold, supporting the idea that monotremes may be a rich source for the identification of novel proteins. It is hypothesized that MLP in monotreme milk has evolved to specifically support the unusual lactation strategy of this lineage and may have played a central role in the evolution of these mammals.

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14

Warren, Wesley C., and Frank Grützner. "The enigma of the platypus genome." Australian Journal of Zoology 57, no. 4 (2009): 157. http://dx.doi.org/10.1071/zo09051.

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Over two centuries after the first platypus specimen stirred the scientific community in Europe, the whole-genome sequence of the duck-billed platypus has been completed and is publicly available. After publication of eutherian and marsupial genomes, this is the first genome of a monotreme filling an important evolutionary gap between the divergence of birds more that 300 million years ago and marsupials more than 140 million years ago. Monotremes represent the most basal surviving branch of mammals and the platypus genome sequence allows unprecedented insights into the evolution of mammals and the fascinating biology of the egg-laying mammals. Here, we discuss some of the key findings of the analysis of the platypus genome and point to new findings and future research directions, which illustrate the broad impact of the platypus genome project for understanding monotreme biology and mammalian genome evolution.

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15

Woodburne, Michael O. "Monotremes as Pretribosphenic Mammals." Journal of Mammalian Evolution 10, no. 3 (September 2003): 195–248. http://dx.doi.org/10.1023/b:jomm.0000015104.29857.f0.

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16

Proske, U., J. E. Gregory, and A. Iggo. "Sensory receptors in monotremes." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 353, no. 1372 (July 29, 1998): 1187–98. http://dx.doi.org/10.1098/rstb.1998.0275.

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This is a summary of the current knowledge of sensory receptors in skin of the bill of the platypus, Ornithorhynchus anatinus , and the snout of the echidna, Tachyglossus aculeatus . Brief mention is also made of the third living member of the monotremes, the long–nosed echidna, Zaglossus bruijnii . The monotremes are the only group of mammals known to have evolved electroreception. The structures in the skin responsible for the electric sense have been identified as sensory mucous glands with an expanded epidermal portion that is innervated by large–diameter nerve fibres. Afferent recordings have shown that in both platypuses and echidnas the receptors are excited by cathodal (negative) pulses and inhibited by anodal (positive) pulses. Estimates give a total of 40 000 mucous sensory glands in the upper and lower bill of the platypus, whereas there are only about 100 in the tip of the echidna snout. Recordings of electroreceptor–evoked activity from the brain of the platypus have shown that the largest area dedicated to somatosensory input from the bill, S1, shows alternating rows of mechanosensory and bimodal neurons. The bimodal neurons respond to both electrosensory and mechanical inputs. In skin of the platypus bill and echidna snout, apart from the electroreceptors, there are structures called push rods, which consist of a column of compacted cells that is able to move relatively independently of adjacent regions of skin. At the base of the column are Merkel cell complexes, known to be type I slowly adapting mechanoreceptors, and lamellated corpuscles, probably vibration receptors. It has been speculated that the platypus uses its electric sense to detect the electromyographic activity from moving prey in the water and for obstacle avoidance. Mechanoreceptors signal contact with the prey. For the echidna, a role for the electrosensory system has not yet been established during normal foraging behaviour, although it has been shown that it is able to detect the presence of weak electric fields in water. Perhaps the electric sense is used to detect moving prey in moist soil.

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17

Watson, JM. "Monotreme Genetics and Cytology and a Model for Sex-Chromosome Evolution." Australian Journal of Zoology 37, no. 3 (1989): 385. http://dx.doi.org/10.1071/zo9890385.

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The protherian mammals consist of three species: the platypus, the Australian echidna and the Niugini echidna. These mammals diverged from the therian line of descent about 150-200 million years ago; hence comparisons of gene arrangements and gene control mechanisms between prototherian and therian mammals may yield significant data about gene rearrangements during mammalian evolution and about the evolution of complex genetic control systems. The chromosome complements of the three monotreme species are highly conserved. In particular, the X (or X1) chromosomes are G-band identical and share considerable G-band homology with the Y chromosomes. Replication asynchrony between X chromosomes suggests that X chromosome inactivation operates in females, and is apparently tissue- specific (as it is in marsupials), and confined to the differential region of the X (X1) chromosome (as it is in eutherian mammals). These results suggest that sex chromosome differentiation in the monotremes represents an intermediate stage in the evolution of the dimorphic sex chromosomes of therian mammals and that X-chromosome inactivation may also represent a comparatively primitive stage. Studies of gene location in the platypus using platypus-rodent cell hybrids suggested that HPRT and PGK are syntenic in the platypus, but it was not possible to assign the syntenic group to a particular chromosome. In situ hybridisation was used to assign three genes, located on the X in eutherians and marsupials, to the monotreme X. However, human X short-arm markers were found by in situ hybridisation to be autosomal in monotremes (as they are in marsupials). A model for the evolution of mammalian sex chromosome differentiation and X-chromosome inactivation is presented in which a gradual reduction of the Y chromosome, and recruitment of newly unpaired loci on the X into a system of X-chromosome inactivation, has accompanied eutherian evolution.

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18

Watson, JM, and JAM Graves. "Monotreme Cell-Cycles and the Evolution of Homeothermy." Australian Journal of Zoology 36, no. 5 (1988): 573. http://dx.doi.org/10.1071/zo9880573.

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We have studied the effects of temperature on the phases of the cell cycle in cells derived from the monotreme mammals, platypus and echidna, which have the unusually low body temperature of 32�C. We report here that M phase and the cycle time conform to expectations, but in the case of cycle time this is due to different effects of high and low temperatures on GI, G2 and S phases. The finding that the G2 and S phases apparently have an inverse linear relationship with temperature up to 37�C (the upper lethal temperature) suggests that the low body temperature of the monotremes is not primitive, but rather has been the result of a lowering of the body temperature during their evolutionary history.

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19

Grutzner, F., A. Casey, and T. Daish. "105. MEIOTIC ACROBATS: MONOTREME SEX CHROMOSOME ORGANISATION DURING SPERMATOGENESIS." Reproduction, Fertility and Development 22, no. 9 (2010): 23. http://dx.doi.org/10.1071/srb10abs105.

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Monotremes feature an extraordinarily complex sex chromosome system which shares extensive homology with bird sex chromosomes but no homology to sex chromosomes of other mammals (1,2,3). At meiotic prophase I the ten sex chromosomes in platypus (nine in echidna) assemble in a sex chromosome chain. We previously identified the multiple sex chromosomes in platypus and echidna that form the meiotic chain in males (1,2,4). We showed that sex chromosomes assembly in the chain in a specific order (5) and that they segregate alternately (1). In secondary spermatocytes we observed clustering of X and Y chromosomes in sperm (6). Our current research investigates the formation of the synaptonemal complex, recombination and meiotic silencing of monotreme sex chromosomes. Meiotic sex chromosome inactivation (MSCI) has been observed in eutherian mammals, marsupials and birds but has so far not been investigated experimentally in monotremes. We found that during pachytene the X5Y5 end of the chain closely associates with the nucleolus and accumulates repressive chromatin marks (e.g. histone variant mH2A). In contrast to the differential accumulation of mH2A we observe extensive loading of the cohesin SMC3 on sex chromosomes in particular during the pachytene stage of meiotic prophase I. We have also used markers of active transcription and gene expression analysis to investigate gene activity in platypus meiotic cells. I will discuss how these findings contribute to our current understanding of the meiotic organisation of monotreme sex chromosomes and the evolution of MSCI in birds and mammals. (1) Grützner et al. (2004), Nature 432: 913–917.(2) Rens et al. (2007), Genome Biology 16;8(11): R243.(3) Veyrunes et al. (2008), Genome Research, 18(6): 995–1004.(4) Rens et al. (2004), Proceedings of the National Academy of Sciences USA. 101 (46): 16 257–16 261.(5) Daish et al. (2009), Reprod Fertil Dev. 21(8): 976–84.(6) Tsend-Ayush et al. (2009), Chromosoma 118(1): 53–69.

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20

Sinclair, Andrew H., Jacyln M. Wrigley, and Jennifer A. Marshall Graves. "Autosomal assignment of OTC in marsupials and monotremes: implications for the evolution of sex chromosomes." Genetical Research 50, no. 2 (October 1987): 131–36. http://dx.doi.org/10.1017/s0016672300023533.

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SummaryThe OTC gene coding for ornithine transcarbamylase is sex linked and subject to X inactivation in humans and mice. We have used a rat cDNA probe to localize OTC by in situ hybridization in marsupials and monotremes. The gene maps to an autosomal site in two distantly related marsupial species and in one monotreme (the platypus); the first demonstration that a gene X-linked in one mammalian species may be autosomal in another. Since the conservation of the mammalian X is thought to be a consequence of its isolation by the inactivation mechanism, we propose that an autosomal or pseudoautosomal segment containing OTC has been recruited into the inactivated region of the X rather recently in eutherian evolution while it remained autosomal, or was translocated to an autosome, in metatherian and prototherian mammals.

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21

Rowe, M. J., D. A. Mahns, R. C. Bohringer, K. W. S. Ashwell, and V. Sahai. "Tactile neural mechanisms in monotremes." Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 136, no. 4 (December 2003): 883–93. http://dx.doi.org/10.1016/j.cbpb.2003.06.001.

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22

Behringer, Richard R., Guy S. Eakin, and Marilyn B. Renfree. "Mammalian diversity: gametes, embryos and reproduction." Reproduction, Fertility and Development 18, no. 2 (2006): 99. http://dx.doi.org/10.1071/rd05137.

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The class Mammalia is composed of approximately 4800 extant species. These mammalian species are divided into three subclasses that include the monotremes, marsupials and eutherians. Monotremes are remarkable because these mammals are born from eggs laid outside of the mother’s body. Marsupial mammals have relatively short gestation periods and give birth to highly altricial young that continue a significant amount of ‘fetal’ development after birth, supported by a highly sophisticated lactation. Less than 10% of mammalian species are monotremes or marsupials, so the great majority of mammals are grouped into the subclass Eutheria, including mouse and human. Mammals exhibit great variety in morphology, physiology and reproduction. In the present article, we highlight some of this remarkable diversity relative to the mouse, one of the most widely used mammalian model organisms, and human. This diversity creates challenges and opportunities for gamete and embryo collection, culture and transfer technologies.

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23

Hayward, John S., and Paul A. Lisson. "Evolution of brown fat: its absence in marsupials and monotremes." Canadian Journal of Zoology 70, no. 1 (January 1, 1992): 171–79. http://dx.doi.org/10.1139/z92-025.

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Species from all extant families of marsupials and monotremes were examined to clarify whether these mammalian subclasses possess brown adipose tissue. To optimize the chance of finding this tissue, special emphasis was given to sampling species adapted to colder regions, species with small adult body size, and individuals at a stage of development equivalent to the newborn stage of placentals (late pouch life in the case of marsupials). Evidence based on gross morphology and light, electron, and fluorescence microscopy failed to show the presence of brown adipose tissue in any marsupial or monotreme. All adipose tissue was typical white fat, including special instances where multilocularity of lipid droplets occurred in association with white adipocyte development or with fat mobilization resulting from nutritional or cold stress. These results, combined with lack of positive identification of brown adipose tissue in birds or other vertebrates, indicate that brown adipose tissue is unique to eutherian (placental) mammals and probably evolved early in the radiation of this subclass. This uniqueness presents the opportunity to suggest a more satisfactory name for the subclass: Thermolipia (from the Greek for "warm fat") or, commonly, thermolipials.

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24

Snipes, RL, H. Snipes, and FN Carrick. "Morphometric data on the intestines of five Australian marsupials (Marsupialia)." Australian Mammalogy 25, no. 2 (2003): 193. http://dx.doi.org/10.1071/am03193.

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THE nutritional biology of marsupials has been a subject of numerous studies, culminating in valuable compilations covering a wide range of aspects (Osman Hill and Rewell 1954; Walton and Richardson 1989; Hume 1982, 1999; Kerle 2001). Despite this thorough coverage, there remains a scarcity of morphometric data on the intestines of monotremes and marsupials. In an attempt to approach this need, an effort was initiated to provide morphometric data on monotremes (Snipes et al. 2002) and marsupials (Snipes et al. 1993, 2003).

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25

Ashwell, Ken W. S., and Boaz Shulruf. "Vestibular development in marsupials and monotremes." Journal of Anatomy 224, no. 4 (December 2, 2013): 447–58. http://dx.doi.org/10.1111/joa.12148.

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26

Pridmore, Peter A. "Terrestrial locomotion in monotremes (Mammalia: Monotremata)." Journal of Zoology 205, no. 1 (August 20, 2009): 53–73. http://dx.doi.org/10.1111/j.1469-7998.1985.tb05613.x.

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Hill, W. C. Osman, and R. E. Rewell. "The caecum of monotremes and marsupials." Transactions of the Zoological Society of London 28, no. 2 (July 7, 2010): 185–240. http://dx.doi.org/10.1111/j.1096-3642.1954.tb00234.x.

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28

Dobrovic, A., and Marshall Graves. "Gene mapping in marsupials and monotremes." Cytogenetic and Genome Research 41, no. 1 (1986): 9–13. http://dx.doi.org/10.1159/000132189.

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29

Dawson, G. W., and Marshall Graves. "Gene mapping in marsupials and monotremes." Cytogenetic and Genome Research 42, no. 1-2 (1986): 80–84. http://dx.doi.org/10.1159/000132256.

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30

Dawson, G. W., P. G. Johnston, and Marshall Graves. "Gene mapping in marsupials and monotremes." Cytogenetic and Genome Research 45, no. 1 (1987): 1–4. http://dx.doi.org/10.1159/000132415.

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31

Wong, Emily SW, Anthony T. Papenfuss, and Katherine Belov. "Immunome database for marsupials and monotremes." BMC Immunology 12, no. 1 (2011): 48. http://dx.doi.org/10.1186/1471-2172-12-48.

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32

Cooper, D. W., P. G. Johnston, J. M. Watson, and J. A. M. Graves. "X-inactivation in marsupials and monotremes." Seminars in Developmental Biology 4, no. 2 (April 1993): 117–28. http://dx.doi.org/10.1006/sedb.1993.1014.

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33

Haynes, Julie Irene. "Parathyroids and ultimobranchial bodies in monotremes." Anatomical Record 254, no. 2 (February 1, 1999): 269–80. http://dx.doi.org/10.1002/(sici)1097-0185(19990201)254:2<269::aid-ar13>3.0.co;2-g.

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34

Hope, RM, S. Cooper, and B. Wainwright. "Globin Macromolecular Sequences in Marsupials and Monotremes." Australian Journal of Zoology 37, no. 3 (1989): 289. http://dx.doi.org/10.1071/zo9890289.

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We have reviewed published data on haemoglobin and myoglobin DNA and protein sequences from marsupial and monotreme mammals, and drawn attention to the difficulties that have been encountered in using these data to estimate dates of evolutionary divergence. We argue that continuing studies of marsupial and monotreme globins, particularly molecular studies on gene organisation and regulation, are likely to contribute significantly to our understanding of gene and organismal evolution. In this context we suggest that studies on the globin genes of a monotreme and a South American marsupial would be especially rewarding.

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35

Buschiazzo, E., and N. J. Gemmell. "Evolutionary and phylogenetic significance of platypus microsatellites conserved in mammalian and other vertebrate genomes." Australian Journal of Zoology 57, no. 4 (2009): 175. http://dx.doi.org/10.1071/zo09038.

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Building on the recent publication of the first monotreme genome, that of the platypus, and the discovery that many platypus microsatellites are found in the genomes of three mammals (opossum, human, mouse) and two non-mammalian vertebrates (chicken, lizard), we investigated further the evolutionary conservation of microsatellites identified in the monotreme lineage and tested whether the conservation of microsatellites we observe in vertebrates has phylogenetic signal. Most conserved platypus microsatellites (75%) were found in one species, with the platypus sharing many more microsatellites with mammals than with reptiles (83% versus 30%). Within mammals, unexpectedly, many more platypus microsatellites had orthologues in the opossum genome than in that of either human or mouse, which was at odds with the very well supported view that monotremes diverged from a lineage containing both eutherians and marsupials (Theria hypothesis). We investigated the phylogenetic significance of microsatellite conservation through Bayesian and maximum parsimony tree reconstruction using presence/absence data of microsatellite loci conserved in a total of 18 species, including the platypus. Although models of evolution implemented in current phylogenetic reconstruction algorithms are not tailor-made for microsatellite data, we were able to construct vertebrate phylogenies that correspond well to the accepted mammalian phylogeny, with two of our three reconstructions supporting the Theria hypothesis. Our analysis provides ground for new theoretical development in phylogeny-based analyses of conserved microsatellite data.

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36

Jenkins, Farish A. "Monotremes and the Biology of Mesozoic Mammals." Netherlands Journal of Zoology 40, no. 1-2 (1989): 5–31. http://dx.doi.org/10.1163/156854289x00165.

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37

Pascual, Rosendo, Michael Archer, Edgardo Ortiz Jaureguizar, José L. Prado, Henk Godthelp, and Suzanne J. Hand. "First discovery of monotremes in South America." Nature 356, no. 6371 (April 1992): 704–6. http://dx.doi.org/10.1038/356704a0.

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38

Finkel, E. "Genome Speaks to Transitional Nature of Monotremes." Science 320, no. 5877 (May 9, 2008): 730. http://dx.doi.org/10.1126/science.320.5877.730.

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39

Brice, Peter H. "Thermoregulation in monotremes: riddles in a mosaic." Australian Journal of Zoology 57, no. 4 (2009): 255. http://dx.doi.org/10.1071/zo09039.

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The three extant genera of the Monotremata have evolved, probably from a pre-Cretaceous Gondwanan origin, independently of the Theria to display a variety of ancestral and derived features. A comparison of their thermoregulation reveals a diversity of physiology that might represent both plesiomorphic and apomorphic elements within this mosaic. In the tachyglossids, the echidnas Tachyglossus and Zaglossus, body temperature is often labile, rising as a result of activity and allowed to decline during inactivity. This daily heterothermy, which is not necessarily torpor, may combine with typical mammalian hibernation to provide substantial energy economy in a wide variety of often unproductive habitats. Only when incubating do free-ranging echidnas display classic mammalian thermoregulation, the facultative nature of which suggests echidna-like physiology as an example of a protoendothermic stage in the evolution of endothermy. Similarly, physiological response to heat in Tachyglossus, at least, may be plesiomorphic, relying on the cyclic loss of heat stored during activity. Tachyglossids neither exhibit a panting response nor spread saliva to facilitate evaporative cooling and Tachyglossus, though not Zaglossus, lacks functional sweat glands. By contrast, the only extant ornithorhynchid, the platypus Ornithorhynchus, does not utilise heterothermy of any kind and maintains its body temperature more tightly than several semiaquatic eutherians. Although not necessarily required, it responds to heat via sweating, but not panting or saliva spreading. The classic nature of ornithorhynchid thermoregulation stands in marked contrast to the more diverse thermoregulatory responses shown by the tachyglossids, making it difficult to determine which aspects of monotreme thermoregulation are plesiomorphic and which are apomorphic.

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Graves, JAM. "Sex-Chromosome Function in Marsupials and Monotremes." Australian Journal of Zoology 37, no. 3 (1989): 409. http://dx.doi.org/10.1071/zo9890409.

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41

Peel, E., and K. Belov. "Immune-endocrine interactions in marsupials and monotremes." General and Comparative Endocrinology 244 (April 2017): 178–85. http://dx.doi.org/10.1016/j.ygcen.2017.01.026.

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42

Parkinson, A. L., A. T. Whittington, P. B. S. Spencer, G. Grigg, L. Hinds, C. Gallagher, P. Kuchel, and N. S. Agar. "Comparative erythrocyte metabolism in marsupials and monotremes." Comparative Biochemistry and Physiology Part C: Pharmacology, Toxicology and Endocrinology 110, no. 3 (March 1995): 261–65. http://dx.doi.org/10.1016/0742-8413(95)00010-l.

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43

Graves, J. A. M. "Gene Maps of Monotremes (Mammalian Subclass Prototheria)." ILAR Journal 39, no. 2-3 (January 1, 1998): 225–28. http://dx.doi.org/10.1093/ilar.39.2-3.225.

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44

Asahara, Masakazu, Masahiro Koizumi, Thomas E. Macrini, Suzanne J. Hand, and Michael Archer. "Comparative cranial morphology in living and extinct platypuses: Feeding behavior, electroreception, and loss of teeth." Science Advances 2, no. 10 (October 2016): e1601329. http://dx.doi.org/10.1126/sciadv.1601329.

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The modern platypus,Ornithorhynchus anatinus, has an eye structure similar to aquatic mammals; however, platypuses also have a “sixth sense” associated with the bill electro- and mechanoreception that they use without opening their eyes underwater. We hypothesize thatOrnithorhynchusand the Miocene taxonObdurodonhave different sensory capacities, which may have resulted from differences in foraging behavior. To estimate differences in foraging, sensory systems, and anatomical divergence between these monotremes, we compared their skull morphologies. Results indicate that the bill ofObdurodonis more dorsally deflected than that ofOrnithorhynchus, suggesting a pelagic foraging behavior inObdurodoncompared to the bottom-feeding behavior inOrnithorhynchus. The infraorbital foramen ofObdurodon, through which the maxillary nerve passes sensory data from the bill to the brain, is relatively less developed than that ofOrnithorhynchus. Whereas bill-focused sensory perception was likely shared among Mesozoic monotremes, the highly developed electrosensory system ofOrnithorhynchusmay represent an adaptation to foraging in cloudy water. Computed tomography imagery indicates that the enlarged infraorbital canal ofOrnithorhynchusrestricts the space available for maxillary tooth roots. Hence, loss of functional teeth inOrnithorhynchusmay possibly have resulted from a shift in foraging behavior and coordinate elaboration of the electroreceptive sensory system. Well-developed electroreceptivity in monotremes is known at least as far back as the early Cretaceous; however, there are differences in the extent of elaboration of the feature among members of the ornithorhynchid lineage.

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45

Antonsson, Annika, and Nigel A. J. McMillan. "Papillomavirus in healthy skin of Australian animals." Journal of General Virology 87, no. 11 (November 1, 2006): 3195–200. http://dx.doi.org/10.1099/vir.0.82195-0.

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Papillomaviruses are a group of ubiquitous viruses that are often found in normal skin of humans, as well as a range of different vertebrates. In this study, swab samples collected from the healthy skin of 225 Australian animals from 54 species were analysed for the presence of papillomavirus DNA with the general skin papillomavirus primer pair FAP59/FAP64. A total of five putative and potential new animal papillomavirus types were identified from three different animal species. The papillomaviruses were detected in one monotreme and two marsupial species: three from koalas, and one each from an Eastern grey kangaroo and an echidna. The papillomavirus prevalence in the three species was 14 % (10/72) in koalas, 20 % (1/5) in echidnas and 4 % (1/23) in Eastern grey kangaroos. Phylogenetic analysis was performed on the putative koala papillomavirus type that could be cloned and it appears in the phylogenetic tree as a novel putative papillomavirus genus. The data extend the range of species infected by papillomaviruses to the most primitive mammals: the monotremes and the marsupials.

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Averianov, A. O., and A. V. Lopatin. "On the phylogenetic position of monotremes (Mammalia, Monotremata)." Paleontological Journal 48, no. 4 (July 2014): 426–46. http://dx.doi.org/10.1134/s0031030114040042.

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47

Meitzen, J. "Neurobiology of Monotremes. Ken W. S. Ashwell, editor." Integrative and Comparative Biology 54, no. 1 (April 9, 2014): 87–88. http://dx.doi.org/10.1093/icb/icu011.

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48

Rich, Thomas H., Timothy F. Flannery, Peter Trusler, Lesley Kool, Nicholas A. Van Klaveren, and Patricia Vickers-Rich. "Evidence that monotremes and ausktribosphenids are not sistergroups." Journal of Vertebrate Paleontology 22, no. 2 (July 8, 2002): 466–69. http://dx.doi.org/10.1671/0272-4634(2002)022[0466:etmaaa]2.0.co;2.

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49

Nixon, B., H. Ecroyd, J. L. Dacheux, F. Dacheux, V. Labas, S. D. Johnston, and R. C. Jones. "Formation and Dissociation of Sperm Bundles in Monotremes." Biology of Reproduction 95, no. 4 (August 24, 2016): 91. http://dx.doi.org/10.1095/biolreprod.116.140491.

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Thorp, B. H., and J. M. Dixon. "Cartilaginous bone extremities of growing monotremes appear unique." Anatomical Record 229, no. 4 (April 1991): 447–52. http://dx.doi.org/10.1002/ar.1092290403.

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