Electron-microscopic study of monotreme neuroglia.

Glia cells were examined in the brains of a mature platypus and an immature echidna. In the echidna a few dark, organelle-rich glia cells were encountered. The lighter glia cells had resemblances with the single type of glia cell encountered in the brain of the platypus. These cells were characterised by highly homogeneous areas of nuclear chromatin and light cytoplasm containing dark, finely granular condensations which frequently surrounded Golgi membranes. Microtubules were present within the cytoplasm but neither filaments nor glycogen-like particles were encountered. It was concluded that the cells described conformed to the types of neither astrocytes nor oligodendrocytes as encountered in metatherian and eutherian mammals. Among their functional capacities such cells presumably include, either in the immature or mature forms, the roles of both astrocytes and oligodendrocytes.     

The evolution of marsupial and monotreme chromosomes

Marsupial and monotreme mammals fill an important gap in vertebrate phylogeny between reptile-mammal divergence 310 million years ago (mya) and the eutherian (placental) mammal radiation 105 mya. They possess many unique features including their distinctive chromosomes, which in marsupials are typically very large and well conserved between species. In contrast, monotreme genomes are divided into several large chromosomes and many smaller chromosomes, with a complicated sex chromosome system that forms a translocation chain in male meiosis. The application of molecular cytogenetic techniques has greatly advanced our understanding of the evolution of marsupial chromosomes and allowed the reconstruction of the ancestral marsupial karyotype. Chromosome painting and gene mapping have played a vital role in piecing together the puzzle of monotreme karyotypes, particularly their complicated sex chromosome system. Here, we discuss the significant insight into karyotype evolution afforded by the combination of recently sequenced marsupial and monotreme genomes with cytogenetic analysis, which has provided a greater understanding of the events that have shaped not only marsupial and monotreme genomes, but the genomes of all mammals.     

Some monotreme milk "whey" and blood proteins

1. Electrophoretic studies are made of mature phase milk "whey" proteins and blood serum proteins of echidna (Tachyglossus aculeatus) and platypus (Ornithorhynchus anatinus). The echidna milk bands are designated A-M, those of platypus A-G. Some of the proteins are isolated and characterized. 2. Echidna band A protein has some similarity to high cystine "whey" proteins. Band E protein (apparent Mr 21,000) may be a beta-lactoglobulin-like protein. Band M is lysozyme. Band C is serum albumin. Bands G-K are transferrins. 3. Platypus milk bands A, C, D, F and G are isolated. Bands F and G are transferrins. 4. Lactose synthase and lytic activities are examined.     

Instrumental discrimination: Reversal learning in the monotreme Tachyglossus aculeatus setosus

Tasmanian echidnas, Tachyglossus aculeatus setosus, were tested in serial discrimination-reversal tasks, comparing their operant behaviour in reversal-shift and non-reversal-shift conditions, using positional and visual/tactile cues. Learning-set formation of the pattern characteristic of eutherian mammals was observed in all tests for all subjects, but performances were superior in tests of positional discrimination and in reversal-shift conditions. The results were consistent with those obtainable for eutherian mammals in comparable tests and suggest that echidnas can be used as subjects in experimental studies of operant learning.     

Review of the monotreme fossil record and comparison of palaeontological and molecular data

Monotremes have traditionally been considered a remnant group of mammals descended from archaic Mesozoic stock, surviving to the present day on the relatively isolated Australian continent. Challenges to this orthodoxy have been spurred by discoveries of 'advanced' Cretaceous monotremes (Steropodon galmani, Archer, M., et al., 1985. First Mesozoic mammal from Australia-an Early Cretaceous monotreme, Nature. 318, 363-366) as well as by results from molecular data linking monotremes to therian mammals (specifically to marsupials in some studies). This paper reviews the monotreme fossil record and briefly discusses significant new information from additional Cretaceous Australian material. Mesozoic monotremes (including S. galmani) were a diverse group as evidenced by new material from the Early Cretaceous of New South Wales and Victoria currently under study. Although most of these new finds are edentulous jaws (limiting dental comparisons and determination of dietary niches), a range of sizes and forms has been determined. Some of these Cretaceous jaws exhibit archaic features-in particular evidence for the presence of a splenial bone in S. galmani-not seen in therian mammals or in post-Mesozoic (Tertiary and Quaternary) monotreme taxa. Tertiary monotremes were either archaic ornithorhynchids (toothed platypuses in the genera Monotrematum and Obdurodon) or tachyglossids (large echidnas in the genera Megalibgwilia and Zaglossus). Quaternary ornithorhynchid material is referable to the sole living platypus species Ornithorhynchus anatinus. Quaternary echidnas, however, were moderately diverse and several forms are known (Megalibgwilia species; 'Zaglossus' hacketti; Zaglossus species and Tachyglossus aculeatus).     

Characterization of immunoglobulin gamma 1 from a monotreme, Tachyglossus aculeatus

A full-length immunoglobulin gamma clone from the echidna (Tachyglossus aculeatus) was isolated from a spleen cDNA library. The clone was 1,664 base pairs long and encoded the entire open reading frame, incorporating the V, D, J and C regions. The echidna clone had approximately 41% identity and 67% similarity at the amino acid level with both marsupial and eutherian IgG molecules. The presence of IgG in the monotremes confirms that the appearance of IgG occurred prior to the separation of the three extant mammalian lineages, but after their separation from the reptilian lineage, pinpointing the date to between 310 and 170 million years ago. Phylogenetic analyses using the immunoglobulin sequence data strongly support the 'Theria' hypothesis, with the monotreme lineage diverging prior to the separation of the marsupial and eutherian lineages.     

Observations on the Breeding Kittiwake

The drought conditions prevailing in the Marismas of the Guadalquivir (SW Spain) during the winter 1982–83 caused a large proportion of the wintering Greylag Goose population to use the same flooded areas throughout the winter at very high densities. Results indicate that Greylags prefer small Scirpus rhizomes to large ones, the geese taking an increasing amount of larger rhizomes as smaller rhizomes are depleted. A combination of factors (abundance, extraction and handling times, nutritive quality) could make smaller rhizomes more profitable food for Greylags than larger rhizomes. The large concentrations of birds in some areas probably determined the depletion of preferred resources and this could have led some geese to steal food from conspecifics; some aspects of this behaviour are discussed.     

Active cation transport and Na+K+Mg ATPase of the monotreme erythrocytes

The erythrocytes of the echidna (Tachyglossus aculeatus) and platypus (Ornithorhynchus anatinus), which are practically devoid of intracellular ATP content (1), were examined for active Rb⁸⁶ influx and for the presence of Na+K+Mg ATPase. We found that intact erythrocytes of both species possess the ability to actively transport cations. Ouabain sensitive Rb⁸⁶ influx in the echidna was approximately 0.17 μmoles/ml cells × hr, whereas the platypus exhibited a higher value of 0.43 μmoles/ml cells × hr. Surprisingly, ouabain sensitive Na+K+Mg ATPase activity of isolated membranes was high amounting to some 15 to 25 fold higher than the human erythrocyte counterpart determined under identical conditions. These findings suggest that a trace amount of ATP is sufficient to maintain active cation transport across the monotreme cell membranes.