Short-beaked Echidna Tachyglossus Aculeatus Research Articles

Tachyglossus aculeatus (Monotremata: Tachyglossidae)

AbstractTachyglossus aculeatus (Shaw, 1792) is a monotreme commonly called the short-beaked echidna. Although considered Australia’s most common native mammal because of its continent-wide distribution, its population numbers everywhere are low. It is easily distinguished from all other native Australian mammals because of its spine-covered body, hairless beak, and unique “rolling” gait. The five subspecies, one of which is found in Papua New Guinea, show variations in fur density, spine diameter, length, and number of grooming claws. The Kangaroo Island short-beaked echidna Tachyglossus aculeatus multiaculeatus is listed as “Endangered” but all other Tachyglossus are listed as “Least Concern” in the 2016 International Union for Conservation of Nature and Natural Resources Red List.

Energy Homeostasis in Monotremes.

In 1803, the French anatomist Étienne Geoffroy Saint-Hilaire decided that the newly described echidna and platypus should be placed in a separate order, the monotremes, intermediate between reptiles and mammals. The first physiological observations showed monotremes had low body temperatures and metabolic rates, and the consensus was that they were at a stage of physiological development intermediate between “higher mammals” and “lower vertebrates.” Subsequent studies demonstrated that platypuses and echidnas are capable of close thermoregulation in the cold although less so under hot conditions. Because the short-beaked echidna Tachyglossus aculeatus, may show very large daily variations in body temperature, as well as seasonal hibernation, it has been suggested that it may provide a useful model of protoendotherm physiology. Such analysis is complicated by the very significant differences in thermal relations between echidnas from different climates. In all areas female echidnas regulate Tb within 1°C during egg incubation. The lactation period is considered to be the most energetically expensive time for most female mammals but lactating echidnas showed no measurable difference in field metabolic rate from non-lactating females, while the lactation period is more than 200 days for Kangaroo Island echidnas but only 150 days in Tasmania. In areas with mild winters echidnas show reduced activity and shallow torpor in autumn and early winter, but in areas with cold winters echidnas enter true hibernation with Tb falling as low as 4.5°C. Monotremes do not possess brown adipose tissue and maximum rates of rewarming from hibernation in echidnas were only half those of marmots of the same mass. Although echidnas show very large seasonal variations in fat stores associated with hibernation there is no relationship between plasma leptin and adiposity. Leptin levels are lowest during post-reproductive fattening, supporting suggestions that in evolutionary terms the anorectic effects of leptin preceded the adiposity signal. BMR of platypuses is twice that of echidnas although maximum metabolism is similar. High levels of thyroid hormones in platypuses may be driving metabolism limited by low body temperature. Monotremes show a mosaic of plesiomorphic and derived features but can still inform our understanding of the evolution of endothermy.

Interaction of hibernation and male reproductive function in wild Tasmanian echidnasTachyglossus aculeatus setosus

The short-beaked echidna Tachyglossus aculeatus is a seasonally breeding mammal with a near ubiquitous distribution throughout Australia. In Tasmania, breeding follows a period of deep hibernation, and males begin mating approximately 30 days after the termination of hibernation. The echidna has exceptionally large testes, which may reach a maximum of 1% of body mass during the mating period. As involution of gonads is considered a prerequisite for entering hibernation and hibernation typically suppresses all reproductive function, this raises questions about the timing of testes recrudescence in the Tasmanian echidna. We measured plasma testosterone concentrations and used ultrasonography to measure testicular and crural gland volume through the annual cycle in wild Tasmanian echidnas. Testes were at their minimum size (0.06% of body mass) in December (early summer); testes recrudescence occurred prior to entry into hibernation when plasma testosterone concentrations were low; and testes were maintained at 75% of their maximum volume throughout the hibernation period. The crural glands, which are secondary reproductive structures in the echidna, also exhibited an annual pattern of recrudescence and involution, with recrudescence occurring after males emerged from hibernation, when plasma testosterone was rising. We suggest that the unusual strategy of testes recrudescence occurring prior to hibernation in the Tasmanian echidna is a consequence of extremely high competition between males.

Natural History of Human’s Most Distant Living Mammalian Relatives

In comparison to the more than 1,200 genera of placentals and marsupials, the three extant monotreme genera make up only a tiny part of modern mammalian diversity. However, the significance of monotremes to mammalian evolutionary history and biology is far more than can be measured by their few genera. The evolutionary stature of monotremes as the first group to diverge among extant mammal lineages has been corroborated by an overwhelming body of scientific evidence from fossils, comparative morphology, and molecular information on the genomic scale. With their highly specialized physiological and functional adaptations, distinctive developmental pattern and karyotypes, these egg-laying mammals push the envelope of human imagination regarding what is possible for mammalian biological diversity. For evolutionists, monotremes represent the extant phylogenetic bracket for the common ancestor of all modern mammals (crown Mammalia). For physiologists and functional morphologists, monotremes give meaning to mammalian structural and functional diversities. For ecologists and conservation biologists, the monotremes are an integral element of an ecosystem on Gondwanaland from the deep times of the Earth. Since the echidna and platypus became known to western science in 1792 and 1800, respectively, monotremes have always fascinated the scientific community and the public (Moyal 2001). But monotremes are more than a curiosity—they are an indispensable group for all scientists in pursuit of any area of mammalian comparative biology to consider. In Echidna—An Extraordinary Egg-Laying Mammal, Michael Augee, Brett Gooden, and Anne Musser have written an excellent primer on the biology and natural history of the shortbeaked echidna—Tachyglossus aculeatus or the spiny anteater. This book of 136 pages is a concise, informative, and immensely readable review of the structure, function, physiology, behavior, and life history of the echidna. It is well aimed at a general scientific readership and contains very interesting information on all aspects of the natural history and biology J Mammal Evol (2007) 14:283–285 DOI 10.1007/s10914-007-9059-1

The pretectal nuclei in two monotremes: the short-beaked echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus)

We have examined the organization of the pretectal area in two monotremes (the short beaked echidna-Tachyglossus aculeatus, and the platypus-Ornithorhynchus anatinus) and compared it to that in the Wistar strain rat, using Nissl staining in conjunction with enzyme histochemistry (acetylcholinesterase and NADPH diaphorase) and immunohistochemistry for parvalbumin, calbindin, calretinin and non-phosphorylated neurofilament protein (SMI-32 antibody). We were able to identify distinct anterior, medial, posterior (now called tectal gray) and olivary pretectal nuclei as well as a nucleus of the optic tract, all with largely similar topographical and chemoarchitectonic features to the homologous regions in therian mammals. The positions of these pretectal nuclei correspond to the distributions of retinofugal terminals identified by other authors. The overall size of the pretectum in both monotremes was found to be at least comparable in size, if not larger than, the pretectum of representative therian mammals of similar brain and body size. Our findings suggest that the pretectum of these two monotreme species is comparable in both size and organization to that of eutherian mammals, and is more than just an undifferentiated area pretectalis. The presence of a differentiated pretectum with similar chemoarchitecture to therians in both living monotremes lends support to the idea that the stem mammal for both prototherian and therian lineages also had a differentiated pretectum. This in turn indicates that a differentiated pretectum appeared at least 125 million years ago in the mammalian lineage and that the stem mammal for proto- and eutherian lineages probably had similar pretectal nuclei to those identified in its descendants.

Cyto- and chemoarchitecture of the amygdala of a monotreme, Tachyglossus aculeatus (the short-beaked echidna)

We have examined the cyto- and chemoarchitecture of the temporal and extended amygdala in the brain of a monotreme (the short-beaked echidna Tachyglossus aculeatus) using Nissl and myelin staining, enzyme histochemistry for acetylcholine esterase and NADPH diaphorase, immunohistochemistry for calcium binding proteins (parvalbumin, calbindin and calretinin) and tyrosine hydroxylase. While the broad subdivisions of the eutherian temporal amygdala were present in the echidna brain, there were some noticeable differences. No immunoreactivity for parvalbumin or calretinin for somata was found in the temporal amygdala of the echidna. The nucleus of the lateral olfactory tract could not be definitively identified and the medial nucleus of amygdala appeared to be very small in the echidna. Calbindin immunoreactive neurons were most frequently found in the ventrolateral part of the lateral nucleus, intraamygdaloid parts of the bed nucleus of the stria terminalis and the lateral part of the central nucleus. Neurons strongly reactive for NADPH diaphorase with filling of the dendritic tree were found mainly scattered through the cortical, central and lateral subnuclei, while neurons showing only somata reactivity for NADPH diaphorase were concentrated in the basomedial and basolateral subnuclei. Most of the components of the extended amygdala of eutherians could also be identified in the echidna. Volumetric analysis indicated that the temporal amygdala in both the platypus and echidna is small compared to the same structure in both insectivores and primates, with the central and medial components of the temporal amygdala being particularly small.

Local extinction and nestedness of small-mammal faunas in fragmented forest of central Victoria, Australia

A survey of small mammals was undertaken in eight forest fragments of three sizes (2.5, 10 and 40 ha) and in five "pseudofragments" within a large area of State Forest. The latter were used to provide "reference" results against which the fragments could be compared. There was a paucity of dasyurid marsupials in fragments and pseudofragments, but arboreal "herbivores" (possums and a glider) were 7.5 times more abundant in fragments than in pseudofragments. The Short-beaked Echidna Tachyglossus aculeatus was recorded in both fragments and pseudofragments. All sites were impoverished, with a maximum of four native species of small mammals recorded at any one site, and six native species recorded overall. There was significant faunal "nesting" as a function of fragment size, with the small-mammal fauna of smaller fragments being subsets of larger fragments. The extant fauna in fragments appears to be a result of a sequence of local extinctions such that some species are more vulnerable to habitat loss, fragmentation and degradation and become locally extinct earlier than other, hardier species. The impoverishment within pseudofragments seems to be a function of broad-scale habitat modifications and especially timber harvesting, which maintains the forest as a dense array of small, pole-sized trees with few large, old trees. Several of the arboreal mammals are dependent on hollows found in larger trees, so the absence of the latter probably constrains the occurrence and density of the hollow users.

Platypus and Echidnas

Platypus and Echidnas presents the proceedings of a conference held at the University of New South Wales in July 1991. Platypus and Echidnas incorporates an extensive information source obtained from studies undertaken since the first symposium on "Monotreme Biology" in 1978, while highlighting deficiencies in our knowledge, and subsequently suggests further avenues for research. The theme of evolution re-occurs throughout the publication and the studies demonstrate how patterns of mammalian phylogeny may be derived from various sources including palaeontology, gene mapping, DNA hybridization, reproductive physiology and endocrinology. Interest in this publication will extend to: (i) scholars of phylogeny and evolution especially part 1); (ii) comparative physiologist, physiological ecologists and anatomists (parts 1, 3, 4 and 5); (iii) ecologists and sacio-ecologists (parts 3, 5 and 6); (iv) natural historians; (v) keepers of captive wildlife colonies (parts 3 and 6); (vi) wildlife veterinary surgeons (part 6); and (vii) wildlife managers (especially part 6). The book deals primarily with the short-beaked echidna Tachyglossus aculeatus and the platypus Ornithorhynchus anatinus, for which most information is available.