Immunocytochemical study of the endocrine pancreas in the grey kangaroo (Macropus fuliginosus)

Summary The endocrine pancreas of the grey kangaroo,Macropus fuliginosus, was investigated by means of immunocytochemistry using the PAP method on the same section at the light- and electron-microscopic levels. Semithin plastic sections were stained individually with primary antibodies for insulin, glucagon, somatostatin and pancreatic polypeptide (PP), and then photographed. Sections were osmicated, re-embedded in BEEM capsules, and ultrathin sections made and examined. The same labelled cells as in the semithin sections were localised in the thin sections, photographs taken and the morphology of secretory granules studied. The insulin cells were pleomorphic; their secretory granules displayed an electron-dense core surrounded by an empty halo. The glucagon cells possessed granules with an electron-dense core usually surrounded by a halo of less dense granular material. Somatostatin cells had larger, less dense secretory granules. The PP cells showed small, dense secretory granules. In order for an ultrastructural study to be considered reliable for the definite identification of endocrine cell types, it is essential that it be corroborted by correlated immunocytochemical data at the light-and electron-microscopic levels.     

The α-Globin Gene Family of an Australian Marsupial, Macropus eugenii: The Long Evolutionary History of the θ-Globin Gene and Its Functional Status in Mammals

Comparative evolutionary analyses of gene families among divergent lineages can provide information on the order and timing of major gene duplication events and evolution of gene function. Here we investigate the evolutionary history of the α-globin gene family in mammals by isolating and characterizing α-like globin genes from an Australian marsupial, the tammar wallaby, Macropus eugenii. Sequence and phylogenetic analyses indicate that the tammar α-globin family consists of at least four genes including a single adult-expressed gene (α), two embryonic/neonatally expressed genes (ζ and ζ′), and θ-globin, each orthologous to the respective α-, ζ-, and θ-globin genes of eutherian mammals. The results suggest that the θ-globin lineage arose by duplication of an ancestral adult α-globin gene and had already evolved an unusual promoter region, atypical of all known α-globin gene promoters, prior to the divergence of the marsupial and eutherian lineages. Evolutionary analyses, using a maximum likelihood approach, indicate that θ-globin, has evolved under strong selective constraints in both marsupials and the lineage leading to human θ-globin, suggesting a long-term functional status. Overall, our results indicate that at least a four-gene cluster consisting of three α-like and one β-like globin genes linked in the order 5′–ζ–α–θ–ω–3′ existed in the common ancestor of marsupials and eutherians. However, results are inconclusive as to whether the two tammar ζ-globin genes arose by duplication prior to the radiation of the marsupial and eutherian lineages, with maintenance of exon sequences by gene conversion, or more recently within marsupials.Reviewing Editor: Dr. John Oakeshott     

Exsheathment of the infective larva of Labiostrongylus eugenii, a nematode parasite of the Kangaroo Island wallaby Macropus eugenii.

The infective larva of L. eugenii is enveloped in two cuticles which are discarded when the larva exsheaths in the sacculated portion of the wallaby's stomach. In vitro larvae exsheathed in a 0·85% solution of sodium chloride at 37°C, buffered to pH 7 with bicarbonate ion and 40% carbon dioxide. Survival was enhanced if the liquid phase contained medium 199 and serum, and exsheathment was quicker if exposure to carbon dioxide was 1 h rather than 1 day or 7 days. As larvae exsheathed, contractions of the pharynx commenced, and medium was ingested, even when larvae were enveloped in both cuticles. The stimuli for exsheathment and the subsequent pattern of events are like those already recognised in some trichostrongyles.     

Linkage of the β-Like ω-Globin Gene to α-Like Globin Genes in an Australian Marsupial Supports the Chromosome Duplication Model for Separation of Globin Gene Clusters

The structure, function, and evolutionary history of globin genes have been the subject of extensive investigation over a period of more than 40 years, yet new globin genes with highly specialized functions are still being discovered and much remains uncertain about their evolutionary history. Here we investigate the molecular evolution of the -globin gene family in a marsupial species, the tammar wallaby, Macropus eugenii. We report the complete DNA sequences of two -like globin genes and show by phylogenetic analyses that one of these genes is orthologous to embryonically expressed -globin genes of marsupials and eutherians and the other is orthologous to adult expressed -globin genes of marsupials and eutherians. We show that the tammar wallaby contains a third functional -like globin gene, -globin, which forms part of the -globin gene cluster. The position of -globin on the 3 side of the -globin cluster and its ancient phylogenetic history fit the criteria, originally proposed by Jeffreys et al. (1980), of a fossil -globin gene and suggest that an ancient chromosome or genome duplication preceded the evolution of unlinked clusters of - and -globin genes in mammals and avians. In eutherian mammals, such as humans and mice, -globin has been silenced or translocated away from the -globin locus, while in marsupials -globin is coordinately expressed with the adult -globin gene just prior to birth to produce a functional hemoglobin (_{2 2}).     

The interdependence of fire, grass, kangaroos and Australian Aborigines: a case study from central Arnhem Land, northern Australia

Aim To describe the nexus between Aboriginal landscape burning and patterns of habitat use by kangaroos in a tropical savanna habitat mosaic, and to provide evidence to evaluate the claim that Aboriginal landscape burning is a game management tool. Location Central Arnhem Land, a stronghold of traditional Aboriginal culture, in the monsoon tropics of northern Australia. Methods The abundance of kangaroo scats was recorded throughout a landscape burnt by Aboriginal people, and used as a proxy for the intensity of habitat use by kangaroos. Scat abundance was assessed along field traverses totalling 112 km, at three time periods: (1) 1–4 weeks following mid‐dry season burning (July 2003); (2) in the late dry season (November 2003); and (3) in the following mid‐dry season (July 2004). We compared the intensity with which kangaroos used burnt vs. unburnt areas in various habitat types, with time since mid‐dry season burning. Scats were collected from areas that had been burnt to a varying extent and the abundance of carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) and carbon to nitrogen ratios (C : N) determined. Results There was clear evidence of an interaction between burning and habitat type on the abundance of kangaroo scats. Scats were much more abundant in burnt vs. unburnt areas in the moist habitats, but the opposite effect was observed in the dry rocky habitats, with higher scat abundance in unburnt areas. This interactive effect of burning and habitat type on scat abundance was observed immediately (< 4 weeks) following fire, and was still present one year later. High concentrations of nitrogen in resprouting grasses indicate that burnt areas may provide kangaroos with greater access to nutrients. The isotopic composition of scats indicates that kangaroos feeding in extensively burnt areas were consuming more grasses, and possibly sedges, than kangaroos feeding in unburnt areas. Main conclusions The fine‐scale mosaic of burnt and unburnt areas created by mid‐dry season Aboriginal landscape burning has clear effects on the distribution of kangaroos. Kangaroos move into burnt moist habitats and away from burnt dry, rocky habitats. Isotopic analysis of scats suggests that the mechanism driving this effect is the increased abundance of nitrogen rich grasses in burnt moist habitats.     

Diet of four rock‐dwelling macropods in the Australian monsoon tropics

Abstract An unusually high diversity of macropods inhabit the rocky areas in the monsoon tropics of the Northern Territory, Australia, yet the mechanisms that allow their niche separation are not clear. Previous studies suggest that the nabarlek, Petrogale concinna, may have a more grazing diet than the short‐eared rock‐wallaby, Petrogale brachyotis, with whom it coexists. Thus, diet may be an important mechanism of niche separation between these species. We examined the diet of the four sympatric species (the black wallaroo Macropus bernardus, common wallaroo Macropus robustus, P. brachyotis and P. concinna) to determine whether there are differences in the dominant plant groups eaten by the species across the landscape and with season. Diets were determined with a macroscopic analysis of the seed and fruit content of scats and an analysis of the ¹²C to ¹³C isotope ratios of scats using mass spectrometry. In the dry season the rock‐wallaby species predominantly consumed browse and/or forbs, and the larger wallaroos predominantly consumed grass. However, there was large variation across the landscape in the dry season diets of P. brachyotis, M. bernardus and M. robustus; including high proportions of grass eaten at some sites and high proportions of browse at other sites. In the wet season, greater proportions of grass were eaten by P. brachyotis and M. bernardus than in the dry season. Generally, there was little evidence to support the previous suggestion that P. concinna is more of a grazer than P. brachyotis, but there was some evidence than M. bernardus consumes greater amounts of browse and/or forbs than M. robustus.     

Mosquito host-feeding patterns and implications for Japanese encephalitis virus transmission in northern Australia and Papua New Guinea

Japanese encephalitis (JE) virus spread to northern Australia during the 1990s, transmitted by Culex annulirostris Skuse and other mosquitoes (Diptera: Culicidae). To determine the relative importance of various hosts for potential vectors of JE virus, we investigated the host-feeding patterns of mosquitoes in northern Australia and Western Province of Papua New Guinea, with particular attention to pigs, Sus scrofa L. - the main amplifying host of JE virus in South-east Asia. Mosquitoes were collected by CDC light traps baited with dry ice and 1-octen-3-ol, run 16.00-08.00 hours, mostly set away from human habitations, if possible in places frequented by feral pigs. Bloodmeals of 2569 mosquitoes, representing 15 species, were identified by gel diffusion assay. All species had fed mostly on mammals: only <10% of bloodmeals were from birds. The predominant species was Cx. annulirostris (88%), with relatively few (4.4%) bloodmeals obtained from humans. From all 12 locations sampled, the mean proportion of Cx. annulirostris fed on pigs (9.1%) was considerably lower than fed on other animals (90.9%). Highest rates of pig-fed mosquitoes (>30%) were trapped where domestic pigs were kept close to human habitation. From seven of eight locations on the Australian mainland, the majority of Cx. annulirostris had obtained their bloodmeals from marsupials, probably the Agile wallaby Macropus agilis (Gould). Overall proportions of mosquito bloodmeals identified as marsupial were 60% from the Gulf Plains region of Australia, 78% from the Cape York Peninsula and 64% from the Daru area of Papua New Guinea. Thus, despite the abundance of feral pigs in northern Australia, our findings suggest that marsupials divert host-seeking Cx. annulirostris away from pigs. As marsupials are poor JE virus hosts, the prevalence of marsupials may impede the establishment of JE virus in Australia.