Selective stimulation and blockade of β-adrenergic receptors in the mandibular gland of the red kangaroo, Macropus rufus

Intracarotid infusions of noradrenaline (0.15 nmol · kg⁻¹ · min⁻¹) either alone or accompanied by phentolamine (1.5 nmol · kg⁻¹ · min⁻¹) caused similar-sized increases in salivary protein, magnesium and bicarbonate, and decreases in osmolality, sodium, potassium and chloride whereas intravenous noradrenaline stimulated much smaller responses. Concurrent infusions of the β₁-antagonist, CGP20712A, blocked these noradrenaline-induced changes in salivary composition more effectively than equimolar infusions of the β₂-antagonist, ICI118551, thereby confirming the presence of β₁-adrenoceptors. Intracarotid infusion of salbutamol at 0.15, 0.3 and 1.5 nmol · kg⁻¹ · min⁻¹ caused increasing but qualitatively similar changes in salivary composition, sodium excepted, to intracarotid noradrenaline with 0.3 nmol being most similar quantitatively. Intravenous infusion of salbutamol caused larger changes in salivary composition than equimolar intravenous noradrenaline thereby indicating that the response to salbutamol may, in part, be mediated by reflex increases in general sympathetic tone triggered by lowered blood pressure. Eliminating this hypotensive effect by concurrent intravenous and intracarotid infusions of β₁-(CGP or atenolol) and β₂-(ICI118551) antagonists with intracarotid salbutamol showed that ICI118551 was more potent than the β₁-antagonists thereby demonstrating the presence of β₂-receptors. It was concluded that the kangaroo mandibular has functional β₁- and β₂-adrenoceptor subtypes in both endpieces and excurrent ducts and that the duct system has two populations of cells, each expressing one receptor subtype. Accepted: 26 July 2000     

Circadian variation in resource quality: leaf water content and its relevance to eastern grey kangaroo Macropus giganteus and common wombat Vombatus ursinus

Green leaves of six grass species in temperate Australia showed considerable circadian variation (especially in summer) in water content, which peaked late in the night and fell from sunrise to an afternoon minimum. In summer, water content of a set of ‘wetter’ species (Axonopus affinis, Pennisetum clandestinum and Paspalum dilatatum) was consistently higher and varied less profoundly through the 24 h than that of a ‘drier’ set (Imperata cylindrica, Poa labillardieri and Themeda triandra). Hour‐to‐hour and day‐to‐day variation in leaf water content of P. dilatatum in summer partly but imperfectly reflected ambient temperature. Recognizing the risks for herbivores of visiting water sources, we considered leaf water content as a source of free water for leaf‐grazing herbivores, eastern grey kangaroos Macropus giganteus and common wombats Vombatus ursinus. Using known field metabolic rates, energy requirements and digestive efficiencies, we calculated these two species' free‐water intakes when satisfying their energy needs with these grasses but distributing their grazing in different schedules. Both species would obtain more free water by their observed foraging schedules than by random or daytime‐only schedules. We calculated that the measured grasses could satisfy the water requirements of wombats but not always those of kangaroos, who would need to drink when forage water content was less than about 70%. Water content of grass leaf could rise above and fall below this value within a day, creating some scope for kangaroos to manage their need to visit water by adjusting foraging schedules or choice of grass species. In future studies, circadian variation in leaf water content should be considered as a factor (together with their thermal physiology) driving herbivores' activity scheduling, and affecting their dietary selection.     

Are dingoes a trophic regulator in arid Australia? A comparison of mammal communities on either side of the dingo fence

The direct and indirect interactions that large mammalian carnivores have with other species can have far‐reaching effects on ecosystems. In recent years there has been growing interest in the role that Australia's largest terrestrial predator, the dingo, may have in structuring ecosystems. In this study we investigate the effect of dingo exclusion on mammal communities, by comparing mammal assemblages where dingoes were present and absent. The study was replicated at three locations spanning 300 km in the Strzelecki Desert. We hypothesized that larger species of mammal subject to direct interactions with dingoes should increase in abundance in the absence of dingoes while smaller species subject to predation by mesopredators should decrease in abundance because of increased mesopredator impact. There were stark differences in mammal assemblages on either side of the dingo fence and the effect of dingoes appeared to scale with body size. Kangaroos and red foxes were more abundant in the absence of dingoes while Rabbits and the Dusky Hopping‐mouse Notomys fuscus were less abundant where dingoes were absent, suggesting that they may benefit from lower red fox numbers in the presence of dingoes. Feral cats and dunnarts (Sminthopsis spp.) did not respond to dingo exclusion. Our study provides evidence that dingoes do structure mammal communities in arid Australia; however, dingo exclusion is also associated with a suite of land use factors, including sheep grazing and kangaroo harvesting that may also be expected to influence kangaroo and red fox populations. Maintaining or restoring populations of dingoes may be useful strategies to mitigate the impacts of mesopredators and overgrazing by herbivores.     

Coccidiosis in wild grey kangaroos

Deaths occurred among wild grey kangaroos (Macropus giganteus) whose habitat was subject to flooding. A sample of the involved juvenile animals was hypoproteinaemic, and extensive haemorrhagic enteritis, associated with the presence of coccidial life cycle stages was found in the small intestine at necropsy. Masses of small schizonts infected cells of the lamina propria; large schizonts occupied clusters of hypertrophied cells; macrogametes and microgametocytes were observed in cells of the lamina propria. The species of coccidia involved could not be determined, although oocysts of Eimeria cunnamullensis and E. kogoni were found in faeces. Overcrowding, food shortage, damp conditions and possibly feed supplementation with hay on the ground were considered probable epizootiological factors contributing to an outbreak of coccidiosis among juvenile animals.     

Molecular population genetics of the red kangaroo (Macropus rufus): mtDNA variation

The genetic population structure of a large, wide-ranging marsupial, the red kangaroo ( Macropus rufus ) was assessed using sequence and haplotype frequency data of mitochondrial DNA (mtDNA) from locations across the species range in Australia. Results from sequence data revealed extensive haplotype diversity within the red kangaroo (32/34 sequences were unique). Sequence diversity was distributed within rather than between geographical regions across the species range. Genetic connectivity across the range of the species has therefore been maintained over the long term. On a smaller within-region scale, significant genetic structuring was evident from heterogeneity of haplotype frequencies amongst sampling sites. The geographical scale of panmictic populations differed across the continent with more restricted genetic populations occurring in areas with greater topographic and habitat complexity. We propose that these differences in area of genetic populations are the result of population responses to limiting ecological factors during drought.     

The effect of carbonic anhydrase inhibitors on secretion by the parotid and mandibular glands of red kangaroos Macropus rufus

Summary The effects of carbonic anhydrase inhibitors on secretion by macropodine parotid and mandibular glands were investigated using anaesthetized red kangaroos. In the parotid gland, acetazolamide (500 mol·l^-1) reduced a stable acetylcholine-evoked, half-maximal flow rate of 2.02±0.034 to 0.27±0.023 ml·min^-1 (87% reduction). Concurrently, salivary bicarbonate concentration and secretion fell (129.4±1.46 to 80.9±1.63 mmol·l^-1 and 264.8±7.96 to 22.3±2.30 mol·min^-1, respectively), phosphate and chloride concentrations rose (14.0±0.79 to 27.6±0.85 mmol·l^-1 and 5.6±0.25 to 27.5±1.32 mmol·l^-1, respectively), sodium concentration and osmolality were unaltered, and potassium concentration fell (8.8±0.33 to 6.4±0.29 mmol·l^-1). High-rate cholinergic stimulation during acetazolamide blockade was unable to increase salivary flow beyond 11±0.9% of that for equivalent unblocked control stimulation. However, superimposition of isoprenaline infusion on the acetylcholine stimulation caused a three-fold increase in the blocked flow rate. These treatments were accompanied by small increases in salivary phosphate and chloride concentrations but not bicarbonate concentration. Methazolamide infusion caused similar changes in parotid secretion. In the mandibular gland, acetazolamide infusion had no effect on salivary flow rate during either low- or high-level acetylcholine stimulation. Acetazolamide caused no alterrations in salivary electrolyte secretion at low flow rates, but curtailed the rise in bicarbonate concentration associated with high-level acetylcholine stimulation. Acetazolamide administration did not affect the increase in salivary flow rate associated with isoprenaline infusion, but did block the concomitant increase in bicarbonate concentration and secretion substantially. It was concluded that neither cholinergic nor adrenergic stimulation of mandibular fluid secretion depends on secretion of bicarbonate derived from catalysed hydration of CO₂, but a substantial proportion of the increase in bicarbonate secretion during isoprenaline administration, which is probably ductal in origin, is so dependent. In contrast to other salivary glands, including the ovine parotid, fluid secretion by the kangaroo parotid gland during cholinergic stimulation is largely dependent (about 90%) on secretion of bicarbonate derived from hydration of CO₂ catalysed by glandular carbonic anhydrase. Fluid secretion during adrenergic stimulation is not bicarbonate dependent.Abbreviations b.w. body weight - PAH p-aminohippurate - PCO₂ partial pressure carbon dioxide - PCO₂ partial pressure of oxygen     

Germination of native and introduced plants from scats of Fallow Deer (Dama dama) and Eastern Grey Kangaroo (Macropus giganteus) in a south‐eastern Australian woodland landscape

Introduced deer occur in many forests and woodlands in Australia and potentially play an important role in influencing the floristics and structure of these landscapes through eating plants and disseminating seeds. In a glasshouse trial, we tested whether field‐collected scats of Fallow Deer (Dama dama) contained viable plant seeds. Scats of deer obtained from a woodland study area in Kosciuszko National Park, New South Wales, produced seedlings from a range of native and introduced plant species. Forbs and herbs were dominant in these samples, confirming the grazing behaviour of deer at the time scats were collected. Samples of scats from Eastern Grey Kangaroos (Macropus giganteus), collected contemporaneously from the same sites as deer scats, also produced plant germinants. By volume, deer scats produced a greater diversity of plant germinants, including native and weed species, than did kangaroo scats. Although no weed species emanating from deer or kangaroo scats were of national significance, several species were of regional environmental significance, including Common Mullein (Verbascum thapsis), which was only found germinating out of deer scat, Stinkgrass (Eragrostis cilianensis) and Purpletop (Verbena bonariensis). In addition to dispersing viable seeds, Fallow Deer may also influence vegetation structure through their browsing. Further research is necessary to elucidate their respective role in dispersing native and introduced plants as well as any impacts that foraging behaviour might be having on woodland landscapes, to better inform management of the resident deer population.     

Molecular Evidence for the Last Survivor of an Ancient Kangaroo Lineage

The Australasian marsupial family Macropodidae includes potoroos and bettongs (Potoroinae) as well as larger kangaroos, wallabies, and pademelons (Macropodinae). Perhaps the most enigmatic macropodid is the banded hare wallaby, Lagostrophus fasciatus, a taxon listed as vulnerable by the IUCN. Lagostrophus had traditionally been grouped as a sister-taxon to hare wallabies (Lagorchestes), in a clade with hypsodont macropodines, or intercalated in some other fashion within Macropodinae. Flannery (1983, 1989) proposed a radically different hypothesis wherein Lagostrophus is outside of Macropodinae and is more closely related to extinct sthenurine (short-faced) kangaroos. Given this controversy, we addressed the phylogenetic placement of the banded hare wallaby using molecular sequences for three mitochondrial genes (12S rRNA, valine tRNA, 16S rRNA) and one nuclear gene (protamine P1). Diverse phylogenetic methods all provided robust support for a macropodine clade that excludes the banded hare wallaby. The split between macropodines and the banded hare wallaby was estimated at approximately 20 million years ago (mya) using the Thorne/Kishino relaxed molecular clock method. Whereas our molecular results neither corroborate nor refute the sthenurine hypothesis, since all short-faced kangaroos and their immediate ancestors are extinct, the overriding implication of molecular phylogenetic analyses is manifest: the banded hare wallaby is the only living relict of an ancient kangaroo lineage. Regardless of its precise relationships, special efforts should be directed at conserving this unique and endangered taxon, which has not been recorded from mainland Australia since 1906 and is now restricted to two tiny islands off the coast of Western Australia.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022697300092     

Promotion of exotic weed establishment by endangered giant kangaroo rats (Dipodomys ingens) in a California grassland

Giant kangaroo rats (Dipodomys ingens) continually modify their burrow precincts by digging tunnels, clipping plants, and other activities. In the valley grasslands of the Carrizo Plain Natural Area (San Luis Obispo County, California), this chronic disturbance to soil and vegetation promoted the establishment of exotic ruderal and early successional plant species. Erodium cicutarium, Bromus madritensis ssp. rubens, and other Mediterranean annuals were found to constitute a very large proportion of the vegetation on giant kangaroo rat precincts. When vegetation on precincts was compared with the vegetation in less disturbed intermediate areas located between precincts, species richness, cover and frequency of exotic plants were significantly greater on precincts. The reverse was found for native species. In addition, exotic species encountered in this study had significantly larger seeds than did native species, suggesting that these granivorous kangaroo rats preferentially cache large weed seeds on their precincts. Since the kangaroo rats depend on exotic plants for food and the exotic plants depend upon the kangaroo rats to disturb their habitat continually, the weed-kangaroo rat relationship is mutualistic. This strong relationship may also inhibit population growth of native grassland plants which occupy disturbed habitats but have difficulty competing with exotic weeds for resources. From a conservation perspective, this mutualism presents an intractable management dilemma. Restoration of valley grasslands where endangered giant kangaroo rats occur, to conditions where native species dominate, may be impossible.