Survivable hypothermia or torpor in a wild-living rat: rare insights broaden our understanding of endothermic physiology

Maintaining a high and stable body temperature as observed in endothermic mammals and birds is energetically costly. Thus, it is not surprising that we discover more and more heterothermic species that can reduce their energetic needs during energetic bottlenecks through the use of torpor. However, not all heterothermic animals use torpor on a regular basis. Torpor may also be important to an individual’s probability of survival, and hence fitness, when used infrequently. We here report the observation of a single, ~ 5.5 h long hypothermic bout with a decrease in body temperature by 12 °C in the native Australian bush rat (Rattus fuscipes). Our data suggest that bush rats are able to rewarm from a body temperature of 24 °C, albeit with a rewarming rate lower than that expected on the basis of their body mass. Heterothermy, i.e. the ability to withstand and overcome periods of reduced body temperature, is assumed to be an evolutionarily ancestral (plesiomorphic) trait. We thus argue that such rare hypothermic events in species that otherwise appear to be strictly homeothermic could be heterothermic rudiments, i.e. a less derived form of torpor with limited capacity for rewarming. Importantly, observations of rare and extreme thermoregulatory responses by wild animals are more likely to be discovered with long-term data sets and may not only provide valuable insight about the physiological capability of a population, but can also help us to understand the constraints and evolutionary pathways of different phenologies.

The diet of a Sooty Owl from Yarrangobilly Caves, NSW

ABSTRACT A total of 783 dietary items from a Sooty Owl Tyto tenebricosa tenebricosa with suspected partial xanthochromism (yellow plumage colouration) was identified from Yarrangobilly Caves, NSW. Observations of the owl at the cave and collection of feathers suggest that prey items accumulated between 2011 and 2018. A total of 12 mammal species was detected in the diet, with the Bush Rat Rattus fuscipes, Agile Antechinus Antechinus agilis, Sugar Glider Petaurus breviceps and Rabbit Oryctolagus cuniculus dominating. The diet also included three threatened species, the Eastern Pygmy Possum Cercartetus nanus, Smoky Mouse Pseudomys fumeus and Broad-toothed Rat Mastacomys fuscus. The diversity of prey identified in the diet contrasts markedly with that found in studies of subfossil deposits from the area, supporting evidence of extensive mammal declines since European settlement.

The mitochondrial genome of Angiostrongylus mackerrasae is distinct from A. cantonensis and A. malaysiensis

The native rat lungworm (Angiostrongylus mackerrasae) and the invasive rat lungworm (Angiostrongylus cantonensis) occur in eastern Australia. The species identity of A. mackerrasae remained unquestioned until relatively recently, when compilation of mtDNA data indicated that A. mackerrasae sensu Aghazadeh et al. (2015b) clusters within A. cantonensis based on their mitochondrial genomes (mtDNA). To re-evaluate the species identity of A. mackerrasae, we sought material that would be morphologically conspecific with A. mackerrasae. We combined morphological and molecular approaches to confirm or refute the specific status of A. mackerrasae. Nematodes conspecific with A. mackerrasae from Rattus fuscipes and Rattus rattus were collected in Queensland, Australia. Morphologically identified A. mackerrasae voucher specimens were characterized using amplification of cox1 followed by the generation of reference complete mtDNA. The morphologically distinct A. cantonensis, A. mackerrasae and A. malaysiensis are genetically distinguishable forming a monophyletic mtDNA lineage. We conclude that A. mackerrasae sensu Aghazadeh et al. (2015b) is a misidentified specimen of A. cantonensis. The availability of the mtDNA genome of A. mackerrasae enables its unequivocal genetic identification and differentiation from other Angiostrongylus species.

Assessment of Hazardous Metal Concentrations in Organs of Selected Game Animals in the Natural Environment

The study was conducted to determine the levels of hazardous metals in game animals. A total of eighteen (18) animals which comprised six species of three (3) each from the same location were trapped or hunted and sacrificed. Organs analyzed for hazardous metal levels were skin, liver, kidney and heart using Atomic Absorption Spectrometry and content expressed in mgkg-1. The statistical analysis was done with Genstat (2007). Results obtained showed that all the hazardous metals under study were present in the organs at variable concentrations. Lead: skin (0.18 – 0.46) mgkg-1, liver (0.03 – 0.4) mgkg-1, heart (0.25 – 0.58) mgkg-1 and kidney (0.38 1.12) mgkg-1; Cadmium: skin (0.08 – 0.58) mgkg-1 and kidney (0.09 – 0.7) mgkg-1; Zinc : skin ( 0.46 – 0.66) mgkg-1, liver (90.04 – 0.82) mgkg-1, heart (0.42 – 1.21) mgkg-1 and kidney (0.43 – 1.58) mgkg-1; Copper: skin (6.13 – 12.57) mgkg-1, liver (5.1 – 9.56) mgkg-1, heart (6.89 - 15.15) mgkg-1 and kidney (7.63 – 24.87) mgkg-1; Iron : skin (9.53 – 26.35) mgkg-1, liver (8.07 -28.08) mgkg-1, heart (13.83 - 46.40) mgkg-1 and kidney (12.43 – 47.61) mgkg-1. Iron was highly (p <0.05) deposited in all species of animals in the heart 19.88 mgkg-1, 46.40 mgkg-1, 40.83 mgkg-1, 13.83 mgkg-1 and 41.38 mgkg-1 respectively for civet (Civettictis civeta), antelope (Antilocapra americana), grasscutter (Thryonomys swiderianus), hedgehog (Atelerix albiventris) and bush dog (Speothos venaticus) except the bush rat (Rattus fuscipes) that had its highest deposition (46.71 mgkg-1) in the kidney. Copper was also highly deposited in animals after iron with higher concentrations in heart and kidney. The highest concentration was recorded for bush rat (Rattus fuscipes) (15.15 mgkg-1) in heart and 24.87 mgkg-1 in kidney. Due to bioaccumulation of hazardous metals, care should be taken in patronizing bushmeat obtained from the studied ecosystem since failure could be perilous to the health of consumers as their concentrations are beyond the safe limits for the respective metals. It is further recommended that environmental safety principles for safe disposal of hazardous metals are appropriately carried out.

Oils ain’t oils: can truffle-infused food additives improve detection of rare and cryptic mycophagous mammals?

We tested whether an artificial food additive, truffle oil, improved detection of mycophagous mammals when added to a standard bait type of peanut butter and rolled oats used with camera traps. Sixteen mammalian taxa were subsequently recorded, the most common being antechinus, bush rat (Rattus fuscipes), swamp wallaby (Wallabia bicolor) and long-nosed bandicoot (Perameles nasuta) as well as the long-nosed potoroo (Potorous tridactylus) and southern brown bandicoot (Isoodon obesulus). The only species for which detection rate was improved by the addition of truffle oil to standard bait was the ringtail possum (Pseudocheirus peregrinus), a species that has never been recorded eating fungi. In contrast, the total number of detections of all species at any given site was significantly higher, on average, using standard bait without truffle oil, as was the average number of detections of the partially mycophagous bush rat. Time to first detection of bush rats and swamp wallabies was significantly shorter using the standard bait type, compared with one with truffle oil added. Overall, the use of the truffle oil additive did not improve the chance or rate of detecting mycophagous mammals. To maximise the number of detections of mammals at camera traps the use of a standard bait type of peanut butter and rolled oats is recommended.

Habitat selection by two sympatric rodent species in an alpine resort

Conservation of small mammal species relies on an understanding of their habitat use. We used trapping surveys and telemetry to examine habitat selection and use by the broad-toothed rat (Mastacomys fuscus mordicus) and the bush rat (Rattus fuscipes) in an alpine resort in Victoria. M. fuscus occurred at low numbers, nesting in subalpine wet heathland and foraging in that habitat as well as small patches of disturbed woodland. In contrast, R. fuscipes was more common and nested in woodlands. Although foraging primarily in woodlands, R. fuscipes also foraged in all other available habitats. Both species showed strong selection for woodland fragments within ski runs. Although highly disturbed, these habitats may provide important habitat and connectivity between less disturbed and larger habitat patches.

Fire affects microhabitat selection, movement patterns, and body condition of an Australian rodent ( Rattus fuscipes )

Resource selection by animals influences individual fitness, the abundance of local populations, and the distribution of species. Further, the degree to which individuals select particular resources can be altered by numerous factors including competition, predation, and both natural- and human-induced environmental change. Understanding the influence of such factors on the way animals use resources can guide species conservation and management in changing environments. In this study, we investigated the effects of a prescribed fire on small-scale (microhabitat) resource selection, abundance, body condition, and movement pathways of a native Australian rodent, the bush rat ( Rattus fuscipes ). Using a before-after, control-impact design, we gathered data from 60 individuals fitted with spool and line tracking devices. In unburnt forest, selection of resources by bush rats was positively related to rushes, logs and complex habitat, and negatively related to ferns and litter. Fire caused selection for spreading grass, rushes, and complex habitat to increase relative to an unburnt control location. At the burnt location after the fire, rats selected patches of unburnt vegetation, and no rats were caught at a trapping site where most of the understory had been burnt. The fire also reduced bush rat abundance and body condition and caused movement pathways to become more convoluted. After the fire, some individuals moved through burnt areas but the majority of movements occurred within unburnt patches. The effects of fire on bush rat resource selection, movement, body condition, and abundance were likely driven by several linked factors including limited access to shelter and food due to the loss of understory vegetation and heightened levels of perceived predation risk. Our findings suggest the influence of prescribed fire on small mammals will depend on the resulting mosaic of burnt and unburnt patches and how well this corresponds to the resource requirements of particular species.

A 10-year demographic study of a small mammal community in the Australian Alps

This paper describes a 10-year study of the community of two species of small rodents (Mastacomys fuscus, Rattus fuscipes) and one species of dasyurid marsupial (Antechinus swainsonii) in the subalpine zone of the Australian Alps. Each species exhibited differing life-histories with respect to population numbers, intra- and interannual fluctuations in numbers, reproduction, proportion of young in the population, winter survival, immigration and longevity. Of the two species of rodents, M. fuscus had the lowest population numbers, was the least fecund, had the highest rate of survival, and the smallest fluctuations in numbers. A. swainsonii was the least numerous species, and the winter die-off of males and the high fecundity of females resulted in much greater fluctuations in numbers than for either rodent. For all species, there were interannual variations in most demographic parameters, suggesting considerable flexibility in response to annual variations in the environment. None of the three species is known to hibernate, nor is there any evidence of cyclicity, as shown by some species of subarctic and arctic small mammals. Comparisons are made with subalpine small mammals in other parts of the world and the influence of the subalpine environment in determining population numbers is considered.