The behavioral energetics of New Zealand's bats: Daily torpor and hibernation, a continuum

Virome analysis of New Zealand's bats reveals cross-species viral transmission among the Coronaviridae

The lesser short-tailed bat (Mystacina tuberculata) and the long-tailed bat (Chalinolobus tuberculatus) are Aotearoa New Zealand's only native extant terrestrial mammals and are believed to have migrated from Australia. Long-tailed bats arrived in New Zealand an estimated two million years ago and are closely related to other Australian bat species. Lesser short-tailed bats, in contrast, are the only extant species within the Mystacinidae and are estimated to have been living in isolation in New Zealand for the past 16-18 million years. Throughout this period of isolation, lesser short-tailed bats have become one of the most terrestrial bats in the world. Through a metatranscriptomic analysis of guano samples from eight locations across New Zealand, we aimed to characterise the viromes of New Zealand's bats and determine whether viruses have jumped between these species over the past two million years. High viral richness was observed among long-tailed bats with viruses spanning seven different viral families. In contrast, no bat-specific viruses were identified in lesser short-tailed bats. Both bat species harboured an abundance of likely dietary- and environment-associated viruses. We also identified alphacoronaviruses in long-tailed bat guano that had previously been identified in lesser short-tailed bats, suggesting that these viruses had jumped the species barrier after long-tailed bats migrated to New Zealand. Of note, an alphacoronavirus species discovered here possessed a complete genome of only 22,416 nucleotides with entire deletions or truncations of several non-structural proteins, thereby representing what may be the shortest genome within the Coronaviridae identified to date. Overall, this study has revealed a diverse range of novel viruses harboured by New Zealand's only native terrestrial mammals, in turn expanding our understanding of bat viral dynamics and evolution globally.

Evolution of Flight Muscle Contractility and Energetic Efficiency

The powered flight of animals requires efficient and sustainable contractions of the wing muscles of various flying species. Despite their high degree of phylogenetic divergence, flight muscles in insects and vertebrates are striated muscles with similarly specialized sarcomeric structure and basic mechanisms of contraction and relaxation. Comparative studies examining flight muscles together with other striated muscles can provide valuable insights into the fundamental mechanisms of muscle contraction and energetic efficiency. Here, we conducted a literature review and data mining to investigate the independent emergence and evolution of flight muscles in insects, birds, and bats, and the likely molecular basis of their contractile features and energetic efficiency. Bird and bat flight muscles have different metabolic rates that reflect differences in energetic efficiencies while having similar contractile machinery that is under the selection of similar natural environments. The significantly lower efficiency of insect flight muscles along with minimized energy expenditure in Ca2+ handling is discussed as a potential mechanism to increase the efficiency of mammalian striated muscles. A better understanding of the molecular evolution of myofilament proteins in the context of physiological functions of invertebrate and vertebrate flight muscles can help explore novel approaches to enhance the performance and efficiency of skeletal and cardiac muscles for the improvement of human health.

Does the New Zealand rockwren (Xenicus gilviventris) hibernate?

In this study, we examined the thermal physiology of the endangered New Zealand rockwren (Xenicus gilviventris), a member of the Acanthisittidae, a family unique to New Zealand. This family, derived from Gondwana, is thought to be the sister taxon to all other passerines. Rockwrens permanently reside above the climatic timberline at altitudes from 1000 to 2900 m in the mountains of South Island. They feed on invertebrates and in winter face ambient temperatures far below freezing and deep deposits of snow. Their body temperature and rate of metabolism are highly variable. The rockwrens in our study regulated their body temperature at ca. 36.4°C, which in one individual decreased to 33.1°C at an ambient temperature of 9.4°C; its rate of metabolism decreased by 30% and its body temperature then spontaneously returned to 36°C. The rate of metabolism in a second individual twice decreased by 35%, nearly to the basal rate expected from its mass without a decrease in body temperature. The New Zealand rockwren's food habits, entrance into torpor and continuous residence in a thermally demanding environment suggest that it may hibernate. However, for that conclusion to be accepted, evidence of its use of torpor for extended periods is required. Acanthisittids are distinguished from other passerines by the combination of their permanent temperate distribution, thermal flexibility and a propensity to evolve a flightless condition. These characteristics may principally reflect their geographical isolation in a temperate environment isolated from Gondwana for 82 million years in the absence of mammalian predators.

Faecal analyses and alimentary tracers reveal the foraging ecology of two sympatric bats

We used three complementary methods to assess the diet of two insectivorous bat species: one an obligate aerial hunter, Miniopterus natalensis, and the other Myotis tricolor whose morphology and taxonomic affiliation to other trawling bats suggests it may be a trawler (capturing insects from the water surface with its feet and tail). We used visual inspection, stable isotope values and fatty acid profiles of insect fragments in bat faeces sampled across five sites to determine the contribution of aquatic and terrestrial arthropods to the diets of the two species. The niche widths of M. tricolor were generally wider than those of Miniopterus natalensis but with much overlap, both taking aquatic and terrestrial insects, albeit in different proportions. The diet of M. tricolor had high proportions of fatty acids (20:5ω3 and 22:6ω3) that are only obtainable from aquatic insects. Furthermore, the diet of M. tricolor had higher proportions of water striders (Gerridae) and whirligig beetles (Gyrinidae), insects obtainable via trawling, than Miniopterus natalensis. These results suggest both species are flexible in their consumption of prey but that M. tricolor may use both aerial hawking and trawling, or at least gleaning, to take insects from water surfaces. The resultant spatial segregation may sufficiently differentiate the niches of the two species, allowing them to co-exist. Furthermore, our results emphasize that using a combination of methods to analyse diets of cryptic animals yields greater insights into animal foraging ecology than any of them on their own.

Hibernation and daily torpor in Australian and New Zealand bats: does the climate zone matter?

We aim to summarise what is known about torpor use and patterns in Australian and New Zealand (ANZ) bats from temperate, tropical/subtropical and arid/semiarid regions and to identify whether and how they differ. ANZ bats comprise ~90 species from 10 families. Members of at least nine of these are known to use torpor, but detailed knowledge is currently restricted to the pteropodids, molossids, mystacinids, and vespertilionids. In temperate areas, several species can hibernate (use a sequence of multiday torpor bouts) in trees or caves mostly during winter and continue to use short bouts of torpor for the rest of the year, including while reproducing. Subtropical vespertilionids also use multiday torpor in winter and brief bouts of torpor in summer, which permit a reduction in foraging, probably in part to avoid predators. Like temperate-zone vespertilionids they show little or no seasonal change in thermal energetics during torpor, and observed changes in torpor patterns in the wild appear largely due to temperature effects. In contrast, subtropical blossom-bats (pteropodids) exhibit more pronounced daily torpor in summer than winter related to nectar availability, and this involves a seasonal change in physiology. Even in tropical areas, vespertilionids express short bouts of torpor lasting ~5 h in winter; summer data are not available. In the arid zone, molossids and vespertilionids use torpor throughout the year, including during desert heat waves. Given the same thermal conditions, torpor bouts in desert bats are longer in summer than in winter, probably to minimise water loss. Thus, torpor in ANZ bats is used by members of all or most families over the entire region, its regional and seasonal expression is often not pronounced or as expected, and it plays a key role in energy and water balance and other crucial biological functions that enhance long-term survival by individuals.