Journal of Experimental Biology

Jacob, Fyda, Thomas;Connor, Spencer,;Martin, Jastroch,;J., Gaudry, Michael

doi: 10.1242/jeb.223974pmid: 32620708

Uncoupling protein 1 (UCP1) governs non-shivering thermogenesis in brown adipose tissue. It has been estimated that pigs lost UCP1 ∼20 million years ago (MYA), dictating cold intolerance among piglets. Our current understanding of the root causes of UCP1 loss are, however, incomplete. Thus, examination of additional species can shed light on these fundamental evolutionary questions. Here, we investigated UCP1 in the Chacoan peccary ( Catagonus wagneri ), a member of the Tayassuid lineage that diverged from pigs during the late Eocene–mid Oligocene. Exons 1 and 2 have been deleted in peccary UCP1 and the remaining exons display additional inactivating mutations. A common nonsense mutation in exon 6 revealed that UCP1 was pseudogenized in a shared ancestor of pigs and peccaries. Our selection pressure analyses indicate that the inactivation occurred 36.2–44.3 MYA during the mid–late Eocene, which is much earlier than previously thought. Importantly, pseudogenized UCP1 provides the molecular rationale for cold sensitivity and current tropical biogeography of extant peccaries.

Fritz, Geiser,;R., Willis, Craig K.;Mark, Brigham, R.

doi: 10.1242/jeb.229518pmid: 32788270

We write this because we are concerned about problems with scientific rigor in a paper recently published by McNab and Weston (2020). The paper is based on a limited, poor-quality dataset, lacks statistical analysis, focuses on out-dated literature and makes conclusions that are not related to the data presented. The title asks whether a passerine bird, the New Zealand rockwren ( Xenicus gilviventris ), can hibernate. This seems reasonable given that these birds are small and largely sedentary, eat invertebrates and live at high elevation, where they apparently can nest in snow banks. However, the Introduction does not provide a coherent rationale for asking this question and, in the Results, there are no data addressing the question. Instead, much of the Introduction is devoted to Woods et al.’s (2019) evidence that an unrelated non-passerine, the common poorwill ( Phalaenoptilus nuttallii ), hibernates, with some discussion of a few passerines that enter shallow torpor. The rationale leading to the main question of the paper is weak and in the Introduction, the text on whether poorwills hibernate is contradictory. The argument in the Introduction that hibernation can only occur under constant cold thermal conditions has been refuted in many recent papers reporting data on free-ranging individuals ( Stawski et al., 2014 ; Woods et al., 2019 ; Nowack et al., 2020 ). More alarmingly, though, the data that follow provide no evidence to support the paper's title or conclusions. One rockwren reduced body temperature ( T b ) from a normothermic, resting level of 36.4°C, to a minimum of 33.1°C, a drop of 3.3°C. Dehydrated camels ( Camelus dromedarius ) and other large mammals reduce their T b more than this ( Hetem et al., 2016 ) and, clearly, they are not hibernators. Based on most thresholds in the literature used to define torpor in endotherms, a drop of only 3.3°C or a minimum T b of 33.1°C would barely qualify as shallow torpor, let alone provide evidence of hibernation. Hibernating mammals and birds reduce T b by vastly more than this, often by 35 to 40°C below normothermia to approximately 5°C on average ( McKechnie and Lovegrove, 2002 ; Ruf and Geiser, 2015 ). McNab and Weston (2020) report that metabolism in two rockwrens during single measurements was somewhat reduced, ostensibly by 30–35%. The authors note that birds did not settle in the chamber, so this result is unreliable but, in any case, this reduction is not sufficient evidence for hibernation, when hibernators often reduce metabolism by 99% or more. As for T b , based on the metabolic data reported, there is no evidence that the rockwrens hibernated, and it is questionable whether they even entered torpor. Metabolism and T b data are shown in Fig. 1, but the figure is uninterpretable. There is no explanation for how ‘regression’ lines were derived, only three of six individuals are identified and no statistical analysis is described in the paper. The authors' claim that thermal energetics of rockwrens differ from those of other passerines is also incorrect. In general, passerines seem to be homeothermic or do not express deep torpor, but reductions in resting T b by 5 to 15°C from approximately 40°C have been commonly reported (e.g. McKechnie and Lovegrove, 2002 ; Schleucher, 2004 ). Tits ( Parus spp.), even though they express shallow torpor, reduce T b by approximately twice as much (by 5–10°C) as rockwrens. The authors contend that rockwrens spontaneously rewarmed from 33.1 to 36.0°C and, therefore, conclude that the T b reduction was controlled. However, as clearly shown in Fig. 2, this ‘arousal’ only occurred after exposure to an ambient temperature of 30.1°C, not the 9.4°C at which minimum T b was recorded. Given this, it is just as likely that the birds exhibited shallow, uncontrolled hypothermia in response to cold exposure, and rewarming was aided by the rise in ambient temperature. There are also problems with the methodology and reporting of it. The Materials and Methods state that metabolic rates were recorded for 6 h from 19:00 to 01:00 h and T b was measured (using a device and procedure never identified) in intervals of 1.5 to 2 h. Therefore, it is of no surprise that birds did not enter torpor as they were prevented from doing so because they were frequently disturbed. Entry into avian torpor can take many hours, almost never occurs within 1–2 h of the start of measurements or after a disturbance, and usually requires a calm, undisturbed animal. The respirometry protocol is also problematic. The authors used 1.5 liter chambers to measure metabolism and the lowest flow rate was 105 ml min −1 , meaning that 66 min would be needed to reach 99% equilibrium ( Withers, 2001 ). Thus, oxygen consumption values averaged over only 20 min are not accurate. Although less serious than problems of methodology and inference, most of the thermal energetics citations are out of date and recent thermal biology studies on free-ranging passerines are missed. For example, Romano et al. (2019) reported that Australian fairy-wrens ( Malurus cyaneus ) reduce skin temperature by approximately 14°C from 41 to 27°C, followed by endogenous rewarming. The one recent study on babblers ( Pomatostomus superciliosus ) that is cited is misreported. Although these birds reduce T b at night similar to rockwrens, Douglas et al. (2017) emphasize that babblers do not express torpor, but rather use huddling to save energy. We were motivated to point out the issues with this paper not only to inform non-specialist readers but also as mentors of students whom we are trying to train to be critical of the peer-review process. References Douglas , T. K. , Cooper , C. E. and Withers , P. C. ( 2017 ). Avian torpor or alternative thermoregulatory strategies for overwintering? J. Exp. Biol. 220 , 1341 - 1349 . https://doi.org/10.1242/jeb.154633 Google Scholar Crossref Search ADS Hetem , R. S. , Maloney , S. K. , Fuller , A. and Mitchell , D. ( 2016 ). Heterothermy in large mammals: inevitable or implemented? Biol. Rev. 91 , 187 - 205 . https://doi.org/10.1111/brv.12166 Google Scholar Crossref Search ADS McKechnie , A. E. and Lovegrove , B. G. ( 2002 ). Avian facultative hypothermic responses: a review . Condor 104 , 705 - 724 . https://doi.org/10.1093/condor/104.4.705 Google Scholar Crossref Search ADS McNab , B. K. and Weston , K. A. ( 2020 ). Does the New Zealand rockwren (Xenicus gilviventris) hibernate? J. Exp. Biol. 223 , jeb212126 . https://doi.org/10.1242/jeb.212126 Google Scholar Crossref Search ADS Nowack , J. , Levesque , D. L. , Reher , S. and Dausmann , K. H. ( 2020 ). Variable climates lead to varying phenotypes: ‘weird’ mammalian torpor and lessons from lower latitudes . Front. Ecol. Evol . https://doi.org/10.3389/fevo.2020.00060 Google Scholar Romano , A. B. , Hunt , A. , Welbergen , J. A. and Turbill , C. ( 2019 ). Nocturnal torpor by superb fairy-wrens: a key mechanism for reducing winter daily energy expenditure . Biol. Lett. 15 , 20190211 . https://doi.org/10.1098/rsbl.2019.0211 Google Scholar Crossref Search ADS Ruf , T. and Geiser , F. ( 2015 ). Daily torpor and hibernation in birds and mammals . Biol. Rev. 90 , 891 - 926 . https://doi.org/10.1111/brv.12137 Google Scholar Crossref Search ADS Schleucher , E. ( 2004 ). Torpor in birds: taxonomy, energetics, and ecology . Physiol. Biochem. Zool. 77 , 942 - 949 . https://doi.org/10.1086/423744 Google Scholar Crossref Search ADS Stawski , C. , Willis , C. K. R. and Geiser F. ( 2014 ). The importance of temporal heterothermy in bats . J. Zool. 292 , 86 - 100 . https://doi.org/10.1111/jzo.12105 Google Scholar Crossref Search ADS Withers , P. C. ( 2001 ). Design, calibration and calculation for flow-through respirometry systems . Aust. J. Zool. 49 , 445 - 461 . https://doi.org/10.1071/ZO00057 Google Scholar Crossref Search ADS Woods , C. P. , Czenze , Z. J. and Brigham , R. M. ( 2019 ). The avian ‘hibernation’ enigma: thermoregulatory patterns and roost choice of the common poorwill . Oecologia 189 , 47 - 53 . https://doi.org/10.1007/s00442-018-4306-0 Google Scholar Crossref Search ADS © 2020. Published by The Company of Biologists Ltd 2020

Stefania, Casagrande,;Antoine, Stier,;Pat, Monaghan,;L., Loveland, Jasmine;Winifred, Boner,;Sara, Lupi,;Rachele, Trevisi,;Michaela, Hau,

doi: 10.1242/jeb.222513pmid: 32532864

Telomeres are DNA structures that protect chromosome ends. However, telomeres shorten during cell replication and at critically low lengths can reduce cell replicative potential, induce cell senescence and decrease fitness. Stress exposure, which elevates glucocorticoid hormone concentrations, can exacerbate telomere attrition. This phenomenon has been attributed to increased oxidative stress generated by glucocorticoids (‘oxidative stress hypothesis’). We recently suggested that glucocorticoids could increase telomere attrition during stressful periods by reducing the resources available for telomere maintenance through changes in the metabolic machinery (‘metabolic telomere attrition hypothesis’). Here, we tested whether experimental increases in glucocorticoid levels affected telomere length and mitochondrial function in wild great tit ( Parus major ) nestlings during the energy-demanding early growth period. We monitored resulting corticosterone (Cort) concentrations in plasma and red blood cells, telomere lengths and mitochondrial metabolism (metabolic rate, proton leak, oxidative phosphorylation, maximal mitochondrial capacity and mitochondrial inefficiency). We assessed oxidative damage caused by reactive oxygen species (ROS) metabolites as well as the total non-enzymatic antioxidant protection in plasma. Compared with control nestlings, Cort-nestlings had higher baseline corticosterone, shorter telomeres and higher mitochondrial metabolic rate. Importantly, Cort-nestlings showed increased mitochondrial proton leak, leading to a decreased ATP production efficiency. Treatment groups did not differ in oxidative damage or antioxidants. Hence, glucocorticoid-induced telomere attrition is associated with changes in mitochondrial metabolism, but not with ROS production. These findings support the hypothesis that shortening of telomere length during stressful periods is mediated by glucocorticoids through metabolic rearrangements.

Oana, Birceanu,

doi: 10.1242/jeb.214437pmid: N/A

Our intricate history with alcohol production and consumption dates to the Neolithic era. However, our evolutionary history with naturally produced alcohol, mainly ethanol, goes back even further, to our fruit- and nectar-eating ancestors, who used the odours of alcohols produced by natural fermentation to guide them during foraging. Approximately 10 million years ago, many humans developed a mutation that allowed alcohol-digesting enzymes, called alcohol dehydrogenases, to become 40 times more efficient at breaking down ethanol. This ability starts in our throats and continues in our stomachs. But have alcohol dehydrogenases evolved in the same manner and to the same degree in all fruit- and nectar-eating mammals? And do any of these animals get drunk? To answer these questions, a team of researchers at University of Calgary in Canada, led by postdoctoral scholar, Mareike Janiak, looked at differences in the enzyme alcohol dehydrogenase IV – the main ethanol-digesting enzyme – across a variety of mammalian species. Using a public database of the genetic code (or genome) of different mammals, she found that the ability to break down ethanol varied among species and it is influenced by diet. Animals from the cetacean family, such as whales, porpoises and narwhals, along with carnivores, insectivores and herbivores appeared to have lost their alcohol dehydrogenase IV and the ability to break down ethanol entirely. The research team concluded that this loss was due to the animals’ fruit- and nectar-free diets. What struck the research group was that the ability to break down alcohol was also lost in herbivores, which was a surprise because plants produce their own alcohols, although they are very different from the ethanol produced by fruit. Through their analysis of the differences in mammal gut length and structure, Janiak and colleagues concluded that the smaller stomachs of herbivores allow food to pass into the intestine faster, where it is then digested by the gut bacteria. While the animals themselves may have lost the ability to break down alcohols, the authors suggest that perhaps gut bacteria compensate by digesting the alcohol on the animal's behalf. With this new discovery, the authors concluded that a combination of diet and gut size plays a role in the ability of mammals to break down alcohols. But are there exceptions to the rule linking diet and gut length to the ability to digest alcohol? The authors found that koalas have set themselves apart, because they can digest ethanol, even though they do not eat fruit or nectar. In fact, they eat eucalyptus leaves, which are toxic to most mammals. Could their improved and efficient alcohol dehydrogenase IV serve other purposes and protect them from the poison in their diet? The team thinks so and urges researchers to explore the activity of this enzyme in koalas in the future. Based on this research, though, how likely is it that mammals get drunk? Depending on the species, the authors think it is likely, but caution us not to attribute human characteristics, such as intoxication, to animal behaviour. If we want to have animal models for human diseases, such as alcoholism, Mareike Janiak and her group advise us to look at the physiology of individual species and how it connects to their evolution and ecology before labelling a certain behaviour as drunkenness. The authors suggest that we should not let our current understanding of our own physiology cloud how we see behaviour in other species without connecting it to its genetic history and habitat. There is no definitive manual of answers to every question of mammalian physiology; every species is, after all, unique. References Janiak , M. C. , Pinto , S. L. , Duytschaever , G. , Carrigan , M. A. and Melin , A. D. ( 2020 ). Genetic evidence of widespread variation in ethanol metabolism among mammals: revisiting the ‘myth’ of natural intoxication . Biol. Lett. 16 , 20200070 . https://doi.org/10.1098/rsbl.2020.0070 Google Scholar Crossref Search ADS © 2020. Published by The Company of Biologists Ltd 2020

Miranda, Rew-Duffy,;F., Cameron, Skye;J., Freeman, Natalie;Rebecca, Wheatley,;M., Latimer, Jessica;S., Wilson, Robbie

doi: 10.1242/jeb.218503pmid: 32561634

Introduced predators combined with habitat loss and modification are threatening biodiversity worldwide, particularly the ‘critical weight range’ (CWR) mammals of Australia. In order to mitigate the impacts of invasive predators on native species in different landscapes, we must understand how the prey's morphology and performance determine their survival. Here, we evaluated how phenotypic traits related to escape performance predict the probability of survival for an endangered CWR mammal, the northern quoll ( Dasyurus hallucatus ). We measured mass, body size, body shape, body condition and age, as well as maximum sprint speed, acceleration and agility of female quolls over two consecutive years. Those with higher body condition and agility around a 135 deg corner were more likely to survive their first 21 months of life but were not more likely to survive after this period. No other morphological or performance traits affected survival. Heavier second-year individuals were more agile than first years but second years experienced higher mortality rates throughout the year. Females with higher body condition and agility around a 135 deg corner tended to have shorter limbs and feet but longer heads. Our findings suggest that higher body condition and agility are advantageous for survival in female northern quolls. These results can be used to develop predictive models of predator–prey interactions based on performance capacity and how performance is affected by habitat, aiding conservation efforts to predict and manage the impact of introduced predators on native species.

Kathryn, Knight,

doi: 10.1242/jeb.232835pmid: N/A

View large Download slide Arachnocampa flava larvae glowing under an overhang. Photo credit: David Merritt. View large Download slide Arachnocampa flava larvae glowing under an overhang. Photo credit: David Merritt. What look like mesmerising sparkles on the roof of dank Australian rainforest caves spell almost certain doom for the insects and other creepy-crawlies lured in by the fatal illumination. David Merritt, from The University of Queensland, Australia, explains that each pinprick of light is produced by an Arachnocampa flava larva, which glimmers continually from dusk to dawn. Adding that the spectacle also lures in human tourists, Merritt explains that the light show is produced by a modified portion of the Malpighian tubule – the insect kidney – and it was thought that the brake that inactivates the light by day is itself dramatically deactivated at night by the anaesthetic effects of CO 2 . In addition, Merritt knew that the glow-worms turn up the brightness when they sense the vibrations produced by torrential rain, yet he wasn't so sure exactly how these two unrelated phenomena trigger the larvae to turn up their brightness, so he and student Hamish Charlton began investigating. The pair drove to Springbrook National Park at dusk to collect the glowing larvae from the steep earthen banks beside a waterfall, and then provided each animal with its own personal mud-lined mini-cave to keep them comfortable back in Brisbane. Then they increased the CO 2 supply to the insects and watched; ‘The light brightened, casting a blue-green glow’, describes Merritt. However, when the duo tested the effects of various anaesthetics, including ethyl acetate and diethyl ether, on the larvae – to see whether these would also raise a glimmer – they found none, ruling out the possibility that CO 2 also works by anaesthetising the brake, allowing the insects to put on their light show. In a bid to narrow down exactly whether the brain or the glowing light organ responds directly to CO 2 to flip on the light switch, Merritt and Charlton supplied both organs individually with the gas and waited for the insects to begin to glimmer. ‘The larvae are only 1–2 cm long and the light organ is only 1 mm or so in diameter, so dissecting the larvae and removing the light organ without damaging the cells was a challenge’, admits Merritt. However, when the duo bathed the brains of larvae in CO 2 , they were not able to trigger light production, which Merritt says casts doubt on the models suggesting that signals from the brain repress bioluminescence. In contrast, bathing the light organ in CO 2 did trigger a glow, showing that the gas triggers light production directly in the light organ. Also, when the team tested the effects of rainfall on the insects’ ability to produce light, giving them a shake ranging from 180 to 200 Hz, the insects slowly turned up the glow to dazzling levels, leading Merritt to conclude that the increase in light is signalled from the brain. Taking all of the observations into account, Merritt suspects that instead of switching off suppression of the larvae's glow to allow the brilliant insects to shine at night, the insects’ nervous system actively activates the light show by delicately regulating the balance of CO 2 and oxygen – which fuels the production of light – in the cells that produce the enigmatic glow. Although accessing the insects to learn more about their ethereal light show became more challenging when the parks closed during the initial stages of the 2020 coronavirus pandemic, they have now reopened, allowing scientists and tourists alike to return and delight in the bewitching experience. References Charlton , H. R. and Merritt , D. J. ( 2020 ). Carbon dioxide-induced bioluminescence increase in Arachnocampa larvae . J. Exp. Biol. 223 , jeb225151 . https://doi.org/10.1242/jeb.225151 Google Scholar Crossref Search ADS © 2020. Published by The Company of Biologists Ltd 2020

Christian, Kropf,;Karl, Fent,;Stephan, Fischer,;Ayako, Casanova,;Helmut, Segner,

doi: 10.1242/jeb.221069pmid: 32532865

Fish gills are a structurally and functionally complex organ at the interface between the organism and the aquatic environment. Gill functions include the transfer of organic molecules, both natural ones and xenobiotic compounds. Whether the branchial exchange of organic molecules involves active transporters is currently not known. Here, we investigated the presence, diversity and functional activity of ATP-binding cassette (ABC) transporters in gills of juvenile rainbow trout. By means of RT-qPCR, gene transcripts of members from the abcb , abcc and abcg subfamilies were identified. Comparisons with mRNA profiles from trout liver and kidney revealed that ABC transporters known to have an apical localization in polarized epithelia, especially abcc2 and abcb1 , were under-represented in the gills. In contrast, ABC transporters with mainly basolateral localization showed comparable gene transcript levels in the three organs. The most prominent ABC transporter in gills was an abcb subfamily member, which was annotated as abcb5 based on the synteny and phylogeny. Functional in vivo assays pointed to a role of branchial ABC transporters in branchial solute exchange. We further assessed the utility of primary gill cell cultures to characterize transporter-mediated branchial exchange of organic molecules, by examining ABC transporter gene transcript patterns and functional activity in primary cultures. The gill cultures displayed functional transport activity, but the ABC mRNA expression patterns were different to those of the intact gills. Overall, the findings of this study provide evidence for the presence of functional ABC transporter activity in gills of fish.

Ferhat, Karakas,;E., Maas, Amy;W., Murphy, David

doi: 10.1242/jeb.221499pmid: 32587067

The clap-and-fling mechanism is a well-studied, unsteady lift generation mechanism widely used by flying insects and is considered obligatory for tiny insects flying at low to intermediate Reynolds numbers, Re . However, some aquatic zooplankters including some pteropod (i.e. sea butterfly) and heteropod species swimming at low to intermediate Re also use the clap-and-fling mechanism. These marine snails have extremely flexible, actively deformed, muscular wings which they flap reciprocally to create propulsive force, and these wings may enable novel lift generation mechanisms not available to insects, which have less flexible, passively deformed wings. Using high-speed stereophotogrammetry and micro-particle image velocimetry, we describe a novel cylindrical overlap-and-fling mechanism used by the pteropod species Cuvierina atlantica . In this maneuver, the pteropod's wingtips overlap at the end of each half-stroke to sequentially form a downward-opening cone, a cylinder and an upward-opening cone. The transition from downward-opening cone to cylinder produces a downward-directed jet at the trailing edges. Similarly, the transition from cylinder to upward-opening cone produces downward flow into the gap between the wings, a leading edge vortex ring and a corresponding sharp increase in swimming speed. The ability of this pteropod species to perform the cylindrical overlap-and-fling maneuver twice during each stroke is enabled by its slender body and highly flexible wings. The cylindrical overlap-and-fling mechanism observed here may inspire the design of new soft robotic aquatic vehicles incorporating highly flexible propulsors to take advantage of this novel lift generation technique.

K., McNab, Brian;A., Weston, Kerry

doi: 10.1242/jeb.230524pmid: 32788271

The recently published results from our experimental study describing the thermal flexibility of the rockwren ( Xenicus gilviventris ), combined with the unique alpine ecology of this species, led us to raise the question, as the title of our article clearly indicates, ‘Does the New Zealand rockwren ( Xenicus gilviventris ) hibernate?’. The study of the rockwren is of special importance. This species combines having a small mass and largely insectivorous diet with living above the climatic timberline in the mountains of the South Island of New Zealand year-round. The response of this species to the challenging alpine conditions is of great interest. Within the Introduction of our article ( McNab and Weston, 2020 ), we critically define the difference between a period of short-term torpor and hibernation. Although caprimulgids exhibit a range in observed torpor period lengths, there is no clear evidence that one of them, the common poorwill ( Phalaenoptilus nuttalli ), goes into hibernation. We introduce the characteristics of the rockwrens' alpine ecology, which provides the rationale for the hypothesis of a unique thermal behavior in this species. As Geiser et al. (2020) state, our results are based on a limited data set of six individuals. We showed that this species enters shallow torpor at ambient temperatures well above those encountered in their natural environment. We were not able to demonstrate the length of the period of torpor, which is required to separate short-term torpor from hibernation along a temperature continuum. For that to be demonstrated, it must be done in the field. We do not claim to have answered the question within our study whether rockwrens hibernate; rather, we state that ‘evidence of an extended period of torpor is required to conclude that the rockwren hibernates…’ (p. 4, McNab and Weston, 2020 ). We do, however, leave the reader with the enduring question of whether it may be possible that this unique alpine passerine species hibernates. This should encourage further research on the species. Geiser et al. (2020) also agree this question ‘seems reasonable, given that these birds are small and largely sedentary, eat invertebrates and live at high altitudes, where they apparently can nest in snowbanks’. Unfortunately, some misunderstandings of our article were present in the analysis of Geiser et al. (2020) . The statement that the birds ‘did not settle in the chamber’ is incorrect: this occurred only in one individual (p. 3, McNab and Weston, 2020 ). The limited amount of data that we have reflects the highly endangered status of the New Zealand rockwren and the necessary restrictions around the time that individuals were held in captivity. With such a limited sample size, the application of robust statistical testing becomes irrelevant and therefore we have simply presented a summary of the raw data, always providing the variance around the data. We did not address torpor in other passerines because we were concerned with rockwrens; none of the other passerines face similar conditions. We could not expose the rockwrens to low ambient temperatures – they were neither available nor permissible for this study. We are aware that the occurrence of hibernation in this species remains an open question, and believe if anything, that this study stands to demonstrate to students the difficulties of working with highly endangered species in remote mountainous locations. Above all, we hope that this study and the limitations that it presents motivate further research into determining the over-wintering strategy of this rare and unique alpine passerine. References Geiser , F. , Willlis , C. K. R. and Brigham , R. M. ( 2020 ). No evidence for hibernation in rockwrens . J. Exp. Biol . 223 , jeb229518 . https://doi.org/10.1242/jeb.229518 Google Scholar Crossref Search ADS McNab , B. K. and Weston , K. A . ( 2020 ). Does the New Zealand rockwren (Xenicus gilviventris) hibernate? J. Exp. Biol. 223 , jeb212126 . https://doi.org/10.1242/jeb.212126 Google Scholar Crossref Search ADS © 2020. Published by The Company of Biologists Ltd 2020

Kathryn, Knight,

doi: 10.1242/jeb.232314pmid: N/A

My diving is terrible – I can never clear my ears properly, even within 1 m of the surface – which makes the achievements of diving Atlantic puffins even more impressive, plummeting 150 m down with no apparent concern for their ears. ‘It is conceivable that the air-filled sinuses and auditory abilities are modified in auks, perhaps to withstand deep dives or enable underwater hearing’, says Aran Mooney, from the Woods Hole Oceanographic Institution, USA. Yet, it wasn't clear how the puffins’ amphibious lifestyle might impact their hearing out of water and whether they are distressed by noise. Mooney explains that other species are clearly disturbed by human noise, spending less time on the nest when people are around. Joining Ole Larsen and Kirstin Hansen, from the University of Southern Denmark, and Marianne Rasmussen, from the University of Iceland, Mooney and Adam Smith travelled to northern Iceland to collect puffins as they emerged from their burrows, to test their hearing. ‘The burrows are often on high cliffs, so are a bit perilous to approach and work near, given the sheer drop and potential instability’, says Mooney, who eventually captured nine birds. After transporting them to an improvised lab in a nearby farm shed, the team gently sedated the animals and inserted fine electrodes beneath their skin before recording their responses to clicks ranging from low-pitched 125 Hz tones to 8 kHz beeps at a 20 dB whisper up to 100 dB to find out which frequencies the puffins were most sensitive to. Although the birds could hear sounds up to 6 kHz, their hearing was sharpest between 750 Hz and 3 kHz. And, when the team compared the birds’ hearing with that of other similarly sized birds, it seemed that their aquatic lifestyle has not affected their hearing at all: it's just as good as that of birds that never plunge beneath the waves. However, the team suspects that the windswept locations of the birds’ nesting sites with the noise of waves crashing below could limit their hearing above ground. The hearing of these charismatic birds is probably fine-tuned to the cries of their own chicks and other puffins. In addition, they are also less likely to be disturbed by their noisy surroundings when secluded in their burrows. However, Mooney believes that the thud of approaching human feet is likely to penetrate their otherwise peaceful homes. ‘Given the influence of human encroachment on bird colonies, the sensitive hearing of these animals and the fact that puffins are a major tourist attraction in many countries, we suggest that human disturbance noise, even low-level sounds from hikers and visitors, has the potential to disturb puffins’, he says. References Mooney , T. A. , Smith , A. , Larsen , O. N. , Hansen , K., A. and Rasmussen , M. ( 2020 ). A field study of auditory sensitivity of the Atlantic puffin, Fratercula arctica . J. Exp. Biol. 223 , jeb228270 . https://doi.org/10.1242/jeb.228270 Google Scholar Crossref Search ADS © 2020. Published by The Company of Biologists Ltd 2020