Robyn S. Hetem | University of Canterbury/Te Whare Wānanga o Waitaha (original) (raw)

Papers by Robyn S. Hetem

Data and R code in support of manuscript

<p>Physiological measurements to quantify the selective brain cooling attriubutes in water-... more <p>Physiological measurements to quantify the selective brain cooling attriubutes in water-deprived sheep, while also measuring water turnover. </p

Ecology and evolution, Apr 1, 2024

Climate change responses, Nov 28, 2016

In the face of climate change, the life history traits of large terrestrial mammals will prevent ... more In the face of climate change, the life history traits of large terrestrial mammals will prevent them from adapting genetically at a sufficient pace to keep track with changing environments, and habitat fragmentation will preclude them from shifting their distribution range. Predicting how habitat-bound large mammals will respond to environmental change requires measurement of their sensitivity and exposure to changes in the environment, as well as the extent to which phenotypic plasticity can buffer them against the changes. Behavioural modifications, such as a shift to nocturnal foraging or selection of a cool microclimate, may buffer free-living mammals against thermal and water stress, but may carry a cost, for example by reducing foraging time or increasing predation risk. Large mammals also use physiological responses to buffer themselves against changing environments, but those buffers may be compromised by a changing physical environment. A decrease in the available food energy or water leads to a trade-off in which the precision of homeothermy is relaxed, resulting in large daily fluctuations in body temperature. Understanding how large mammals prioritise competing homeostatic systems in changing environments, and the consequences of that prioritisation for their fitness, requires long-term monitoring of identifiable individual animals in their natural habitat. Although body size predicts general ecological and energetic patterns of terrestrial mammals, high intraspecific and interspecific variability means that a species-directed approach is required to accurately model responses of large mammals to climate change.

Veterinary Research, Aug 4, 2022

Foot-and-mouth disease (FMD) is one of the most important livestock diseases restricting internat... more Foot-and-mouth disease (FMD) is one of the most important livestock diseases restricting international trade. While African buffalo (Syncerus caffer) act as the main wildlife reservoir, viral and immune response dynamics during FMD virus acute infection have not been described before in this species. We used experimental needle inoculation and contact infections with three Southern African Territories serotypes to assess clinical, virological and immunological dynamics for thirty days post infection. Clinical FMD in the needle inoculated buffalo was mild and characterised by pyrexia. Despite the absence of generalised vesicles, all contact animals were readily infected with their respective serotypes within the first two to nine days after being mixed with needle challenged buffalo. Irrespective of the route of infection or serotype, there were positive associations between the viral loads in blood and the induction of host innate pro-inflammatory cytokines and acute phase proteins. Viral loads in blood and tonsil swabs were tightly correlated during the acute phase of the infection, however, viraemia significantly declined after a peak at four days postinfection (dpi), which correlated with the presence of detectable neutralising antibodies. In contrast, infectious virus was isolated in the tonsil swabs until the last sampling point (30 dpi) in most animals. The pattern of virus detection in serum and tonsil swabs was similar for all three serotypes in the direct challenged and contact challenged animals. We have demonstrated for the first time that African buffalo are indeed systemically affected by FMD virus and clinical FMD in buffalo is characterized by a transient pyrexia. Despite the lack of FMD lesions, infection of African buffalo was characterised by high viral loads in blood and oropharynx, rapid and strong host innate and adaptive immune responses and high transmissibility.

bioRxiv (Cold Spring Harbor Laboratory), Nov 26, 2021

To investigate the role of the angularis oculi vein (AOV) in selective brain cooling (SBC), we me... more To investigate the role of the angularis oculi vein (AOV) in selective brain cooling (SBC), we measured brain and carotid blood temperatures in six adult female Dorper sheep. Halfway through the study, a section of the AOV, just caudal to its junction with the dorsal nasal vein, was extirpated on both sides. Before and after AOV surgery, the sheep were housed outdoors at 21-22°C and were exposed in a climatic chamber to daytime heat (40°C) and water deprivation for 5 days. In sheep outdoors, SBC was significantly lower after the AOV had been cut, with its 24-h mean reduced from 0.25 to 0.01°C (t 5 ϭ 3.06, P ϭ 0.03). Carotid blood temperature also was lower (by 0.28°C) at all times of day (t 5 ϭ 3.68, P ϭ 0.01), but the pattern of brain temperature was unchanged. The mean threshold temperature for SBC was not different before (38.85 Ϯ 0.28°C) and after (38.85 Ϯ 0.39°C) AOV surgery (t 5 ϭ0.00, P ϭ 1.00), but above the threshold, SBC magnitude was about twofold less after surgery. SBC after AOV surgery also was less during heat exposure and water deprivation. However, SBC increased progressively by the same magnitude (0.4°C) over the period of water deprivation, and return of drinking water led to rapid cessation of SBC in sheep before and after AOV surgery. We conclude that the AOV is not the only conduit for venous drainage contributing to SBC in sheep and that, contrary to widely held opinion, control of SBC does not involve changes in the vasomotor state of the AOV.

International Journal of Gynecology & Obstetrics

Anatomical, physiologic, and socio‐cultural changes during pregnancy and childbirth increase vuln... more Anatomical, physiologic, and socio‐cultural changes during pregnancy and childbirth increase vulnerability of women and newborns to high ambient temperatures. Extreme heat can overwhelm thermoregulatory mechanisms in pregnant women, especially during labor, cause dehydration and endocrine dysfunction, and compromise placental function. Clinical sequelae include hypertensive disorders, gestational diabetes, preterm birth, and stillbirth. High ambient temperatures increase rates of infections, and affect health worker performance and healthcare seeking. Rising temperatures with climate change and limited resources heighten concerns. We propose an adaptation framework containing four prongs. First, behavioral changes such as reducing workloads during pregnancy and using low‐cost water sprays. Second, health system interventions encompassing Early Warning Systems centered around existing community‐based outreach; heat‐health indicator tracking; water supplementation and monitoring for h...

European Journal of Public Health, 2020

Background Exposure to high ambient temperatures during pregnancy may increase the risk of advers... more Background Exposure to high ambient temperatures during pregnancy may increase the risk of adverse pregnancy outcomes due to physiological and anatomical changes in pregnancy compromising the ability to thermoregulate. Methods A systematic review and meta-analysis of studies that assessed associations between ambient heat, and preterm birth, birth weight and stillbirths. Articles were identified through a search of Medline (PubMed) and Web of Science. Titles and abstracts were screened, eligible studies extracted and risk of bias assessed using the Joanna Briggs Institute appraisal tools. Results 14,880 records were screened and a total of 70 studies included. In 40 of 47 studies, preterm births were more frequent at higher than lower temperatures. In random effects meta-analysis, the odds of a preterm birth rose 1.05-fold per 1 °C increase in temperature (95%CI=1.03, 1.07), and 1.16 fold during heat waves (95%CI=1.10, 1.23). Reduced birth weight associated with higher temperature w...

Scientific Reports, 2018

Domestic species can make the distinction between several human sub-groups, especially between fa... more Domestic species can make the distinction between several human sub-groups, especially between familiar and unfamiliar persons. The Domestication hypothesis assumes that such advanced cognitive skills were driven by domestication itself. However, such capacities have been shown in wild species as well, highlighting the potential role of early experience and proximity with humans. Nevertheless, few studies have been focusing on the use of acoustic cues in wild species and more comparative studies are necessary to better understand this ability. Cheetah is a vocal, semi-social species, often hand raised when captive, making it therefore a good candidate for studying the ability to perceive differences in human voices. In this study, we used playback experiments to investigate whether cheetahs are able to distinguish between the voices of their familiar caretakers and visitors. We found that cheetahs showed a higher visual attention, changed activity more often and faster when the voic...

Journal of Zoology, 2017

Social integration underpins the ability of wild female vervet monkeys (Chlorocebus pygerythrus) ... more Social integration underpins the ability of wild female vervet monkeys (Chlorocebus pygerythrus) to resist cold stress. Here we ask whether sociability is similarly salient for male vervet monkeys, who reside in non-natal groups as adults and who must consequently, therefore, develop social relationships on arrival. We use body temperature and social data from 15 free-ranging male vervet monkeys to determine whether the number of grooming partners is as important for them during winter and whether the length of residency is positively associated with body temperature. We also assess whether larger body size and higher dominance rank mitigate the need for social partnerships. Like females, male vervets respond to lower 24 h ambient temperatures and winter's progression by decreasing minimum and mean 24 h body temperatures and by becoming more heterothermic. Male rank had no effect, while body size was associated primarily with reduced heterothermy. Males with more social partners also sustained higher minimum and mean body temperatures but, unexpectedly, were consistently more heterothermic. Further analysis revealed that higher minimum and mean temperatures were a function of the number of female partners, while increased heterothermy was driven by the number of male partners. As winter and the mating season overlap, we interpret this as indicating that a need to sustain male associations incurs physiological stress that is reflected as a thermoregulatory cost. Lastly, we show that longer residency is associated with higher minimum body temperatures independently of social affiliation and suggest possible causes that might be investigated.

BMJ, 2020

ObjectiveTo assess whether exposure to high temperatures in pregnancy is associated with increase... more ObjectiveTo assess whether exposure to high temperatures in pregnancy is associated with increased risk for preterm birth, low birth weight, and stillbirth.DesignSystematic review and random effects meta-analysis.Data sourcesMedline and Web of Science searched up to September 2018, updated in August 2019.Eligibility criteria for selecting studiesClinical studies on associations between high environmental temperatures, and preterm birth, birth weight, and stillbirths.Results14 880 records and 175 full text articles were screened. 70 studies were included, set in 27 countries, seven of which were countries with low or middle income. In 40 of 47 studies, preterm births were more common at higher than lower temperatures. Exposures were classified as heatwaves, 1°C increments, and temperature threshold cutoff points. In random effects meta-analysis, odds of a preterm birth rose 1.05-fold (95% confidence interval 1.03 to 1.07) per 1°C increase in temperature and 1.16-fold (1.10 to 1.23) d...

The 86th Annual Meeting of the American Association of Physical Anthropologists, New Orleans, Apr 1, 2017

Biology Letters, Jul 1, 2017

Aardvarks (Orycteropus afer) are elusive burrowing mammals, predominantly nocturnal and distribut... more Aardvarks (Orycteropus afer) are elusive burrowing mammals, predominantly nocturnal and distributed widely throughout Africa except for arid deserts. Their survival may be threatened by climate change via direct and indirect effects of increasing heat and aridity. To measure their current physiological plasticity, we implanted biologgers into six adult aardvarks resident in the semi-arid Kalahari. Following a particularly dry and hot summer, five of the study aardvarks and 11 other aardvarks at the study site died. Body temperature records revealed homeothermy (35.4-37.28C) initially, but heterothermy increased progressively through the summer, with declining troughs in the nychthemeral rhythm of body temperature reaching as low as 258C before death, likely due to starvation. Activity patterns shifted from the normal nocturnal to a diurnal mode. Our results do not bode well for the future of aardvarks facing climate change. Extirpation of aardvarks, which play a key role as ecosystem engineers, may disrupt stability of African ecosystems.

Global Ecology and Conservation, Oct 1, 2022

Physiology & Behavior, Oct 1, 2017

Stress-induced hyperthermia following rectal thermometry is reported in normothermic rats, but ap... more Stress-induced hyperthermia following rectal thermometry is reported in normothermic rats, but appears to be muted or even absent in febrile rats. We therefore investigated whether the use of rectal thermometry affects the accuracy of temperature responses recorded in normothermic and febrile rats. Using intraabdominally implanted temperature-sensitive radiotelemeters we measured the temperature response to rectal temperature measurement in male Sprague Dawley rats (~200 g) injected subcutaneously with Brewer's yeast (20 ml/kg of a 20% Brewer's yeast solution = 4000mg/kg) or saline (20 ml/kg of 0.9% saline). Rats had been preexposed to, or were naive to rectal temperature measurement before the injection. The first rectal temperature measurement was taken in the plateau phase of the fever (18 hours after injection) and at hourly intervals thereafter. In normothermic rats, rectal temperature measurement was associated with an increase in abdominal temperature (0.66 ± 0.27 ºC) that had a rapid onset (5-10 min), peaked at 15-20 min and lasted for 35-50 minutes. The hyperthermic response to rectal temperature measurement was absent in febrile rats. Exposure to rectal temperature measurement on two previous occasions did not reduce the hyperthermia. There was a significant positive linear association between temperatures recorded using the two methods, but the agreement interval identified that rectal temperature measured with a thermocouple probe could either be 0.7 ºC greater or 0.5 ºC lower than abdominal temperature measured with radiotelemeter. Thus, due to stress-induced hyperthermia, rectal thermometry does not ensure accurate recording of body temperature in short-spaced, intermittent intervals in normothermic and febrile rats.

Conservation Physiology, 2017

Some mammals have the ability to lower their hypothalamic temperature below that of carotid arter... more Some mammals have the ability to lower their hypothalamic temperature below that of carotid arterial blood temperature, a process termed selective brain cooling. Although the requisite anatomical structure that facilitates this physiological process, the carotid rete, is present in members of the Cetartiodactyla, Felidae and Canidae, the carotid rete is particularly well developed in the artiodactyls, e.g. antelopes, cattle, sheep and goats. First described in the domestic cat, the seemingly obvious function initially attributed to selective brain cooling was that of protecting the brain from thermal damage. However, hyperthermia is not a prerequisite for selective brain cooling, and selective brain cooling can be exhibited at all times of the day, even when carotid arterial blood temperature is relatively low. More recently, it has been shown that selective brain cooling functions primarily as a water-conservation mechanism, allowing artiodactyls to save more than half of their daily water requirements. Here, we argue that the evolutionary success of the artiodactyls may, in part, be attributed to the evolution of the carotid rete and the resulting ability to conserve body water during past environmental conditions, and we suggest that this group of mammals may therefore have a selective advantage in the hotter and drier conditions associated with current anthropogenic climate change. A better understanding of how selective brain cooling provides physiological plasticity to mammals in changing environments will improve our ability to predict their responses and to implement appropriate conservation measures.

American Journal of Physiology-regulatory Integrative and Comparative Physiology, 2008

To study their thermal responses to climatic stress, we implanted seven greater kudu (Tragelaphus... more To study their thermal responses to climatic stress, we implanted seven greater kudu (Tragelaphus strepsiceros) with intra-abdominal, brain, carotid, and subcutaneous temperature data loggers, as well as an activity logger. Each animal was also equipped with a collar holding a miniature black globe thermometer, which we used to assess thermoregulatory behavior. The kudu ranged freely within succulent thicket vegetation of the Eastern Cape Province, South Africa. The kudu spontaneously developed a bacterial pneumonia and consequent fever that lasted between 6 and 10 days. The fever was characterized by a significant increase in mean 24-h abdominal temperature from 38.9 Ϯ 0.2°C to 40.2 Ϯ 0.4°C (means Ϯ SD, t6 ϭ 11.01, P Ͻ 0.0001), although the amplitude of body temperature rhythm remained unchanged (t6 ϭ 1.18, P ϭ 0.28). Six of the kudu chose warmer microclimates during the fever than when afebrile (P Ͻ 0.0001). Despite the selection of a warmer environment, on the first day of fever, the abdominal-subcutaneous temperature difference was significantly higher than on afebrile days (t5 ϭ 3.06, P ϭ 0.028), indicating vasoconstriction. Some kudu displayed increased frequency of selective brain cooling during the fever, which would have inhibited evaporative heat loss and increased febrile body temperatures, without increasing the metabolic maintenance costs of high body temperatures. Average daily activity during the fever decreased to 60% of afebrile activity (t6 ϭ 3.46, P ϭ 0.014). We therefore have recorded quantitative evidence for autonomic and behavioral fever, as well as sickness behavior, in the form of decreased activity, in a free-living ungulate species.

Frontiers in Physiology, Jul 7, 2020

Shifting activity to cooler times of day buffers animals from increased heat and aridity under cl... more Shifting activity to cooler times of day buffers animals from increased heat and aridity under climate change. Conversely, when resources are limited, some nocturnal species become more diurnal, reducing energetic costs of keeping warm at night. Aardvarks (Orycteropus afer) are nocturnal, obligate ant-and termite-eating mammals which may be threatened directly by increasing heat and aridity, or indirectly by the effects of climate change on their prey. We hypothesised that the minimum 24-h body temperature of aardvarks would decline during energy scarcity, and that aardvarks would extend their active phases to compensate for reduced resource availability, possibly resulting in increased diurnal activity when aardvarks were energetically compromised. To measure their thermoregulatory patterns and foraging activity, we implanted abdominal temperature and activity data loggers into 12 adult aardvarks and observed them for varying durations over 3 years in the Kalahari. Under non-drought conditions, aardvarks tightly controlled their 24-h body temperature rhythm (mean amplitude of the 24-h body temperature rhythm was 1.8 ± 0.3 • C during summer and 2.1 ± 0.1 • C during winter) and usually were nocturnal. During a summer drought, aardvarks relaxed the precision of body temperature regulation (mean 24-h amplitude 2.3 ± 0.4 • C) and those that subsequently died shifted their activity to progressively earlier times of day in the weeks before their deaths. Throughout the subsequent winter, the aardvarks' minimum 24-h body temperatures declined, causing exaggerated heterothermy (4.7 ± 1.3 • C; absolute range 24.7 to 38.8 • C), with one individual's body temperature varying by 11.7 • C within 8 h. When body temperatures were low, aardvarks often emerged from burrows during daytime, and occasionally returned before sunset, resulting in completely diurnal activity. Aardvarks also shortened their active periods by 25% during food scarcity, likely to avoid energetic costs incurred by foraging. Despite their physiological and behavioural