Phenotypic flexibility in body mass, basal metabolic rate and summit metabolism in southern red bishops (Euplectes orix) : responses to short term thermal acclimation

Avian basal metabolic rate (BMR) and summit metabolism (Msum) vary within individuals in response to seasonal acclimatization in free-ranging birds, and thermal acclimation under laboratory conditions. We examined relationships between acclimation air temperature (Tacc) and body mass (Mb), BMR and Msum in female southern red bishops (Euplectes orix) from a relatively mild coastal site and a seasonally colder, inland site. Following acclimation for 21 days to Tacc = 10, 22 or 35 °C, Mb, BMR and Msum were all significantly and negatively related to Tacc. The significant relationship between BMR and Tacc did not remain after Mb was included as a covariate, whereas that between Msum and Tacc did. A subsequent reverse acclimation protocol, where bishops were acclimated to a second Tacc value and then re-acclimated to the first, revealed that short-term changes in Mb and BMR were completely reversible, but changes in Msum were only partially reversible. Following the reverse-acclimation protocol, metabolic expansibility (Msum/BMR) varied significantly with air temperature, being greatest at Tacc = 35 °C. Our data suggest that the intraspecific variation in seasonal metabolic variation previously reported for this species is at least partly driven by factors other than temperature.The National Research Foundation (NRF) for N.M. and A.E.Mhttp://www.elsevier.com/locate/cbpahb2013ab201

Seasonal metabolic variation in two populations of an Afrotropical euplectid bird

Many birds exhibit seasonal phenotypic flexibility in basal metabolic rate (BMR) and summit metabolism (Msum), but very little information is available for species from subtropical latitudes or for conspecific populations from sites that vary in climate. We measured body mass (Mb), BMR, and Msum in summer and winter in two populations of the southern red bishop Euplectes orix, a passerine that is widespread in southern Africa. One population occurs at a comparatively warmer coastal site (mean daily minimum air temperature [Ta] inmidwinter, 8.3 C) and the other at a colder inland site (mean daily minimum Ta in midwinter, 2.8 C). Bishops from both populations significantly increased Mb in winter. However, seasonal metabolic adjustments differed considerably between the populations. The inland population significantly increased BMR by approximately 58%, mass-specific BMR by approximately 31%, and Msum by approximately 15% in winter, although massspecific Msum did not change significantly. In contrast, the coastal population showed no significant seasonal change in BMR and significant winter reductions in mass-specific BMR (∼15%), Msum (∼8%), and mass-specific Msum (∼15%). The interpopulation differences in the magnitude and direction of seasonal mass-specific BMR changes are qualitatively consistent with global patterns, although the increase shown by the inland population is larger than expected. Our data reveal that avian seasonal metabolic adjustments can vary greatly within subtropical species depending on the climatic conditions experienced by the birds, and our findings reiterate the need to better understand metabolic flexibility in species that inhabit lower latitudes.The National Research Foundation (NRF) to N.M. and A.E.M.http://www.journals.uchicago.edu/toc/pbz/currentam2013ab201

The costs of keeping cool : behavioural trade-offs between foraging and thermoregulation are associated with significant mass losses in an arid-zone bird

Please read abstract in the article.The DST-NRF Centre of Excellence at the FitzPatrick Institute.http://link.springer.com/journal/4422020-09-01hj2019Zoology and Entomolog

High temperatures are associated with substantial reductions in breeding success and offspring quality in an arid-zone bird

Please read abstract in the article.The DSI-NRF Centre of Excellence at the FitzPatrick Institutehttp://link.springer.com/journal/4422021-04-15hj2020Zoology and Entomolog

How hornbills handle heat : sex-specific thermoregulation in the southern yellow-billed hornbill

At a global scale, thermal physiology is correlated with climatic variables such as temperature and aridity. There is also evidence that thermoregulatory traits vary with fine-scale microclimate, but this has received less attention in endotherms. Here, we test the hypothesis that avian thermoregulation varies with microclimate and behavioural constraints in a non-passerine bird. Male and female southern yellowbilled hornbills (Tockus leucomelas) experience markedly different microclimates while breeding, with the female sealing herself into a tree cavity and moulting all her flight feathers during the breeding attempt, becoming entirely reliant on the male for provisioning. We examined interactions between resting metabolic rate (RMR), evaporative water loss (EWL) and core body temperature (Tb) at air temperatures (Ta) between 30°C and 52°C in male and female hornbills, and quantified evaporative cooling efficiencies and heat tolerance limits. At thermoneutral Ta, neither RMR, EWL nor Tb differed between sexes. At Ta >40°C, however,RMRand EWL of females were significantly lower than those of males, by ∼13% and ∼17%, respectively, despite similar relationships between Tb and Ta, maximum ratio of evaporative heat loss to metabolic heat production and heat tolerance limits (∼50°C). These sex-specific differences in hornbill thermoregulation support the hypothesis that avian thermal physiology can vary within species in response to fine-scalemicroclimatic factors. In addition,Q10 for RMR varied substantially, with Q10 ≤2 in some individuals, supporting recent arguments that active metabolic suppression may be an underappreciated aspect of endotherm thermoregulation in the heat.The National Research Foundation SARChI chair for Mammal Behavioural Ecology and Physiology, the SARChI chair of Conservation Physiology, the Centre of Excellence at the FitzPatrick Institute of African Ornithology and the Claude Leon Foundation.http://jeb.biologists.orgam2022Mammal Research InstituteZoology and Entomolog

Effects of climate change on pup growth and survival in a cooperative mammal, the meerkat

Please read abstract in the article.The European Research Council [Research Grant Nos 294494 and 742808 to T.H. Clutton‐Brock since 1/7/2012] and the University Research Office and the Brain Function Research Group of the University of the Witwatersrand.http://wileyonlinelibrary.com/journal/fec2021-01-01hj2019Mammal Research Institut

Functional morphology of the ankle extensor muscle‐tendon units in the springhare Pedetes capensis shows convergent evolution with macropods for bipedal hopping locomotion

This study assesses the functional morphology of the ankle extensor muscle‐tendon units of the springhare Pedetes capensis, an African bipedal hopping rodent, to test for convergent evolution with the Australian bipedal hopping macropods. We dissect and measure the gastrocnemius, soleus, plantaris, and flexor digitorum longus in 10 adult springhares and compare them against similar‐sized macropods using phylogenetically informed scaling analyses. We show that springhares align reasonably well with macropod predictions, being statistically indistinguishable with respect to the ankle extensor mean weighted muscle moment arm (1.63 vs. 1.65 cm, respectively), total muscle mass (41.1 vs. 29.2 g), total muscle physiological cross‐sectional area (22.9 vs. 19.3 cm2), mean peak tendon stress (26.2 vs. 35.2 MPa), mean tendon safety factor (4.7 vs. 3.6), and total tendon strain energy return capacity (1.81 vs. 1.82 J). However, total tendon cross‐sectional area is significantly larger in springhares than predicted for a similar‐sized macropod (0.26 vs. 0.17 cm2, respectively), primarily due to a greater plantaris tendon thickness (0.084 vs. 0.048 cm2), and secondarily because the soleus muscle‐tendon unit is present in springhares but is vestigial in macropods. The overall similarities between springhares and macropods indicate that evolution has favored comparable lower hindlimb body plans for bipedal hopping locomotion in the two groups of mammals that last shared a common ancestor ~160 million years ago. The springhare’s relatively thick plantaris tendon may facilitate rapid transfer of force from muscle to skeleton, enabling fast and accelerative hopping, which could help to outpace and outmaneuver predators.A South African Claude Leon Foundation Postdoctoral Fellowship and a University of the Witwatersrand FRC Individual Grant.https://onlinelibrary.wiley.com/journal/146975802021-09-01hj2020Anatomy and PhysiologyCentre for Wildlife ManagementParaclinical Science

How dryland mammals will respond to climate change : the effects of body size, heat load and a lack of food and water

Mammals in drylands are facing not only increasing heat loads but also reduced water and food availability as a result of climate change. Insufficient water results in suppression of evaporative cooling and therefore increases in body core temperature on hot days, while lack of food reduces the capacity to maintain body core temperature on cold nights. Both food and water shortage will narrow the prescriptive zone, the ambient temperature range over which body core temperature is held relatively constant, which will lead to increased risk of physiological malfunction and death. Behavioural modifications, such as shifting activity between night and day or seeking thermally buffered microclimates, may allow individuals to remain within the prescriptive zone, but can incur costs, such as reduced foraging or increased competition or predation, with consequences for fitness. Body size will play a major role in predicting response patterns, but identifying all the factors that will contribute to how well dryland mammals facing water and food shortagewill copewith increasing heat loads requires a better understanding of the sensitivities and responses ofmammals exposed to the direct and indirect effects of climate change.The South African National Research Foundation (NRF), the Carnegie Corporation of New York, the Claude Leon Foundation, the Global Change System for Analysis, Research and Training (START), the Oppenheimer Memorial Trust, the Tswalu Foundation, the University of the Witwatersrand, and the Australian Research Council.http://jeb.biologists.orgam2022Anatomy and PhysiologyCentre for Veterinary Wildlife StudiesParaclinical Science

Phenotypic flexibility in body mass, basal metabolic rate and summit metabolism in southern red bishops (Euplectes orix): Responses to short term thermal acclimation

Avian basal metabolic rate (BMR) and summit metabolism (Msum) vary within individuals in response to seasonal acclimatization in free-ranging birds, and thermal acclimation under laboratory conditions. We examined relationships between acclimation air temperature (Tacc) and body mass (Mb), BMR and Msum in female southern red bishops (Euplectes orix) from a relatively mild coastal site and a seasonally colder, inland site. Following acclimation for 21 days to Tacc = 10, 22 or 35 °C, Mb, BMR and Msum were all significantly and negatively related to Tacc. The significant relationship between BMR and Tacc did not remain after Mb was included as a covariate, whereas that between Msum and Tacc did. A subsequent reverse acclimation protocol, where bishops were acclimated to a second Tacc value and then re-acclimated to the first, revealed that short-term changes in Mb and BMR were completely reversible, but changes in Msum were only partially reversible. Following the reverse-acclimation protocol, metabolic expansibility (Msum/BMR) varied significantly with air temperature, being greatest at Tacc = 35 °C. Our data suggest that the intraspecific variation in seasonal metabolic variation previously reported for this species is at least partly driven by factors other than temperature.The National Research Foundation (NRF) for N.M. and A.E.Mhttp://www.elsevier.com/locate/cbpahb2013ab201