9 research outputs found
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
(âŒ15%), Msum (âŒ8%), and mass-specific Msum (âŒ15%). 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 âŒ13% and âŒ17%, respectively, despite similar
relationships between Tb and Ta, maximum ratio of evaporative heat
loss to metabolic heat production and heat tolerance limits
(âŒ50°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 â€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. CluttonâBrock 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 muscleâtendon 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 muscleâtendon 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 similarâsized 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 crossâsectional 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 crossâsectional area is significantly larger in springhares than predicted for a similarâsized 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 muscleâtendon 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 springhareâs 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