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Accueil du site → Doctorat → Afrique du Sud → 2009 → Adapting to climate change : the effect of desertification on the physiology of free-living ungulates

University of the Witwatersrand (2009)

Adapting to climate change : the effect of desertification on the physiology of free-living ungulates

Hetem, Robyn Sheila

Titre : Adapting to climate change : the effect of desertification on the physiology of free-living ungulates

Auteur : Hetem, Robyn Sheila

Université de soutenance : University of the Witwatersrand

Grade : Doctor of Philosophy 2009

For long-lived species, physiological plasticity provides the best option to counter extinction and survive climate change, yet we understand very little about long-term physiological adaptations of arid-zone artiodactyls. Variation within a morphological trait, for example, may provide pre-adaptation to changing climatic conditions. Using intra-abdominal miniature data loggers, I measured core body temperature in female springbok (Antidorcas marsupialis) of three colour morphs (black, normal and white) and showed that the pelt colour does indeed have thermoregulatory significance. The black springbok seem able to reduce energy expenditure in winter, but experience higher solar heat load in hot conditions. Therefore lighter coloured individuals may be selected for in the future as conditions get progressively hotter and drier with climate change. Small individuals also may be selected for in the future. Hypothetically, small artiodactyls would have the advantage of smaller resource requirements and greater access to refuge sites than do larger artiodactyls, but they are likely to be disadvantaged by a high mass-specific metabolic rate, high water turnover and less capacity to store heat. I measured body temperature, activity and microclimate selection in free-ranging Arabian oryx (Oryx leucoryx, 70 kg) and the smaller Arabian sand gazelle (Gazella subgutturosa marica, 15 kg) inhabiting one of the hottest and driest regions, Arabian Desert environment, at the same time. Despite the oryx having a body mass more than four-fold that of the sand gazelle, both species responded remarkably similarly to changes in environmental conditions. Both species employed heterothermy and cathemerality, and selected the same cool microclimates during times of heat stress. In combination with high ambient temperatures, water stress appeared to be the primary driver towards heterothermy in the Arabian oryx, potentially resulting from dehydration or the combined effects of dehydration hyperthermia and starvation hypothermia. To investigate the physiological consequences of habitat transformation, of the kind expected to occur with climate change, I monitored body temperature and activity patterns of Angora goats inhabiting both desertified and intact sites. I was able to demonstrate physiological changes in response to desertification. Following shearing, goats that inhabited the transformed site displayed an increased 24-h amplitude of body temperature rhythm and were generally less active compared to goats that inhabited the intact site, which may reflect a trend towards heterothermy and cathemerality, as was observed in the Arabian oryx and sand gazelle. Finally, the physiology studies required to better understand the mechanisms of phenotypic plasticity underlying responses to climate change cannot be confined to the function of healthy animals as pathogens are predicted to spread with climate change. I therefore investigated the physiological consequences of infection in freeliving kudu (Tragelaphus strepsiceros). Not only did I record quantitative evidence for autonomic and behavioural fever, but I also recorded the first evidence of sickness behaviour, in the form of decreased activity, in a free-living artiodactyl. Artiodactyl hosts are likely to have to contend with an increased costs of immunity superimposed on the chronic physiological stress of having to adapt to the climatically unsuitable areas to which they are confined. In conclusion, I have revealed some of the physiological mechanisms that will be brought into action if long-lived artiodactyls are able to adapt phenotypically to climate change in Africa. Activity patterns and microclimate selection are flexible behavioural processes which are likely to represent an animal’s primary defence to changes in climatic conditions. If behavioural processes are insufficient to maintain homeothermy, we may observe changes in an animal’s body temperature, a sensitive indicator of infection, dehydration, nutrition and environmental stress. Such physiological measurements need to be incorporated into long-term physiological monitoring projects, and bioclimatic envelope models, so that we can better predict how species will respond to climate change.


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