Adapting to climate change: the effect of desertification on the physiology of free-living ungulates
Date
2010-04-14T09:06:21Z
Authors
Hetem, Robyn Sheila
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Abstract
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.