Most animals are well prepared to capitalise on times of plenty and live off their fat when food is scarce, but how are they going to cope if regular food supplies are affected dramatically by climate change? Cindy Canale and her colleagues from the Muséum National d'Histoire Naturelle, France, explain that the frequency of extreme environmental events, such as droughts and cyclones, is expected to increase, dramatically and unpredictably affecting food supplies. Curious to find out how one animal, the grey mouse lemur, may cope with sudden unexpected food loss, Canale, Martine Perret, Marc Théry and Pierre-Yves Henry measured the body temperatures and activity levels of the tiny primates when their food supply was suddenly cut short (p. 551).
Canale and her colleagues explain that grey mouse lemurs inhabit the island of Madagascar, where they regularly experience hardship courtesy of El Niño–La Niña climate oscillations. Selecting females from the museum's captive colony of lemurs, the team simulated times of plenty – by feeding half of the animals on a healthy diet of fruit, carbohydrates and protein (the diet that covered 100% of the animal's energy requirements) – and lean seasons – by restricting the diet of the remaining animals to 60% of the well-fed animals' diet. Next the team simulated the devastation wreaked by a drought or cyclone. They cut the diets of all of the animals to 20% of the 100% diet for 12 days to find out which strategies the well-fed and undernourished animals might use to survive.
Knowing that grey mouse lemurs routinely conserve energy using torpor – dropping their body temperature and metabolism while resting – the team wondered whether the tiny primates may be able to adjust this energy saving pattern in response to a catastrophic decrease in food supply. The lemurs did. Even before times got really hard, the lemurs on the 60% diet entered torpor 4.4 h earlier than the well-fed individuals; they also dropped their temperature lower. When the ‘severe drought’ hit and the lemurs had to get by on a 20% ration, the lean season lemurs began dropping their body temperature 5.9 h earlier than the well-fed animals. The team also looked at the length of each torpor bout after the reduction of their food supply and found that both the well-fed and lean season lemurs dropped their body temperatures for a longer period. The lean season lemurs also cooled more than the well-fed animals, getting down to 24.3°C compared with 29.4°C for the well-fed lemurs.
Next the team analysed the lemur's activity levels and found that instead of reducing their activity when the food supply was cut, the tiny primates were more active immediately after bouts of torpor. And the lemurs on the lean season diet became twice as active as the better-fed animals when their rations were cut. However, when the team looked at the total activity levels of the well-fed and undernourished lemurs, they found that the two groups behaved the same.
So grey mouse lemurs are able to rapidly adjust their behaviour and metabolism in response to a catastrophic decrease in their food supply. Also, the undernourished animals seemed better prepared for hardship than better-fed members of their species. ‘We suggest that physiological flexibility of energy saving mechanisms would be a key adaptation to respond to increased climate instability,’ say Canale and her colleagues.