We're all at risk from climate change, but cold-blooded animals (ectotherms) that depend on the environment to maintain their body temperatures could be at more risk than most. And with weather patterns becoming more unstable, it may not just be a case of adapting to a warmer or cooler climate, but to more hot and cold snaps too. Curious to find out how ectotherms adapt to short- and long-term temperature changes, Fabien Aubret from the CNRS à Moulis, France, and Richard Shine from the University of Sydney, Australia, decided to find out how hatchling tiger snakes respond to cool and warm conditions ().
The duo built three habitats, each with an incandescent light bulb at one end to create a temperature gradient in the enclosure, and allowed the snakes to thermoregulate by basking where ever they found the temperature comfortable. The light bulb in one enclosure switched off when the ground temperature reached 22°C to create a cool environment, the bulb in the second enclosure switched off when the top temperature reached 26°C (warm environment), and the bulb in the third enclosure was on continually between 06.00 h and 21.00 h to make it really hot.
Monitoring the young snakes' health, growth and body temperatures over 14 months, the duo was surprised to see that, despite the snakes' dramatically different environments the young animals' ability to maintain similar mean and maximum body temperatures was impressive. The snakes had adapted their behaviour to ensure that they all maintained a similar body temperature, and the snakes in the cold enclosure had compensated for the cooler climate by basking for longer. However, the cold-adapted snakes seemed to have paid a price for survival in the cold: they were smaller than their warm-adapted siblings.
Aubret and Shine put the differences in the snakes' sizes down to several possibilities. They suggest that the cold snakes may be smaller because they have to devote more energy to finding warm basking spots, or it may simply be easier for small snakes to get warm compared with larger snakes. Alternatively, the warmer snakes could have grown larger because digestion is more efficient in warm conditions, allowing them to make the most of mice dinners.
So, young tiger snakes seem to be able to adapt to long-term environmental change, but how would they manage during a warm or cold snap? Could they adjust their behaviour to take account of a sudden change in temperature?
Aubret and Shine switched on all of the bulbs over the enclosures to warm all three climates as much as possible and watched how the snakes responded. Would they adjust their basking habits? They did not. The snakes that had grown up in cold conditions basked for longer than snakes that were used to the heat; and their body temepratures were warmer by 2.1°C. And when the team took away the lamps and plunged the snakes into a cold snap, the hot-adapted snakes' temperatures fell on average by 1.5°C because they basked for a fraction of the time that the cold-adapted snakes basked.
Despite adapting well to long-term climate conditions when they were young, the snakes were unable to adapt to short-term climate fluctuations when they were older. `Our data provide a striking example of how an ectotherm's thermoregulatory tactics and mean selected body temperature can depend more upon previously encountered conditions than upon current thermal challenge,' say Aubret and Shine.
