There is a reason astronomers are constantly looking for signs of water on other planets – water is life. For animals living on land, this statement is perhaps most true for amphibians which are tied to water during each part of their life cycle. Not only do they breed and lay their eggs in water, but they need to keep themselves moist to avoid losing too much water to evaporation through their skin. So, how do forest-dwelling amphibians – such as spotted salamanders (Ambystoma maculatum) – know if they are in a wet enough area to avoid drying out? Danilo Giacometti and Glenn Tattersall of Brock University, Canada, think that these salamanders can sense the humidity in the air around them and seek out places where the air is humid or drier to help keep their skin at the perfect level of wetness.
To find out if their idea was correct, Giacometti and Tattersall collected 44 adult spotted salamanders near Bat Lake in Ontario, Canada, in the spring of 2024 and brought them back to the lab. After making sure the salamanders were well hydrated, they placed the amphibians in a ring-like chamber for 12 h, which allowed the salamanders to choose the humidity they preferred (ranging from 30% to 96%) while the air was 17°C. The team found that salamanders generally avoided the areas with the lowest humidity, and that the smaller salamanders favoured areas where the air was the most humid, suggesting that they may be aware of the amount of water they are losing to the air. But would the salamanders prefer an even higher humidity if the air was hotter?
When the scientists increased the temperature to 22°C, they were surprised to see that the salamanders remained at the humidities they preferred at the cooler temperature. Normally, making the temperature hotter would also lower the humidity of the air, but thanks to the ingenious design of their humidity chamber ring, Giacometti and Tattersall were able to keep the humidity the same even though the temperature was higher. This suggests that the salamanders are choosing the area based on the amount of water in the air, not the temperature they are sensing. ‘Rather than being passive victims of their environment, salamanders actively choose conditions that help them stay hydrated’, says Giacometti. So, if the temperatures are scorching or frigid, these salamanders are going to use their humidity thermostat to make sure they at least stay hydrated.
