Dan Greenberg at Simon Fraser University in Burnaby, Canada and his colleague Wendy Palen experimented with three species: the coastal tailed frog (Ascaphus truei), which lives near cold mountain streams, the desert-adapted great basin spadefoot toad (Spea intermontana), and the Pacific tree frog (Pseudacris regilla), which can adjust to various habitats.
The scientists measured the animals’ jumping distances after placing them in environmental chambers to control their body temperature and dehydration levels.
They found that the more dehydrated the amphibians were, the shorter the distance they could cover in one jump. Once dehydration had led the frogs to lose 30 per cent of their body weight – 45 per cent for the toad – they just stopped jumping entirely.
The scientists also found that a combination of dehydration and temperature increases – ranging from 15 to 30 °C, depending on the species – led to even shorter jumps.
All the frogs and toads rapidly recovered their jumping ability after being placed back in water, says Greenberg.
The two researchers think they may know why dehydration has this effect. Dehydration disrupts the ion exchanges in the cells as well as the supply of nutrients and removal of waste within the muscles, affecting their function, Greenberg says. It can also make the blood more viscous, challenging the heart’s pumping efficiency, and making physical movement more difficult.
The two researchers think the effect might apply to other ectothermic animals such as insects, arthropods and reptiles.
The findings highlight the importance of considering water loss, in addition to heat, when estimating the impact of global warming on frogs and other animals, says Greenberg.
“When we look at water loss and take it in concert with temperature, it really changes how we think about the way climate change is going to reorganise the ecological systems on Earth in the coming centuries,” he says.
It’s something the scientists already see in the frogs’ behaviour. “As soon as the temperatures went up a little bit, the tree frogs in particular would sort of hunker down in a way that reduces water loss, as if they were thinking, ‘This isn’t going to be good for me’,” says Greenberg.
Journal reference: Proceedings of the Royal Society B , DOI: 10.1098/rspb.2020.2273
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