14 October 2011, by Tamera Jones
A population of green turtles nesting on an island in the mid-Atlantic has evolved the ability to cope with heat, a new study reveals.
Green turtle.
This could mean they are less vulnerable to the warmer temperatures expected under climate change than previously thought.
The researchers found that green turtles nesting at a beach on Ascension Island with hot, black sand laid eggs which withstand high temperatures better than eggs from turtles nesting on a cooler white beach just six kilometres away.
But the scientists warn that this tolerance for heat will have evolved over many generations and at a much slower pace than the speed of climate change.
'It may have taken over 600 years for this adaptation to take place,' says Dr Jonathan Blount from the University of Exeter, one of the authors of the study published in Proceedings of the Royal Society B. 'It's encouraging that green turtles have a capacity to evolve thermal tolerance, but this doesn't mean we should relax about their prospects in the face of climate change.'
'This doesn't mean we should relax about their prospects in the face of climate change.'
Dr Jonathan Blount, University of Exeter
Scientists are worried about how sea turtles will fare under climate change, as sea levels rise and the beaches they nest on disappear. Not just that, but warmer temperatures have a feminizing effect on turtle eggs, and so may result in populations becoming dominated by females.
But, until now, very few studies have looked at whether or not cold-blooded creatures like marine turtles have any natural ability to adapt to changes in heat.
So Blount and colleagues from Exeter, the University of Groningen and Ascension Island decided to investigate.
Ascension Island's green turtles nest at one of two beaches. One, called Long Beach, has white sand, while the other – Northeast Bay – has black, volcanic sand. The difference in colour means the sand at Northeast Bay is on average 2.6°C warmer.
The island is home to one of the world's largest breeding populations of green turtles. Animals that hatch on the island spend their first 25 to 30 years feeding off the coast of Brazil until they're old enough to breed. Then they find their way back to Ascension, swimming across 2000 kilometres of ocean.
Blount and his colleagues knew that each green turtle returning to Ascension goes back to the same beach it hatched on, so they wondered if the Northeast Bay turtles have adapted to cope with hotter sand.
To find out, they placed turtles' eggs from each of the two beaches into incubators at two different temperatures – 29°C or 32.5°C – and monitored their progress.
They found that offspring from mothers which nested on a naturally hot beach survived better and grew larger in the hot incubator compared with the offspring of females nesting on the white sand beach.
This is the first time scientists have shown that marine turtles have adapted to the environmental conditions at a specific location at such a fine scale.
Heat-tolerant populations could be crucial if species are going to adapt to a warming world, and this study highlights the need for conservation strategies which protect diversity in animal populations.
'These results may mean that if the worse came to the worst and we had to choose which population to conserve, it might be better to focus on the heat-tolerant turtles,' explains Blount. 'What it certainly shows is that working out which creatures to conserve is a lot more complicated than you might think.'