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Sea turtles evolve to suit changing climate

Scientists at the University of Western Australia testing Loggerhead Turtle eggs have found that genes to help them withstand increased temperatures could be passed on to future generations.

This research, carried out earlier this year, is the first done with turtles before they hatch when they are at their most vulnerable to changes in their environment.

“The problem with sea turtle females is they go back to where they were born,” said Dr Nicola Mitchell, supervising researcher on the project.

“There’ll be pressure for them to shift their rookeries to cooler areas as it gets hotter, but it’s going to be thwarted to some extent by females tending to go back to where they came from.

“We’re delving into the molecular routes they might have to adapt, if they can’t relocate.”,

Dr Mitchell and her PhD student, Jamie Tedeschi, extracted RNA from the unhatched eggs to see whether certain genes were active. These genes control molecules called heat shock proteins in the embryo’s cells. When the cells are under stress from high temperatures, heat shock proteins activate by splitting into two pieces. One piece acts like scaffolding, helping other proteins in the cell to form correctly, while the other signals the cell’s nucleus to produce more protective proteins.

Dr Mitchell and her team found the eggs inherit both how many of these protective proteins they produce in their cells and how sensitive they should be to the signals to produce more. This could allow eggs to adapt, over several generations, to higher and more unpredictable temperatures.

“If that variation is there, we’ll get evolution,” Mitchell said.

The team collected 1200 eggs from Dirk Hartog island and Bungalup Beach, around 850 kilometres north of Perth. While Mitchell said this was “a tiny fraction of the total nesting effort that season”, it was still a significant effort to collect and transport so many samples.

"You go out at dusk, and you might stay out until three or four in the morning waiting for the turtles to come up,” Dr Mitchell said.

"They get spooked really easily if they see you, but they're kind of locked in once the eggs start falling out.

“That's the hard part - it's a lot of stealth, and waiting, and disappointment if the turtle changes its mind and heads back out to sea.”

The future of turtle research may be a lot less hands on. Samples from their experiments have been preserved so that the effects of heat on all the egg’s systems, rather than just a few proteins, can be examined using a technique called transcriptomics.

Mitchell is also working on computer simulations of turtle’s nest sites based on the physics of the sun and sand to determine the temperature in the nest, to help spot patterns in historical and future populations.

Despite the challenges they face, Dr Mitchell is optimistic about the turtles’ future.

“You may not need to save the sea turtles”, she said.


References:

Moritomo, R 1993, ‘Cells in Stress: Transcriptional Activation of Heat Shock Genes’, Science, vol. 259, issue 5100, pp. 1409-1410.

Woolgar, L, Trocini, S & Mitchell, N 2013, ‘Key parameters describing temperature-dependent sex determination in the southernmost population of loggerhead sea turtles, Journal of Experimental Marine Biology and Ecology, November 2013, Vol. 449, pp. 77-84.

Tedeschi, JN, Kennington, WJ, Tomkins, JL, Berry, O, Whiting, S, Meekan, MG & Mitchell NJ 2016 ‘Heritable variation in heat shock gene expression: a potential mechanism for adaptation to thermal stress in embryos of sea turtles.’ Proc. R. Soc. B 283: 20152320.