Sand Color Influences Green Sea Turtle Egg Incubation




It has been suggested that sea turtles may face an uncertain future, as climate warming could threaten to reduce their reproductive viability. However, new research led by the University of Exeter shows that some turtles are naturally heat-tolerant, when it comes to their nesting sites.

Green sea turtle hatchling

Sand color influences the incubation temperature for green turtle eggs on Ascension Island.

The study focused on green sea turtles breeding on Ascension Island, a UK overseas territory in the South Atlantic ocean. Scientists from the universities of Exeter in the UK and Groningen in the Netherlands found that eggs laid by female turtles nesting on a naturally hot beach withstand high temperatures better than eggs produced by those nesting on a cooler beach just a relatively short distance away.

The warmer beach has dark sand, which absorbs and retains the heat, whereas the neighboring beach is 2-3°C (3.6-5.4°F) cooler because it has white sand, which reflects the warmth of the sun's rays. Green sea turtles travel from off the shore of South America to this tiny island for breeding purposes. Since most of these female turtles nest on the beaches where they themselves hatched, populations become adapted to specific nesting locations.

Incubation differences

The researchers placed some of the eggs laid on each beach into incubators at either 32.5°C (90.5°F) or 29°C (84°F) and monitored their progress. They found that the eggs from the warmer beach were better able to thrive in the hot incubator than those from the cooler beach.

Dr. Jonathan Blount of the University of Exeter, who led the research, said: "We believe this is the first time that adaptation to local environmental conditions has been demonstrated in sea turtles, which is all the more remarkable given that the beaches in question are just under four miles apart."

A survival strategy for the future?

Heat-tolerant populations may be crucial in allowing species to adapt to a warming world. These findings highlight the need for conservation strategies that protect diversity in animal populations.

University of Exeter Ph.D student Dr. Sam Weber, lead author of the study, said: "Such adaptations probably evolve over many generations, so whether turtle evolution can keep pace with the rapid climate change that scientists have predicted remains to be seen. However, occasional movements of heat-adapted turtles to other nesting sites could help to spread their favorable genes."

Reference:  S. B. Weber, A. C. Broderick, T. G. G. Groothuis, J. Ellick, B. J. Godley, J. D. Blount. Fine-scale thermal adaptation in a green turtle nesting population. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.1238

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