Weber, S.B., Broderick, A.C., Groothuis, T.G.G., Ellick, J., Godley, B.J. and Blount, J.D. 2012. Fine-scale thermal adaptation in a green turtle nesting population. Proceedings of the Royal Society B 279: 1077-1084.
The authors write that "temperature has a profound effect on hatching success, embryonic development and sex in marine turtles," which effects have logically led to "growing concerns regarding the impacts of climate warming on their reproductive success."
What was done
In a study designed to explore this subject, Weber et al. conducted a test for "local adaptation in an island-nesting population of green turtles (Chelonia mydas) where incubation temperatures vary dramatically among closely adjacent nesting beaches," one with pale sand (Long Beach, LB) and one with dark sand (Northeast Bay, NEB), which was consistently 2-3°C warmer than the pale sand beach only 6 km distant from it. This they did using "a combination of in situ and common-garden approaches to compare survival (as a measure of fitness), developmental rates and size at hatching for offspring of LB and NEB females at different incubation temperatures, while simultaneously accounting for egg-mediated maternal effects."
What was learned
The six scientists found that the offspring of female turtles nesting on the naturally hot (black sand) beach "survived better and grew larger at hot incubation temperatures" compared with the offspring of females nesting on the cooler (pale sand) beach, which differences, in their words, were due to "shallower thermal reaction norms in the hot beach population, rather than shifts in thermal optima, and could not be explained by egg-mediated maternal effects." And they also conclude that "the results of the common-garden experiment suggest that the increased heat-tolerance of NEB turtles has a genetic basis."
What it means
Weber et al. say their results suggest that "marine turtle nesting behavior can drive adaptive differentiation at remarkably fine spatial scales," and they therefore opine that "previous studies may have underestimated the extent of adaptive structuring in marine turtle populations that may significantly affect their capacity to respond to environmental change." In their concluding paragraph, therefore, they state that whereas "global warming is predicted to have multiple deleterious effects on the reproductive success of marine turtles, including the loss of nesting beaches to rising sea levels, increasingly feminized populations and reduced hatching success," their results suggest that "in at least one of these respects, marine turtles have the capacity to adapt to warmer temperatures."