Natural selection and adaptation to temperature in corals: is Darwin back?

As corals are threatened by ocean warming and acidification the question emerged of wether they could adapt to these changes. Following a Darwinian reasoning, this would require that

i) not all coral individuals are identical in their response to thermal stress

ii) these differences should be genetically determined (the offspring should present a similar response to their parents)

iii) the differences in thermotolerance provide an advantage in survival or reproduction (hopefully higher tolerance could lead to higher survival or reproduction in situation of thermal stress)

The first point (differences between individuals in the same species) has been observed in natural and experimental conditions. It remained to know if these differences are heritable.

An indirect response has recently been published by Dixon et al. in Science (http://www.sciencemag.org/content/348/6242/1460.short). They crossed coral individuals (same species) from two locations, one with higher temperature (location PC) than the other (location OI). Among other results, they performed an experiment of artificial selection by retaining only the larvae most resistant to heat stress. They looked at the genome of these larvae (not exactly the whole genome) and they observed that some part of the genome where much more frequent in the larvae than expected. For the regions, the copy (what we call the allele) coming from the PC location (with higher temperature) was more frequent than the copy from the other location. This suggests that these parts of the genome are implicated in thermotolerance: the larvae with alleles from PC had better survival than other larvae.

These results are really important and innovative: the authors suggest that corals facing climate change could evolve through natural selection. Nevertheless other studies will be required, for example to test if these genes are really implicated in adaptation and if they provide higher survival and / or reproduction in natural conditions.

Bleachedcoral

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