A new paper, published in the leading evolutionary journal, The
American Naturalist, investigates the potential for corals to evolve
greater resistance to bleaching.
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The joint study, carried out by scientists from Queen’s
University in Canada and the Australian Institute of Marine
Science (AIMS) presents a new way of examining how coral reefs
may respond to climate change.
The mutualistic relationship between corals and the algae that
live within their tissues can break down in response to stress,
leaving the white calcium carbonate skeleton of the coral
visible and hence a bleached appearance. In this new study,
population genetic models were developed that explore factors
that could affect the rate at which resistance to bleaching
might evolve. |
Bleached corals on the Keppel
Islands, Great Barrier Reef. Photo: Dr Ray Berkelmans.
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The study examined the effects of four factors on the evolution of
bleaching resistance: (i) the existence of tradeoffs where an
evolutionary advantage conferred by one trait is accompanied by a
disadvantage conferred by another; (ii) whether the zooxanthellae are
expelled from the coral tissue or die during bleaching; (iii) the
nature of the genetic control of bleaching resistance; and (iv) the
mode of reproduction, sexual or asexual, of the corals and their
symbionts.
This research does not indicate that corals are safe from climate
change. Instead it provides a framework for assessing the potential
for corals to evolve a greater ability to cope with such changes.
"These models demonstrate for the first time that in spite of the
complex nature of the interactions between these algal symbionts and
their coral hosts, there is no necessary impediment to them evolving
greater bleaching resistance. However, predicting the precise rates at
which this may occur, or whether the rate will be sufficient to
outpace projected sea temperature rise as a result of climate change,
will require much more information about many aspects of the biology
of these species," said Dr. Troy Day of Queen’s University.
"Prior to this study, we had a theory about the conditions under
which mutualistic relationships were likely to form and breakdown, but
not how they evolve once established", said Dr Julian Caley of AIMS.
"It is also likely that the theory developed in this study can be
applied to understanding evolution in other mutualistic relationships
which are a common component of biodiversity".
Although these results open up a new line of inquiry for how corals
might be evolutionarily buffered from temperature stress, there is no
reason to become complacent about human impacts on the environment.
"While this study helps us to understand how coral reefs might evolve
in response to climate change, these icons of biodiversity are still
under threat from it," said Dr. van Oppen of AIMS. As Dr. Laura Nagel
put it, "This project is important for providing a more complete
understanding of the risks of climate change faced by coral reefs, and
to help us to start thinking about how knowledge of these evolutionary
dynamics might help to us to better manage these risks".
This research was conducted with part funding support from the
Australian Government’s Marine and Tropical Sciences Research
Facility.
