Corals are able to build large reef structures in many of the worlds shallow tropical environments because they contain symbiotic micro-algae called Symbiodinium (and often referred to as zooxanthellae). Distinct symbiont species which are found in different corals look nearly identical. Credit: Todd C LaJeunesse |
For
nearly 260 years—since Carl Linnaeus developed his system of naming
plants and animals—researchers classified species based on visual
attributes like color, shape and size. In the past few decades,
researchers found that sequencing DNA can more accurately identify
species. A group of single-celled algae—Symbiodinum—that live inside
corals and are critical to their survival—are only now being separated
into species using DNA analysis, according to biologists.
“Unfortunately
with Symbiodinium, scientists have been hindered by a traditional
morphology-based system of species identification that doesn’t work
because these organisms all pretty much look the same—small round brown
cells,” said Todd LaJeunesse, assistant professor of biology, Penn
State. “This delay in adopting the more accurate convention of
identifying species using genetic techniques has greatly impeded
progress in the research of symbiotic reef-building corals, especially
with regard to their ability to withstand global warming.”
LaJeunesse
and his colleagues looked at Symbiodinium that previously had been
grouped together as subsets of the same species. They report their
results in the current (Sept.) issue of the Journal of Phycology. They
examined specific DNA markers—identifiers—from the organisms cell
nuclei, mitochondria and chloroplasts. Even though the symbionts
appeared very much the same, except for their size, genetic evidence
confirmed that the two are different species altogether.
These
findings indicate that hundreds of other coral symbionts already
identified with preliminarily genetic data are also distinct species
with unique ecological distributions.
“The
recognition of symbiont species diversity should substantially improve
research into reef-building corals and facilitate breakthroughs in our
understanding of their complex biology,” said LaJeunesse.
He
began his work of classifying Symbiodinium using genetic techniques as
part of his research into their ecology and evolution and in later
studies of coral bleaching events related to global warming.
“Knowing
exactly which Symbiodinium species you’re dealing with is important
because certain species of Symbiodinium associate with certain species
of coral,” he said. “Although many corals are dying as a result of
global climate change, some may be able to survive because they
associate with Symbiodinium species that are better adapted to warm
water temperatures.”
Other
researchers on this project were John Everett Parkinson, graduate
student in biology, Penn State, and James Davis Reimer, associate
professor of biology, University of the Ryukyus, Okinawa.
The National Science Foundation supported this research.
Source: Penn State University
