"Key Found To Moonlight Romance"
Coral Reef Studies - 19 October 2007
An international team of Australian and Israeli researchers has
discovered what could be the aphrodisiac for the biggest moonlight sex
event on Earth.
An ancient light-sensitive gene has been isolated by researchers from
the ARC Centre of Excellence for Coral Reef Studies (CoECRS) that
appears to act as a trigger for the annual mass spawning of corals
across a third of a million square kilometres of Australia's Great
Barrier Reef, shortly after a full moon.
The genes, known as a cryptochromes, occur in corals, insects, fish and
mammals - including humans - and are primitive light-sensing pigment
mechanisms which predate the evolution of eyes.
In a new paper published in the international journal Science today, the
team, headed by Marie Curie Scholar Dr Oren Levy of CoECRS and the
University of Queensland, reports its discovery that the Cry2 gene,
stimulated by the faint blue light of the full moon, appears to play a
central role in triggering the mass coral spawning event, one of
nature's wonders.
Professor Ove Hoegh-Guldberg, who leads the University of Queensland
laboratory in which the genes were discovered, said "This is the key to
one of the central mysteries of coral reefs. We have always wondered how
corals without eyes can detect moonlight and get the precise hour of the
right couple of days each year to spawn."
What allows corals to spawn simultaneously along the immense length of
the Great Barrier Reef - and also in other parts of the world - has been
a scientific mystery till now, though researchers knew that tide, water
temperature and weather conditions played a part, says Dr Levy. However
the remarkable synchronisation of spawning occurring all along the Reef
immediately following a full moon suggested that moonlight was a key
factor.
Exposing corals to different colours and intensities of light and
sampling live corals on reefs around the time of the full moon, Dr Levy
found the Cry2 gene at its most active in Acropora corals during full
moon nights. "We think these genes developed in primitive life forms in
the Precambrian, more than 500 million years ago, as a way of sensing
light," he explains. "The fact they are linked with the system that
repairs damage from ultraviolet (UV) radiation suggests they may evolved
in eyeless creatures which needed to avoid high daytime UV by living
deep in the water, but still needed to sense the blue light shed by the
moon to synchronise their body clocks and breeding cycles."
"They are, in a sense, the functional forerunners of eyes," Professor
Hoegh-Guldberg said. In humans, cryptochromes still operate as part of the circadian system
that tunes us to the rhythms of our planet, though their light-sensing
function appears lost to us, he went on to explain.
"They play important roles in regulating the body-clocks of many
species, from corals to fruit flies, to zebra fish and mice. The
proteins they produce are similar to those in humans and other mammals,
though they appear to function more like those in the fruit fly," says
Professor David Miller of CoECRS and JCU.
The coral cryptochrome genes were initially identified by Dr Levy and Dr
Bill Leggat working with Professor Hoegh-Guldberg (UQ) on Heron Island.
Prof. Miller and Dr David Hayward, of the Australian National
University, were able to add information on the coral cryptochromes from
a large library of coral genes that they have been compiling (so far
they have catalogued about 10,000 out of an estimated 20-25,000 genes in
coral), and leading circadian clock biologists from Bar-Ilan and
Tel-Aviv Universities in Israel played important roles in interpreting
the data.
"Many of these genes developed in deep time, in the earliest phases of
organised life on the planet," Dr Leggat says. "They were preserved for
hundreds of millions of years before being inherited by corals when they
developed about 240 million years ago, and are still found today in
modern animals and humans. They are an indicator that corals and humans
are in fact distant relatives, sharing a common ancestor way back."
Whether they have anything at all to do with human associations between
the full moon and romance is not known, but cryptochromes probably still
play a part in our body clock.
