Coral rhythms help them beat night blues

New Worlds: A new species of parrot-sized dinosaur – the first discovered with only one finger – has been unearthed in Inner Mongolia, China.

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February 20, 2011 02:36
4 minute read.
Coral rhythms help them beat night blues

coral 248 88. (photo credit: Courtesy)

The world’s corals not only display stunning underwater beauty and diversity – they also have rhythm that helps keep them going through the lonely low-point of the night, when their partner (symbiotic algae) robs them blind. That corals, among the simplest of Earth’s creatures, have some curiously humanlike attributes is emerging in a fresh set of revelations by an international team of coral geneticists from Bar-Ilan and Tel Aviv Universities, in collaboration with Australia's ARC Center of Excellence for Coral Reef Studies (CoECRS).

The findings highlight some of the things humans and corals have in common. The team’s paper, titled “Complex cycles of gene expression in coral-algal symbiosis,” appeared recently in Science.

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Both corals and people have circadian rhythms that govern body functions according to changes in day and night or by season. Corals use these rhythms to dictate their feeding and breeding, and to manage their symbiotic relationship with algae. But unlike many people who are helpless without a wristwatch, the corals appear to have taken rhythm to the point where they have developed an internal “clock” that ticks reliably even if the corals are no longer stimulated by external signals such as the change from day to night or full moon to total darkness.

To study the process, the team used microarray analysis, taking samples every four hours under conditions of normal light/dark and total darkness. This enabled them to see that the corals were running two separate circadian systems in parallel. Coral chronobiologist Dr. Oren Levy BIU’s Goodman Faculty of Life Sciences, along with Paulina Kaniewska of the University of Queensland, conducted much of the field and lab work associated with the project, applying their genetics expertise to what has become the “guinea pig” coral for molecular analysis, Acropora millepora. TAU bio-informatics expert Shahar Alon supplied the core mathematical analysis for the study.

“This work is a smoking gun for further research on the subject,” said Levy. “We think this new insight will further our understanding of how circadian clock evolution evolved from simple to much more complex organisms,” he added. Independently of the internal clock, another typically vertebrate-like response saves the corals from “suffocating” during the hours of darkness, when their symbiotic algae (zooxanthellae) reverse their usual supportive role in the partnership and begin to rob the corals of precious oxygen, which the algae need for survival until daylight returns. (In separate research, Levy is currently involved in a project looking at the effects of global warming on coral reefs.) During this deep, dark period, the coral responds by making more of the same enzymes that help a sprinter’s muscles deal with a lack of oxygen, says Prof. D. Miller of JCU Australia, enabling it to struggle through this period of oxygen-stressed depression and live to see another day, when the algae will be powered again by the sun and return to nourishing the coral.

Close study of the genes involved in this subtle interaction has persuaded the international team that coral’s rhythms in response to light/dark cycles operate in two distinctly different ways at the same time – there are those that are primed directly by the coral’s own molecular timekeeper (some of these being “hard-wired” to the coral clock), but also other coral genes that respond indirectly to light/dark cycles by sensing changes in oxygen levels in the coral tissue that result from algal activity.

Both systems are necessary to the survival of the symbiotic “marriage” of the coral animal with a completely different life form, a plant. “Like any marriage, symbiosis is demanding – and one partner often has to make big changes to accommodate the other,” observes Prof. Ove Hoegh-Guldberg, of CoECRS and The University of Queensland. “The zooxanthellae appear to have forced these enormous changes on the corals – but then, corals have had at least 240 million years to adapt to symbiosis. It’s a fresh example of the marvelous complexity and interplay that enable them to survive with the other’s quirks.”

FINGER-POINTING DINO

A new species of parrot-sized dinosaur – the first discovered with only one finger – has been unearthed in Inner Mongolia, China.

Scientists named the new dinosaur Linhenykus monodactylus, after the nearby city of Linhe. The work was published online in Proceedings of the National Academy of Sciences (PNAS). The new dinosaur belongs to the Alvarezsauroidea, a branch of the carnivorous dinosaur group Theropoda, which gave rise to modern birds and include such famous dinosaurs as Tyrannosaurus and Velociraptor.

An international team of palaeontologists found the fossil preserved in rocks of the Upper Cretaceous Wulansuhai Formation, which is located near the border between Linhenykus most likely weighed only as much as a large parrot. The new theropod is unusual in having just one large claw, which may have been used to dig into insect nests, on each paw. This feature makes the specimen the only known dinosaur with one finger, and highlights the wide variety of evolutionary modifications of the hand that existed in different theropods.

It also lived alongside small mammals, lizards, clubbed dinosaurs and horned dinosaurs.


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