How marine animals survive stress

Washington, May 26 (ANI): A study, conducted by an international team of researchers, has shed new light on how marine animals survive stress.

From 2002 through 2008, a team led by Tufts University Professor of Biology L. Michael Romero studied corticosterone levels in iguanas on Santa Fe Island before and after the El Niño that struck in late 2002.

The team included co-author Martin Wikelski from the Max Planck Institute for Ornithology and Konstanz University.

The Galapagos Islands' marine iguanas are a suitable model for study because they live in predictable natural conditions.

The animals feed exclusively on marine algae. Their greatest and almost only threat or stress occurs during recurrent El Niño-induced food shortages, when a decrease of algae can lead to starvation.

The scientists captured 98 healthy male iguanas on the island in December 2002, just weeks before the El Niño.

They injected a group of the animals with a hormone to stimulate a biological process called negative feedback, which lowers the natural corticosterone levels in the animals' blood.

The animals responded in one of two ways.

Some reacted by shutting shut down the release of corticosterone.

In other iguanas, the secretion of corticosterone continued, producing excessive concentrations of the hormone in the blood.

Romero and Wikelski returned to Santa Fe Island in July 2003.

Twenty-three of the animals had starved to death, but seventy-five had survived.

According to Romero, the dead iguanas were imperilled by their inability to turn off their stress response.

This produced elevated corticosterone levels.

In this condition, the animals had depleted the protein reserves that could be processed into energy during a stressful event.

In their weakened condition, these iguanas were more susceptible to starvation than their counterparts.

Romero pointed out to several major implications of the findings.

First, negative feedback is a vital component of a successful stress response.

He said: "The results from the iguanas indicate that the better an individual is at coping with stress - by turning off the response as soon as possible - the better the chance they have to survive."

The ultimate goal of the research, said Romero, is "to understand what causes stress in wild animals; what physiological mechanisms are turned on in response to stress and how those mechanisms help the animals survive in their natural habitats."

This work has immediate implications for the current oil spill in the Gulf of Mexico.

Romero said: "As animals encounter the spill, they will have a robust release of corticosterone to help them cope with the consequences of the oil.

"However, those animals that can best turn off their corticosterone response once the initial danger from the oil has passed will probably be the most likely to survive."

The study has appeared in the May 26 online issue of the Proceedings of the Royal Society. (ANI)