Chromosome ends hold clues to a bird's longevity

Short telomeres tied to higher mortality in Indian Ocean warblers

9:56pm, November 20, 2012
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The long and short of a bird’s life may be recorded in the tips of its chromosomes, a new study suggests.

A study of Seychelles warblers living on a small island in the Indian Ocean suggests that the length of telomeres — bits of DNA that cap chromosome ends — can predict a bird’s chance of dying better than its chronological age can. Warblers with shorter telomeres were less likely to survive another year, especially if the truncation happened rapidly, David S. Richardson, a molecular ecologist at the University of East Anglia in Norwich, England, and colleagues report online November 20 in Molecular Ecology.

The study “provides very important evidence that backs up what has been found in the laboratory — changes in telomere length matter a lot,” says animal ecologist Pat Monaghan of the University of Glasgow in Scotland.

Increasing age and body mass were also linked to shorter telomeres in the birds. That result stands in contrast to a recent large study of people in northern California that found telomeres get shorter with age, but that higher body mass is associated with longer telomeres (SN Online, 11/11/12).

Like shoestring aglets, telomeres stop chromosomes from unraveling or being eaten away at the ends. Cells with very short telomeres become decrepit or die, but it has been unclear whether that has any effect on whole body.

Most studies of telomere lengths have taken snapshots of people or animals at one point in time, or have measured individuals’ telomeres over a very short period, Monaghan says. The warbler study followed birds over the course of their natural lives; on average, Seychelles warblers live about six years, but some have reached age 17.

Young birds started with roughly the same size telomeres, Richardson says. But some warblers’ telomeres shorten faster than others as the birds age. Although there are no predators on Cousin Island, the protected area in the Seychelles where the study was conducted, life does present other stresses and strains, Richardson says. Some parts of the island may have less food. Birds may get infected with malaria parasites. And reproduction and caring for young may take its toll on female birds.

So far, the researchers haven’t linked any of these challenges to telomere length, but that’s one of the next items on the research plan, Richardson says. He’d also like to know if parents can pass along shortened telomeres to offspring.

It’s also not clear whether telomere shortening leads to poor health and death, or if truncated chromosome tips are a side effect of stress and disease. Even if losing a little off the chromosome tips isn’t enough to kill outright, “telomeres might be acting as an indicator of the sort of hard life you’re going through,” Richardson says.

These results may not apply directly to humans, says Geraldine Aubert of the Terry Fox Laboratory at the British Columbia Cancer Research Center in Vancouver. For instance, telomeres were measured in different types of cells in the warbler study than are usually used in human studies, which might give different results. Even in the birds, telomere length is not a perfect predictor of mortality.

“I don’t think that measuring your telomere length will tell you that you’re going to die soon,” Aubert says, “but it may highlight areas you want to concentrate on to maintain telomere length as best you can.”

Those measures include the usual health advice: Exercise, eat a healthy diet, don’t smoke and avoid undue stress.  

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