New York, Jan 17 (IANS): Offspring produced by older parents often do not live as long and researchers have now discovered why this is so.

The age of the parents influences offspring longevity, in part, through its effects on offspring telomeres, structures of proteins that cap off and protect our DNA at the tips of chromosomes like the aglets or clear tips of shoelaces, says a new study.

"Telomeres function a bit like the plastic caps at the ends of shoelaces and protect the coding DNA from loss during cell division. Telomere loss reduces the lifespan of cells and is thought to be involved in the ageing process," said one of the researchers Britt Heidinger, assistant professor of biological sciences at North Dakota State University, Fargo, US.

Individuals with longer telomeres or slower rates of telomere loss have been shown to have greater longevity in a wide range of species.

The study was conducted on a free-living population of European shags (Phalacrocorax aristotelis) that breed on the Isle of May National Nature Reserve in the Firth of Forth, Scotland.

The socially monogamous seabirds are long lived, sometimes as much as 22 years.

Researchers focused on nests where one of the parent's age was known, as the population of shags in this location has been studied for more than 30 years.

In the chicks being studied, researchers collected small blood samples to measure the telomere length of the offspring.

Study results showed that chicks produced by older mothers and fathers had significantly greater telomere loss than chicks produced by younger parents, but the loss appeared to occur during nestling growth, rather than during the pre-natal period.

Results also seemed to indicate that the maternal age effect is stronger than the paternal age effect, said the study published in the journal Functional Ecology.