Scientists studying the Seychelles Warbler have discovered that limited romantic options of parent birds are harmful to their offsprings’ chromosomes.
By Rex Graham
Inbreeding has led to an unhealthy shortening of the warblers’ telomeres, the protective caps on the ends of chromosomes. Telomeres become smaller over an individual’s lifetime, but prematurely short telomeres reflect poor health and short lifespans in everything from insects and worms to reptiles and humans.
Too short telomeres
A report published May 16 in Molecular Ecology by researchers in the U.K., The Netherlands and the Seychelles document for the first time that inbreeding of parents is linked to shorter telomeres at the birth of their offspring. This effect of inbreeding has not been discovered in other animal groups.
“In humans, things like smoking, eating foods that are bad for you, and putting your body through extreme physical or mental stress all have a shortening effect on telomeres,” said Kat Bebbington, lead author of the study and a Ph.D. student at the University of East Anglia. “In the wild, inbred animals are less able to cope when the environment is bad, and the stress of such situations causes further telomere shortening.”
Telomeres too long
For birds and humans, longer telomeres are better indicators of health that short ones. There are no telomere-enhancing vitamins, which could be an even bigger problem because cells with longer and longer telomeres become immortal. Almost all cancer cells can grow their telomeres. Drug companies are developing telomere-maintenance drugs to reverse the cellular immortality and treat cancer.
Long-lived animals also retain long telomeres longer. Even naked mole rats under what scientists expect would be telomere-shortening stress of low levels of oxygen in their deep burrows live about 58 years. Newborn mole rats usually don’t live long, but once one reaches maturity its chances of living to old age improve dramatically.
Telomeres are tricky terrain because nobody knows what’s too long or too short. The complexity is seen in birds.
German and Dutch scientists recently reported that in one species of fish-eating seabird, those with the best reproductive performance also had the shortest telomeres. Pairs of unsuccessful Common Terns (those that lost their chicks) experienced less stress and had longer telomeres.
Adapting to what life dished out may be the key to healthy telomeres. “Individuals that best tolerate telomere-shortening processes may perform best,” the German and Dutch scientists said in a report in the Proceedings of the Royal Society B.
Birds that live on small islands face a unique problem. They would seem to be particularly vulnerable to the telomere-shortening stress caused by mating with close relatives. Such inbreeding results in a variety of problems, such as the expression of unhealthy, normally hidden, genes. Birds and other animals that are endemic, or found only in a single small area, inevitably face inbreeding stress.
“Inbreeding is a big step that island endemics must overcome,” Bebbington said. “One mechanism to avoid inbreeding is to make sure that offspring disperse away from the home territory. Another is to have some kind of recognition of family members so accidental matings between relatives don’t happen.”
Songbirds are the most successful of the roughly 30 orders of birds, representing over half of all bird species. Genetic analyses show that Passeriformes are most closely related to parrots, and less so to falcons and other birds.