Bird species that suffer from more predation tend to age faster, a new study finds. That supports an old theory intended to explain why animals have such widely varying lifespans, scientists claim.
The researchers couldn’t say whether the findings might help explain human lifespan as well. But it seems to hold “at least in birds, where the necessary data are available for many species”—some 1,400 of them, whose longevities vary by some 25-fold, according to a statement from the Max Planck Institute for Ornithology in Seewiesen, Germany, where the study was conducted.
“We were able to confirm” the theory “on a broad geographical scale,” said Mihai Valcu, a co-author of the study, published online April 25 in the journalEcography.
Some fish, turtles or even invertebrates can live to hundreds of years, while the neon pygmy goby—a small fish—reaches ripe old age at only 60 days. In birds, parrots such as the Sulfur-crested cockatoo can live to over 100 years, while the small Allen’s hummingbird tops out at just four.
The classical “evolution ary theory of ageing,” proposed by evolutionary biologist George C. Williams over 50 years ago, claims shorter lifespans will afflict adult animals that suffer high predation, exposure to parasites and other randomly occurring events.
One way to look at why, is that nature or evolution won’t bother expending much “effort” to extend the lifespan of creatures that will probably die young anyway. Of course, that’s not the real reason, as evolution isn’t considered a conscious process. Evolution occurs when individuals have more offspring than others as a result of having more “favorable” genes. This lets them spread their favorable genes through the population, so that gradually, whole species change. The way those genes arise in the first place is just as any new genes do: mutation.
So the aging theory can be expressed like this: if a species suffers high predation or rates of parasitic attack, most individuals will already be killed before the rare mutations that cause healthier ageing can make an evolutionary difference.
Mihai Valcu and Bart Kempenaers from the institute used a large database on estimates of maximum life-span of bird species. Using a complex statistical analysis they found that maximum longevity goes down as the number of predator species within the same area goes up. The relationship held when other life history traits known to influence longevity, such as size and clutch size, were taken into account. It also held no matter how the analysis was done: at the species level, at a finer regional scale (groups of species within a certain area) or even when comparing entire “bioregions,” they said.
Source : http://www.world-science.net/