On being the right size
Wild house sparrows would seem to have little in common with our own survival rate. In fact, as all life forms become obviously much more closely related in some ways than we ever thought, many organisms have an obvious link between their size and survival. Size does seem to be important after all.
The evolution of body size was a basic starter for Thor Harald Ringsby and his fellow researchers study. His work at the Norwegian University of Science and Technology was complemented by fellow workers in the University of Glasgow and especially by the sparrows on the small Norwegian island of Leka. What they found is that telomere length of chromosomes is not only associated with life span. It is also very much correlated with the size of an individual. While big animals and small animals live for differing times, depending very much on species, this discovery has great importance for individuals.
Those house sparrows, Passer domesticus, that had a
skeletally-bigger body had shorter telomeres. These telomeres are the chromosome ends that often disappear in the normal process of cell division. As those cells replace others or simply make the animal larger, it is a natural process for them to literally drop off! The length of chromosome remaining in the typical individual is now found to be related to its size.
Further interest in the extensive study was found in a special breeding programme on Leka Island in which the birds had been selectively bred for larger size. The coincidence of this project was that the larger birds also developed even shorter telomeres (and lived for a shorter time.)
The significance of such research is more than exciting. Larger humans and animals close to us such as dogs have long been known to have short lives when they have a great body size. There is a defined relationship between life span and size in for example a small terrier and the large breeds such as the Great Dane.
Growing faster (to achieve a greater body size in adulthood) could also damage the telomeres further, but a simple relationship between the size of all animals and their chromosome length has now been established. R lives have very much been affected by a few sparrows on an island!
More on this can be located in the journal, Proceedings of the Royal Society B, under the title
On being the right size: increased body size is associated with reduced telomere length under natural conditions. Our own meagre production on human life span can be viewed in our story on Senescence or eternal youth where cells are disposed of when they become older and less useful!