Telomere length as an age estimator

Field biologists often work with organisms with an unknown history. A marker of an animal’s age would offer insight into how age affects reproductive success, dynamics of population growth, and the management of endangered species. In the photo on the left, I am taking a blood sample from a Leach's storm-petrel. From a drop of blood we can measure the birds telomeres. The inverse relationship between telomere length and organismal age allows for the classification of unknown individuals into broad age classes.
 

Telomere shortening rates vary with lifespan

There is a wide range in maximum lifespan among species. I discovered that across species, the rate of telomere shortening in erythrocytes is inversely correlated with longevity in birds and mammals, so that long-lived species lose fewer telomeres with age than short-lived species. Unexpectedly, telomere length does not shorten with age in the particularly long-lived Leach’s storm-petrel, but instead lengthens. This novel finding suggests that regulation of telomere length is associated not only with cellular replicative life span, but also with organismal life span. It appears that very long-lived organisms may have escaped any telomeric constraint on cellular replicative life span and it may be that the longest-lived petrels have found a way to lengthen their telomeres.

           
 

Telomerase activity underlies variation in telomere shortening rates between species

To determine if telomerase activity is the underlying mechanism behind variation in telomere shortening across species I determined telomerase activity in bone marrow of short and long-lived bird species. I found that telomerase is expressed in bone marrow throughout life in the long-lived species, whereas in the short-lived species telomerase expression is reduced after fledging. This difference in telomerase activity in the bone marrow may explain the different shortening rates found among bird species. Long-lived species appear to invest more in telomere maintenance than short-lived ones. Telomerase activity in the bone marrow may explain why telomeres apparently lengthen with age in the long-lived storm-petrels (shown in the picture to the left).
 

Telomeres are linked to survival

There is mounting evidence that absolute telomere length is associated with longevity within a species. Previous work, in humans and C. elegans have shown that late in life, individuals possessing long telomeres have higher survival rates than those with relatively short telomeres. The gel to the left shows telomere length arrays in different individuals. I have shown that short telomere lengths in 1-yr-old female tree swallows are associated with low return rates and survival. This study is the first to show a relationship between telomere length and survival in a natural population, and suggests that individuals with short telomeres may not only have increased mortality near the end of life but also early on.
 

Telomere dynamics and individual quality

Currently, Robert Mauck and I are exploring mechanisms which affect telomere length in individuals. We are using both natural and experimental variation in chick nutritional conditions to examine the dynamics of telomere shortening and maintenance during the two-month chick development period when rates of telomere change are the highest. We are also exploring the apparent telomere elongation in this species.