Telomeres show variation in length, both between and within species, and have been proposed as a biomarker of biological ageing, providing information on the current physiological state of individuals, and reflecting (accumulated) somatic damage over time. The underlying causes of variation in telomere length remain unclear. In this thesis, I studied telomere dynamics in a wild passerine population. First, I assessed the methodological consequences of storage of blood in ethanol for the subsequent measurement of telomere length using qPCR. I found that telomere length estimates shorten in a quadratic relationship when blood samples are stored for relatively long periods. I then show that telomeres shorten with age within individuals, and that individuals with shorter telomeres disappear more quickly from the population. Moreover, individuals showed low repeatability of telomere length over time, with some individuals showing significant elongation of telomeres.
Using pedigree information, I then estimated the heritability of telomere length, and concluded that this is low in house sparrows, and the variation in telomere length of offspring was explained more by the year of birth. In addition, the age of the biological father had a negative effect on offspring telomere length. I also found that the age of the rearing male had a positive effect on offspring telomere length, but only at the population level. This, again, indicates the selective disappearance of individual adults and/or offspring with shorter telomeres.
In conclusion, my results show that telomeres may not reflect accumulated damage but may instead be more plastic than previously thought. Telomeres may instead reflect more immediate circumstances of the individual. Regardless, individuals overall still showed significant telomere attrition with age, and individuals with relatively short telomeres disappeared from the population, supporting the use of telomeres as a biomarker of ageing in wild passerines.
