Evolutionary ecology of telomere dynamics in two island bird populations
With: Arie J van Noordwijk & Simon Verhulst
Senescence, the decline in reproduction and/or survival with increasing age, is a general phenomenon that is still poorly understood. Because both survival and reproduction depend strongly on interactions between organisms and environments, the occurence and degree of sencescence is best studied in natural populations. Moreover, there is often important population heterogeneity, with longer living individuals having a higher reproduction, thus masking effects of senescence in population averages of age classes. It is therefore important to follow individuals throughout their lives, i.e. study senescence longitudinally.
On the island of Vlieland, great and blue tits have been studied since 1955 and since then nearly all nestlings have been ringed and their parents have been identified. For both species there are two sub-populations with limited exchange and consistent differences in recruitment and adult survival.
Telomeres are regions of non-coding DNA at the end of eukaryotic chromosomes, consisting of repeated highly conserved DNA sequence (5'-TTAGGG-3')n. They play an important role in the protection of chromosome integrity, and there are indications that telomere length predicts remaining life span. Telomere shortening rate is accelerated by oxidative stress. Since oxidative stress is often considered a major agent of senescence, this provides a potential mechanistic link explaining associations between telomeres and life span, in that shorter telomeres may indicate that the organism experienced higher levels of oxidative stress. Thus, telomere length, and perhaps telomere shortening rate in particular, can potentially be used as a proxy for the 'life stress' experienced by individual organisms. Variation in habitat quality, as indicated by spatial variation between sub-populations on Vlieland, is an important potential source of 'life stress', and we hypothesise that this may be reflected in telomere shortening rate.
To discover the role of telomere dynamics in wild populations, we will follow a substantial number of individuals throughout their lives, measure survival and reprodution and investigate heritable and environmental components in variation in telomere length and shortening rare. The two differing sub-populations allow us to work both at the level of between sub-population comparisons and at the level of individual variation. Furthermore, we will study the effects of prolonged higher workloads of the birds to establish whether there is a causal relationship between 'life stress' and the rate of senescence and telomere shortening. This will be done through equipping great tits with a backpack of about 0.9 gram (5% of body weight) for one year. This experiment has a dual purpose: on the one hand this will induce a higher workload, thereby simulating a poorer environment, and on the other hand many studies are now carried out with radio-transmitters of up to 5% of body weight and this study will contribute to an assessment of the effects of such techniques on animal welfare.