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To discover the role of telomere dynamics in wild populations, we will follow a substantial number of individuals throughout their lives, measure survival and reproduction and investigate heritable and environmental components in telomere length variation

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Telomeres (the ends of chromosomes) become shorter with increasing age. There is increasing evidence that telomere shortening reflects senescence and thus functions as a biomarker of biological aging. We will study telomere shortening in great and blue tits on Vlieland, where sub-populations differ consistently in survival rates, but in opposite direction in the two species. Further, family trees are well known, yielding high power to detect heritable components in variation in telomere length and dynamics. We will test experimentally whether telomere shortening and senescence are accelerated when ‘life stress’ increases by letting the birds carry a small weight.

This project: To discover the role of telomere dynamics in wild populations, we will follow a substantial number of individuals throughout their lives, measure survival and reproduction and investigate heritable and environmental components in telomere length variation and the rate of shortening of these. Vlieland great tits and to a lesser extent blue tits, because of smaller population size, offer almost unique opportunities to collect data on several hundred individuals as nestlings and as adults. Because family trees are unusually well known, the prospects to demonstrate heritable components are excellent (see below). 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. 

Objectives and scientific approach:

1. Compare rate of senescence and telomere shortening, between East and West Vlieland, and between great and blue tits, building on the finding that West Vlieland is more favourable for blue tit survival while East Vlieland is more favourable for great tit survival (Fig.1). Thus the prediction is that telomere shortening is higher in the sub-population where the rate of senescence is higher.

This question will be answered through repeated sampling of several hundred individual great tits and about 100 blue tits of each sex, thereby extending the existing database that will be available for this project. Senescence will be taken to be the rate of decline in reproductive value with age, including both mortality senescence and reproductive senescence.

2. Relate telomere shortening at the individual level to survival and reproductive senescence. Are individuals that lost more base pairs more likely to die and/or produce fewer offspring?

This question will be answered by combining the measurements made with the parameters obtained from the ongoing population study.

3. What is the heritability of telomere length and of telomere shortening rate? How do these heritabilities depend on age and sex? We will make use of the unique situation that samples can be collected from relatively large numbers of birds with different degrees of relatedness. Depending on the observed difference between sub-populations we will study the heritable component further through cross-fostering.

Heritabilities will be estimated using animal models (Postma and Charmantier, 2007, Kruuk et al., 2008). The power to estimate heritabilities is high, see separate section below. Nestlings will be sexed using molecular techniques (Lessells et al 1998), allowing separate assessment of genetic and environmental effects in the two sexes.

4. Is there a causal relationship between ‘life stress’, as affected by for example habitat quality, and the rates of telomere shortening and senescence?

This question will be answered by equipping about 100 nestlings and some 50 adults of each sex in each species with a small backpack using the extensive experience obtained in avian telemetry studies. Such a small weight will make locomotion energetically more expensive, and hence reduce foraging success measured as net intake rate. There will be two control treatments: empty backpacks (weighing 0.1 g) and no backpack at all.  

 

 

Fieldwork at Vlieland: