Abstract
Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies. Telomeres usually shorten with age and shortening is frequently associated with environmental stressors and increased subsequent mortality. Telomere lengthening - an apparent increase in telomere length between repeated samples from the same individual - also occurs. However, the exact circumstances, and consequences, of telomere lengthening are poorly understood. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we tested whether telomere lengthening - which occurs in adults of this species - is associated with specific stressors (reproductive effort, food availability, malarial infection and cooperative breeding) and predicts subsequent survival. In females, telomere shortening was observed under greater stress (i.e., low food availability, malaria infection), while telomere lengthening was observed in females experiencing lower stress (i.e., high food availability, assisted by helpers, without malaria). The telomere dynamics of males were not associated with the key stressors tested. These results indicate that, at least for females, telomere lengthening occurs in circumstances more conducive to self-maintenance. Importantly, both females and males with lengthened telomeres had improved subsequent survival relative to individuals that displayed unchanged, or shortened, telomeres - indicating that telomere lengthening is associated with individual fitness. These results demonstrate that telomere dynamics are bidirectionally responsive to the level of stress that an individual faces, but may poorly reflect the accumulation of stress over an individuals lifetime.
Highlights
Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies
We deliberately focused on a restricted set of fixed effects – chosen a priori based on logic and evidence of influencing telomere dynamics – to avoid data dredging, which could generate false-positive associations
Greater telomere shortening was observed in females with higher reproductive effort when living in areas of poorer food availability, as well as in individuals infected with malaria
Summary
Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies. The telomere dynamics of males were not associated with the key stressors tested These results indicate that, at least for females, telomere lengthening occurs in circumstances more conducive to selfmaintenance. Due to the ‘end replication problem’ (Watson, 1972), telomeres shorten with each cell division, until a critical length is reached where cells can no longer divide (Olovnikov, 1996; Campisi, 2003) Telomeres shorten when exposed to sources of cellular damage, such as reactive oxygen species (Von Zglinicki, 2002; Reichert and Stier, 2017) Both the number of cell-divisions and cell damage load are cumulative (i.e. age-dependent) and variable in rate. Telomere length shortens with increasing age in a broad range of taxa (Barrett et al, 2013; Bendix et al, 2014; Stier et al, 2015) but see Fairlie et al (2016)
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