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- Higher mercury contamination is associated with shorter telomeres in a long-lived seabird – A direct effect or a consequence of among-individual variation in phenotypic quality?Publication . Bauch, Christina; Gatt, Marie C.; Verhulst, Simon; Granadeiro, José P.; Catry, PauloMercury is a heavy metal, which is pervasive and persistent in the marine environment. It bioaccumulates within organisms and biomagnifies in the marine food chain. Due to its high toxicity, mercury contamination is a major concern for wildlife and human health. Telomere length is a biomarker of aging and health, because it predicts survival, making it a potential tool to investigate sublethal effects of mercury contamination. However, the relationship between telomeres and mercury contamination is unclear. We measured feather mercury concentration in Cory's Shearwaters Calonectris borealis, long-lived seabirds and top predators, between 9 and 35 years of age and related it to telomere length in erythrocytes. Cory's Shearwaters with higher mercury concentrations had shorter telomeres and the effect was sex-dependent, reaching significance in males only. This may be explained by the fact that males have longer telomeres and higher and more variable mercury concentrations than females in this population. The mercury effect on telomere length was stronger on longer telomeres in the genome within individuals. We discuss the hypotheses that the negative correlation could either be a direct effect of mercury on telomere shortening and/or a consequence of variation in phenotypic quality among individuals that results in a covariation between mercury contamination and telomere length.
- Costs of reproduction and migration are paid in later return to the colony, not in physical condition, in a long-lived seabirdPublication . Gatt, Marie Claire; Versteegh, Maaike; Bauch, Christina; Tieleman, Irene; Granadeiro, José Pedro; Catry, PauloLife history theory suggests a trade-off between costly activities such as breeding and migration and somatic self-maintenance. However, how the short-term cost of parental effort is expressed in species with a slow pace-of-life is not well understood. Also, investigating carry-over effects of migration is most meaningful when comparing migratory strategies within the same population, but this has rarely been done. We explore this hypothesis in a long-lived, pelagic seabird, the Cory's Shearwater, Calonectris borealis, where males display partial migration. By manipulating reproductive effort and taking advantage of the natural variation in migratory strategy, we investigate whether early reproductive failure and migratory strategy had implications on the physical condition of males on return to the colony the following year. We experimentally induced breeding failure from mid-incubation, tracked the over-winter movements of these males and of males that invested in parental effort, and assessed innate immunity, stress, and residual body mass the following year. Early breeding failure resulted in earlier return to the colony among all males, associated with greater probability of reproductive success. Residents had a lower tail feather fault bar intensity, an indicator of stress during the non-breeding period, compared to migrants. Reproductive effort and migratory strategy had no impact on physiological condition otherwise. Our results provide evidence that in species with a slow-pace of life, such as the Cory's Shearwater, somatic maintenance is prioritised, with the costs of reproduction and migration paid in delayed arrival date.
- Sex‐specific telomere length and dynamics in relation to age and reproductive success in Cory's ShearwatersPublication . Bauch, Christina; Gatt, Marie Claire; Granadeiro, José Pedro; Verhulst, Simon; Catry, PauloIndividuals in free-living animal populations generally differ substantially in reproductive success, lifespan and other fitness-related traits and the molecular mechanisms underlying this variation are poorly understood. Telomere length and dynamics are candidate traits explaining this variation, as long telomeres predict a higher survival probability and telomere loss has been shown to reflect experienced "life stress". However, telomere dynamics among very long-lived species are unresolved. Additionally, it is generally not well understood how telomeres relate with reproductive success or sex. We measured telomere length and dynamics in erythrocytes to assess their relation to age, sex and reproduction in Cory's Shearwaters (Calonectris borealis), a long-lived seabird, in the context of a long-term study. Adult males had on average 231 bp longer telomeres than females independent of age. In females, telomere length changed relatively little with age, whereas male telomere length declined significantly. Telomere shortening within males from one year to the next was three times higher than the inter-annual shortening rate based on cross-sectional data of males. Past long-term reproductive success was sex-specifically reflected in age-corrected telomere length: males with on average high fledgling production were characterised by shorter telomeres, whereas successful females had longer telomeres and we discuss hypotheses that may explain this contrast. In conclusion, telomere length and dynamics in relation to age and reproduction are sex dependent in Cory's Shearwaters and these findings contribute to our understanding of what characterises individual variation in fitness.