LAUSR

For almost a century, telomeres have been increasingly studied in biological and biomedical sciences with the ultimate hope that changes in telomere DNA length (abbreviated as TL) might offer a promising avenue for limiting biological aging and protecting against diverse age-specific mortality risk, especially cancer (1). From a molecular point of view, telomeres are complex nucleoprotein structures that avoid chromosome extremities to be recognized as accidental double-stranded DNA breaks, thereby avoiding unwanted DNA recombination and DNA damage checkpoint activation (1). In a large range of organisms, including all vertebrates, telomeres are formed by an array of TTAGGG DNA repeats specifically associated with a noncoding RNA named TERRA and a protein protective complex named shelterin. The duplication of telomeric DNA is not completed by the conventional replication machinery and therefore relies on a specialized reverse transcriptase named telomerase. In the somatic cells of several vertebrates, the expression of telomerase is repressed, thus preventing the full replenishment of telomeric DNA during the cell cycle. Therefore, over cellular divisions, telomere DNA length decreases, until critically short TL triggers proaging effects (e.g., cellular senescence) (2) and ultimately impairs survival prospects (1). In addition to this developmentally controlled telomerase down-regulation, TL shortening can result from exposure to a wide range of environmental stressors (e.g., social adversity, environmental harshness) through still elusive processes involving stress hormones and oxidative stress (1). In the last two decades, numerous studies have quantified TL dynamics (i.e., changes in TL during lifetime) in the wild. They revealed that the decline in TL in somatic cells constitutes the rule rather than the exception (3) and that short TLs are, in several species, associated with a higher mortality risk (4). Despite this pattern of TL decline throughout life largely documented in the living world, empirical studies have pointed out a striking variability in telomere dynamics, both within and across species. Identifying the ecoevolutionary causes and consequences of individual variation in TL has recently become a popular topic (5). In that context, the study by Dupou e et al. (6) among populations of lizards subjected to a continuum of environmental harshness pushes the field forward by shedding an exciting light on the ecological relevance of TL.