Why are telomeres the length that they are? Insight from a phylogenetic comparative analysis

Telomeres are short repeating nucleotide sequences at the ends of chromosomes that shorten with every cellular replication. Despite the importance of keeping telomere length within a critical homeostatic range, adult telomere length can differ by two orders of magnitude across vertebrate species. Why telomere length varies so widely remains unknown, though popular hypotheses suggest that body size, lifespan, and endothermy are key variables that have coevolved with telomere length. To test the relationship among telomere length, telomerase activity (which extends telomeres), and these variables, we modeled the evolution of telomere length across 123 vertebrate species. We failed to find an influence of body mass, though lifespan was negatively correlated with telomere length. Furthermore, we found an effect of thermal biology, with endotherms having on average shorter telomeres than ectotherms. The presence of telomerase activity was positively correlated with telomere length across the 58 species where data for both existed. Taken together, our findings suggest that thermal biology and lifespan may have influenced the evolution of telomere length across vertebrates and indicate that telomerase activity and telomere length may have coevolved.