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 122 vertebrate species. We failed to find an influence of
body mass, lifespan, or baseline metabolism on telomere length. However,
we found a significant interactive effect between baseline metabolism and
body mass. 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 body mass may have
differentially influenced the evolution of telomere length in endotherms
and ectotherms and indicate that telomerase activity and telomere length
may have coevolved.