# Is Telomere Length Optimized in Hatchling Sand Lizards?

## TL;DR

This study explores how telomere length in baby sand lizards affects their survival and reproduction, finding that average-length telomeres are most beneficial.

## Contribution

The study provides the first evidence of natural selection on telomere length in free-ranging ectothermic vertebrates.

## Key findings

- Hatchlings with average-length telomeres had the highest lifespan and reproductive success.
- Shorter telomeres in hatchlings elongated during juvenile life but at the cost of lower body condition.
- Telomere length in hatchlings is under natural selection in sand lizards.

## Abstract

Telomeres (repeat‐DNA‐protein structures primarily located at the ends of chromosomes) protect coding DNA against attacks by reactive molecules and the cells’ own DNA repair systems. If that capacity is costly, but enhances an individual's viability, we might expect to see natural selection acting on telomere length: that is, individuals with optimal telomere lengths should have higher lifetime reproductive success than conspecifics with shorter or longer telomeres. Some recent studies on humans broadly support that prediction, but no data are available for free‐ranging ectothermic vertebrates that, unlike mammals, can facultatively adjust telomere length during an individual's lifetime. In our decade‐long study of a natural population of sand lizards (Lacerta agilis), including measurement of 2736 telomeres across > 1700 hatchling lizards and their > 500 parents, but with a very high hatchling mortality reducing later‐life sample sizes, we found that lifespan, lifetime reproductive success and offspring recruitment rate were highest for hatchlings with “average‐length” telomeres. Hatchlings with shorter‐than‐average telomeres elongated their telomeres during juvenile life, attaining the population‐average telomere length by the time of sexual maturity; but that compensatory telomere growth was associated with lower body condition.

Our manuscript is based on a long and detailed ecological study of free‐ranging sand lizards, incorporating data on hatchlings’ future lifespan, lifetime reproductive success and recruitment of breeders from their produced young. We use these unique data to explore a topic that has been ignored in previous work—that is, how does natural selection in an ectothermic (“cold‐blooded”) species act on a high‐profile trait (telomere length) that has attracted massive research effort in endothermic (“warm‐blooded”) vertebrates? Our analyses support the hypothesis that telomere length in hatchlings is under selection in these free‐ranging sand lizards, with benefits high enough to warrant costly adjustment processes during juvenile life.

The graphical abstract image depicts the complex interplay of factors driving telomere dynamics (with permission from Dr. Chris Friesen).