# No Evidence for Pace of Life Evolution Along Elevational Gradients in Squamate Reptiles

## TL;DR

The study finds no clear evidence that life-history traits in squamate reptiles evolve consistently along elevation gradients as predicted by the pace of life syndrome hypothesis.

## Contribution

The research challenges the universality of the pace of life syndrome hypothesis by showing inconsistent trait patterns in squamates across elevation.

## Key findings

- Most traits in squamate reptiles showed no significant elevational patterns.
- Snakes exhibited significant elevational differences in body size and fecundity, while lizards did not.
- Elevation-latitude interactions suggest life-history evolution is taxonomically constrained.

## Abstract

Ecological conditions can significantly influence the trade‐off between survival, growth and reproduction, driving life‐history divergence among populations in different environments. The pace of life syndrome hypothesis (POLS) proposes that additional suites of traits, from physiology to behaviour, adaptively co‐evolve with life‐history traits along a slow‐fast continuum. Using data from 192 studies representing 104 squamate species, we performed phylogenetic meta‐analyses testing whether traits vary predictably across elevation within species in accordance with POLS. Results show there is no clear evidence for an overall intraspecific elevational pace‐of‐life syndrome in squamate reptiles. While high elevation populations had significantly lower body temperatures and larger egg sizes, most traits—including body size, longevity, fecundity and thermal tolerance—exhibited non‐significant elevational patterns. Critically, lizards and snakes responded fundamentally differently: snakes showed significant differences in adult female and neonate body size and fecundity across elevation, while lizards showed no significant divergence. Elevation‐latitude interactions provide further evidence against a single pace‐of‐life solution to elevation. Our findings challenge the applicability of POLS theory within species, revealing that life‐history evolution is more context‐dependent and taxonomically constrained than syndrome‐based approaches suggest. These results contribute to growing evidence that universal trait syndromes rarely emerge across environmental gradients in diverse taxonomic groups.

Ecological conditions can significantly influence the trade‐off between survival, growth, and reproduction, leading to evolutionary divergence in life‐history traits among populations experiencing different environments. The pace of life syndrome hypothesis (POLS) proposes that additional suites of traits, from physiology to behaviour, adaptively co‐evolve with life‐history traits along this continuum. Using data from 192 studies representing 104 species, we find no clear evidence for an overall intraspecific elevational POLS in squamates, with most traits showing no significant patterns and a fundamental divergence between lizards (no response) and snakes (significant differences in adult female and neonate body size and fecundity). These findings challenge the broad applicability of POLS theory, suggesting that life‐history evolution is more context‐dependent and taxonomically constrained than universal syndrome‐based approaches predict.