Variation in the rates of molecular evolution among lineages (heterotachy) has been widely documented throughout the tree of life. However, the processes influencing the speed at which DNA evolves in different lineages are not well understood.

In our most recent publication (Barrera-Redondo et al., 2018) we explored the correlation between rates of molecular evolution and several morphological and environmental factors across the core tree ferns  (Cyatheales). We revealed direct and indirect effects of variation in body size, productivity and temperature on changes in substitution rate, where smaller tree ferns, living in warmer and less productive environments tend to have faster rates of molecular evolution. These results support the idea that differences in effective population size, associated with body size and productivity, have significant effects on rate variation in tree ferns. We propose that macroevolutionary hypotheses should go beyond explaining variation in the rate of molecular evolution in terms of mutation rate and instead, should integrate population-level factors to better understand the processes affecting the tempo of evolution at the molecular level.

Correlations between substitution rates in the chloroplast versus one morphological and three ecological variables in core tree ferns. Time-calibrated phylogeny for core tree ferns (Cyatheales) colored according to substitution rates.