Calibrating the avian molecular clock

TLDR

Molecular clocks are widely used to date phylogenetic events, yet evidence supporting the constancy of their rates over time and across lineages is weak. Here, we present 90 candidate avian clock calibrations derived from fossils and biogeographical events. Cross‑validation techniques were employed to identify and discard 16 inconsistent calibration points. The 74 retained calibrations of cytochrome b reveal an approximately clock‑like rate of ~2.1 % per million years over 12 Myr across most of 12 orders, with minor but significant lineage‑specific variance not explained by generation time, body size, or latitude.

Abstract

Molecular clocks are widely used to date phylogenetic events, yet evidence supporting the rate constancy of molecular clocks through time and across taxonomic lineages is weak. Here, we present 90 candidate avian clock calibrations obtained from fossils and biogeographical events. Cross-validation techniques were used to identify and discard 16 inconsistent calibration points. Molecular evolution occurred in an approximately clock-like manner through time for the remaining 74 calibrations of the mitochondrial gene, cytochrome b. A molecular rate of approximately 2.1% (+/- 0.1%, 95% confidence interval) was maintained over a 12-million-year interval and across most of 12 taxonomic orders. Minor but significant variance in rates occurred across lineages but was not explained by differences in generation time, body size or latitudinal distribution as previously suggested.