Heterotachy

Definition

Shifts in site-specific evolutionary rates over time. In the field of molecular evolution, the principle of heterotachy states that the substitution rate of sites in a gene can change through time [P. Lopez, D. Casane and H. Philippe. Heterotachy, an Important Process of Protein Evolution. Molecular Biology and Evolution 19:1-7 (2002)] . It has been proposed that the positions that show switches in substitution rate over time --i.e., "heterotachous sites"-- are good indicators of functional divergence. However, it appears that heterotachy is a much more general process, since most variable sites of homologous proteins with no evidence of functional shift are "heterotachous".

Variants

The covarion hypothesis is a specific form of heterotachy. Some studies have proposed functional divergence models that are also heterotachous. Additionally, some mixture models that do not explicitly account for rate-shift but site-partitions evolving at different relative substitution rates across lineages are mathematically heterotachous.

References