Time-Linearized Maximum Likelihood analysis of Harp Seals
Given a Maximum
Likelihood tree of clade relationships with variable
branch lengths, we can construct a time-linearized model
in which all branch "tips" [left] come out
contemporaneous. The model assumes a statistically constant "molecular
clock" of molecular evolution. The bars around each
internal branch indicate its 95% confidence interval.
Time linearization permits the genetic evidence to be fitted to geological evidence of temperature variation over the last 200,000 years. Observed that the Sangamon inter-glacial warming [red peak] ca 120 ~ 130 KYBP coincides with the separation of the newer western (ABC) lineages from the older eastern lineages (DEF). Inter-glacials correspond to rises in sea level, so that coastal populations such as harp seals would be separated from each other. None of the observed harp seal genetic divergences occured in the most recent inter-glacial. Population structure in Harp Seals is old.
Time linearization permits the genetic evidence to be fitted to geological evidence of temperature variation over the last 200,000 years. Observed that the Sangamon inter-glacial warming [red peak] ca 120 ~ 130 KYBP coincides with the separation of the newer western (ABC) lineages from the older eastern lineages (DEF). Inter-glacials correspond to rises in sea level, so that coastal populations such as harp seals would be separated from each other. None of the observed harp seal genetic divergences occured in the most recent inter-glacial. Population structure in Harp Seals is old.