A variable-rate quantitative trait evolution model using penalized-likelihood
2
)
also
evolves by Brownian motion on a logarithmic scale. Unfortunately, it’s not possible to simultaneously estimate the rates of evolution along each edge of the tree
and
the rate of evolution of σ
2
itself using Maximum Likelihood. As such, I propose a penalized-likelihood method in which the penalty term is equal to the log-transformed probability density of the rates under a Brownian model, multiplied by a ‘smoothing’ coefficient, λ, selected by the user. λ determines the magnitude of penalty that’s applied to rate variation between edges. Lower values of λ penalize rate variation relatively little; whereas larger λ values result in minimal rate variation among edges of the tree in the fitted model, eventually converging on a single value of σ
2
for all of the branches of the tree. In addition to presenting this model here, I have also implemented it as part of my
phytools
R package in the function
multirateBM
. Using different values of the penalty coefficient, λ, I fit the model to simulated data with: Brownian rate variation among edges (the model assumption); uncorrelated rate variation; rate changes that occur in discrete places on the tree; and no rate variation at all among the branches of the phylogeny. I then compare the estimated values of σ
2
to their known true values. In addition, I use the method to analyze a simple empirical dataset of body mass evolution in mammals. Finally, I discuss the relationship between the method of this article and other models from the phylogenetic comparative methods and finance literature, as well as some applications and limitations of the approach.
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Bradley Efron, Gail Gong
Joseph Felsenstein
Thomas F. Hansen
Brian C. O'Meara
Emmanuel Paradis, Klaus Schliep
Matthew W. Pennell, Jonathan M. Eastman, Graham J. Slater et al.
Liam J. Revell
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Yu K Mo, Matthew W Hahn · 2026
Bruce S Martin, Gideon S Bradburd · 2022
Liam J. Revell, Ken S. Toyama · 2022
- Published
- Aug 17, 2021
- Vol/Issue
- 9
- Pages
- e11997
- License
- View
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