Construct A Block of Tip Age Calibrations for Use with Tip-Dating Analyses in MrBayes
Takes a set of tip ages (in several possible forms, see below), and outputs a set of tip age calibrations for use with tip-dating analyses (sensu Zhang et al., 2016) in the popular phylogenetics program MrBayes. These calibrations are printed as a set of character strings, as well as a line placing an offset exponential prior on the tree age, either printed in the R console or in a named text file, which can be used as commands in the MrBayes block of a NEXUS file for use with (you guessed it!) MrBayes.
createMrBayesTipCalibrations( tipTimes, ageCalibrationType, whichAppearance = "first", treeAgeOffset, minTreeAge = NULL, collapseUniform = TRUE, anchorTaxon = TRUE, file = NULL )
tipTimes: This input may be either: (a) a timeList object, consisting of a list of length = 2, composed of a table of interval upper and lower time boundaries (i.e., the earlier and latter bounds of the intervals) and a table of first and last intervals for taxa, or (b) a matrix with row names corresponding to taxon names, matching those names listed in the MrBayes block, with either one, two or four columns containing ages (respectively) for point occurrences with precise dates (for a single column), uncertainty bounds on a point occurrence (for two columns), or uncertainty bounds on the first and last occurrence (for four columns). Note that precise first and last occurrence dates should not be entered as a two column matrix, as this will instead be interpreted as uncertainty bounds on a single occurrence. Instead, either select which you want to use for tip-dates and give a one-column matrix, or repeat (and collate) the columns, so that the first and last appearances has uncertainty bounds of zero.
ageCalibrationType: This argument decides how age calibrations are defined, and currently allows for four options: "fixedDateEarlier" which fixes tip ages at the earlier (lower) bound for the selected age of appearance (see argument whichAppearance for how that selection is made), "fixedDateLatter"
which fixes the date to the latter (upper) bound of the selected age of appearance, "fixedDateRandom" which fixes tips to a date that is randomly drawn from a uniform distribution bounded by the upper and lower bounds on the selected age of appearance, or (the recommended option) "uniformRange" which places a uniform prior on the age of the tip, bounded by the latest and earliest (upper and lower) bounds on the the selected age.
whichAppearance: Which appearance date of the taxa should be used: their 'first' or their 'last' appearance date? The default option is to use the 'first' appearance date. Note that use of the last appearance date means that tips will be constrained to occur before their last occurrence, and thus could occur long after their first occurrence (!).
treeAgeOffset: A parameter given by the user controlling the offset between the minimum and expected tree age prior. mean tree age for the offset exponential prior on tree age will be set to the minimum tree age, plus this offset value. Thus, an offset of 10 million years would equate to a prior assuming that the expected tree age is around 10 million years before the minimum age.
minTreeAge: if NULL (the default), then minTreeAge will be set as the oldest date among the tip age used (those used being determine by user choices (or oldest bound on a tip age). Otherwise, the user can supply their own minimum tree, which must be greater than whatever the oldest tip age used is.
collapseUniform: MrBayes won't accept uniform age priors where the maximum and minimum age are identical (i.e. its actually a fixed age). Thus, if this argument is TRUE (the default), this function will treat any taxon ages where the maximum and minimum are identical as a fixed age, and will override setting ageCalibrationType = "uniformRange" for those dates. All taxa with their ages set to fixed by the behavior of anchorTaxon or collapseUniform
are returned as a list within a commented line of the returned MrBayes block.
anchorTaxon: This argument may be a logical (default is TRUE, or a character string of length = 1. This argument has no effect if ageCalibrationType is not set to "uniformRange", but the argument may still be evaluated. If ageCalibrationType = "uniformRange", MrBayes will do a tip-dating analysis with uniform age uncertainties on all taxa (if such uncertainties exist; see collapseUniform). However, MrBayes does not record how each tree sits on an absolute time-scale, so if the placement of every tip is uncertain, lining up multiple dated trees sampled from the posterior (where each tip's true age might differ) could be a nightmare to back-calculate, if not impossible. Thus, if ageCalibrationType = "uniformRange", and there are no tip taxa given fixed dates due to collapseUniform (i.e. all of the tip ages have a range of uncertainty on them), then a particular taxon will be selected and given a fixed date equal to its earliest appearance time for its respective whichAppearance. This taxon can either be indicated by the user or instead the first taxon listed in tipTimes will be arbitrary selected. All taxa with their ages set to fixed by the behavior of anchorTaxon or collapseUniform
are returned as a list within a commented line of the returned MrBayes block.
file: Filename (possibly with path) as a character string to a file which will be overwritten with the output tip age calibrations. If NULL, tip calibration commands are output to the console.
If argument file is NULL, then the tip age commands are output as a series of character strings.
All taxa with their ages set to fixed by the behavior of anchorTaxon or collapseUniform
are returned as a list within a commented line of the returned MrBayes block.
Beware: some combinations of arguments might not make sense for your data.
(But that's always true, is it not?)
# load retiolitid dataset data(retiolitinae) # uniform prior, with a 10 million year offset for # the expected tree age from the earliest first appearance createMrBayesTipCalibrations( tipTimes = retioRanges, whichAppearance = "first", ageCalibrationType = "uniformRange", treeAgeOffset = 10) # fixed prior, at the earliest bound for the first appearance createMrBayesTipCalibrations( tipTimes = retioRanges, whichAppearance = "first", ageCalibrationType = "fixedDateEarlier", treeAgeOffset = 10 ) # fixed prior, sampled from between the bounds on the last appearance # you should probably never do this, fyi createMrBayesTipCalibrations( tipTimes = retioRanges, whichAppearance = "first", ageCalibrationType = "fixedDateRandom", treeAgeOffset = 10 ) ## Not run: createMrBayesTipCalibrations( tipTimes = retioRanges, whichAppearance = "first", ageCalibrationType = "uniformRange", treeAgeOffset = 10, file = "tipCalibrations.txt" ) ## End(Not run)
Zhang, C., T. Stadler, S. Klopfstein, T. A. Heath, and F. Ronquist. 2016. Total-Evidence Dating under the Fossilized Birth-Death Process. Systematic Biology 65(2):228-249.
createMrBayesConstraints, createMrBayesTipDatingNexus
David W. Bapst. This code was produced as part of a project funded by National Science Foundation grant EAR-1147537 to S. J. Carlson.