RRphylo (version 2.5.9)

search.shift: Locating shifts in phenotypic evolutionary rates

Description

The function search.shift (Castiglione et al. 2018) tests whether individual clades or isolated tips dispersed through the phylogeny evolve at different RRphylo rates as compared to the rest of the tree. Instances of rate shifts may be automatically found.

Usage

search.shift(RR, status.type = c("clade", "sparse"),node = NULL, state
  = NULL, cov = NULL, nrep = 1000, f = NULL,foldername=NULL,filename)

Arguments

RR

an object fitted by the function RRphylo.

status.type

whether the "clade" or "sparse" condition must be tested.

node

under the "clade" condition, the node (clade) to be tested for the rate shift. When multiple nodes are tested, they need to be written as in the example below. If node is left unspecified, the function performs under the 'auto-recognize' feature, meaning it will automatically test individual clades for deviation of their rates from the background rate of the rest of the tree (see details).

state

the state of the tips specified under the "sparse" condition.

cov

the covariate to be indicated if its effect on rate values must be accounted for. Contrary to RRphylo, cov needs to be as long as the number of tips of the tree.

nrep

the number of simulations to be performed for the rate shift test, by default nrep is set at 1000.

f

the size of the smallest clade to be tested. By default, nodes subtending to one tenth of the tree tips are tested.

foldername

has been deprecated; please see the argument filename instead.

filename

a character indicating the name of the pdf file and the path where it is to be saved. If no path is indicated the file is stored in the working directory

Value

Under all circumstances, search.shift provides a vector of $rates. If 'cov' values are provided, rates are regressed against the covariate and the residuals of such regression form the vector $rates. Otherwise, $rates are the same rates as with the RR argument.

Under "clade" case without specifying nodes (i.e. 'auto-recognize') a list including:

$all.clades for each detected node, the data-frame includes the average rate difference (computed as the mean rate over all branches subtended by the node minus the average rate for the rest of the tree) and the probability that it do represent a real shift. Probabilities are contrasted to simulations shuffling the rates across the tree branches for a number of replicates specified by the argument nrep. Note that the p-values refer to the number of times the real average rates are larger (or smaller) than the rates averaged over the rest of the tree, divided by the number of simulations. Hence, large rates are significantly larger than the rest of the tree (at alpha = 0.05), when the probability is > 0.975; and small rates are significantly small for p < 0.025.

$single.clades the same as with 'all.clades' but restricted to the largest/smallest rate values along a single clade (i.e. nested clades with smaller rate shifts are excluded). Large rates are significantly larger than the rest of the tree (at alpha = 0.05), when the probability is > 0.975; and small rates are significantly small for p < 0.025.

Under "clade" condition by specifying the node argument:

$all.clades.together if more than one node is tested, this specifies the average rate difference and the significance of the rate shift, by considering all the specified nodes as evolving under a single rate. As with the 'auto-recognize' feature, large rates are significantly larger than the rest of the tree (at alpha = 0.05), when the probability is > 0.975; and small rates are significantly small for p < 0.025.

$single.clades this gives the significance for individual clades, tested separately. As previously, large rates are significantly larger than the rest of the tree (at alpha = 0.05), when the probability is > 0.975; and small rates are significantly small for p < 0.025.

Under the "sparse" condition:

$state.results for each state, the data-frame includes the average rate difference (computed as the mean rate over all leaves evolving under a given state, minus the average rate for each other state or the rest of the tree) and the probability that the shift is real. Large rates are significantly larger (at alpha = 0.05), when the probability is > 0.975; and small rates are significantly small for p < 0.025. States are compared pairwise.

Details

The function search.shift takes the object produced by RRphylo. Two different conditions of rate change can be investigated. Under the "clade" condition the vector of node or nodes subjected to the shift must be provided. Alternatively, under the "sparse" case the (named) vector of states (indicating which tips are or are not evolving under the rate shift according to the tested hypothesis) must be indicated. In the "clade" case, the function may perform an 'auto-recognize' feature. Under such specification, the function automatically tests individual clades (from clades as large as one half of the tree down to a specified clade size) for deviation of their rates from the background rate of the rest of the tree, which is identical to the "clade" case. An inclusive clade with significantly high rates is likely to include descending clades with similarly significantly high rates. Hence, with 'auto-recognize' the search.shift function is written as to scan clades individually and to select only the node subtending to the highest difference in mean absolute rates as compared to the rest of the tree. A plot of the tree highlighting nodes subtending to significantly different rates is automatically produced. Caution must be put into interpreting the 'auto-recognize' results. For instance, a clade with small rates and another with large rates could be individuated even under BM. This does not mean these clades are actual instances for rate shifts. Clades must be tested on their own without the 'auto-recognize' feature, which serves as guidance to the investigator, when no strong a priori hypothesis to be tested is advanced. The 'auto-recognize' feature is not meant to provide a test for a specific hypothesis. It serves as an optional guidance to understand whether and which clades show significantly large or small rates as compared to the rest of the tree. Individual clades are tested at once, meaning that significant instances of rate variation elsewhere on the tree are ignored. Conversely, running the "clade" condition without including the 'auto-recognize' feature, multiple clades presumed to evolve under the same shift are tested together, meaning that their rates are collectively contrasted to the rest of the tree, albeit they can additionally be compared to each other upon request. Under both the "clade" and "sparse" conditions, multiple clades could be specified at once, and optionally tested individually (for deviation of rates) against the rates of the rest of the tree and against each other. The histogram of random differences of mean rates distribution along with the position of the real difference of means is automatically generated by search.shift. Regardless of which condition is specified, the function output produces the real difference of means, and their significance value.

References

Castiglione, S., Tesone, G., Piccolo, M., Melchionna, M., Mondanaro, A., Serio, C., Di Febbraro, M., & Raia, P.(2018). A new method for testing evolutionary rate variation and shifts in phenotypic evolution. Methods in Ecology and Evolution, 9: 974-983.doi:10.1111/2041-210X.12954

See Also

search.shift vignette

Examples

# NOT RUN {
data("DataOrnithodirans")
DataOrnithodirans$treedino->treedino
DataOrnithodirans$massdino->massdino
DataOrnithodirans$statedino->statedino


RRphylo(tree=treedino,y=massdino)->dinoRates

# Case 1. Without accounting for the effect of a covariate

# Case 1.1 "clade" condition
# with auto-recognize
search.shift(RR=dinoRates,status.type="clade",
             filename=paste(tempdir(), "SSauto", sep="/"))
# testing two hypothetical clades
search.shift(RR=dinoRates,status.type="clade",node=c(696,746),
             filename=paste(tempdir(), "SSclade", sep="/"))

# Case 1.2 "sparse" condition
# testing the sparse condition.
search.shift(RR=dinoRates,status.type= "sparse",state=statedino,
             filename=paste(tempdir(), "SSsparse", sep="/"))


# Case 2. Accounting for the effect of a covariate

# Case 2.1 "clade" condition
search.shift(RR=dinoRates,status.type= "clade",cov=massdino,
             filename=paste(tempdir(), "SSclade_cov", sep="/"))

# Case 2.2 "sparse" condition
search.shift(RR=dinoRates,status.type="sparse",state=statedino,cov=massdino,
             filename=paste(tempdir(), "SSstate_cov", sep="/"))
    
# }