Testing RRphylo methods overfit

Silvia Castiglione, Carmela Serio, Pasquale Raia


  1. overfitRR basics
  2. Results
    1. search.shift results
    2. search.trend results
    3. search.conv results
    4. PGLS_fossil results
  3. Guided examples

overfitRR basics

Methods using a large number of parameters risk being overfit. This usually translates in poor fitting with data and trees other than the those originally used. With RRphylo methods this risk is usually very low. However, the user can assess how robust the results got by applying search.shift, search.trend, search.conv, or PGLS_fossil are by running overfitRR. The basic idea of overfitRR is using alternative tree topologies to test for both phylogenetic and sampling uncertainty at the same time. Such alternative phylogenies can be provided by the user as a multiPhylo object, otherwise are automatically generated within overfitRR. In this latter case, the original tree and data are subsampled by specifying a s parameter, that is the proportion of tips to be removed from the tree, and species positions are shuffled by using the function swapONE.

overfitRR always takes an object generated by RRphylo and all the data used to produce it (besides necessary phenotypic data, any other argument such as covariate, predictor, and so on, passed to RRphylo). If no phylo.list is available, the arguments s and swap.args can be used to set the intensity of subsampling and phylogenetic alterations to be applied. Depending on which tool is under testing, the user supplies to the function one or more among trend.args, shift.args, conv.args, and pgls.args each of them being a list of arguments specific to the namesake function (see the examples below).


The output of overfitRR is a RRphyloList object whose elements depend on the case under testing (see below).

In some cases, removing as many tips as imposed by s would delete too many tips right in clades and/or states under testing. In these cases, the function maintains no less than 5 species at least in each clade/state under testing (or all species if there is less), reducing the sampling parameter s if necessary. Thus, the first element of the output list ($mean.sampling) is the mean proportion of species actually removed over the iterations.

In any case, the function returns a multiPhylo and a RRphyloList object including the modified phylogenies ($tree.list) and the outputs of RRphylo performed on them ($RR.list), respectively. Both objects are treated as regular lists. overfitRR also derives the 95% confidence interval around the original phenotypic value estimated at the tree root ($rootCI) and the regression parameters describing the relation between the original values at internal nodes and the corresponding figure after subsampling and swapping ($ace.regressions). A regression slope close to one indicates a better matching between original and subsampled values, suggesting the estimation is robust to phylogenetic uncertainty and subsampling.

search.shift results

When the robustness of search.shift is tested, the function returns separate results for clade and sparse conditions ($shift.results). The first (clade) includes the proportion of simulations producing significant and positive (p.shift+) or significant and negative (p.shift-) rate shifts for each single node, and for all the clades taken as a whole (see Testing rate shifts pertaining to entire clades for further details). Under the sparse condition (sparse), the same figures as before are reported for each state category compared to the rest of the tree and for all possible pair of categories (see Testing rate shifts pertaining to phylogenetically unrelated species for further details).

search.trend results

When testing for search.trend robustness, overfitRR returns results for both the entire tree and specific clades if indicated ($trend.results). Results for the entire tree (tree) summarize the proportion of simulations producing positive (slope+) or negative (slope-) slopes significantly higher (p.up) or lower (p.down) than BM simulations for either phenotypes or rescaled rates versus time regressions. Such evaluations is based on p.random only (see Temporal trends on the entire tree,for further details). When specific clades are under testing, the same set of results as for the whole tree is returned for each node (node). In this case, for phenotype versus age regression through nodes, the proportion of significant and positive/negative slopes (slope+p.up,slope+p.down,slope-p.up,slope-p.down) is accompanied by the same figures for the estimated marginal mean differences (p.emm+ and p.emm-). As for the temporal trend in absolute rates through node, the proportion of significant and positive/negative estimated marginal means differences (p.emm+ and p.emm-) and the same figure for slope difference (p.slope+ and p.slope-) are reported (see Temporal trends at clade level). Finally when more than one node is tested, the $trend.results object also includes results for the pairwise comparison between nodes.

search.conv results

Results for robustness of search.conv ($conv.results) include separate objects for convergence between clades or between/within states. Under the first case (clade), the proportion of simulations producing significant instance of convergence (p.ang.bydist) or convergence and parallelism (p.ang.conv) between selected clades are returned (see Morphological convergence between clades for further details). As for convergence between/within discrete categories (state), overfitRR reports the proportion of simulations producing significant instance of convergence either accounting (p.ang.state.time) or not accounting (p.ang.state) for the time intervening between the tips in the focal state Morphological convergence within/between categories for explanations).

PGLS_fossil results

Results for robustness of PGLS_fossil ($pgls.results) include separate objects for the pgls performed on the original tree ($tree) or on the tree rescaled according to RRphylo rates (i.e. tree branches rescaled to the absolute branch-wise rate values while keeping the total evolutionary time constant; $RR).

Guided examples


# load the RRphylo example dataset including Ornithodirans tree and data
DataOrnithodirans$treedino->treedino # phylogenetic tree
DataOrnithodirans$massdino->massdino # body mass data
DataOrnithodirans$statedino->statedino # locomotory type data

### Testing search.shift
# perform RRphylo Ornithodirans tree and data

# perform search.shift under both "clade" and "sparse" condition
search.shift(RR=dinoRates, status.type= "clade")->SSnode
search.shift(RR=dinoRates, status.type= "sparse", state=statedino)->SSstate

# test the robustness of search.shift results
overfitRR(RR=dinoRates,y=massdino,swap.args =list(si=0.2,si2=0.2),
          shift.args = list(node=rownames(SSnode$single.clades),state=statedino),

### Testing search.trend
# Extract Pterosaurs tree and data
extract.clade(treedino,748)->treeptero # phylogenetic tree
massdino[match(treeptero$tip.label,names(massdino))]->massptero # body mass data

# perform RRphylo and search.trend on Pterosaurs tree and data 
# by specifying a clade to be tested

search.trend(RR=RRptero, y=log(massptero),node=143,cov=NULL,ConfInt=FALSE)->STnode

# test the robustness of search.trend results
overfitRR(RR=RRptero,y=log(massptero),trend.args = list(node=143),nsim=10)

### Applying overfitRR on multiple RRphylo
# load the RRphylo example dataset including Cetaceans tree and data
DataCetaceans$treecet->treecet # phylogenetic tree
DataCetaceans$masscet->masscet # logged body mass data
DataCetaceans$brainmasscet->brainmasscet # logged brain mass data
DataCetaceans$aceMyst->aceMyst # known phenotypic value for the most recent 
                               # common ancestor of Mysticeti

# cross-reference the phylogenetic tree and body and brain mass data. Remove from
# both the tree and vector of body sizes the species whose brain size is missing

# peform RRphylo on the variable (body mass) to be used as additional predictor

# create the predictor vector: retrieve the ancestral character estimates 
# of body size at internal nodes from the RR object ($aces) and collate them
# to the vector of species' body sizes to create

# peform RRphylo and search.trend on the brain mass 
# by using the body mass as additional predictor

search.trend(RR=RRmulti, y=brainmasscet,x1=x1.mass)->STcet

# test the robustness of search.trend results
overfitRR(RR=RRmulti,y=brainmasscet,trend.args = list(),x1=x1.mass,nsim=10)

### Testing PGLS_fossil
# peform RRphylo on cetaceans brain mass

# perform PGLS_fossil by using the original tree

# perform PGLS_fossil rescaling the tree according to RRphylo rates

# test the robustness of PGLS_fossil results

### Testing search.conv
# load the RRphylo example dataset including Felids tree and data
DataFelids$PCscoresfel->PCscoresfel # mandible shape data
DataFelids$treefel->treefel # phylogenetic tree
DataFelids$statefel->statefel # conical-toothed or saber-toothed condition

# perform RRphylo on Felids tree and data

# search for morphologicl convergence between clades (automatic mode) 
# and within the category
search.conv(RR=RRfel, y=PCscoresfel, min.dim=5, min.dist="node9"))->SC.clade

search.conv(tree=treefel, y=PCscoresfel, state=statefel)->SC.state

# test the robustness of seach.conv results
overfitRR(RR=RRfel, y=PCscoresfel,conv.args=