A Bayesian implementation of the Poisson tree processes (PTP) model for species delimitation.
By Jiajie Zhang 19-02-2014. Questions and bugs report please sent to bestzhangjiajie[at]gmail[dot]com. Before reading the following text, please check: https://github.com/zhangjiajie/SpeciesCounting for latest updates
========================================================================= (0) What's new
I implemented a Markov chain Monte Carlo sampler for the PTP model - bPTP.py, it can generate posterior probability of species delimitations on phylogenetic trees. Since I give a flat prior to all possible delimitations, bPTP.py now replaces the old maximal likelihood search program PTP.py. bPTP.py searches a much large space and gives Bayesian support values to delimitations. PTP.py is now used for bootstrap analysis if you have trees from bootstrap analysis. The new programs also feature various improvements, such as NEXUS format support, rooting on outgroups, SVG tree output and code optimizations.
(1) What's in the package?
This package contains several programs written in Python that can give species delimitation hypothesis based on a gene trees inferred from molecular sequences. We introduce a new model called Poisson tree processes(PTP) model. In PTP, we model speciations or branching events in terms of number of mutations. So it only requires a phylogenetic input tree, for example the output of RAxML. To be more clear, the branch lengths should represent number of mutations. Our numerous tests show PTP outperforms GMYC. Furthermore, PTP is much easier to use, since it can use the phylogenetic tree directly without needing the difficult and error prone procedures of time calibration required by GMYC. bPTP.py A Bayesian implementation of the PTP model for species delimitation. It uses a Markov chain Monte Carlo sampler to produce posterior probability of species delimitations on phylogenetic trees. bPTP.py can work both on a single phylogenetic tree, and multiple trees from Bayesian phylogenetic analysis. Using trees from Bayesian phylogenetic analysis can account for uncertainties in phylogenetics inference, but with the cost of much longer run time. To find out how to use it, type: python bPTP.py PTP.py Maximal likelihood search of the PTP model by heuristics, it can also provide bootstrap support values of species delimitation if given multiple phylogenetic trees derived from bootstrap analysis. To find out how to use it, type: python PTP.py
(2) Which operating system is required?
I wrote and tested all the python code under Ubuntu Linux. So everything should run well under Linux if you follow the instructions below or the output of the python programs. I did not have the time and chance to test them under windows or mac yet, however, I think bPTP.py, PTP.py and GMYC.py should be able to run on windows and mac if you have properly installed the dependent python packages (see below). EPA_PTP.py was designed to run with NGS data, which means the calculations might be intense if you have say 10,000 reads. So ideally it should be run on a multi-core Linux server such that it can speedup using the PTHREADS version of RAxML. The biodiversity soup data in our paper, for example, will need 24-48 hour to finish on our 8-core i7 server. If you encounter any problems to run the program under Linux, simply drop me an e-mail.
(3) Install dependent python packages
Requires python3.6 pip3 install -r requirments.txt python3 setup.py install
(4) Prepare input data
bPTP.py: accept phylogenetic trees in Newick format and NEXUS format. The trees should NOT be annotated, if bPTP.py can not parse your tree, you can try to use FigTree to convert the tree format. If you input NEXUS format, your trees will be automatically detranslated if possible. However, if taxon are named using only numbers, this step is will cause errors and you should rename your taxa. If a single tree is used as input, this should ideally be a maximal likelihood tree inferred by, for example RAxML or PhlML. Alternatively, this single tree can also be the consensus tree from Bayesian or bootstrap phylogenetic analysis. If multiple trees are used, those trees should come from Bayesian phylogenetic analysis programs such as MrBayes. PTP.py: accept the same tree format as bPTP.py, both single and multiple trees can be used as input. Multiple trees should come from bootstrap phylogenetic analysis.
a) outputname.PTPPartitions.txt: bPTP - MCMC samples of delimitations after thinning, all posterial probabilities are computed based this file. PTP - bootstrap delimitations. b) outputname.PTPllh.txt: Posterial Log likelihood trace file. c) outputname.llh.pdf: Posterial Log likelihood trace plot, visual check for convergence. d) outputname.PTPPartitonSummary.txt: bPTP - summary of Posterial Prob. of delimited species. PTP - bootstrap values of delimited species. e) outputname.PTPhSupportPartition.txt: bPTP - highest posterial Prob. supported delimitation. PTP - highest bootstrap supported delimitation. f) outputname.PTPhSupportPartition.txt.png/svg: Tree plot from e g) outputname.PTPMLPartition.txt: Maximal likelihood species delimitation h) outputname.PTPMLPartition.txt.png/svg: Tree plot from g bPTP.py: Support values shown on the tree plot are computed as the "number of occurrence of all the descendants under this node"/ "number of samples from MCMC sampling". They are the posterial probabilities of those taxa form one species under the PTP model and a flat prior. From tests on simulated data, support values are strongly correlated with the accuracy of the delimitation, r = 0.91. If input a single tree, output will be a - h; if using multiple trees, output will be a - e PTP.py: Support values shown on the tree plot are the bootstrap support of all taxa under this node form one species under the PTP model. Output will always be: a, d, e and f
python3 bPTP.py -t example/ptp_example.tre -o example/myoutput -s 1234 -r
(7) How to cite
If you find PTP and bPTP useful to your research, please cite: J. Zhang, P. Kapli, P. Pavlidis, A. Stamatakis: "A General Species Delimitation Method with Applications to Phylogenetic Placements". In Bioinformatics (2013), 29 (22): 2869-2876.
(8) Web server
There is also a web server avaliable for bPTP: http://species.h-its.org/ptp/ The server version only accept a single input tree and has limitation on the number of MCMC iterations.