A support vector machine based test for incongruence between sets of trees in tree space.
BACKGROUND
The increased use of multi-locus data sets for phylogenetic reconstruction has increased the need to determine whether a set of gene trees significantly deviate from the phylogenetic patterns of other genes. Such unusual gene trees may have been influenced by other evolutionary processes such as selection, gene duplication, or horizontal gene transfer.


RESULTS
Motivated by this problem we propose a nonparametric goodness-of-fit test for two empirical distributions of gene trees, and we developed the software GeneOut to estimate a p-value for the test. Our approach maps trees into a multi-dimensional vector space and then applies support vector machines (SVMs) to measure the separation between two sets of pre-defined trees. We use a permutation test to assess the significance of the SVM separation. To demonstrate the performance of GeneOut, we applied it to the comparison of gene trees simulated within different species trees across a range of species tree depths. Applied directly to sets of simulated gene trees with large sample sizes, GeneOut was able to detect very small differences between two set of gene trees generated under different species trees. Our statistical test can also include tree reconstruction into its test framework through a variety of phylogenetic optimality criteria. When applied to DNA sequence data simulated from different sets of gene trees, results in the form of receiver operating characteristic (ROC) curves indicated that GeneOut performed well in the detection of differences between sets of trees with different distributions in a multi-dimensional space. Furthermore, it controlled false positive and false negative rates very well, indicating a high degree of accuracy.


CONCLUSIONS
The non-parametric nature of our statistical test provides fast and efficient analyses, and makes it an applicable test for any scenario where evolutionary or other factors can lead to trees with different multi-dimensional distributions. The software GeneOut is freely available under the GNU public license.
Department of Statistics, University of Kentucky, 725 Rose Street, Lexington, KY 40536-0082, USA.
David C
DC
Haws
Peter
P
Huggins
Eric M
EM
O'Neill
David W
DW
Weisrock
Ruriko
R
Yoshida
D001483:Base Sequence; D020440:Gene Duplication; D022761:Gene Transfer, Horizontal; D005796:Genes; D010802:Phylogeny; D017422:Sequence Analysis, DNA / Q000379:methods*; D012984:Software; D060388:Support Vector Machine