BMC Evolutionary Biology BioMed Central Research article Open Access Inferring phylogenies with incomplete data sets: a 5-gene, 567-taxon analysis of angiosperms J Gordon Burleigh*1,2, Khidir W Hilu3 and Douglas E Soltis2 Address: 1National Evolutionary Synthesis Center (NESCent), Durham, NC 27705, USA, 2Department of Botany and Zoology, University of Florida, Gainesville, FL 32611, USA and 3Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24061, USA Email: J Gordon Burleigh* - [email protected]; Khidir W Hilu - [email protected]; Douglas E Soltis - [email protected] * Corresponding author Published: 17 March 2009 Received: 16 April 2008 Accepted: 17 March 2009 BMC Evolutionary Biology 2009, 9:61 doi:10.1186/1471-2148-9-61 This article is available from: http://www.biomedcentral.com/1471-2148/9/61 © 2009 Burleigh et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Phylogenetic analyses of angiosperm relationships have used only a small percentage of available sequence data, but phylogenetic data matrices often can be augmented with existing data, especially if one allows missing characters. We explore the effects on phylogenetic analyses of adding 378 matK sequences and 240 26S rDNA sequences to the complete 3-gene, 567-taxon angiosperm phylogenetic matrix of Soltis et al. Results: We performed maximum likelihood bootstrap analyses of the complete, 3-gene 567- taxon data matrix and the incomplete, 5-gene 567-taxon data matrix. Although the 5-gene matrix has more missing data (27.5%) than the 3-gene data matrix (2.9%), the 5-gene analysis resulted in higher levels of bootstrap support. Within the 567-taxon tree, the increase in support is most evident for relationships among the 170 taxa for which both matK and 26S rDNA sequences were added, and there is little gain in support for relationships among the 119 taxa having neither matK nor 26S rDNA sequences. The 5-gene analysis also places the enigmatic Hydrostachys in Lamiales (BS = 97%) rather than in Cornales (BS = 100% in 3-gene analysis). The placement of Hydrostachys in Lamiales is unprecedented in molecular analyses, but it is consistent with embryological and morphological data. Conclusion: Adding available, and often incomplete, sets of sequences to existing data sets can be a fast and inexpensive way to increase support for phylogenetic relationships and produce novel and credible new phylogenetic hypotheses. Background [6], few phylogenetic analyses of angiosperms have Molecular data have had an enormous impact on included more than a thousand sequences. We examine angiosperm phylogenetic hypotheses (e.g. [1-5]), and the whether augmenting existing plant data matrices with abundance of new sequence data provides the potential for incomplete data assembled from publicly available sources further resolving angiosperm relationships. Still, molecular can enhance the understanding of the backbone phyloge- phylogenetic studies across all angiosperms have utilized netic relationships across angiosperms. only a small fraction of the available sequence data. While GenBank currently contains over 1.7 million core nucle- The sampling strategies of phylogenetic studies across otide sequences from angiosperms, with over 160,000 of angiosperms demonstrate a tradeoff between taxonomic these being from often phylogenetically useful plastid loci sampling and the number of gene sequences per taxon. Page 1 of 11 (page number not for citation purposes) BMC Evolutionary Biology 2009, 9:61 http://www.biomedcentral.com/1471-2148/9/61 On one extreme, phylogenetic analyses using single genes atpB, and rbcL) 567-taxon matrix of P. Soltis et al. ([1], see such as rbcL [7,8], 18S rDNA [9], and matK [10] have sam- also [2,3]). Both matK and the nuclear 26S rDNA have pled hundreds, or even thousands [8], of taxa. In some been informative in large-scale angiosperm phylogenetic cases, analyses of single genes have provided strong sup- studies (e. g., matK: [10,22,23]; 26S rDNA: [29-32]), and port for many angiosperm relationships (e.g. [10]), but consequently, sequence data from both genes are availa- other parts of the single-gene trees have been unresolved, ble for many angiosperm taxa. We assembled the availa- in disagreement with other single gene trees (albeit often ble 26S rDNA and matK sequences from taxa represented without strong support), or simply anomalous (e.g. [7]). in the 3-gene matrix and compared results from maxi- On the other extreme, the advent of chloroplast genome mum likelihood phylogenetic analyses of the 3-gene 567- sequencing has led to phylogenetic analyses of taxon complete matrix with the 5-gene 567-taxon incom- angiosperms using sequences from up to 81 genes, plete matrix. Specifically, we examine if and how aug- although often with limited taxon sampling [11-17]. The menting complete data sets with incomplete data affects limited taxon sampling can have undesirable effects on our view of angiosperm phylogeny. phylogenetic inferences from complete chloroplast genome sequences, as well as other large molecular data Results sets (see [13,14,18,19]). Other studies have used sam- Data set pling strategies that attempt to compromise between We performed analyses on a 3-gene and a 5-gene data taxon and gene sampling. For example, Qiu et al. [20,21] matrix that have the same set of 567-taxa (Fig. 1). In the used 5 genes and 105 taxa, and later studies have used 9 3-gene (18S rDNA, atpB, and rbcL), matrix, all taxa have genes and 100 taxa [22] or 8 genes and 162 taxa [23]. sequences from all genes. The matrix is 4592 characters These studies generally have focused on the basal long and it contains 2.9% missing data, representing angiosperm splits, and more comprehensive taxon sam- indels or small sections of missing gene sequences. The 5- pling is necessary to address backbone relationships gene matrix comprises the available matK and 26S rDNA throughout the angiosperms. The most comprehensive sequences concatenated to the 3-gene matrix. The acces- taxon sampling across angiosperms using multiple genes sion numbers for the matK and 26S rDNA sequences, as includes a study using atpB and rbcL [24] and a 567-taxon well as the 5-gene character matrix, are included as addi- study with 18S rDNA, atpB, and rbcL [1-3]. tional files (see Additional files 1, 2 and 3). In the 5-gene matrix, 170 (29.9%) taxa have sequences from all 5 genes, While more data are needed to further resolve backbone and 119 (20.9%) taxa have data from only the original 3- relationships in angiosperms, it is not clear what the most genes (18S rDNA, atpB, and rbcL; Fig. 1). In total 47.0% of efficient sampling strategies for adding new data would be. the matK and 26S rDNA alignments are missing data, Previous analyses of molecular data across all angiosperms largely due to missing whole gene sequences, and overall, mostly used complete or nearly complete data matrices 27.5% of the cells in the 5-gene 567-taxon matrix are (but see [25,26]), in which all taxa have sequences from all, missing data. or nearly all, genes. Often it is possible to increase the number of taxa or genes in a phylogenetic matrix greatly using existing data by allowing small amounts of missing data (e.g. [27]). Furthermore, recent simulation studies have demonstrated that in some cases the total amount of 6 DWS% UEF/ PDW. U'1$ data in a phylogenetic matrix may determine the perform- ance of a phylogenetic analysis more than the percentage of 7D[D 6U'1$ 7D[D missing data [28]. This suggests that adding sequences from genes with incomplete taxonomic coverage to existing complete data matrices can, at least in some cases, improve the phylogenetic inference. Generating large, complete data 7D[D matrices can be both logistically daunting (e.g., assembling &KDUDFWHUV &KDUDFWHUV &KDUDFWHUV DNA samples from all taxa) and prohibitively expensive. In DiagramgeneFigure data 1 representing matrix the distribution of data in the total 5- contrast, there is a wealth of publicly available sequence Diagram representing the distribution of data in the data that can be readily assembled into phylogenetic data total 5-gene data matrix. All taxa in the matrix contain matrices, providing a relatively fast and inexpensive way to sequences from the first 3 genes (18S rDNA, atpB, and rbcL), augment existing data sets and possibly improve our phyl- 378 taxa have matK sequences, and 240 taxa have 26S rDNA ogenetic inferences. sequences. Only 170 taxa have sequences from both matK and 26S rDNA, and 119 taxa have no matK or 26S rDNA We explore the effect of adding existing plastid matK and sequences. nuclear 26S rDNA sequences to the 3-gene (18S rDNA, Page 2 of 11 (page number not for citation purposes) BMC Evolutionary Biology 2009, 9:61 http://www.biomedcentral.com/1471-2148/9/61 SummaryFigure 2 of the majority rule consensus from the 3-gene (18S rDNA, atpB, and rbcL) ML analysis Summary of the majority rule consensus from the 3-gene (18S rDNA, atpB, and rbcL) ML analysis. Names of the orders and informal names follow APG II [4] and Soltis et al. [2,3], with Hydrostachys in Cornales. Numbers above the branches are bootstrap percentages. This tree was rooted using all gymnosperm taxa as outgroups. Phylogenetic Analyses sis than the 3-gene analysis (0.963 vs. 0.934; Table 1). The bootstrap trees from the 5-gene and 3-gene analyses Still, bootstrap support for some clades, decreased. For are included as additional data (see Additional files 4 and example, bootstrap support for monocot, eudicot, and 5).