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20
On the approximation of computing evolutionary trees
 in Proceedings of the 11th International Computing and Combinatorics Conference (COCOON’05
, 2005
"... Abstract. Given a set of leaflabelled trees with identical leaf sets, the wellknown MAST problem consists of finding a subtree homeomorphically included in all input trees and with the largest number of leaves. MAST and its variant called MCT are of particular interest in computational biology. Th ..."
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Cited by 12 (4 self)
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Abstract. Given a set of leaflabelled trees with identical leaf sets, the wellknown MAST problem consists of finding a subtree homeomorphically included in all input trees and with the largest number of leaves. MAST and its variant called MCT are of particular interest in computational biology. This paper presents positive and negative results on the approximation of MAST, MCT and their complement versions, denoted CMAST and CMCT. For CMAST and CMCT on rooted trees we give 3approximation algorithms achieving significantly lower running times than those previously known. In particular, the algorithm for CMAST runs in linear time. The approximation threshold for CMAST, resp. CMCT, is shown to be the same whenever collections of rooted trees or of unrooted trees are considered. Moreover, hardness of approximation results are stated for CMAST, CMCT and MCT on small number of trees, and for MCT on unbounded number of trees.
Rooted Maximum Agreement Supertrees
, 2005
"... Given a set T of rooted, unordered trees, where each Ti ∈ T is distinctly leaflabeled by a set �(Ti) and where the sets �(Ti) may overlap, the maximum agreement supertree problem (MASP) is to construct a distinctly leaflabeled tree Q with leaf set �(Q) ⊆ ∪Ti ∈T �(Ti) such that �(Q)  is maximiz ..."
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Cited by 11 (2 self)
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Given a set T of rooted, unordered trees, where each Ti ∈ T is distinctly leaflabeled by a set �(Ti) and where the sets �(Ti) may overlap, the maximum agreement supertree problem (MASP) is to construct a distinctly leaflabeled tree Q with leaf set �(Q) ⊆ ∪Ti ∈T �(Ti) such that �(Q)  is maximized and for each Ti ∈ T, the topological restriction of Ti to �(Q) is isomorphic to the topological restriction of Q to �(Ti). Let n = � �∪Ti ∈T �(Ti) � � , k =T , and D = maxTi ∈T {deg(Ti)}. We first show that MASP with k = 2 can be solved in O ( √ Dn log(2n/D)) time, which is O(n log n) when D = O(1) and O(n1.5) when D is unrestricted. We then present an algorithm for MASP with D = 2 whose running time is polynomial if k = O(1). On the other hand, we prove that MASP is NPhard for any fixed k ≥ 3 when D is unrestricted, and also NPhard for any fixed D ≥ 2 when k is unrestricted even if each input tree is required to contain at most three leaves. Finally, we describe a polynomialtime (n/log n)approximation algorithm for MASP.
V.: Physic ist: cleaning source trees to infer more informative supertrees
 BMC Bioinformatics
, 2008
"... Background: Supertree methods combine phylogenies with overlapping sets of taxa into a larger one. Topological conflicts frequently arise among source trees for methodological or biological reasons, such as long branch attraction, lateral gene transfers, gene duplication/loss or deep gene coalescenc ..."
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Cited by 11 (3 self)
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Background: Supertree methods combine phylogenies with overlapping sets of taxa into a larger one. Topological conflicts frequently arise among source trees for methodological or biological reasons, such as long branch attraction, lateral gene transfers, gene duplication/loss or deep gene coalescence. When topological conflicts occur among source trees, liberal methods infer supertrees containing the most frequent alternative, while veto methods infer supertrees not contradicting any source tree, i.e. discard all conflicting resolutions. When the source trees host a significant number of topological conflicts or have a small taxon overlap, supertree methods of both kinds can propose poorly resolved, hence uninformative, supertrees. Results: To overcome this problem, we propose to infer nonplenary supertrees, i.e. supertrees that do not necessarily contain all the taxa present in the source trees, discarding those whose position greatly differs among source trees or for which insufficient information is provided. We detail a variant of the PhySIC veto method called PhySIC IST that can infer nonplenary supertrees. PhySIC IST aims at inferring supertrees that satisfy the same appealing theoretical properties as with PhySIC, while being as informative as possible under this constraint. The informativeness of a supertree is estimated using a variation of the CIC (Cladistic Information Content) criterion, that takes into account both the presence of multifurcations and the absence of some taxa.
Improved Parameterized Complexity of the Maximum Agreement Subtree and . . .
 IEEE/ACM TRANSACTIONS ON COMPUTATIONAL BIOLOGY AND BIOINFORMATICS
, 2006
"... Given a set of evolutionary trees on a same set of taxa, the maximum agreement subtree problem (MAST), respectively maximum compatible tree problem (MCT), consists of finding a largest subset of taxa such that all input trees restricted to these taxa are isomorphic, respectively compatible. These ..."
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Cited by 9 (4 self)
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Given a set of evolutionary trees on a same set of taxa, the maximum agreement subtree problem (MAST), respectively maximum compatible tree problem (MCT), consists of finding a largest subset of taxa such that all input trees restricted to these taxa are isomorphic, respectively compatible. These problems
PhySIC: A Veto Supertree Method with Desirable Properties
, 2007
"... This paper focuses on veto supertree methods; i.e., methods that aim at producing a conservative synthesis of the relationships agreed upon by all source trees. We propose desirable properties that a supertree should satisfy in this framework, namely the noncontradiction property (PC) and the indu ..."
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Cited by 9 (2 self)
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This paper focuses on veto supertree methods; i.e., methods that aim at producing a conservative synthesis of the relationships agreed upon by all source trees. We propose desirable properties that a supertree should satisfy in this framework, namely the noncontradiction property (PC) and the induction property (PI). The former requires that the supertree does not contain relationships that contradict one or a combination of the source topologies, whereas the latter requires that all topological information contained in the supertree is present in a source tree or collectively induced by several source trees. We provide simple examples to illustrate their relevance and that allow a comparison with previously advocated properties. We show that these properties can be checked in polynomial time for any given rooted supertree. Moreover, we introduce the PhySIC method (PHYlogenetic Signal with induction and nonContradiction). For k input trees spanning a set of n taxa, this method produces a supertree that satisfies the abovementioned properties in O(kn3 + »4) computing time. The polytomies of the produced supertree are also tagged by labels indicating areas of conflict as well as those with insufficient overlap. As a whole, PhySIC enables the user to quickly summarize consensual information of a set of trees and localize groups of taxa for which the data require consolidation. Lastly, we illustrate the behaviour of PhySIC on primate data sets of various sizes, and propose a supertree covering 95 % of all primate extant genera. The PhySIC algorithm is available at http://atgc.lirmm.fr/cgibin/PhySIC.
INFERRING PHYLOGENETIC RELATIONSHIPS AVOIDING FORBIDDEN ROOTED TRIPLETS
, 2006
"... To construct a phylogenetic tree or phylogenetic network for describing the evolutionary history of a set of species is a wellstudied problem in computational biology. One previously proposed method to infer a phylogenetic tree/network for a large set of species is by merging a collection of known ..."
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Cited by 6 (2 self)
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To construct a phylogenetic tree or phylogenetic network for describing the evolutionary history of a set of species is a wellstudied problem in computational biology. One previously proposed method to infer a phylogenetic tree/network for a large set of species is by merging a collection of known smaller phylogenetic trees on overlapping sets of species so that no (or as little as possible) branching information is lost. However, little work has been done so far on inferring a phylogenetic tree/network from a specified set of trees when in addition, certain evolutionary relationships among the species are known to be highly unlikely. In this paper, we consider the problem of constructing a phylogenetic tree/network which is consistent with all of the rooted triplets in a given set C and none of the rooted triplets in another given set F. Although NPhard in the general case, we provide some efficient exact and approximation algorithms for a number of biologically meaningful variants of the problem.
Solving the maximum agreement subtree and the maximum compatible tree problems on many bounded degree trees
 Proceedings of the 17th Annual Symposium on Combinatorial Pattern Matching (CPM’06
, 2006
"... Given a set of leaflabeled trees with identical leaf sets, the wellknown Maximum Agreement SubTree problem (MAST) consists of finding a subtree homeomorphically included in all input trees and with the largest number of leaves. Its variant called Maximum Compatible Tree (MCT) is less stringent, as ..."
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Cited by 4 (0 self)
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Given a set of leaflabeled trees with identical leaf sets, the wellknown Maximum Agreement SubTree problem (MAST) consists of finding a subtree homeomorphically included in all input trees and with the largest number of leaves. Its variant called Maximum Compatible Tree (MCT) is less stringent, as it allows the input trees to be refined. Both problems are of particular interest in computational biology, where trees encountered have often small degrees. In this paper, we study the parameterized complexity of MAST and MCT with respect to the maximum degree, denoted by D, of the input trees. Although MAST is polynomial for bounded D [1, 6, 3], we show that the problem is W[1]hard with respect to parameter D. Moreover, relying on recent advances in parameterized complexity we obtain a tight lower bound: while MAST can be solved in O(N O(D)) time where N denotes the input length, we show that an O(N o(D) ) bound is not achievable, unless SNP ⊆ SE. We also show that MCT is W[1]hard with respect to D, and that MCT cannot be solved in O(N o(2D/2)) time, unless SNP ⊆ SE. 1
Fixedparameter tractability of the maximum agreement supertree problem (Extended Abstract)
, 2007
"... Given a ground set L of labels and a collection of trees whose leaves are bijectively labelled by some elements of L, the Maximum Agreement Supertree problem (SMAST) is the following: find a tree T on a largest label set L′ ⊆ L that homeomorphically contains every input tree restricted to L′. The p ..."
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Cited by 3 (0 self)
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Given a ground set L of labels and a collection of trees whose leaves are bijectively labelled by some elements of L, the Maximum Agreement Supertree problem (SMAST) is the following: find a tree T on a largest label set L′ ⊆ L that homeomorphically contains every input tree restricted to L′. The problem finds applications in several fields, e.g. phylogenetics. In this paper we focus on the parameterized complexity of this NPhard problem. We consider different combinations of parameters for SMAST as well as particular cases, providing both FPT algorithms and intractability results.
Linear time 3approximation for the MAST problem
, 2009
"... Given a set of leaflabeled trees with identical leaf sets, the wellknown Maximum Agreement Subtree (MAST) problem consists in finding a subtree homeomorphically included in all input trees and with the largest number of leaves. MAST and its variant called Maximum Compatible Tree (MCT) are of parti ..."
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Cited by 1 (0 self)
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Given a set of leaflabeled trees with identical leaf sets, the wellknown Maximum Agreement Subtree (MAST) problem consists in finding a subtree homeomorphically included in all input trees and with the largest number of leaves. MAST and its variant called Maximum Compatible Tree (MCT) are of particular interest in computational biology. This paper presents a lineartime approximation algorithm to solve the complement version of MAST, namely identifying the smallest set of leaves to remove from input trees to obtain isomorphic trees. We also present an O(n2 + kn) algorithm to solve the complement version of MCT. For both problems, we thus achieve significantly lower running times than previously known algorithms. Fast running times are especially important in phylogenetics where large collections of trees are routinely produced by resampling procedures, such as the non parametric bootstrap or Bayesian MCMC methods.