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Documents authored by Scornavacca, Celine

Document
DOI: 10.4230/LIPIcs.WABI.2025.15
Average-Tree Phylogenetic Diversity of Networks

Authors: Leo van Iersel, Mark Jones, Jannik Schestag, Celine Scornavacca, and Mathias Weller

Published in: LIPIcs, Volume 344, 25th International Conference on Algorithms for Bioinformatics (WABI 2025)

Abstract
Phylogenetic diversity is a measure used to quantify the biodiversity of a set of species. Here, we introduce the "average-tree" phylogenetic diversity score in rooted binary phylogenetic networks and consider algorithms for computing and maximizing the score on a given network. Basically, the score is the weighted average of the phylogenetic diversity scores in all trees displayed by the network, with the weights determined by the inheritance probabilities on the reticulation edges used in the embeddings. We show that computing the score of a given set of taxa in a given network is #P-hard, directly implying #P-hardness of finding a subset of k taxa achieving maximum diversity score and, thereby, ruling out polynomial-time algorithms for these problems unless the polynomial hierarchy collapses. However, we show that both problems can be solved efficiently if the input network is close to being a tree in the sense that its reticulation number is small. More precisely, we prove that we can solve the optimization problem in networks with n leaves and r reticulations in 2^{𝒪(r)}⋅ n⋅ k time. Using experiments on data produced by simulating a reticulate-evolution process, we show that our algorithm runs efficiently on networks with hundreds of taxa and tens of reticulations.
Cite as

Leo van Iersel, Mark Jones, Jannik Schestag, Celine Scornavacca, and Mathias Weller. Average-Tree Phylogenetic Diversity of Networks. In 25th International Conference on Algorithms for Bioinformatics (WABI 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 344, pp. 15:1-15:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{vaniersel_et_al:LIPIcs.WABI.2025.15,
  author =	{van Iersel, Leo and Jones, Mark and Schestag, Jannik and Scornavacca, Celine and Weller, Mathias},
  title =	{{Average-Tree Phylogenetic Diversity of Networks}},
  booktitle =	{25th International Conference on Algorithms for Bioinformatics (WABI 2025)},
  pages =	{15:1--15:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-386-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{344},
  editor =	{Brejov\'{a}, Bro\v{n}a and Patro, Rob},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WABI.2025.15},
  URN =		{urn:nbn:de:0030-drops-239405},
  doi =		{10.4230/LIPIcs.WABI.2025.15},
  annote =	{Keywords: phylogenetic diversity, phylogenetic networks, network phylogenetic diversity, algorithms, computational complexity}
}
Document
DOI: 10.4230/LIPIcs.WABI.2021.6
Treewidth-Based Algorithms for the Small Parsimony Problem on Networks

Authors: Celine Scornavacca and Mathias Weller

Published in: LIPIcs, Volume 201, 21st International Workshop on Algorithms in Bioinformatics (WABI 2021)

Abstract
Phylogenetic reconstruction is one of the paramount challenges of contemporary bioinformatics. A subtask of existing tree reconstruction algorithms is modeled by the Small Parsimony problem: given a tree T and an assignment of character-states to its leaves, assign states to the internal nodes of T such as to minimize the parsimony score, that is, the number of edges of T connecting nodes with different states. While this problem is polynomial-time solvable on trees, the matter is more complicated if T contains reticulate events such as hybridizations or recombinations, i.e. when T is a network. Indeed, three different versions of the parsimony score on networks have been proposed and each of them is NP-hard to decide. Existing parameterized algorithms focus on combining the number of possible character-states with the number of reticulate events (per biconnected component). Here, we consider the treewidth of the undirected graph underlying the input network as parameter, presenting dynamic programming algorithms for (slight generalizations of) all three versions of the parsimony problem on networks. Our algorithms use a formulation of the treewidth that may facilitate formalizing treewidth-based dynamic programming algorithms on phylogenetic networks for other problems.
Cite as

Celine Scornavacca and Mathias Weller. Treewidth-Based Algorithms for the Small Parsimony Problem on Networks. In 21st International Workshop on Algorithms in Bioinformatics (WABI 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 201, pp. 6:1-6:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{scornavacca_et_al:LIPIcs.WABI.2021.6,
  author =	{Scornavacca, Celine and Weller, Mathias},
  title =	{{Treewidth-Based Algorithms for the Small Parsimony Problem on Networks}},
  booktitle =	{21st International Workshop on Algorithms in Bioinformatics (WABI 2021)},
  pages =	{6:1--6:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-200-6},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{201},
  editor =	{Carbone, Alessandra and El-Kebir, Mohammed},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WABI.2021.6},
  URN =		{urn:nbn:de:0030-drops-143591},
  doi =		{10.4230/LIPIcs.WABI.2021.6},
  annote =	{Keywords: Phylogenetics, parsimony, phylogenetic networks, parameterized complexity, dynamic programming, treewidth}
}
Document
DOI: 10.4230/LIPIcs.WABI.2018.5
Reconciling Multiple Genes Trees via Segmental Duplications and Losses

Authors: Riccardo Dondi, Manuel Lafond, and Celine Scornavacca

Published in: LIPIcs, Volume 113, 18th International Workshop on Algorithms in Bioinformatics (WABI 2018)

Abstract
Reconciling gene trees with a species tree is a fundamental problem to understand the evolution of gene families. Many existing approaches reconcile each gene tree independently. However, it is well-known that the evolution of gene families is interconnected. In this paper, we extend a previous approach to reconcile a set of gene trees with a species tree based on segmental macro-evolutionary events, where segmental duplication events and losses are associated with cost delta and lambda, respectively. We show that the problem is polynomial-time solvable when delta <= lambda (via LCA-mapping), while if delta > lambda the problem is NP-hard, even when lambda = 0 and a single gene tree is given, solving a long standing open problem on the complexity of the reconciliation problem. On the positive side, we give a fixed-parameter algorithm for the problem, where the parameters are delta/lambda and the number d of segmental duplications, of time complexity O(ceil[delta/lambda]^d * n * delta/lambda). Finally, we demonstrate the usefulness of this algorithm on two previously studied real datasets: we first show that our method can be used to confirm or refute hypothetical segmental duplications on a set of 16 eukaryotes, then show how we can detect whole genome duplications in yeast genomes.
Cite as

Riccardo Dondi, Manuel Lafond, and Celine Scornavacca. Reconciling Multiple Genes Trees via Segmental Duplications and Losses. In 18th International Workshop on Algorithms in Bioinformatics (WABI 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 113, pp. 5:1-5:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{dondi_et_al:LIPIcs.WABI.2018.5,
  author =	{Dondi, Riccardo and Lafond, Manuel and Scornavacca, Celine},
  title =	{{Reconciling Multiple Genes Trees via Segmental Duplications and Losses}},
  booktitle =	{18th International Workshop on Algorithms in Bioinformatics (WABI 2018)},
  pages =	{5:1--5:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-082-8},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{113},
  editor =	{Parida, Laxmi and Ukkonen, Esko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WABI.2018.5},
  URN =		{urn:nbn:de:0030-drops-93079},
  doi =		{10.4230/LIPIcs.WABI.2018.5},
  annote =	{Keywords: Gene trees/species tree reconciliation, phylogenetics, computational complexity, fixed-parameter algorithms}
}
Document
DOI: 10.4230/LIPIcs.CPM.2017.28
On the Weighted Quartet Consensus Problem

Authors: Manuel Lafond and Celine Scornavacca

Published in: LIPIcs, Volume 78, 28th Annual Symposium on Combinatorial Pattern Matching (CPM 2017)

Abstract
In phylogenetics, the consensus problem consists in summarizing a set of phylogenetic trees that all classify the same set of species into a single tree. Several definitions of consensus exist in the literature; in this paper we focus on the Weighted Quartet Consensus problem, a problem with unknown complexity status so far. Here we prove that the Weighted Quartet Consensus problem is NP-hard and we give a 1/2-factor approximation for this problem. During the process, we propose a derandomization procedure of a previously known randomized 1/3-factor approximation. We also investigate the fixed-parameter tractability of this problem.
Cite as

Manuel Lafond and Celine Scornavacca. On the Weighted Quartet Consensus Problem. In 28th Annual Symposium on Combinatorial Pattern Matching (CPM 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 78, pp. 28:1-28:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{lafond_et_al:LIPIcs.CPM.2017.28,
  author =	{Lafond, Manuel and Scornavacca, Celine},
  title =	{{On the Weighted Quartet Consensus Problem}},
  booktitle =	{28th Annual Symposium on Combinatorial Pattern Matching (CPM 2017)},
  pages =	{28:1--28:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-039-2},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{78},
  editor =	{K\"{a}rkk\"{a}inen, Juha and Radoszewski, Jakub and Rytter, Wojciech},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CPM.2017.28},
  URN =		{urn:nbn:de:0030-drops-73284},
  doi =		{10.4230/LIPIcs.CPM.2017.28},
  annote =	{Keywords: phylogenetic tree, consensus tree, quartets, complexity, fixed-parameter tractability}
}
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