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2018 Trees within trees: simple nested coalescents
Airam Blancas, Jean-Jil Duchamps, Amaury Lambert, Arno Siri-Jégousse
Electron. J. Probab. 23: 1-27 (2018). DOI: 10.1214/18-EJP219


We consider the compact space of pairs of nested partitions of $\mathbb{N} $, where by analogy with models used in molecular evolution, we call “gene partition” the finer partition and “species partition” the coarser one. We introduce the class of nondecreasing processes valued in nested partitions, assumed Markovian and with exchangeable semigroup. These processes are said simple when each partition only undergoes one coalescence event at a time (but possibly the same time). Simple nested exchangeable coalescent (SNEC) processes can be seen as the extension of $\Lambda $-coalescents to nested partitions. We characterize the law of SNEC processes as follows. In the absence of gene coalescences, species blocks undergo $\Lambda $-coalescent type events and in the absence of species coalescences, gene blocks lying in the same species block undergo i.i.d. $\Lambda $-coalescents. Simultaneous coalescence of the gene and species partitions are governed by an intensity measure $\nu _s$ on $(0,1]\times{\mathcal M} _1 ([0,1])$ providing the frequency of species merging and the law in which are drawn (independently) the frequencies of genes merging in each coalescing species block. As an application, we also study the conditions under which a SNEC process comes down from infinity.


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Airam Blancas. Jean-Jil Duchamps. Amaury Lambert. Arno Siri-Jégousse. "Trees within trees: simple nested coalescents." Electron. J. Probab. 23 1 - 27, 2018.


Received: 6 March 2018; Accepted: 3 September 2018; Published: 2018
First available in Project Euclid: 18 September 2018

zbMATH: 06964788
MathSciNet: MR3858922
Digital Object Identifier: 10.1214/18-EJP219

Primary: 60G09 , 60G57 , 60J35 , 60J75 , 92D10 , 92D15

Keywords: coming down from infinity , Evolution , Exchangeable , Gene tree , Lambda-coalescent , Partition , Phylogenetics , Population genetics , Random tree , Species tree


Vol.23 • 2018
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