| 1. |
- Bertrand, Yann, et al.
(author)
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First Dating of a Recombination Event in Mammalian Tick-borne Flaviviruses
- 2012
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In: PLoS ONE. - San Francisco : Public Library of Science (PLoS). - 1932-6203. ; 7:2
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Journal article (peer-reviewed)abstract
- The mammalian tick-borne flavivirus group (MTBFG) contains viruses associated with important human and animal diseases such as encephalitis and hemorrhagic fever. In contrast to mosquito-borne flaviviruses where recombination events are frequent, the evolutionary dynamic within the MTBFG was believed to be essentially clonal. This assumption was challenged with the recent report of several homologous recombinations within the Tick-borne encephalitis virus (TBEV). We performed a thorough analysis of publicly available genomes in this group and found no compelling evidence for the previously identified recombinations. However, our results show for the first time that demonstrable recombination (i.e., with large statistical support and strong phylogenetic evidences) has occurred in the MTBFG, more specifically within the Louping ill virus lineage. Putative parents, recombinant strains and breakpoints were further tested for statistical significance using phylogenetic methods. We investigated the time of divergence between the recombinant and parental strains in a Bayesian framework. The recombination was estimated to have occurred during a window of 282 to 76 years before the present. By unravelling the temporal setting of the event, we adduce hypotheses about the ecological conditions that could account for the observed recombination.
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| 2. |
- Bertrand, Yann
(author)
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Relationships between nomenclature, phylogenetics and systematics
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Systematists have become increasingly aware of the limits imposed by the current system of nomenclature for accurately representing evolutionary relationships and managing efficiently names associated with clades. In reaction, a new system of nomenclature, the PhyloCode is being developed that fully recognizes the historical nature of taxonomy and the importance of the cladistics revolution. As a consequence, questions emerge about the new historical entities of systematics, questions that can be apprehended through the lens of epistemology, philosophy of language and metaphysics. What is the ontological nature of entities that lack any other essential features besides spatiotemporal properties? How to depart from the fixed realm of immutable and transcendental essence into a worldview wherein all biological entities are characterized by their temporality and materiality? What are the consequences of nomenclatural decisions on other sectors of biology? With the ever growing sequencing capacity and tree reconstructing abilities, our conceptualization of phylogenetic relationships is changing at an unprecedented pace. Then it begs the question, what prevents communication break down when the references of clades’ names are changing almost on a daily basis. These are some of the fundamental issues I am tackling in the present work. Addressing the ontological issue, I argue that species and clades are best perceived as mereological sums of individuals, which means that each biological individual is the unique individual composed of all its less inclusive individuals and nothing more. I propose to separate the meanings of “clade” and “monophyletic group”. I suggest to use “monophyletic” for an epithet referring to a defining property of a set (a natural kind) and “clade” for a noun which corresponds to a historical entity (an individual) resulting from evolutionary process. I present the idea that a phyloname is not attached to a single clade but to a natural kind containing as members the clades that would be selected in counterfactual phylogenies. The defining properties of this natural kind are provided by the phylogenetic definition. Finally I stress that taxonomists are also driven by the will to narrate the same sort of history, when they adjust the reference of names in light of new phylogenetic data, which leads me to submit that taxa can also be perceived as narratives.
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| 3. |
- Bertrand, Yann, et al.
(author)
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Taxonomic surrogacy in biodiversity assessments, and the meaning of Linnaean ranks
- 2006
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In: Systematics and Biodiversity. ; 4:2, s. 149-159
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Journal article (peer-reviewed)abstract
- The majority of biodiversity assessments use species as the base unit. Recently, a series of studies have suggested replacing numbers of species with higher ranked taxa (genera, families, etc.); a method known as taxonomic surrogacy that has an important potential to save time and resources in assesments of biological diversity. We examine the relationships between taxa and ranks, and suggest that species/higher taxon exchanges are founded on misconceptions about the properties of Linnaean classification. Rank allocations in current classifications constitute a heterogeneous mixture of various historical and contemporary views. Even if all taxa were monophyletic, those referred to the same rank would simply denote separate clades without further equivalence. We conclude that they are no more comparable than any other, non-nested taxa, such as, for example, the genus Rattus and the phylum Arthropoda, and that taxonomic surrogacy lacks justification. These problems are also illustrated with data of polychaetous annelid worms from a broad-scale study of benthic biodiversity and species distributions in the Irish Sea. A recent consensus phylogeny for polychaetes is used to provide three different family-level classifications of polychaetes. We use families as a surrogate for species, and present Shannon–Wiener diversity indices for the different sites and the three different classifications, showing how the diversity measures rely on subjective rank allocations
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