Taxonomy and biogeography ot aquatic molluscs : which scales for taxa and management units delimitation ? ; Taxonomie et biogéographie des mollusques d'eau douce patrimoniaux : quelles échelles pour la délimitation des taxons et des unités de gestion ?

Abstract

At the age of the 6th extinction, there is an urgent need for conservation stakeholders and field biologists of an operational taxonomy, both for methods (taxonomic expertise) and concepts (checklists). In this work, I test the hypothesis that continental insularity, linked to the structure of the aquifers, whatever the considered scale, leads to the divergence of distinct evolutionary units. This hypothesis is tested by studying two models, the freshwater bivalves at the scale of France and the stygobite gastropods at the scale of the north-Montpellier karstic system. To achieve this, an operational taxonomy approach is developed for these two models, in order to allow setting up effective conservation measures. For these two groups characterized by an unstable taxonomy, morphometric, genetic and biogeographic approaches are developed, in an integrative taxonomy framework. New genetic data allow clarifying the taxonomy and provide a new perspective on the existing conservation units. For the naiads, the results indicate that diversity is overestimated and that geographical barriers play a minor role in distribution of the taxa, which seem to be linked to environmental parameters. On the contrary, the diversity of the stygobite gastropods is largely underestimated and evolutionary units are linked to the hydrogeological units. Environmental variables do not seem to influence the distribution of these species. These contrasted results show that the structure of the diversity differs depending on the taxonomic group and the geographic scale considered, and raise the question of the impact of human activities on the distribution of the naïads. Conservation politics should take into account these integrative taxonomy approaches to (i) define adequately the biological units that should benefit from conservation efforts and (ii) set up these measures at an adequate geographic scale. ; A l'âge de la 6° extinction, il y a un besoin urgent pour les acteurs de la conservation et pour les biologistes de terrain de pouvoir ...