Soutenance de thèse de Soumen Mallick (Université de Rennes 1, ECOBIO)
Distantly related neighbours of host trees can prevent arthropods from matching tree characteristics: a story of arthropod phenotypes and leaf damage on oak trees Abstract: The success of tree-feeding arthropods depends on how well they match tree characteristics. We hypothesised that arthropods match poorly when trees are surrounded by phylogenetically distant neighbours, due to the reduced exchange of arthropods between neighbouring trees. Specifically, phylogenetic isolation prevents arthropods from profiting from (i) resource-rich trees, (ii) trees that burst buds rapidly, and (iii) trees with warm microclimate. We studied whether: (i) there is more herbivory on trees with larger and higher-quality leaves (proportional use of resources), (ii) caterpillars are larger on trees with earlier bursting buds, and pupate earlier on trees with earlier maturing leaves (phenology matching), and (iii) arthropods of small body size dominate on trees with warm microclimate permitting to reach maturity at small size (temperature/size rule). We predicted these relationships to disappear among phylogenetically isolated trees. We focused on the most arthropod-diverse tree species of western Europe, Quercus petraea (hybridised with Q. robur), in a forest in western France. We found that when host trees were phylogenetically isolated (i) herbivory no longer increased proportionally with leaf size, (ii) phenology matching declined in particular on rapidly bursting trees, and (iii) temperature/size relationships shifted. We suggest that phylogenetic isolation prevents arthropods from effectively choosing trees with abundant resources, from matching phenology and from matching microclimate. Our results thus suggest that to avoid excessive herbivory, trees should grow far from phylogenetically closely related species (or alternatively budburst slowly). Jury composition: Julia KORICHEVA - Professor, Royal Holloway, University of London (reviewer) Bastien CASTAGENYROL - Researcher, INRAE – Université de Bordeaux (reviewer) Anne-Marie CORTESERO - Professor, INRAE, Université de Rennes 1 (examiner) Benjamin BERGEROT - Lecturer, EcoBio, Université de Rennes 1 (examiner) Jörg MÜLLER - Professor, Universität Würzburg (examiner) Martin VOLF - Professor, Biology Centre, Czech Academy of Sciences (examiner) Andreas PRINZING - Professor, EcoBio, Université de Rennes 1 (thesis director) Freerk MOLLEMAN - Professor, Uniwersytet im. Adama Mickiewicza Poznań (thesis co-director) This defence will also be broadcasted on zoom via the following link: [https://univ-rennes1-fr.zoom.us/j/83105317181](https://univ-rennes1-fr.zoom.us/j/83105317181) Meeting ID: 831 0531 7181 Passcode: 04021994
