Abstract

Authors: Franić, I, S Prospero, KA, EA, FA, MAA-R, SA, DA, WB, MB, KB, AB, PB, HB, TB, MB Brurberg, TB, DB, MC, JC, DC, GC, K, KD, MdeG, JD, HTDL, RD, JE, ME, CBE, RF, JF, NF, ÁF-M, MG, BG, MH, LH, MKH, MH, MJJ, MK, MK, NK, MK, VK, NL, MVL, JL, ML, HL, CLM, CM, DM, IM, TM, JM, DM, CN, RO'H, FO, TP, TP, BP, HR, JR, AR, AR, BR, KS, CS, V Talgø, МТ, AU, MU, AMV, CV, YW, JW, MZ, R Eschen. Abstract: Non-native pests, climate change, and their interactions are expected to disrupt the relationships between trees and the organisms associated with them, thereby impacting forest health. In order to comprehend and anticipate these changes, it is crucial to identify the factors that shape tree-associated communities. We collected and analysed insects and fungi obtained from dormant twigs of 155 tree species across 51 botanical gardens or arboreta in 32 countries on six continents. Fungi were characterized by high-throughput sequencing. Insects were first reared and then sorted into taxonomic orders and feeding guilds. Herbivorous insects were then grouped into morphospecies and were identified using molecular and morphological approaches. By employing generalized dissimilarity models, we assessed the relative significance of various climatic, host-related, and geographic factors in driving dissimilarities among tree-associated communities. This dataset reveals the diversity of tree- associated taxa, as it contains 12,721 amplicon sequence variants and 208 herbivorous insect morphospecies, sampled across broad geographic and climatic gradients and for many tree species. Mean annual temperature, the phylogenetic distance between hosts, and the geographic distance between locations were the primary determinants of dissimilarities. The increasing influence of high temperatures on community differences suggests that climate change could directly and indirectly impact tree-associated organisms through shifts in host ranges. Furthermore, insect and fungal communities exhibited greater similarity among closely related hosts compared to distantly related hosts, implying that expansion of host ranges could facilitate the emergence of new pests. Additionally, dissimilarities among tree-associated communities increased with geographic distance, suggesting that human-mediated transportation could lead to the introduction of new pests. These study results underscore the importance of limiting the introduction and establishment of tree pests and enhancing the resilience of forest ecosystems in response to climate change.

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Abstract

Phytophthora pseudosyringae is a self-fertile pathogen of woody plants, particularly associated with tree species from the genera Fagus, Notholithocarpus, Nothofagus and Quercus, which is found across Europe and in parts of North America and Chile. It can behave as a soil pathogen infecting roots and the stem collar region, as well as an aerial pathogen infecting leaves, twigs and stem barks, causing particular damage in the United Kingdom and western North America. The population structure, migration and potential outcrossing of a worldwide collection of isolates were investigated using genotyping-by-sequencing. Coalescent-based migration analysis revealed that the North American population originated from Europe. Historical gene flow has occurred between the continents in both directions to some extent, yet contemporary migration is overwhelmingly from Europe to North America. Two broad population clusters dominate the global population of the pathogen, with a subgroup derived from one of the main clusters found only in western North America. Index of association and network analyses indicate an influential level of outcrossing has occurred in this preferentially inbreeding, homothallic oomycete. Outcrossing between the two main population clusters has created distinct subgroups of admixed individuals that are, however, less common than the main population clusters. Differences in life history traits between the two main population clusters should be further investigated together with virulence and host range tests to evaluate the risk each population poses to natural environments worldwide.