Ecological interactions drive evolutionary outcomes: The first example of major host plant shifts mediated by parasitic plants in insects Authors were anonymised during the reviewing process Abstract Phytophagous insects have specialized on virtually every plant lineage. Parasitic plants, however, are uncommon hosts. Among insects, only a single lineage of weevils, the Smicronychini, has successfully radiated on both parasitic and non-parasitic plants in a large panel of distantly related Asterid families. This unusual pattern suggests that major host plant shifts have occurred over the course of their diversification. Through the analysis of a phylogenomic dataset, we reconstruct for the first time their evolutionary history and ancestral host plant associations. Our results show that independent host plant shifts occurred both from parasitic to non-parasitic hosts and between distinct parasitic lineages. These results suggest that host shift mechanisms can be driven by ecological opportunities provided by plant-plant interactions. This first evidence of extreme insect host plant shifts mediated by parasitic plant-plant interactions emphasizes the core importance of ecological interactions as driving forces behind insect host plant shifts. Figures & Tables Figure 1: Host repertoire of Smicronychini weevils. From top to bottom: diagrams represent parasitic interactions between Smicronychini weevils and their host plants. Host plant families that make up the host repertoire of Smicronychini are shown below each corresponding diagram, with examples of associated weevils and known galls. Credits: BZ & JH, except for Orobanchaceae (Clémence Massard) and Asteraceae (@sinaloasilvestre, iNaturalist) pictures; diagrams with BioRender ©. Figure 2: Phylogenomic tree based on the AHE dataset. A. Maximum likelihood tree of the AHE dataset. Nodes poorly supported (SH-aLRT 70% speciesAHE_2024_v8.3_70.nex - Partition file with 1 partition per flanking/coding regions (see Fig. 3B in main text)AHE_2024_v8.3.70.MFPMERGE* - Tree generated with MFP+MERGE model COI: Phylogenetic analyses on COI dataset COI_2025.v1.fasta - fasta alignment of all cytochrome oxydase I samples cleaned from bad sequencesCOI_2025.v1.noemptyseq* - COI tree of all samples, cleaned from empty sequences (corresponding to AHE specimen without COI) grafting: Phylogenomic analyses on extended dataset # Phylogenetic analysesconstraintfile.txt - Backbone generated by AHE analysesAHE_COI_2025.v1* - Grafted tree with all samples, launched without --allnni iqtree option to reduce computation timeAHE_COI_2025.v2.monosp.nex | .phylip - Nexus and phylip files resulting from manual removal of all but one representative of each species based on AHE_COI_2025.v1.grafting.noallnni and COI tree (for dentirostris and rubricatus), see tips highlighted in red in AHE_COI_2025.v1.grafting.noallnni.treefile.keepsp.pdf for samples kept in v2AHE_COI_2025.v2* - Grafted tree with one sample per species # Topology teststopo1.newick - Same topology as AHE_COI_2025.v2bis.grafting.monosp.treefiletopo2* - Alternative topology assuming the monophyly of North American Smicronyx speciestopo3* - Alternative topology assuming the monophyly of North American Smicronyx and Promecotarsus speciestopotest.iqtree - results of the topology test showing no significative difference between the three tested topologies 04_ASR: Ancestral character state estimations (ASR) are run with ASR_v3.R topo1 = paraphyletic Asteraceae-feeding speciestopo2 = monophyletic Asteraceae-feeding speciesBoth topologies are equally likely (cf ../03_TREES/grafting/topotest.iqtree) ACE_HPPM_ER.topo1.pdf - ASR with ace() function on topo1ACE_HPPM_ER.topo2.pdf - ASR with ace() function on topo2ACE_HPPM_Likelihoods.csv - Ancestral state likelihoods at each node of ACE_HPPM_ER.topo2.pdfACE_HP_ER.topo2.png - ASR with ace() function on topo2, with only host plant families as character statesACE_PM_ER.topo2.png - ASR with ace() function on topo2, with only parasitic types as character statesACE_PMNH_ER.topo2.png - ASR with ace() function on topo2, with only parasitic types without hemiparasites as character states on ER matrixACE_PMNH_SYM.topo2.png - ASR with ace() function on topo2, with only parasitic types without hemiparasites as character states on SYM matrixASE_pruned_topo1_collapsed_HPPM_ER.pdf - ASR with Phytools make.simmap etc. on topo1. NA's were removed and bootstraps below thresholds were left polytomicASE_pruned_topo2_collapsed_HPPM_ER.pdf - same on topo2AHE_COI_2025_70coll.v2.grafting.monosp.contree - topo1 collapsed if bootstraps <70AHE_COI_2025.v2.grafting.monosp.contree - topo1host_plants.txt - table with host repertoire of each species (see Table S1)topo2_70coll.rooted.contree - topo2 collapsed if bootstraps <70topo2.rooted.contree - topo2 Raw data & sequences Raw target capture data and assembled AHE have been deposited in GenBank (NCBI) under the accession PRJNA1244829. COI sequences generated for the present study have been deposited on BOLD systems (pending).