{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"institution":[{"name":"bioRxiv"}],"indexed":{"date-parts":[[2026,9,18]],"date-time":"2026-09-18T02:05:41Z","timestamp":1789697141281,"version":"4.0.1"},"posted":{"date-parts":[[2026,9,17]]},"group-title":"Evolutionary Biology","reference-count":0,"publisher":"openRxiv","license":[{"start":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T00:00:00Z","timestamp":1789603200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"award":["#R35GM119816"],"award-info":[{"award-number":["#R35GM119816"]}],"id":[{"id":"https:\/\/ror.org\/01cwqze88","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"accepted":{"date-parts":[[2026,9,17]]},"abstract":"<jats:p>\n                  Macroparasites are among the most important agents of natural selection in their host populations, but anti-macroparasite immunity is poorly understood. Vinegar flies (Drosophilidae) and the parasitoid wasps that infect them are emerging models to study how animals defend against macroparasite attack. The canonical anti-parasitoid immune mechanism in insects is melanotic encapsulation, which involves cell-mediated encapsulation coupled with prophenoloxidase (PPO)-mediated melanization of parasitoid embryos. Recently, we discovered the horizontal transfer (HGT) of a bacterially-derived humoral anti-parasitoid effector, Cytolethal distending toxin B (CdtB), across insects, including four drosophilid lineages. Here, we assessed the prevalence of these two anti-parasitoid immune mechanisms in 406 drosophilid and four outgroup species. We found that melanotic encapsulation was relatively uncommon among species with known anti-parasitoid immune responses. While\n                  <jats:italic>PPO<\/jats:italic>\n                  duplications were found in 88 species, the most salient\n                  <jats:italic>PPO<\/jats:italic>\n                  gene underlying melanotic encapsulation,\n                  <jats:italic>PPO3<\/jats:italic>\n                  , was restricted to\n                  <jats:italic>Drosophila melanogaster<\/jats:italic>\n                  and its close relatives.\n                  <jats:italic>PPO<\/jats:italic>\n                  genes were present in lower copy number per genome in the Drosophilidae than in outgroup lineages and evolved slowly. We found\n                  <jats:italic>cdtB<\/jats:italic>\n                  in the genomes of 93 species and estimated at least 11 independent\n                  <jats:italic>cdtB<\/jats:italic>\n                  gains across the Drosophilidae as early as ~44 mya and as recently as ~6 mya.\n                  <jats:italic>cdtB<\/jats:italic>\n                  acquisition was subsequently associated with higher net diversification rates in some clades. We conclude that humoral immune effectors may play a more important role than previously appreciated in anti-parasitoid immunity in insects and that an immune innovation arising repeatedly from HGT is potentially associated with the evolutionary success of these animals.\n                <\/jats:p>","DOI":"10.64898\/2026.09.15.751804","type":"posted-content","created":{"date-parts":[[2026,9,18]],"date-time":"2026-09-18T01:55:12Z","timestamp":1789696512000},"source":"Crossref","is-referenced-by-count":0,"title":["Horizontal gene transfer rivals gene duplication as a source of anti-parasitoid immune innovation in the Drosophilidae"],"prefix":"10.64898","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-5675-8513","authenticated-orcid":false,"given":"Rebecca L","family":"Tarnopol","sequence":"first","affiliation":[{"name":"University of California, Berkeley; University of California, San Francisco;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0001-9270-4915","authenticated-orcid":false,"given":"Ryan L","family":"Wang","sequence":"additional","affiliation":[{"name":"University of California, Berkeley;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5025-1292","authenticated-orcid":false,"given":"Bernard Y","family":"Kim","sequence":"additional","affiliation":[{"name":"Princeton University"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1448-4678","authenticated-orcid":false,"given":"Noah K","family":"Whiteman","sequence":"additional","affiliation":[{"name":"University of California, Berkeley;"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","container-title":[],"original-title":[],"link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.64898\/2026.09.15.751804","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,18]],"date-time":"2026-09-18T01:55:12Z","timestamp":1789696512000},"score":1,"resource":{"primary":{"URL":"http:\/\/biorxiv.org\/lookup\/doi\/10.64898\/2026.09.15.751804"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,17]]},"references-count":0,"URL":"https:\/\/doi.org\/10.64898\/2026.09.15.751804","relation":{},"subject":[],"published":{"date-parts":[[2026,9,17]]},"subtype":"preprint"}}