Voucher photos lice Sapayoa Myrsidea

Parasites can provide powerful insights into host evolution and biogeography. The bird Sapayoa aenigma, the only Neotropical member of the otherwise Old World clade Eurylaimides, has long puzzled ornithologists due to its phylogenetic placement and uncertain biogeographic origin. To shed light on this puzzle, we investigated the evolutionary origin of a louse in the genus Myrsidea found on Sapayoa. Using genome-wide data from 92 Myrsidea specimens sampled across oscine, suboscine, and non-passerine hosts, we reconstructed a global phylogeny to evaluate hypotheses about the origin of Sapayoa and its parasite. Phylogenomic, molecular dating, and cophylogenetic analyses support a scenario in which the Myrsidea lineage on Sapayoa originated outside the Neotropics and was acquired via host-switching from an Old World oscine. The parasite’s divergence time (24.4–17.9 Ma) postdates the estimated split between Sapayoaand other Eurylaimides, ruling out strict codivergence. Ancestral host reconstruction supports an oscine origin and Old World acquisition, while biogeographic reconstruction yielded nearly equal probabilities for Neotropical and Afrotropical origins, highlighting uncertainty in its ancestral range. Taken together, these findings support a co-dispersal scenario in which Sapayoa acquired its parasite in the Old World and brought it to the Neotropics during colonization. This parasite-based perspective provides novel support for the Old World origin (colonizer) hypothesis for Sapayoa. More broadly, our study highlights the value of permanent parasites as complementary tools for disentangling complex evolutionary and biogeographic histories.