Gene Flow in the Mullerian Mimicry Ring of a Poisonous Papuan Songbird Clade (Pitohui; Aves)

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Pitohui

Mu¨ llerian mimicry rings are remarkable symbiotic species assemblages in which multiple members share a similar phenotype. However, their evolutionary origin remains poorly understood. Although gene flow among species has been shown to generate mimetic patterns in some Heliconius butterflies,mimicry is believed to be due to true convergencewithout gene flowinmany other cases.We investigated the evolutionary history of multiple members of a passerinemimicry ring in the poisonous Papuan pitohuis. Previous phylogenetic evidence indicates that the aposematic coloration shared by many, but not all, members of this genus is ancestral and has only been retained bymembers of the mimicry ring.Using a newly assembled genome and thousands of genomic
DNA markers, we demonstrate gene flow from the hooded pitohui (Pitohui dichrous) into the southern variable pitohui (Pitohui uropygialis), consistent with shared patterns of aposematic coloration. The vicinity of putatively introgressed loci is significantly enriched for genes that are important inmelanin pigment expression and toxin resistance, suggesting that gene flowmay have been instrumental in the sharingofplumagepatterns andtoxicity. These results indicate that interspeciesgeneflowmaybe amore general mechanism in generating mimicry rings than hitherto appreciated.