Sex-specific microbiomes in the prothoracic depressions of oak ambrosia beetle (Platypus koryoensis) adults

Ambrosia beetles cultivate symbiotic fungi within specialized body structures called mycangia. They feed on these fungi rather than their plant host, making this association essential for nutrition and reproduction. Platypus koryoensis, an ambrosia beetle and a major vector of oak wilt in Korea, harbors these symbionts in sexually dimorphic prothoracic depressions. However, the bacterial and fungal communities within these structures have not been comprehensively analyzed. In this study, bacterial 16S and fungal internal transcribed spacer (ITS) metabarcoding were used to characterize these communities in female and male P. koryoensis adults. Bacterial alpha diversity did not differ significantly between sexes, but beta diversity analyses revealed compositional differences. Lacticaseibacillus, Leuconostoc, and Erwiniaceae taxa were more abundant in female beetles. Fungal communities in female adults exhibited significantly greater taxonomic and phylogenetic richness than those in male adults (p < 0.05), and compositional differences were identified between sexes. Raffaelea taxa were detected in both sexes but only in a few samples. Most fungal sequences were affiliated with yeast genera, including Candida, Ambrosiozyma, and Ogataea. Cyberlindnera and Chrysozyma were more common in females, whereas Ambrosiozyma was more abundant in males. This study represents the first metabarcoding-based characterization of microbial communities associated with P. koryoensis, and the sex-based comparison provides molecular evidence supporting a potential role of male prothoracic depressions as mycangia. Our findings highlight the importance of metabarcoding in understanding of the relationship between P. koryoensis and its microbial symbionts.