Integrative species delimitation in the morphologically conservative Stegana subgen. Orthostegana (Diptera, Drosophilidae)

With the increasing number of cryptic species discovered in major branches of the subfamily Steganinae, accurate species identification is becoming challenging. Possible evolutionary stasis often gives rise to the formation of morphological conservatism and cryptic species, as is the case for the members of the Stegana (subgen. Orthostegana). In this study, the species boundaries of all Asian Orthostegana were accessed based on two mitochondrial genes [cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit 2 (ND2)] using different species delimitation methods and evolutionary models. By integrating morphological and molecular evidence, we clearly validated the evolutionary independence of all five known species and identified nine new species from Southwest China: Stegana (Orthostegana) aini Peng & Chen sp. nov., S. (O.) brevivittata Peng & Chen sp. nov., S. (O.) cuodi Peng & Chen sp. nov., S. (O.) fuscofemorata Peng & Chen sp. nov., S. (O.) latipalpula Peng & Chen sp. nov., S. (O.) macrostephana Peng & Chen sp. nov., S. (O.) mohnihei Peng & Chen sp. nov., S. (O.) obscurala Peng & Chen sp. nov., and S. (O.) pinguitia Peng & Chen sp. nov. Moreover, we discussed the relationship between the Asian Orthostegana lineage and the subgen. Oxyphortica, and the necessity of taxonomic re-evaluation for the Neotropical species with molecular data. The high morphological conservatism within Orthostegana is largely the outcome of in situ diversification for adapting to the ecological environment.