Phylogeography of the small grass yellow Eurema brigitta (Stoll, 1780) (Lepidoptera: Pieridae) unveils the existence of distinct taxa within the Palaeotropics

Eurema brigitta (Stoll, 1780) is one of the few butterfly species distributed in most of the Old World tropics. In 2017, we documented its occurrence in Socotra, a UNESCO World Heritage Site. Now, we clarify the origin of this specimen and further describe a phylogeographic pattern of this species by comparing Afrotropical, Malagasy and Oriental-Australian populations using the mitochondrial cytochrome c oxidase subunit I marker. We found a deep split between the Afrotropical and Oriental-Australian populations of this taxon, which are separated by the Indian Ocean and dry eremic habitats on the northern coasts. A less deep but significant split also exists between E. b. brigitta (Stoll, 1780) from mainland Africa and E. b. pulchella (Boisduval, 1833) from Madagascar and surrounding islands. The individual from Socotra clearly originates from Africa. In addition, in accordance with the genetic pattern and the known morphological evidence, we propose to transfer the Oriental-Australian populations into a separate species, Eurema drona (Horsfield, 1829) reinst. stat.