A clear split between eastern and western groups with signatures of gene flow between different subspecies.
In the 18th century, the French naturalist Georges-Louis Leclerc, Comte de Buffon published Planches Enluminées D’Histoire Naturelle, a collection of drawings from animals all around the world. One of these drawings depicted the “Merle des Philippines” (the Blackbird of the Philippines). Modern ornithologists know this species as the Hooded Pitta (Pitta sordida). This small passerine, which occurs from India to New Guinea, was generally considered a single species, but the phenotypic variation among different populations suggests this might not be the case. A recent study in the journal BMC Evolutionary Biology provides some genetic support for this idea.
The Hooded Pitta complex is comprised of numerous populations on different Indo-Pacific islands. These populations differ in several plumage traits, such as the color of the forehead and the crown, the amount of red, black and blue on the flanks and the belly, and the size of a white wing patch. Per Ericson and his colleagues tried to reconstruct the evolutionary history of these populations. They sampled the 13 recognized subspecies across the range of this species complex and sequenced their DNA. For interested readers, the genetic analyses were based on mitogenomes, 23 nuclear genes and about 2.1 million SNPs.
Reconstructing the evolutionary history of these colorful birds revealed two distinct groups that diverged about 2 million years ago. This split coincides to the Wallace Line, which highlights the striking differences in fauna and flora in the eastern and western parts of the Indo-Australasian archipelago. However, the origin of Wallace Line is much older than the split between the groups within the Hooded Pitta. The most likely scenario is that some birds dispersed across the Wallace Line during the Pleistocene (between 2.5 million and 11.000 years ago) when sea levels were lower.
The researchers could not find consistent patterns within the two groups. It seems that recent gene flow between different populations from the same subspecies has partly erased any geographic patterns in the genetic data. During the Pleistocene, fluctuations in sea levels resulted in occasional land-bridges between the different islands, allowing birds to hop from one island to the next. The consequent bursts of gene flow prevented island populations from diverging from one another.
There has also been some gene flow between different subspecies. One individual from the subspecies forsteni, which lives in the eastern part, showed signatures of gene flow from the western part. In addition, samples in the western clade, bangkana from Bangka Island and palawanensis from Palawan, exhibited signs of admixture. The bangkana individual appears to be admixed between the migratory population on the Asian mainland (cucullata) and nearby populations on Sumatra and Borneo (mulleri). The subspecies palawanensis harboured DNA from sordida and mulleri.
Ericson, P. G., Qu, Y., Rasmussen, P. C., Blom, M. P., Rheindt, F. E., & Irestedt, M. (2019). Genomic differentiation tracks earth-historic isolation in an Indo-Australasian archipelagic pitta (Pittidae; Aves) complex. BMC Evolutionary Biology, 19(1), 151.
This paper has been added to the Pittidae page.