Genetic analyses detect three main clades in Indo-Africa, Asia and Australasia.
It only took the genus Zosterops – or white-eyes – about 3 million years to diversify into more than 100 species. Indeed, Jared Diamond referred to these birds as “great speciators”. On this blog, I have covered a few studies on the evolution of particular species (see for example here and here). However, the large-scale phylogeny of the white-eyes remains largely unresolved. Many species are morphologically indistinguishable, making it difficult to determine evolutionary relationships. Moreover, several species of white-eye are known to hybridize, potentially complicating phylogenetic analyses. Resolving the white-eye phylogeny is thus a challenging endeavor. But that did not scare off Chyi Yin Gwee, Kritika Garg, Balaji Chattopadhyay and their colleagues from taking a genomic approach. Their findings recently appeared in the journal eLife.
Three Clades
The researchers extracted DNA from historical and recent samples, representing 33 species from the southern hemisphere. Using specific RNA-probes, they sequenced more than 800 loci across the genome. A variety of phylogenetic methods converged on the same evolutionary tree, showing three main clades that correspond to Indo-Africa, Asia and Australasia. However, the phylogenetic relationships between these three clades could not be resolved confidently. This lack of resolution at the base of the phylogeny can be explained by a rapid succession of speciation events or ancient hybridization. More detailed analyses are needed to untangle this complex web.

Introgression and Conservation
In the figure above, you might have noticed two species without a color: Black-capped White-eye (Z. atricapilla) and Hume’s White-eye (Z. auriventer). The phylogenetic position of these species – which can be found on the Sunda Islands – could not be determined as different methods gave different results. Additional analyses pointed to introgression with other species. Specifically, the sharing of genetic variation between the Sundaic species and two Australasian species – the Sangkar White-eye (Z. melanurus) and the Shy-bellied White-eye (Z. citrinella) – suggests ancient introgression between the ancestors of these species. In other words, it’s complicated. These results also question whether the evolutionary history of white-eyes can be captured in a bifurcating tree. A network approach might be more suitable.
Finally, the researchers noted that all three main clades overlap in the Indonesian archipelago, indicating that this area is an evolutionary hotspot for the diversification of the genus Zosterops. This finding has important consequences for conservation.
The identification of areas in western Indonesia as a major center of modern phylogenetic diversity not only contributes to their recognition as an arena of important evolutionary processes, but also elevates their status as a region of global conservation relevance.
References
Gwee, C. Y., Garg, K. M., Chattopadhyay, B., Sadanandan, K. R., Prawiradilaga, D. M., Irestedt, M., … & Rheindt, F. E. (2020). Phylogenomics of white-eyes, a ‘great speciator’, reveals Indonesian archipelago as the center of lineage diversity. Elife, 9, e62765.
Featured image: Black-capped White-eye (Zosterops atricapilla) © Lip Kee | Wikimedia Commons