Sulawesi birds under TCBR scrutiny

Two members of the TCBR, Dr David Kelly and Dr Nicola Marples, have been leading expeditions to a set of remote Indonesian islands since 1999, facilitated by Operation Wallacea. The latest expedition was a breakthrough as we now have a Material Transfer Agreement with a university in Sulawesi allowing us to bring home feather samples for DNA and stable isotope analysis. Our archipelago, called the Wakatobi islands, turns out to be fascinating because, like the Galapagos, each island is evolving its own sister species of bird. The first birds we looked at were lemon-bellied white-eyes (see Fig 1) on each of the four main islands. Immediately on one of the islands we found an undescribed species which is not even closely related to the white-eyes it flocks with (Fig 2), and a full description of this species is now underway. The phylogenies of the other white-eyes are under construction but our initial analysis of haplotypes, together with morphometric data, suggests that each island contains a unique population of lemon-bellied white-eyes, which is not inter-breeding with the birds on any other of the islands. Similarly the olive-backed sunbirds (Fig 3) are no longer inter-breeding between the most northerly two islands in the chain and the two most southerly, and it’s a similar pattern for the grey-sided flower-peckers (Fig 4).

This is particularly surprising as the islands are close together (less than 10 km apart), easily close enough for any of these birds to fly regularly between them, but the lemon-bellied white-eye, in particular, seems to arrive at an island and settle down for the duration. Once settled, there does not appear to be any mixing with other populations, even on the most closely neighbouring islands. Such examples of speciation in progress are very rare and offer unique opportunities to study the process of evolution in detail.    

The work is planned to continue, and will be taken into a broader phase by our new PhD student, Sean Kelly. His project will look in detail at the three species mentioned above, and their behavioural interactions, diet and ecology. All three species compete for nectar to some extent, but their relative numbers differ widely on the different islands, making their interactions particularly interesting as a potential driver of speciation. Together with the genetic and morphological data already collected, this type of information will allow us to explore the reasons for divergence of these populations on the four islands of the Wakatobi.