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Eyes on stalks

Posted on 06-08-2012 by Astrid Kromhout

One of the animal groups under scrutiny of the researchers during the Borneo expedition, are the stalk-eyed flies. An intriguing lot, like their name. Their eyes are on stalks, sometimes even longer than their bodies. This seems very awkward. What could be the evolutionary advantage? Dr. Hans Feijen explains: The longer the stalks of the male flies, the more attractive they are to the females. Size matters but just a little differently. To impress the females, males position themselves with their stalks outstretched opposite eachother. Whoever has the largest, wins the female. In some species, the male can even obtaina whole harem as a reward. A typical case of sexual selection.

Labyrinth Hans and his wife Cobi Feijen have been working on stalk-eyed flies for more than forty years, starting in 1971. Since then, this unassuming couple with great perseverance have become the worldwide experts on Diopsidae stalk-eyed flies.Several people have tried to fathom the systematics of stalk-eyed flies, but they gave up, riddled by the complexity. Others only work in a certain region. Its a labyrinth, says Hans. It almost sounds like a sigh. At the moment, some 300 species have been described. 400 species have been recognized, but not described yet.And then of course there are the species still unknown to science. Only yesterday we received some boxes from Uganda and Togo. They contained at least 4 or 5 new species, Cobi says. They are also dealing with flies that have been incorrectly described in the past. It truly is a labyrinth Is it still fun? Without hesitation: Yes. This becomes even clearer when they reveal what they are going to do in Borneo.

Teleopsis pallifacies, Sabah (photo Stephen Gaimari)

Teleopsis pallifacies, Sabah (photo Stephen Gaimari)

Ageing flies The main target is looking for endemic species on the mountaintops and their direct relatives in the lower regions. Drawing conclusions on evolution in this extremely rich region is the main research question for all the scientists on this expedition. But Hans has some extra questions. We are originally ecologists, so our questions are broader than taxonomy alone. For example the life history of these flies. In Asia, species produce up to 5 or 6 generations per year, while species in Africa produce only one generation per year. On the other hand, there is one stalk-eyed fly in Borneo that can live up to 1,5 years. How is that possible? Does this have to do with the parasite fungi on the flies, which are killing them? Do the ageing flies in Borneo lack these fungi, or did they find a way to live happily together? We would like to answer these kinds of questions. They also want to know more about the habitat of the Asian flies. We dont know a lot about that yet. The nice thing about this expedition is, that also botanic experts are joining. We can ask them in the field about the plants in the areas the flies live.

God of the flies For this kind of research, they will take a large amount of specimens. Fresh specimens are necessary for DNA research which will take place at the Naturalis barcoding laboratory. And it just so happens that their daughter Frida is working there. The love of biology and of these stalk-eyed flies was clearly passed on by her parents. Frida also made the illustration of the stalk-eyed fly with the largest stalks of the entire family: Teleopsis belzebuth , nicknamed the God of the flies. This species lives in Borneo, and the Feijens would like to find it. And, as many other researchers, they think they will come across a number of new species on this expedition. In fact, the labyrinth will only continue to grow.

All blogposts on the Borneo expedition can be found here.