Island of Contrasts - Fieldwork on Réunion

It has barely struck eleven a.m. and it's already 29 degrees, with over 90 percent humidity. The air is so dense you could cut it with a knife. The first clouds are gathering and, within an hour, it will rain cats and dogs for six long hours. It is January – midsummer on La Réunion. 


Ralf Sommer, Director of the Department for Integrative Evolutionary Biology, and his Project Leader Matthias Herrmann, who is in charge of the research station on La Réunion, landed with their team at 6 a.m. at the island's busy airport. The biologists have come a long way. They have flown 9000 kilometers from the MPI for Developmental Biology in Tübingen to this island 800 kilometers east of Madagascar in the Indian Ocean, to collect specimens of an unusual research subject: a nematode or threadworm less than a millimeter long, the Pristionchus pacificus.


Since 2008 the scientists have worked on the tropical island, once famous for its vanilla and called Île Bourbon. La Réunion, the youngest of the three islands in the Mascarene chain, rose out of the Indian Ocean around two million years ago. On its southeast end one of the most active fire-breathers on earth still threatens. The main volcano, though, burned out some 150,000 years ago after a major eruption, leaving behind the 3,070-meter-high Piton des Neiges and three deep crater valleys, the Cirques. This means that nothing which lives here can be more than two million years old. According to Ralf Sommer, this makes the island a unique open-air laboratory for evolution research.


La Réunion or "Island of Gathering": a fitting name, for here the worldwide variety of Pristionchus pacificus types meet, the cosmopolitans in this group of threadworms. The worms arrive as stowaways on beetles. They arrive from all points of the compass and at various times, but primarily with favorable winds from distant Asia. And from that point on, each develops together with "its" insect.

Having just arrived on the island, the biologists now drive their rental cars to the next supermarket, where everyone stocks up with provisions for the next few days, and with batteries for the so-called "light catch" which will now take place every evening. When this is taken care of, the scientists head for their actual destination. 

In the Max Planck research container in the port town of Le Port, directly behind the insectarium, everything is in motion. Ralf Sommer's co-workers pour nutrient solution into countless Petri dishes – the temporary homes for the catch of the day. In the container two air conditioners are running, otherwise the heat would be unbearable and the threadworm cultures would shrivel up. Now the biologists' principal task begins: the collected beetles must be dissected, and the biologists must wait for this until the threadworms come off of the beetles. Now begins the struggle against mites and maggots, which also like to get some of the beetles' remains.

The researchers allow themselves a short pause, eat their ready-made meals, and get a quick breath of fresh air outside the container. But not for long!

Matthias Herrmann was only outside for a quarter of an hour, and his shoulders have already begun to turn a threatening shade of red. Following the work in the container, it's time to change from lab coat and shoes to rain ponchos and rubber boots, and put the lighting equipment in the car – the next light catch Is about to begin. White fabrics are stretched out and illuminated. This is how the insects which transport the threadworms are lured.

Over the 12-day visit, various destinations on the island will be visited and a variety of scientific questions will be addressed. Jan Mayer, a doctoral student in the Department, studies the beetles' decomposition and succession of threadworms in the soil, mainly in Trois Bassins, on the western part of the Island. The postdoc Eduardo Moreno studies the worms' adaptation to the various oxygen levels in high-elevation populations. And Mark Leaver, postdoc with Tony Hyman at the MPI in Dresden, studies the temperature adaptation of the threadworms in various ecozones across the island. The threadworms collected from the captured beetles are all finally brought back to Tübingen, where they are further characterized and distributed among colleagues. Scarcely has the year's "plunder" been processed before it is once again time to prepare for the next research trip.

Text: Catarina Pietschmann, Nadja Winter