Tess Renahan from the Max Planck Institute for Biology in Tübingen has been awarded this year's PhD prize of the Reinhold and Maria Teufel Foundation. Using nematodes as model organisms, Renahan significantly advanced our understanding of the complex dynamics between different species and how their interactions influence development. The award ceremony took place on July 13 at the University of Tübingen.
Nematodes, ubiquitous worms only a millimeter in length, are prime examples of how organisms adapt to different conditions within a single life span. This makes their interplay with other organisms and the influence of these interactions on worm development particularly interesting.
In her dissertation, Tess Renahan studied nematodes closely associated with scarab beetles. The worms live on the beetles in an arrested developmental state that allows them to survive harsh conditions like lack of food or dense populations. When the beetle dies, the worm comes out of its stasis to feed on microbes that populate the carcass of the beetle.
Renahan investigated the complex ecosystem that ensues the beetle’s death. Together with her collaborators, she observed the populations of Pristionchus pacificus nematodes and microbes on the beetle carcasses for two years. The researchers saw periodic shifts in the composition of the worm population: whenever there were relatively few microbes on the carcass, the nematodes in stasis were the majority, though with many microbes present, feeding worms dominated. Arrested worms either left the carcass in search of better conditions or remained on the carcass indefinitely. This pattern was independent of which types of bacteria were present. “These interactions were previously not studied in the field; since they happen underground, they are extremely hard to observe”, says Ralf Sommer, Renahan’s PhD advisor.
“The smallest Worme will turne, being trodden on.”
But there is more to interactions between the worm and its environment. Early on in its life, each Pristionchus pacificus worm develops one of two drastically different mouth forms that determine its way of life: one mouth form restrict the worm to a bacteria-based diet, the other one allows them to prey on other nematode species. “It is striking that all worms coming out of the arrested stage became predatory”, says Renahan. “This, in combination with the observed dispersal behaviors, shows that ecologically relevant survival strategies involve changes in physiology in response to environmental cues.”
In further work, Renahan and Sommer studied the survival strategies of the related species Pristionchus mayeri. These nematodes strongly tend to develop a mouth form that restricts them to a bacterial diet, even under a variety of lab conditions. However, the researchers discovered that in the wild, Pristionchus mayeri worms develop the predatory mouth form when competing over food with many other nematodes.
“The smallest Worme will turne, being trodden on”, their publication quotes William Shakespeare. “This astute observation describes our results fittingly”, comments Renahan. “Indeed, the ability to change one’s physiology is a beneficial strategy in the face of competition and is employed by copious creatures.”
The PhD Prize of the Reinhold and Maria Teufel Foundation is awarded yearly to several PhD graduates for particularly outstanding dissertations in the fields of biology and law. It is endowed with 5000 euros.