April 14, 2015 | News

Congratulations!

On April 13, 2015 Felix Ringelhan, a doctoral student at the MPIDR, has successfully defended his PhD at the University of Hannover. His dissertation focused on the aging processes of various basal animals, particularly Cnidaria.

The freshwater polyp Hydra does not senesce, thus it is potentially immortal. But what about Hydra’s close relatives, are they non-senescent, too? And, what are the reasons behind non-senescence? These are questions Felix Ringelhan has addressed in his dissertation. Hydra’s mode of life differs from that of other taxa of the same animal class. The polyp is usually sessile (i.e., sedentary), secured to the ground by an adhesive foot called basal disc. It reproduces asexually by budding and cell division.

But many Hydra relatives in the animal kingdom have varying life-cycles, passing through different stages of life: Initially, they are polyps and produce small medusae by budding. These in turn reproduce sexually and produce larvae that develop into sessile polyps.

Felix Ringelhan looked at one of these relatives, Eleutheria dichotoma, over a period of three and a half years. This taxon has a remarkable feature: Medusae reproduce themselves asexually – similar to their polyps and Hydra – but also sexually.

He found out that adult polyp colonies of the cnidarian practically do not do not senesce at all, as with Hydra. But it is a different matter with larvae and young polyps still small. These died within the shortest of time. The medusa, by contrast, showed a peculiar form of aging: an increasing risk of mortality for the young medusae and a declining risk for the older medusae. “In this study we could show that there are varying aging patterns at different levels within the same species. And, non-senescence in the polyp Hydra does not seem to be the exception, it is rather likely that this aging pattern is widespread among lower-level organisms,“ says Felix Ringelhan.