Two types of stress in the ocean

Tübingen researchers discover that many marine animals use the stress hormone noradrenaline

Figure 1 From left to right: an annelid worm, a penis worm, and an acorn worm. These animals are very distantly related to each other but all have the stress hormone noradrenaline, previously known only to exist in vertebrates. Credit: John Gerhart acorn worm image; Mattias Hogvall penis worm image.

Figure 2 A juvenile Platynereis dumerilii worm. Credit: Jürgen Berger

Tübingen, 1st of February 2017. When we are stressed, our heart beats faster we become agitated and start sweating. This reaction is caused be a small molecule called noradrenaline that is released when we are under stress. It exerts its action by binding to specific receptor molecules, the so-called adrenergic receptors.

So far, noradrenaline and the adrenergic receptors were only known to exist in vertebrates like us. In contrast, invertebrates were thought to use different stress hormones. It was known from the fruit fly that it shows typical signs of stress when octopamine, a molecule that is very similar to noradrenaline, binds to octopamine receptors in its nervous system.  Therefore, it was generally accepted that stress responses in vertebrates are mediated by noradrenaline and adrenergic receptors, but in invertebrates by octopamine and octopamine receptors.

Researchers from the Max Planck Institute for Developmental Biology in Tübingen now made a surprising discovery. When studying a marine ragworm, Platynereis dumerilii, they found that it has both types of receptors, and concluded that is must also have both hormones. Extending their research, they found the same situation in other marine animals, including an acorn worm (hemichordate) and a penis worm (priapulid). Although these marine animals all look like worms, they belong to very distantly related groups of animals. From this data, it is apparent that the last common ancestor of these marine worms, ourselves, and fruit flies – an animal that lived approximately 550 million years ago – must already have had both stress hormones. Subsequently, during evolution we lost octopamine and its receptor, while the fruit fly lost noradrealine and the adrenergic receptors.

These exciting results show that studying marine worms – animals that often evolve more slowly – can yield interesting insights into the evolution of the nervous system. Further studies could clarify why there are two systems that are so similar and if both of them were initially related to stress.


Philipp  Bauknecht and Gáspár Jékely: Ancient coexistence of norepinephrine, tyramine, and octopamine signaling in bilaterians. BMC Biology, 2017; 15:6


Gáspár Jékely
Max Planck Institute for Developmental Biology
Phone: +49 (0)7071 601-1310
E-Mail: gaspar.jekely(at)


Nadja Winter (Pressereferentin)
Phone: +49 (0)7071 601-444
E- Mail: presse-eb(at)