Press release: Living fossils with modern limbs

Nr. 24/2015 - 05.02.2015

Göttingen developmental biologists find modern gene regulation in prehistoric onychophorans (velvet worms)

(pug) Over the course of evolution, living creatures developed from simple unicellular organisms into highly specialised life forms with complex organ systems. To date, research had assumed that the genetic steering mechanisms in these living organisms were originally very simple and became more and more complex over the course of evolution. A team of researchers from the Universities of Göttingen and Uppsala was thus quite surprised when they investigated the genetic developmental mechanisms in prehistoric onychophorans and hardly found noteworthy differences to the gene regulation of modern-day arthropods and onychophorans. The findings were published in Evolution & Development.

Zoologists consider onychophorans to be living fossils. They are worm-like animals with short, stumpy limbs that enable their movement. “Roughly 500 million-year-old fossils prove that onychophorans existed even long before the dinosaurs and have hardly changed since that time,” explains Dr. Nikola-Michael Prpic-Schäper of the Göttingen Centre for Molecular Biosciences and co-author of the study. The limbs of onychophorans, a phylum currently only extant in South America, South Africa and Australia, are short, fat and unjointed and therefore only suitable for slow crawling. By contrast, the limbs of arthropods are highly developed, allowing them to jump, run and grasp their prey. “That was why we were expecting there to be major differences in the genetic mechanisms of limb development between arthropods and onychophorans. We thought that we would find only a few and extremely simple gene regulations in the onychophorans,” acknowledged Dr. Ralf Janssen, lead investigator at the University of Uppsala.

To their surprise, the researchers hardly found appreciable differences. “The mechanism that initiates the limb patterning and jointing in arthropods runs a virtually identical course in the limbs of onychophorans – only that the limbs of these velvet worms do not have any joints,” explains Dr. Janssen. At the genetic level, in other words, the onychophorans have everything a creature needs to generate highly developed limbs, but apparently do not make use of this capability. “Even though this appears illogical, it gives us insights into how evolution works. The short onychophoran limbs are a type of precursor to arthropodian legs. Onychophorans possess the genetic stuff to grow more developed limbs, but do not utilise it because their habitat under stones and in marshland areas does not require it,” Dr. Prpic-Schäper continues. “The ancestors of the onychophorans passed on their capability to the first arthropods, who knew how to utilise this gift to the benefit of their own survival. Today, around 200 species of onychophorans exist, whilst arthropodian species number over 10 million.”

Original publication: Janssen et al. Aspects of dorso-ventral and proximo-distal limb patterning in onychophorans, Evolution & Development. Doi: http://onlinelibrary.wiley.com/doi/10.1111/ede.12107/full

Contact address:
Dr. Nikola-Michael Prpic-Schäper
Georg-August-Universität Göttingen
Johann-Friedrich-Blumenbach
Institute for Zoology and Anthropology
Department of Developmental Biology
Justus-von-Liebig-Weg 11, 37077 Göttingen
Phone +49 (551) 39-20817
E-mail: nprpic@uni-goettingen.de
Website: www.uni-goettingen.de/de/ag-dr-nikola-michael-prpic-sch%C3%A4per/55110.html