Research

Onychophorans are ancient animals, which show a disjunct distribution dating back to the break-up of Gondwana. However, the phylogeny and taxonomy of Onychophora is largely unresolved and the number of less than 180 described species certainly does not reflect the actual diversity of the group. We therefore apply morphological, molecular and cytological methods to explore the species diversity, cryptic speciation, phylogeny and geographic distribution of Onychophora. Our taxonomical work involves revisions and species descriptions.

Onychophorans (velvet worms) produce an extremely sticky slime secretion, which they use for prey capture and defence. Preliminary analyses of this protein-rich secretion revealed a great potential of its adhesive properties, but our knowledge of its composition is still limited. We therefore apply biochemical and biomechanical methods to analyse the composition and properties of the onychophoran slime in collaboration with researchers from the Institute of Biochemistry of the University of Leipzig and the Max Planck Institute of Colloids and Interfaces in Golm/Potsdam. Our results will provide insights into the function of this biological adhesive and serve as a basis for synthesising new adhesive peptides, which will be of potential interest for medical and industrial applications.

The ability to perceive light and to process visual information is widespread among animals. Opsin proteins are prerequisites for light perception, as they initiate the phototransduction cascade by absorbing light. To understand the evolutionary history of these proteins and the origin of colour vision in arthropods, we explore the opsin genes in the closest arthropod relatives, the velvet worms (Onychophora) and water bears (Tardigrada). In collaboration with the Lund Vision Group (Lund University, Sweden), we further apply behavioural, anatomical and electrophysiological methods to analyse the visual properties of the onychophoran eye. These studies will provide insights into the evolution of vision and the origin of colour vision in Panarthropoda (Onychophora + Tardigrada + Arthropoda).

The phylogenetic position of tardigrades (water bears) is still controversial, as they are regarded as either the sister group to Arthropoda, to Onychophora, to Onychophora + Arthropoda, or to one of the cycloneuralian taxa, such as Nematoda. Although tardigrades, similar to extant onychophorans and fossil lobopodians, have unjointed limbs, their nervous system shows a segmental organisation resembling that of arthropods. To clarify the phylogenetic position of tardigrades and the ancestral organisation of the nervous system in Panarthropoda, we focus on neural anatomy and development in tardigrades.

In contrast to arthropods, which are characterised by jointed, articulated limbs (arthropodia), onychophorans and tardigrades have unjointed appendages (lobopods) that are also found in fossil lobopodians. To clarify the evolution of the articulated limbs from an ancestral unjointed appendage in the arthropod lineage, we analyse functional anatomy and development of limbs in extant onychophorans and tardigrades. In addition, we focus on the anatomy of limbs in Cambrian lobopodians, which might help reconstruct the transformational steps in the evolution of limbs.

The number of leg pairs in onychophorans varies from 13 to 43, depending on the species and sex. To clarify how these segmental appendages are coordinated during locomotion, we perform extracellular recordings on the onychophoran nervous system. The results of these experiments, which we carry out in collaboration with Prof. Paul A. Stevenson (Institute of Biology, University of Leipzig), will help us to understand the ancestral control mechanisms of locomotion in panarthropods.

Currently, there are two competing hypotheses on the phylogenetic relationships of arthropods. According to the Mandibulata hypothesis, myriapods (centipedes, millipedes and allies) are the closest relatives of crustaceans and insects. However, embryologic evidence and analyses of some molecular datasets have challenged this traditional view and instead suggest a sister group relationship of myriapods to chelicerates (Paradoxopoda/Myriochelata hypothesis). To resolve this controversy and to clarify the phylogenetic position of myriapods, we currently focus on the embryology of onychophorans and tardigrades, as these taxa comprise useful outgroups for character polarisation (ancestral versus derived) among arthropods.

An organisation of the body into serially repeated units or segments is found in distantly related animal groups, including chordates, annelids and arthropods. There is a long history of debate about whether segmentation in these groups has evolved once, twice, or several times in parallel. The assumption of a single origin suggests that the last common bilaterian ancestor was a segmented animal and that segmentation was lost several times independently among bilaterians. In contrast, the hypothesis of multiple origins proposes a gradual evolution of segmentation in each lineage of segmented animals. As one of the closest arthropod relatives, onychophorans play an important role for understanding the evolution of segmentation in panarthropods, as their body shows both segmental and non-segmental features. To clarify the evolutionary history of segmentation in Panarthropoda, we analyse the expression patterns of various segmentation genes, including pair-rule and segment polarity genes, in the onychophoran embryo.

A universal feature of arthropods is the regionalisation of the antero-posterior body axis into distinct functional modules (e.g. head, thorax and abdomen) – a process known as tagmosis. During embryonic development, the regionalisation is mediated by the Hox genes, the expression of which correlates with the identity of tagmata in different arthropod groups. In contrast to arthropods, onychophorans and tardigrades display a less distinct regionalisation of the body, which is why the study of these animals might provide insights into the evolution of tagmata in arthropods. We therefore analyse the expression patterns of Hox genes in onychophorans and tardigrades, which will help us to understand the diversification of body plans in arthropods.

Understanding the composition of the arthropod head has caused much controversy in the past and remains one of the most contentious issues in zoology. The study of the anterior body region in the closest arthropod relatives, thus, might provide useful insights into the cephalisation process in panarthropods. We therefore analyse the organisation of the anterior end in Cambrian lobopodians as well as the anatomy and development of the "head" in extant onychophorans and tardigrades by performing neurobiological, immunohistochemical and gene expression experiments.

Onychophorans or "velvet worms" are close relatives of arthropods and, therefore, of pivotal importance for understanding the evolution of arthropods. Extant onychophorans share ancestral features with the Early Cambrian lobopodians, such as unjointed limbs, simple ocellus-like eyes, and a soft body without an exoskeleton. Notably, the segmentation and regionalisation of the body is also less advanced in these animals as compared to arthropods. Hence, analysing the entire genome of our "model onychophoran" Euperipatoides rowelli will provide insights into the evolution of Panarthropoda (Onychophora, Tardigrada, and Arthropoda). This project is part of a larger initiative to sequence many insect and arthropod genomes within the framework of the i5k initiative.