Peripatopsis balfouri (Peripatopsidae) from South Africa
About Onychophora
Copyright © 2006-2011 by Georg Mayer. All rights reserved.

Current Research Topics

Topic A: Species diversity, taxonomy and phylogeography of Onychophora

Currently, the phylogeny and taxonomy of Onychophora is understudied and the estimated number of 180-200 described species and subspecies apparently does not reflect the actual diversity of the group. In collaboration with other scientists, I therefore apply morphological and molecular methods (involving both mitochondrial and nuclear gene sequences) to study the species diversity, cryptic speciation and phylogeography of Onychophora, which show a disjunct distribution dating back to the break-up of Gondwana (Allwood et al. 2010; Braband et al. 2010). Our taxonomical work involves revisions and descriptions of new species (Mayer 2007; Oliveira et al. 2010).

Topic B: Anatomy and life history of Onychophora

Morphological characters are important for reconstructions of the onychophoran and arthropod phylogenies. My research therefore focuses on the internal and external anatomy of velvet worms (visual organs, nervous system, reproductive, excretory, muscular and locomotory systems) and its implications for the life history of Onychophora and Panarthropoda (Mayer & Koch 2005; Mayer 2006a; Mayer 2006b; Maas et al. 2007; Mayer & Harzsch 2008; Mayer & Tait 2009; Mayer et al. 2010; Oliveira et al. 2010).

Topic C: Evolution of animal body plans

Onychophorans are of pivotal importance for understanding animal evolution. In collaboration with other scientists, I use cutting edge sequencing technologies to analyse the embryonic transcriptome of a representative of Onychophora. Our main objective is to characterise the genes that control body segmentation and nervous system development in comparison to other animals. Our data will clarify the phylogenetic position of velvet worms and help us to understand how new animal body plans evolved.

Topic D: Arthropod phylogeny and the position of myriapods

Currently, there are two competing hypotheses on the phylogenetic relationships within the arthropods. According to the Mandibulata hypothesis, myriapods (centipedes, millipedes, and allies) are the closest relatives to crustaceans and insects. Some recent analyses of molecular data, however, have challenged this traditional view and instead propose a close relationship of myriapods to chelicerates (spiders, scorpions, and allies). This concept is known as the Paradoxopoda or Myriochelata hypothesis. In order to help clarify the phylogenetic position of myriapods, I focus on embryogenesis and development of the nervous system in Onychophora since they are the closest relatives of arthropods and a useful outgroup for character polarization among the panarthropods (Mayer & Whitington 2009a).

Topic E: The arthropod “head problem”

Understanding the composition of the arthropod head has caused much controversy in the past and remains one of the most contentious issues in the fields of comparative morphology and developmental biology. As the closest relatives of arthropods, onychophorans play an important role in this debate. Hence, studying the anterior body region in these animals might provide helpful insights for resolving the arthropod head problem. My aim is therefore to study the structure and development of the onychophoran “head” and associated structures and organs by using neurobiological, cytological and immunohistochemical techniques, in conjunction with gene expression studies, confocal laser scanning microscopy and electron microscopy (Mayer & Koch 2005; Mayer et al. 2005; Mayer et al. 2010).

Topic F: Mesoderm development in Onychophora

According to the traditional Articulata hypothesis, segmentation represents a synapomorphy of annelids and panarthropods. The homology hypothesis of segmentation is mainly based on serially arranged coelomic cavities and nephridia. However, this support is ambiguous since coelomic cavities are lacking and nephridia are strongly modified in most arthropods. In the light of recent phylogenetic analyses based on molecular data, segmentally arranged nephridia and coelomic cavities either arose convergently in annelids and arthropods or represent an ancestral feature of protostomes or even bilaterians. Among the panarthropods, the onychophorans are traditionally considered to share the majority of morphological correspondences with the annelids. In order to contribute to the current discussion on the phylogenetic position of Panarthropoda, I focus on mesoderm development in Onychophora (Mayer et al. 2004; Mayer et al. 2005; Mayer & Koch 2005).