Sensing from both ends - transformation of formerly locomotory into sensory arthropodia in terminal trunk segments of centipedes

• Applicant: Privatdozent Dr. Carsten Müller, since 11/2018
• Subject Area: Systematics and Morphology (Zoology)
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 310332836

The arthropodium has adapted many different shapes and is thus able to perform a vast of different functions. It therefore represents a, or probably even THE, key innovation of the Arthropoda. Among the four main euarthropod taxa, trunk legs, primarily used for locomotion, were transformed convergently into appendages of derived functions. The modification of arthropodia was linked to subdivision of specialized body parts (tagmata). Therefore, they are considered excellent study models to understand paths of adaptive evolution. Examples underlining the enormous evolutionary morphological plasticity of arthropodia are mouthparts, forcipules, antennae, or raptorial legs. The morphology, function and development of these legs were generally well documented on the head and anterior half of the trunk. However, much less is known of the transformations that shaped non-locomotory appendages of the posterior part of the trunk (exceptions: cerci and ovipositors of hexapods). This gap of knowledge appears astonishing as exactly those appendages inserting at the posterior tip of the body show features remarkably different from regular walking legs. In this respect, it is in particular the terminal legs of centipedes (Chilopoda) that attract our attention. Terminal legs of centipedes do not come in contact with the substrate and therefore do not participate in walking. Often correlated with sexual dimorphism, terminal legs may be thickened in various representatives of Lithobiomorpha, Scolopendromorpha, and Geophilomorpha. Even more spectacular are the extremely elongated terminal legs of Scutigeromorpha and some Scolopendromorpha (Newportia spp.) which are extraordinarily thin and may easily exceed the body length of the animal. By their outer appearance scutigeromorph terminal legs resemble antennae. And indeed, preliminary microscopic studies indicate that their terminal legs are well comparable to those found on the antennae, with respect to (ultra-)structural diversity, distribution and abundance of cuticular sensilla (e.g. presence of beak-like sensilla). We want to explore the sensory equipment, innervations patterns and function of the annulated terminal legs of selected species of Scutigeromorpha (e.g. Scutigera coleoptrata, Dendrothereua homa) and Scolopendromorpha (Newportia spp.) using multimodal microscopic (LM, EM, cLSM), immunohistochemical and electrophysiological techniques. Among others, we intend to test the hypothesis whether antenna-like terminal legs of Scutigeromorpha may have been shaped through specific pathway of evolution implying transformation of a pair of regular, most likely locomotory posterior trunk legs and acquisition of sensory and neuronal morphologies typical for antennae. Moreover, we ask if, and if so to which degree, functional and constructional constraints may impact on compartmentalization of those trunk ganglia processing afferents of the terminal leg sensilla (e.g. glomeruli as part of olfactory path).

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Andy Sombke, until 11/2018