Student projects

1. Reconstructing the male copulatory organ of Trilobodrilus axi with histology, 3D-reconstruction (LM and TEM) and behavioural tests. Copulation requires the intricate coordination of muscles, glands, ciliary movement, etc. upon sensing (hormonal) cues. The connection between sensing external cues and triggering the adequate responses in the respective tissues are mediated by neurotransmitters, which are synthetized and transported in the nervous system. Studying copulatory behaviour and it neuromodulation in model organisms is complicated, since many of them show either too complex behaviour, are only accessible in a premature stage or have too high cell numbers to be able to reconstruct the neural circuitry and characterize the individual components. It thereby has only been possible to investigate few species in detail, which revealed a high diversity of behaviours and underlying regulations. Microscopic annelids such as Trilobodrilus axi are small, have a comprehensible cell number and complexity, and still display courtship “rituals”, thereby allowing for a detailed analysis of individual cells and their connections to each other. This allows us to address questions concerning principles of regulation, key elements in neural circuits and the affect of neurotransmitters on modulating behaviour.

The overall objectives of this project are understanding the function of specific neurotransmitters in the copulatory behaviour of an adult annelid, and to study how changes of complexity (cell number, organ size, etc.) affect the regulation of individual elements. This will be done by morphologically mapping the tissues of the copulatory region of T. axi, adding to already acquired data on two morphotypes of the closely related genus Dinophilus. The integrative approach of this study combines histology, immunohistochemistry, advanced bioimaging (CLSM, TEM) and behavioural approaches.

This study will advance the knowledge of neurotransmitters (their distribution pattern and affect on tissues and organs) and their interactions in the nervous system of invertebrates. Furthermore, this study will help the identification of crucial components in neural regulation of copulation, and the establishment of a possible new model system of adult annelids, which will be published in a high-ranked neurobiological journal.   

2. Neuromuscular development of Trilobodrilus axi. The field of evodevo tries to understand the interactions between evolution and development, which lead to the respective organism. Amongst others, some of the questions deal with how conserved certain morphological traits are (e.g. nervous system architecture, developmental sequence of the formation of organ systems), and what causes differences in the adults. An example to study the morphology and the development of organ systems are the closely related Dinophilidae, which are in culture at the Marine Biological Section in Copenhagen and display a variety of life styles (rapid life cycle vs. prolonged encystment stage), behaviours (e.g. courtship behaviour vs. mating with sibling inside the cocoon) and complexities (e.g. 68 cells in the entire organism to several hundred in the copulatory region alone). A recent study focussing on the two morphotypes of Dinophilus analysed the morphogenesis of the nervous and muscular system as well as the overall ciliation patterns, unveiling that the smaller D. gyrociliatus possibly resembles a juvenile stage of the larger D. taeniatus. Trilobodrilus axi represents the second genus of the family Dinophilidae, and although its morphology resembles that of the two dinophilids to a high degree, the arrangement of the commissures in the brain and the ventral nervous system varies, making homology assignments impossible.

The overall objectives of this project are the analysis of common patterns in the development of these annelids, the assessment of the homology of neural elements such as commissures by comparing the patterns between T. axi and the two previously mapped Dinophilus-species, and the documentation of possible affects of the different complexity and life styles on the developmental patterns by understanding and mapping the morphogenesis of the nervous system, musculature, and ciliation patterns of T. axi. The project includes the collection of animals in the field (from Sylt, Germany), rearing them in the laboratory and preparing them for immunohistochemical studies and advanced bioimaging by CLSM. The generation of a developmental atlas of the nervous system, ciliation patterns, and musculature will extend our current knowledge of this family’s development, thereby establishing a detailed resource to correlate morphological and developmental patterns across three species and subsequently identify common traits vs. species- or lineage-specific modifications.

 3. Analysing the nervous system in four species of Ophryotrocha with histology and immunohistochemistry. The nervous system is supposedly the most conserved organ system in especially invertebrates, and might therefore unveil vital information about how species are related to each other, and which traits are more conserved than others. However, a recent study could demonstrate variation in the commissures in the brain and ventral nervous system as well as between the distribution patterns of neurotransmitters between three closely related, microscopic annelids. Furthermore, this study also found neurotransmitters not overlapping with each other, suggesting that each neuron is specific for only one neurotransmitter, furthermore confirming the so-far mainly rebutted Dale’s principle, which states each neuron is specific for only one neurotransmitter. This finding suggests that small brains can still be quite complex, and that overall functionality might be retained in complexity-reduced brains by decreasing the size of areas with certain functions rather than increasing the multifunctionality of individual cells. We have four species of the genus Ophryotrocha in our lab at the Marine Biological Section in Copenhagen, which are closely related to each other, represent a secondarily size-reduced genus, and have a similar life style.

The overall objective of this project is to reconstruct the possible ancestral pattern of Ophryotrocha, elaborate on the use of neural elements for reconstructing phylogenetic relationships, and test the Dale’s principle on miniature brains. This will be done by assessing the neuropil and ventral nervous system configuration in these four species by means of histology, immunohistochemistry, and advanced bioimaging (CLSM). Based on the outcome of the study, the results will be published in a journal aiming at a comparative-morphological to neurobiological audience.        

4. Eye morphology and functionality in meiofaunal animals. Meiofaunal animals are small (less than 1mm in size) and live mainly between the sand grains of sediments, often in marine environments. While some of them have developed eyes, others have reduced them and rely on other senses. Members of the two different genera Trilobodrilus and Dinophilus of the family Dinophilidae show a rather similar overall morphology, however, their habitat (in the sediment vs. on the biofilm on its surface) as well as their behaviour (migrations in the sediment, phototaxis, …) differs. While Dinophilus has clearly formed eyes with two sensory cells and one supporting cell, Trilobodrilus does not have eyes, but anterior ciliated sensory organs, which might resemble the eyes of Protodrilidae (another microscopic group of worms). It has not been tested yet what these ciliated sensory organs look like ultrastructurally, how they are connected to the nervous system, and how they influence behaviour and therefore might affect the behaviour of these animals, especially their reaction to light. These morphological and behavioural studies will be supplemented with electrophysiological measurements in light- and dark-exposed animals of the eyes and ciliated sensory organs to further specify the functionality of the respective sensory cells.      

The overall objective of this study is to study the morphological basis of behaviour and therefore analyse the detailed ultrastructure and behaviour in several different assays of two related animal species, which differ in their life style and habitat. Based on the outcome of the study, the results will be published in a journal aiming at vision.

5. Reconstruction of the nervous system of Diurodrilus (incertae sedis) by serial histology sections and 3D reconstruction as well as dapi and other immunostaining. Diurodrilus is still not positioned in the metazoan tree - the nervous system is an important player and the configuration in Diurodrilus may be central for tracing the evolution i Spiralia. New collecting and studies on live animals.

6. Development of Siboglinidae, with focus on the nervous system. This intriguing groups of annelids contains the whalebone devouring Osedax, and the hair-thin, mud-dwelling Sclerolinum. They generally lack mouth, gut and anus, and live from endo-symbiotic bacteria. Their special life form and life cycle is still understudied due to the deep-sea habitat of most species. However, we can now gain access to a shallow water sclerolinum in Norway and a deep-sea Osedax from Japan. Field work in Japan and Norway is possible.