Biological evolution is the fundamental process in nature. By means of inheritance and modification of characters combined with an irreversible split of lineages, evolution created and still creates the stunning biodiversity on our planet. Linked with this, there is a fascinating diversity of structures, functions and interactions.
The department for Evolution and Biogeography of Meiofauna is focused on historical evolutionary research, i.e. evolutionary patterns of different groups of the meiofauna (benthic animals with body sizes of mostly less than 1 mm) at different time scales are explored. This includes e.g. the genetic-geographic population structure of species. Phylogenetic relationships of whole species groups (taxa), evolutionary modifications of organ systems and the connected adaptation effects are studied, too. The spatial and ecological distribution of species can either be a result or even the source of evolutionary processes. For instance, a sufficiently long geographic separation of populations may lead to new and reproductively isolated species. Therefore, biogeography and historical evolutionary research are inextricably linked with each other. Phylogeography considers relationships between distribution and evolution in rather young time segments, i.e. intraspecific, microevolutionary processes and patterns.
The biology of meiofauna organisms differs to some extend considerably from that of macrobenthic animals. Amongst other effects, this has an influence on their distribution and dispersal ability and hence also on the evolution of these groups. Compared to their “big relatives”, many taxa of the meiofauna are only sparsely explored regarding their morphology, systematics, population structure, biogeography, and biology. This department is involved in finding answers to such questions while currently the focus is on the Gastrotricha as a “model group”.
Different imaging, quantifying and analytical methods and their specific preparation procedures are needed to work on the research topics of the division Evolution and Biogeography of Meiofauna that are introduced on the further subpages.
At the beginning of any research, however, we need to procure samples with suitable objects for our studies. In the simplest case, this might be a sand sample from a beach or a plankton catch from a weeded pond, which can be obtained with relatively little effort. If sediment of deeper water depths is needed, the sampling can be done with snorkelling or diving equipment, or a grab has to be used from a boat. If sediment from oceanic biotopes has to be examined (e.g. deep sea floor, shelf around offshore islands, summit plateaus of seamounts), the effort is considerably greater. In such a case, sampling devices such as a usual Van Veen grab up to remotely operated vehicles (ROVs) need to be deployed from large research ships.
The sediment samples with the containing organisms are chemically fixed immediately. However, fragile taxa such as the gastrotrichs mostly have to be extracted from the sediment alive in order to be prepared carefully for the respective examination method. Different microscopic procedures are available for morphological investigations. These range from conventional light microscopy, fluorescence and confocal laser scanning microscopy to high-resolution scanning and transmission electron microscopy. The analysis of DNA sequences of different genes is meanwhile an important tool for phylogeographic, taxonomic and systematic problems. A reliable identification of various species in an environmental sample via specific gene fragments is becoming more and more important in an age of rapidly advancing, man-made environmental change.
Organs and organ systems are composed of different tissues and these in turn consist of different cell types. In microscopic animals of the meiofauna, some organs such as eyes or excretion organs consist of only a few, highly specialised cells with a complex ultrastructure.
The organ systems are the functional basis of an organism’s different life activities. They serve e.g. for locomotion, ingestion and digestion, excretion and osmoregulation, perception, or reproduction. Evolution has optimised them for their particular functions in a given environment. In systematics, the morphology of organisms and their organs is an important source of information to uncover the phylogenetic system. Sistergroup relationships can be recovered by identifying synapomorphies, i.e. new characters that two evolutionary lineages have inherited from their common ancestor. Thereby we are able to unravel phylogenetic relationships successively. We are likewise able to reconstruct the character evolution on the basis of phylogenetic trees that were generated with other methods (e.g. by the analysis of DNA sequence data). On the one hand, we can thereby test the plausibility of a phylogenetic hypothesis with data that were not used for the initial analysis. On the other hand, we can estimate the adaptive value of evolutionary novelties, e.g. if they correlate with a transition to a new habitat.
For the study of morphology and ultrastructure of organ systems, a broad spectrum of methods is used. The aim is to get a realistic model of the truth for having an ideal data basis for subsequent evolutionary and functional interpretations. In the division Evolution and Biogeography of Meiofauna we use different light-optic (light microscopy, confocal laser scanning microscopy) as well as electron-optic techniques (scanning- and transmission electron microscopy). For data analysis, manual and computer-aided drawing techniques, 3D reconstruction methods, and tools of computer-aided cladistics are available.
Phylogeography is a rather young field of research that studies the spatial distribution and relationships of intraspecific lineages. Created as a neologism of the two terms ‘phylogeny’ and ‘biogeography’, it is nevertheless well-separated from the historic biogeography.
By using different genetic markers, at present usually DNA sequences of mitochondrial genes, phylogeography focuses on the genetic diversity within and between geographic populations of a species.
Each individual of a population represents a particular genetic variant, a so-called haplotype. While some variants are quite frequent, others are less. Moreover, the geographic distribution of different haplotypes is very heterogeneous. Some are widely dispersed and others can only be found in a narrow region. Different methods for analysing the relationships between haplotypes permit a link between spatial and temporal aspects. One important aim of phylogeography is to identify historic processes that have caused the contemporary distribution and degree of genetic diversity, e.g. geographic isolation of populations, range expansions or a genetic depletion due to colonisation processes (genetic bottleneck).
The identification of glacial refugia is another topic of this discipline. A strict separation of intraspecific and interspecific patterns is oftentimes not feasible. The systematic and distribution of closely related species, the occurrence of cryptic species, and patterns of speciation in general are explored, too. In terms of the spatio-temporal distribution of their genetic diversity, species of the meiofauna are very interesting study objects. While usually less than 1mm in size, these organisms theoretically possess a high dispersal capacity. Apparently, this could be true for freshwater meiofauna whereas most of the marine species lack any active or passive dispersal stage and should therefore only have a low dispersal potential.
Imaginable consequences would be a global genetic homogeneity on the one hand, on the other a well-differentiated geographic structure that, for instance, may influence the formation of new species. Taking the Gastrotricha as an example, but also further taxa such as the interstitial microscopic crustaceans of the group Mystacocarida, such processes and patterns are studied in the division for Evolution and Biogeography of Meiofauna.
Species of Gastrotricha form a monophyletic group within the Bilateria and are typical members of the meiofauna. Especially the marine, predominantly interstitial (the spaces between sand grains inhabiting), Macrodasyida are benthic organisms.
The gastrotrich subtaxon Paucitubulatina shows an emphasis of distribution in lacustrine habitats. Marine Paucitubulatina are as well typical elements of the interstitial community whereas there are epipelic, periphytic or even semiplanktonic forms among freshwater species.
The marine genus Neodasys plays a unique part in terms of systematics as it is quite likely the most primitive group. Gastrotrichs are mainly worm-, strap- or flask-shaped animals with complex organ systems and oftentimes complicated surface differentiations such as plates, scales, spines, hooks, or keels. Body length is usually between 100 and 1000 µm, while few species may reach a length of up to 3 mm. Gastrotrichs solely feed on microscopic organisms such as bacteria or unicellular algae.
Taxonomy deals with the description and systematization of species. By means of different microscopic (light microscopy, scanning electron microscopy), graphic (e.g. vector drawing), and molecular techniques (DNA sequencing), new species are described from diverse habitats such as ponds, beaches and the deep sea. The precise knowledge of taxa is crucial to understand diversity patterns of areas and distributions of species. This division is part of different international research projects that aim to uncover such patterns in diverse ecosystems such as the Caribbean Sea, the sublittoral of oceanic islands, or the summit plateaus of seamounts.
Most marine Gastrotricha belong to the interstitial meiofauna, tiny metazoans and protists that live between the sand grains of the ocean. We still do not know much about their dispersal potential and distribution in space and time.
It seems paradox that their adaptations and biology indicate a rather limited dispersal capacity, although many species are reported from very distant places. Numerous species are known, for instance, from different coastal sites of a whole ocean. Several are even regarded as cosmopolitan species. Analyses of certain gene fragments have already demonstrated that some of these ‘cosmopolitans‘ are rather complexes of different species with substantially smaller ranges. Nevertheless, individuals of their ancestors must have crossed enormous distances before they could establish new populations in suitable biotopes at far-off coasts. We want to learn which functions do have geological formations such as oceanic islands and seamounts for a successive dispersion and/or the origin of new species of the interstitial meiofauna. Islands and seamounts provide locally defined sandy shallow water biotopes within the almost endless abyssal plains. The analysis of extensive sample material has already demonstrated the occurrence of species of different taxa on seamounts and at oceanic islands, which were formally only reported from continental coasts. Genetic analyses shall now shed some light on connectivity between remote populations, or, alternatively, on patterns of speciation processes. The sublittoral sample material for our studies is mostly difficult to access. In order to obtain the sediment samples, we deploy different grab types from aboard of various research vessels. We have recently carried out marine research expeditions with, for instance, R/V POLARSTERN to the Arctic Karasik-Seamount, or with R/V METEOR to the Azores Archipelago. The latter cruise occurred within the framework of the BIODIAZ project (Controls in benthic and pelagic BIODIversity of the AZores).
Tardigrada or water bears are a monophyletic taxon whose species are all microscopically small with body sizes ranging from less than 100 µm (0.1 mm) to a few hundred micrometres. Systematically, they represent a subgroup of the Panarthropoda, and are therefore phylogenetically related to the Arthropoda (arthropods) and the Onychophora (velvet worms).
Tardigrades colonize all habitats in which a sufficient film of water is available at least temporarily. The limno-terrestrial species from the taxon Eutardigrada are particularly well known and can be found in a wide variety of limnic habitats, but also live in terrestrial moss cushions, for example. If these biotopes dry out, Eutardigrada can form what is known as “tun state” in which all metabolic processes are virtually “frozen” due to anhydrobiosis. This enables the animals to survive unfavourable and hostile environmental conditions, such as prolonged drought or extreme cold. The taxon Heterotardigrada mainly comprises marine species and these can be found from tidal beaches down to the deep sea. Compared to the more accessible limno-terrestrial tardigrades, the Heterotardigrada are still less well studied. In particular, very little is known about the biodiversity, ecology, bathymetric distribution and biogeography of species from the deep sea, seamounts and the shelf of oceanic islands. In the current project, which is funded by the Deutsche Bundesstiftung Umwelt (DBU) and the German Academic Exchange Service (DAAD), among others, extensive sample material from various expeditions is being analysed in order to expand our knowledge of these little-studied seafloor dwellers.
Lessons at the Carl von Ossietzky Universität Oldenburg
as assistant lecturer
In collaboration with my colleague Dr. Wilko H. Ahlrichs, I supervise different practicals, lectures and field practicals in the course of the Bachelor and Master degree programme ‘Biology’ of the Carl von Ossietzky Universität.
Winter term
5.02.351 Organismische Mikroanatomie – practical & lecture
Summer term
5.02.441 Mikrofauna, Mikroflora und Protista limnischer und mariner Lebensräume – excursion / seminar / practical
5.02.481 / 482 Marinbiologisches Praktikum auf Sylt / Helgoland – practical & seminar
