Recruitment dynamics of North Sea macrozoobenthos in intertidal soft bottoms: larval availability, settlement and dispersal

This thesis investigates how larval supply, larval settlement and secondary dispersal affected recruitment and recovery of macrozoobenthos living in an intertidal sand flat located in the German Wadden Sea. The temporal availability of meroplanktonic bivalve larvae was related to the timing of sea water temperature increase and/or the timing and magnitude of phytoplankton blooms. Larval settlement of the polychaete Lanice conchilega occurred almost exclusively at exposed sites within the adult habitat and was dependend upon the density of the adults. Model simulations revealed that dense L. conchilega patches develop only in areas of high near-bottom flows. In contrast, bivalve larvae settled mainly in sheltered habitats. Both polychaetes and bivalves undergo phases of postlarval dispersal which rapidly changed the spatial patterns generated by larval settlement. In-situ staining experiments showed that secondary dispersal is strongly size/age dependent. The recovery of two macrobenthic assemblages following the severe winter was rapid (<1 year) and influenced by 1) species life histories, 2) habitat conditions, and 3) biotic interactions, namely facilitation. The temporal course of recolonisation was mainly determined by the availability of settling stages (larvae and postlarvae). This thesis elucidates that both pre- and post-settlement processes contribute to the recruitment and recolonisation of macrozoobenthic communities. In dynamic systems, flexibility of life histories, high mobility of benthic life stages and the existence of functionally distinct life stages provide multiple paths to population maintenance and a high resilience. It is highlighted that at the end tides and currents are the decisive processes because they set the boundary conditions to which organisms respond and mediate the function of many processes such as larval drift, larval settlement and secondary dispersal

Observations of a mass occurrene of Macoma balthica larvae in midsummer

In 1995 the seasonal development of concentrations of both phytoplankton and larvae of the bivalve Macoma balthica was studied in the coastal zone behind the back-barrier island of Spiekeroog (German Wadden Sea). In July=August larvaereached maximum concentrations of about 1000 to 4200 ind.

A short C-terminal domain of Yku70p is essential for telomere maintenance.

The Yku heterodimer from Saccharomyces cerevisiae, comprising Yku70p and Yku80p, is involved in the maintenance of a normal telomeric DNA end structure and is an essential component of nonhomologous end joining (NHEJ). To investigate the role of the Yku70p subunit in these two different pathways, we generated C-terminal deletions of the Yku70 protein and examined their ability to complement the phenotypes of a yku70(-) strain. Deleting only the 30 C-terminal amino acids of Yku70p abolishes Yku DNA binding activity and causes a yku(-) phenotype; telomeres are shortened, and NHEJ is impaired. Using conditions in which at least as much mutant protein as full-length protein is normally detectable in cell extracts, deleting only 25 C-terminal amino acids of Yku70p results in no measurable effect on DNA binding of the Yku protein, and the cells are fully proficient for NHEJ. Nevertheless, these cells display considerably shortened telomeres, and significant amounts of single-stranded overhangs of the telomeric guanosine-rich strands are observed. Co-overexpression of this protein with Yku80p could rescue some but not all of the telomere-related phenotypes. Therefore, the C-terminal domain in Yku70p defines at least one domain that is especially involved in telomere maintenance but not in NHEJ

Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled coil arms.

Structural maintenance of chromosome (SMC) complexes form ring-like structures through exceptional elongated coiled coils (CC). Recent studies found that variable CC conformations including open and collapsed forms, which might result from discontinuities in the CC, facilitate the diverse functions of SMCs in DNA organization. However, a detailed description of the SMC CC architecture is still missing. Here, we study the structural composition and mechanical properties of SMC proteins with optical tweezers unfolding experiments using the isolated Psm3 CC as a model system. We find a comparatively unstable protein with three unzipping intermediates, which we could directly assign to CC features by crosslinking experiments and state-of-the-art prediction software. Particularly, the CC elbow is shown to be a flexible, potentially non-structured feature, which divides the CC into sections, induces a pairing shift from one CC strand to the other and could facilitate large-scale conformational changes - most likely via thermal fluctuations of the flanking CC sections. A replacement of the elbow amino acids hinders folding of the consecutive CC region and leads frequently to non-native misalignments, revealing the elbow as a guide for proper folding. Additional in vivo manipulation of the elbow flexibility resulted in impaired cohesin complexes, which directly links the sensitive CC architecture to the biological function of cohesin