Transmission of bacterial symbionts in the gutless oligochaete Olavius algarvensis

The essential role that symbioses between bacteria and animals play for life on earth has been a major topic of scientific research for the past fifty years. We now understand that eukaryotic life could not have evolved without the intricate influence of bacteria, which impact physiological, metabolic, nutritional, developmental and evolutionary processes in many eukaryotic phlya. One model system for such associations is the well-studied symbiosis between the gutless oligochaete Olavius algarvensis, from the island of Elba, Italy, and its obligate consortium of chemoautotrophic sulphide-oxidizing gamma-proteobacteria and sulphate reducing delta-proteobacteria. The complete nutritional dependency of the host to its symbionts has led to the reduction of the digestive tract and the excretory system. The aim of this thesis is to investigate how this symbiosis is maintained over consecutive generations. In particular I examine whether symbionts are transmitted into the next host generation vertically by smearing from the parent worm during oviposition, horizontally by uptake from the environment, or by both these modes. To answer this question further investigation into worm ecology, development and molecular methodological advancement had to be made.