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1.6 BIOLOGICAL SCIENCES
Many marine invertebrates bud vegetatively to produce a modular colony of individuals derived from a single zygote. Fusion of different colonies to produce a genetically composite entity (a chimera) is known from experiements on sponges, hydroids, corals, bryozoans and ascidians-groups which together dominate sessile faunas on marine hard substrates. In this study the fusion behaviour of the colonial ascidian Diplosoma literianum (Milne Edwards) has been investigate. Laboratory experiments were undertaken to assess the influence of relatedness on fusion behaviour in young and adult colonies. The degree of relatedness had a slight effect on the fusion behaviour; nevertheless unrelated colonies fused with a frequency of 15%. These fusion trials were conducted using colonies from the same population and form geographically distant populations. In addition chimeric associations between unrelated colonies were shown to remain stable for over 15 months. The presence and extent of chimerism in natural habitats was investigated applying random amplified polymorphic DNA (RAPD) analysis to individual modules (zooids) dissected from colonies from eight different wild populations. Chimerism was detached in all populations, with varying frequency of up to 61%. Field experiments were designed to test for fitness consequence of fusion in young colonies. Overall, there was no significant difference between fused and unfused treatments regarding the growth of the colonies or the onset of sexual maturation. Finally, the mechanism of fusion was studied in a number of different approaches including the development of a tissue culture protocol for tunic tissue explants. Cells of different genetic origin showed no specific reaction to each other, but intermingle freely both in vivo (in the tunic of chimeras) and in vitro. To evaluate the biological significance of fusion, studies on other species described in the literature were taken into account and discussed with the findings of this work.
Sommerfeldt, A. (2002). Chimerism in a marine protochordate.Doctoral thesis. Technological University Dublin. doi:10.21427/D7KC7X