Chemosynthetische Endosymbiosen an rezenten und fossilen Cold Seep-Standorten

Chemosynthetic Endosymbioses at recent and fossil Cold Seep-habitats

by Anne Dreier
Doctoral thesis
Date of Examination:2013-10-02
Date of issue:2013-11-15
Advisor:PD Dr. Michael Hoppert
Referee:PD Dr. Michael Hoppert
Referee:Prof. Dr. Volker Thiel
Persistent Address: http://dx.doi.org/10.53846/goediss-4153

 

 

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Abstract

English

This thesis is focused on symbiosis between bivalves and autotrophic microorganisms (thiotrophic bacteria and phototrophic algae). The symbiotic relationship leads to special isotopic traces in the organics of the bivalves’ shell. This thesis connects multiple isotopic values (δ13C, δ15N, δ34S) of the bulk organic shell matrix and (δ13C) of shell-lipids with the respective pathways of carbon fixation, nitrogen assimilation and sulfur oxidation in thiotrophic bacteria. These characteristic isotopic patterns were compared to the isotopic composition of the shell-organics from non-symbiotic bivalves inhabiting the same habitat. In case of shells from living bivalves of the same sampling site, it was found that all isotopic values (including δ13C values of shell-lipids) are lower in the organics of thiotrophic compared to non-symbiotic bivalves. Phototrophic bivalves have lower δ13C values of bulk organic shell matrix compared to non-symbiotic bivalves as well. Phototrophic symbiosis could be differentiated from thiotrophic symbiosis, exhibiting lower δ15N values. It turned out that in the case of empty shells the composition and δ13C values of shell-lipids and the δ34S values of the bulk organic shell matrix are unstable and isotopic difference between bivalves’ lifestyles remains inconsistent. Furthermore in one empty shell a contamination with boring microbes was observed. However, generally the quality of the bulk organic matrix was comparable to that of living shells and the isotopic difference of δ13C and δ15N values (bulk organic shell matrix) between symbiotic vs. non-symbiotic bivalve lifestyle was still stable in empty shells. During further diagenetic processes the organic shell matrix could get lost. Under optimal conservation condition like in the case of the subfossil shells from the late Pleistocene (Adriatic sediments) isotopic composition in the remaining organic shell matrix could be identified. The results show that it was possible by using δ13C and δ15N values to deduce a non-symbiotic or thiotrophic lifestyle even for ancient bivalves. Hence, δ 13C and δ15N values of organic shell matrices could be a helpful tool to reconstruct evolution of symbiosis in bivalves and also other shelled mollusks.
Keywords: Symbiosis
 
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