| Abstrakt: |
The existence of gutless animals was known, and their putative nutritional processes investigated for several decades, before the sulfide-oxidizing symbiosis that sustains them was discovered. Research into the large, gutless Pogonophora of the marine, thermal vent communities, and the relatively large, gutless, bivalved mollusc provided an adequate paradigm and stimulated exploration of the evolutionary impact of the symbiosis. These “unwhole” organisms provide an epistemological model for studying the necessity, as well as the limitations of the concept of organism. For non-parasitic gutless animals, and for others with reduced guts, a variety of reductionistic, adaptationistic and organicistic hypotheses were advanced, but despite a general familiarity with parallel symbioses there was a reluctance to transcend the organismic mind-set Free-living sulfide-oxidizing bacteria inhabit a two-dimensional environment: the interface between aerobic and anaerobic environments. A host, such as , adds a third dimension, regulating the supply of necessary oxygen and sulfide at the molecular, functional morphological, and behavioural levels. Morphological correlations of the symbiosis in bivalves include expansion of gills to house bacteria, paedomorphic reduction of outer demibranchs and palps, and reduction or loss of siphons and guts. In symbiont transmission appears to be vertical, , an intimate transferral from one generation to the next. Initial failure to realise that gutless animals are sustained by intracellular bacteria echoes the original response to the endosymbiotic theory of the origins of eukaryotes, which had a larger historical context. Yet evolution by association has periodically produced major advances in the history of organisms. While simplistic reductionism has a false allure, organicism also has limitations that are illustrated by the above case history. Whether we identify ourselves as adaptationistic neo-Darwinists, or require that greater emphasis be placed on the evolution of integrated dynamic wholes, as do the structuralists, we must somehow accommodate the ultraorganismic evolution of new “wholes” by the association of previously independent forms. [ABSTRACT FROM PUBLISHER] |
