In vivo and in vitro studies on an endozoic alga from the giant scallop, Placopecten magellanicus (Gmelin)

Stevenson, Robert Norman (1972) In vivo and in vitro studies on an endozoic alga from the giant scallop, Placopecten magellanicus (Gmelin). Masters thesis, Memorial University of Newfoundland.

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Abstract

A literature survey indicates that much has been published on algal symbiosis with animals, however, few accounts have been presented in which the algal partner is considered parasitic. Previous reports on the endozoic algae of the giant scallop, Placopecten magellanicus (Gmelin), indicates that the relationship is parasitic. This definition is maintained here with the realization that future investigations of both partners are required to fully explain the association. -- Description of the algal colonies within the tissues of the giant scallop is presented. Quantitative analysis of the colonies within the mantle tissue indicates a definite distribution pattern. Algal colony concentration was found to be highest within a very narrow delicate strip of tissue, the shell fold, which lies in direct contact with the shell. Colonies were more numerous and larger within the mid-mantle regions of the shell fold tissue. Theories involved in this distribution pattern are presented. -- Description of the alga involved in symbiosis is difficult to accomplish completely since there are differences in morphology from in vivo and in vitro. It is stressed that in newly reported associations it is necessary to describe the alga both from culture and from the animal. Based on morphology in vivo and in vitro a possible taxonomic position is presented. The alga appears to belong to the Class Chlorophyceae, Order Chlorococcales. Evidence for this position is gained from morphology, reproduction and pigmentation as determined by paper chromatography and spectrophotometry. Designation to a Family is hampered by discrepencies in reproduction in vitro as compared with in vivo. The Family Coccomyxaceae and Family Oocystaceae are suggested as possible positions. However, it is pointed out that positive identification of this endozoic alga will have to await electron microscopy studies. -- Re-infection experiments demonstrate a change in morphology of the algal cells from the in vitro to the in vivo habitat as well as demonstrate the tissue and cellular responses of the giant scallop to the algal cells. -- Besides the tissues previously reported to be infected by the endozoic algae, colonies were found within the gill filaments illustrating that settlement is possible in tissues where ciliary action occurs. Colonies were also found deep within the adductor muscle and on the anus. Algal cells were observed within blood cells of the circulatory system as well as within phagocytes within the infected tissues. -- Theories on the mode of infection are presented based on experimental evidence and literature reports. Initial infection is suggested to be more likely via the digestive system than via mantle penetration as previously suggested. Phagocytosis is suggested to play a major role in the mode of infection and transmission of the algae throughout the scallop tissue as well as spread of the infection to other scallops.

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