Population genetic studies of economically important Gracilaria and Gracilariopsis (Rhodophyta) in the south western Cape

Gracilaria (Rhodophyta) encompasses some of the world's most valuable agarophytes and has accordingly been the subject of much research in recent decades. Gracilaria, however, has presented a problem to taxonomists over the years in that extreme phenotypic variability in certain entities, and the occurrence of similar morphologies among different taxa (in both Gracilaria and Gracilariopsis), combine to impede species recognition. Gracilaria and Gracilariopsis occur naturally from the Eastern Cape Province, South Africa to northern Namibia and the genetic variation within this widespread species or species complex is unknown. In this study, samples were connected from various locations within the Langebaan Lagoon-Saldanha Bay system and the nearby St. Helena Bay. Their positions were accurately mapped with the aid of a Global Positioning System (GPS). Reproductive structures are of great taxonomic importance within the Gracilariaceae. The local utility of reproductive features is questionable however, as south western Cape material is very seldom fertile which presents a problem for identification. External morphology lacks taxonomic significance due to the isomorphic nature of terete taxa. It was found that one cannot differentiate between Gracilaria gracilis and Gracilariopsis longissima based on external morphology. Adding to this, it was found that under varying ecological conditions different external morphologies occur. Although these specimens appear different externally, molecular studies show that they belong to the same species. Various molecular methods have proven successful in differentiating within and between populations, species and genera in the Gracilariaceae. Sequencing results of a 299 bp variable region of the ISS rRNA gene reveal that G. gracilis predominates in the Langebaan Lagoon-Saldanha Bay system, whereas Gp. Longissima predominates in the St. Helena Bay system. From the AFLP data one can infer that Saldanha Bay isolates display moderate divergence, probably due to favourable ecological conditions in this locality.

Grantor dc:publisher.institution

Department of Biological Sciences

Year dc:date.issued

2001

Author dc:creator

• Govender, Kershini

Advisors dc:contributor.advisor

• Bolton, John J
• Coyne, Vernon

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/6258

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/6258