Red Tide

Red Tide

Red Tide provides a discrete model for understanding parasite evolution because most red algal parasites are sister species to their hosts, derived from a recent common ancestor. Therefore, direct genomic and molecular comparisons made between the host and parasite have the potential to unravel the fundamental genomic changes that must occur for an organism, to become parasitic. 80% of these parasites have evolved from the most recent common ancestor with their hosts.

These parasites are known as Adolph parasites ('adelpho' meaning kinsman). Morphologically reduced to a miniature, often colorless pustule, adelphoparasites are highly host dependent and occur exclusively on their sister-taxon. The remaining 20% of red algae parasites are known as allo-parasites ('allo' meaning other) because whereas they also diverged from free-living species, they have since radiated to exploit more distantly related red algal hosts (Margulis, 50). Although this terminology has somewhat fallen out of favor because a full spectrum of host / parasite relationships occur in nature, the terms remain useful to designate differences in the biology of the organisms.

Red algae and all parasitism have arisen independently several times throughout the diversification of the florideophyte lineage, so a range of host-parasite relationships exist providing “windows” into the process of parasite evolution. For example, some parasites are not entirely obligate and have retained limited photosynthetic capabilities while others are highly host specific to their sister species and others have multiple hosts. This range of relationships creates an evolutionary spectrum, allowing for comparative investigations into how these parasites evolve from different living species (Goff and Coleman 1987; Goff, Ashen, and Moon 1997).

The mechanisms by which red algae and all other parasites infect host cells have been extensively studied. Upon contact with the host thallus, the non-motile parasitic spore produces a short filament, or connector cell, that fuses with a surface host cell. Minor variations in the subsequent steps from one species to the next are common, but in established infection proceeds when the parasite deposits a nucleus, mitochondrion and differentiated plastid, known as a prolactin, into a host cell. Once in the host cytoplasm, the parasite nuclei undergo DNA synthesis and the mitochondria divide rapidly (Margulis, 50). This cycle of host infection by the parasite results in the formation of non-photosynthetic heterokaryotic tissue that appears as a gall or pustule on the exterior of the infected host thallus. The parasite cells in the pustule eventually give rise to gametes, 2n carpospores, or 1n tetra spores that are released allowing for the continued dispersal of the parasite. Spores packaged and produced by the parasite contain host-derived proplastids along with parasite nucleus and mitochondrion.Effects on the EnvironmentThe unique nature of the Black Sea, as Europe's most isolated marine area, has as consequence the existence of a distinctive ecosystem, which was considered relatively stable until four decades ago. From the late '60-s until now, events occurred that affected the biological diversity and living resources. The Black Sea ecosystem, in its NW corner, has changed under the influence of human activities. Unfortunately, very little research has been carried out today regarding the present state of the macro algal flora ...