Gregarines: Humble subtenants or highly sophisticated parasites?
|Fakulta / Pracoviště MU|
|Popis||Gregarines (Gregarinassina), comprising archigregarines, eugregarines and neogregarines, are thought to be a group of deep-branching apicomplexans which parasitize invertebrates and urochordates, and that are usually considered to be of no practical importance. Recent phylogenetic analyses, however, have pointed out their close affinity with Cryptosporidium, and have drawn attention to this enigmatic group. Our ultrastructural analyses revealed that cryptosporidian attachment strategy is very similar to that of the eugregarines. Gregarines exhibit an enormous diversity in cell architecture and dimensions, depending on their parasitic strategy and environment. They seem to be a perfect example of a concomitant evolution between a group of parasites and their hosts. It has been assumed that they appeared in marine polychaetes and the most primitive are the archigregarines. Marine gregarines have retained some plesiomorphic characteristics, and could be instrumental in understanding the early evolution of apicomplexans. Although some ancestral features found in gregarines have given them a reputation of being ‘primitive’, majority of them exhibit novel adaptations. It is rare to find any invertebrate group that escaped gregarine infection and thus they must be regarded as very successful parasites. The gregarine sporozoite transforms into a trophozoite, which represents the most conspicuous stage in gregarine lifecycle. Although some coelomic species are not attached to the host cell, gregarine trophozoites exhibit a high degree of polarity in that they possess an anterior part (epimerite, mucron), specialized for attachment to the host cell in general. Gregarines significantly differ also in their nutritive requirements and pathogenic effect. Although only few eugregarines cause pathogenic effects on the host, neogregarines are predominantly intracellular parasites with high nutrition requirements, and the host tissue is gradually destroyed and replaced with oocysts. As the hosts often do not survive heavy infections by neogregarines, they are likely to be potential candidates for biological control of insect pests.|