Gregarines: ‘primitive' apicomplexans or highly sophisticated parasites?
|Název česky||Gregariny: primitivní výtrusovci nebo rafinovaní parazité?|
|Fakulta / Pracoviště MU|
|Popis||Gregarines (Apicomplexa), 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 thein close affinity with Cryptosporidium, and have drawn attention to this enigmatic group. Additional 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. There are several known attachment and development strategies in gregarines, and thus they significantly differ also in their nutritive requirements and pathogenic effect on host organism. 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. Although some ancestral features found in gregarines have given them a reputation of being primitive', majority of them exhibit novel adaptations. For example, several types of movement are recognized in gregarines. Similarly, they exhibit some peculiarities in their gliding motility accompanied by architectural features not described in other apicomplexans. As it is rare to find any invertebrate group that escaped gregarine infection, they must be regarded as very successful parasites. 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 thus could be instrumental in understanding the early evolution of apicomplexans.|