exclusively infect marine invertebrates and mostly their intestines. Eugregarines contain most of the known species and are found in marine, freshwater and terrestrial habitats. Eugregarines inhabit the intestines, coeloms and reproductive vesicles of their invertebrate hosts. Friends or foes? Symbiotic relationships can be either mutualistic (beneficial), commensalistic (no effect) or parasitic (harmful). They can lead to behavioural changes in the host, which could affect the host’s ability to escape predation or compete for space and resources. A recent review by Rueckert et al. (2019) has proposed that gregarine apicomplexans can be found across the entire symbiotic spectrum. A few examples will be presented below. In earwigs, it was observed that food-deprived insects survived longer when they had a gregarine species colonising their gut compared to those without, showing a beneficial relationship between the gregarine and its earwig host. In pseudoscorpions, high prevalence and infection levels of gregarines were reported to be neither beneficial nor harmful. Dragonflies, however, show a decrease in fat content when infected with gregarines. This results in lower muscle power output which negatively affects motility leading to lower mating success. Our understanding of the biological processes that are associated with mutualism, commensalism, and parasitism in the various gregarine species is currently limited. However, the utilisation of a combination of traditional methods and state-of-the-art -omics technologies can help to pinpoint major steps along the symbiotic spectrum that led to the evolution of parasitism. The evolutionary path to obligate intracellular parasitism Despite being of medical and ecological importance, a lot is still to be discovered in the evolution of parasitism in the apicomplexans. It is known that apicomplexans evolved from algal ancestors, but the processes that drove the evolution from a free-living photosynthetic organism to an intracellular Scanning electron micrograph (SEM) showing the general morphology and surface ultrastructure of the archigregarine Selenidium fallax . Sonja Rueckert
89 Microbiology Today October 2022 | microbiologysociety.org
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