Edinburgh Napier University

  Apicomplexans are widely distributed, single-celled organisms that are always described as obligate parasitic. Despite their importance for human health (malaria, toxoplasmosis) and vast literature on their virulence in animals, there is substantial evidence for mutualistic attributes of some apicomplexans (Rueckert et al. 2019; Paight et al., 2018). So far, the majority of research has been focused on the crown apicomplexans, but early diverging gregarines span the whole range of symbiosis from mutualism to parasitism (Rueckert et al. 2019) and thus are critical links in the evolution of symbiosis in the apicomplexans.

Gregarines are endosymbionts that inhabit the intestines, coeloms and reproductive vesicles of invertebrates and have been shown to be highly abundant in most ecosystem (de Vargas et al. 2015; Clearly & Durbin 2016; Mahé et al. 2017; Lentendu et al. 2018). Because gregarines infect almost all invertebrates, they are important players in structuring host populations, communities and ecosystems. However, their impacts are poorly described from only a few, mostly terrestrial, host species.

Mathur et al. (2019) revealed that the parasitic lifestyle has evolved at least three times within the larger clade encompassing Apicomplexa using first omics-data from only six gregarines. This study illustrates how little we know about gregarines, their diversity and evolution, and what opportunities for discovery remain. A focus on gregarines as model systems will enable us to advance the fundamental knowledge on the evolutionary steps of symbiosis in the Apicomplexa, identifying key cellular and molecular transitions in the evolution from free-living relatives to intracellular parasites.

This research is funded in part by the Gordon and Betty Moore Foundation.