ИСТИНА

Larvae of many shore fly species (family Ephydridae) develop in water with high or extremely high salinity, which is unusual enough for insects to live in seawater. Our goal is to clear up the mechanisms of the manifold adaptations to such extreme habitat. We study Ephydra riparia and Paracoenia fumosa flies inhabit White Sea littoral and describe morphological features and symbiotic yeast microbiome that can contribute to halotolerance of that species. For the first time, by silver-staining and scanning electron microscopy, we proved that the larvae of both studied species had anal organs (AO) – specialized structures serve osmoregulatory function and responsible for the transport of ions from the environment to the larval hemolymph, and compared AO with homological structures of extremely halophilic and feshwater shore flies and Drosophila melanogaster. Experiments on the laboratory lines of Drosophila proved the contribution of yeast to fly adaptation to salty substrate. We suggested that halophilic and halotolerant flies may be associated with special groups of symbiotic yeasts. By seeding experiments and analysis of sequences of the ITS rDNA region we studied the content of yeast microbiome of shore flies, substrate, water, and algae. We found that the yeast community of flies was not identical to one of the substrates; the microbiome of imagoes, pupae and larvae differ significantly. The larvae and pupae of P. fumosa had poor enough yeast community, but the intestines of E. riparia are filled with yeasts. Yeast from genera Rhodotorula, Candida, Cystofilobasidium and Debaryomyces are specific for larvae. They might contribute to success adaptation of their host to salt water. The study was funded by the Russian Science Foundation, project No. 22-24-00156, https://rscf.ru/en/project/22-24-00156/.