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Wirts-Parasiten-Interaktion der endobiontischen Pilzgruppe der Nephridiophagidae und ihrem Insektenwirt

Fachliche Zuordnung Ökologie und Biodiversität der Tiere und Ökosysteme, Organismische Interaktionen
Förderung Förderung von 2018 bis 2022
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 397619173
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

Nephridiophagids are unicellular eukaryotes that parasitize the Malpighian tubules of insects. Their life cycle comprises multinucleate vegetative plasmodia that divide into oligonucleate and uninucleate cells, and sporogonial plasmodia that form uninucleate spores. In our project on the interaction of nephridiophagids with their hosts, we had three main aims: i) study fitness effects on the host, ii) elucidate early life cycle features, iii) shed light on the phylogeny of nephridiophagids. In standard rearings, the Nephridiophaga-infected cockroaches (Ni) additionally contain the gut nematode Blatticola blattae (N+Ni). Since this is the normal situation, we decided to include also such a population in selected investigations. We succeeded with most experiments and could thus increase the knowledge on many aspects. i) We clearly showed that an infection with Nephridiophaga (and nematodes) leads to an overall reduced host fitness. Nephridiophaga-infected males (Ni) had clearly lower fat reserves and showed reduced mobility in catching trials. The lifespan of adult hosts was significantly reduced when nematodes were present in addition to Nephridiophaga. Parasitefree females produced more offspring than Ni and N+Ni females, which correlates with their longer productive lifetime. However, immune parameters such as the number of hemocytes and phenoloxidase activity were hardly changed. Quantitative proteomics from hemolymph of parasite-free, Ni and N+Ni populations revealed clear differences in the expression profiles. For example, the observed down-regulation of fatty acid synthases in Ni animals may explain their reduced fat content. ii) It revealed to be difficult to study the early live cycle stages of Nephridiophaga. We could not find a method to induce spore hatching, although we tested a wide range of physical and chemical stimuli and used spores of different ages. Further, we mimicked in vivo conditions by using gut fluids for induction or incubated the spores in a complex medium for yeast growth. No hatching could be observed within two days. In our studies for signs of motility we observed vegetative and sporogenous plasmodia from disrupted Malpighian tubules under a light microscope. Neither migration of the cells nor moving pseudopods were seen. However, we by chance found tiny (ca. 5 µm) stages in squeezed Malpighian tubules that had long, slowly moving pseudopodia and may represent internally hatched sporoplasms. iii) Nephridiophagids are poor in morphological characteristics, and although they have been tentatively identified as early-branching fungi based on the SSU rRNA gene sequences of three species, their exact position within the fungal tree of live remained unclear. The consideration of the LSU rRNA gene has previously been shown to boost the phylogenetic power in tree inferences, allowing to untangle the diversification, e.g., of early-branching fungi. Thus, using long-read sequencing of the nearly complete rDNA operon and adding numerous further parasite species obtained from cockroaches and earwigs to improve the resolution of the phylogenetic analysis, we found a robust affiliation of nephridiophagids with the Chytridiomycota. Chytrids are a group of zoosporic fungi that comprises parasites of diverse host taxa, such as microphytes, plants, and amphibians. We further described two new species of nephridiophagids (Nephridiophaga postici and Nephridiophaga javanicae) from cockroaches. To date, Nephridiophaga species were assumed to be strictly host specific and therefore often named according to their host species. However, we found the same nephridiophagid species in two only distantly related cockroaches, indicating that their host specificity is not 100% strict. A many years long co-cultivation of the species in the same room may have favored the cross-infection. Unfortunately, the type species of the genus Nephridiophaga, i.e., N. apis, was never re-isolated. Since we could show that a nephridiophagid from a non-cockroach (earwig) host has a sistergroup position to all other Nephridiophaga sequences, N. apis from the honey bee probably is also only distantly related to most of the described nephridiophagids. In order to prevent a highly destabilizing introduction of new generic names and published combinations, we proposed a new type species, i.e., Nephridiophaga blattellae, as conserved type.

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