Food preferences of Collembola for myxomycete plasmodia and plasmodium responses in the presence of Collembola
Introduction
The analysis of soil organism interactions is critical for understanding underlying soil mechanics. Soil plays important roles in forests including organic matter decomposition and mineral nutrient cycling. Interactions among soil organisms are species specific (Tordoff et al., 2008; Crowther et al., 2011). Therefore, species-level investigations of biotic interactions are needed to understand soil processes. Myxomycetes and Collembola are abundant in soil and play essential roles in organic matter decomposition (Myxomycetes: Fukasawa et al., 2017; Collembola: Rusek, 1998). However, the consequences of their species-specific interactions remain poorly understood.
Myxomycetes are unicellular eukaryotic organisms that live in decaying wood, plant litter, and soil. During a vegetative stage of their life cycle, myxomycetes form plasmodia (Keller et al., 2017), which feed on bacteria, fungi, or other small organisms and move slowly, in a manner similar to slime, to seek food (Keller et al., 2017). Plasmodia form sclerotia to resist unsuitable living environments (Keller et al., 2017), and their body sizes can reach 1 m in some species (Hagiwara et al., 1995). Due to the large impact plasmodia have on soil, it is important to understand their behaviour to determine their roles in soil.
Myxomycete plasmodia are known to be consumed by Collembola, terrestrial hexapods with a body length of about 1 mm. Collembola feed on fungi and bacteria; species in the collembolan family Neanuridae, which lack molar plates on their mouthparts, consume plasmodia (Greenslade et al., 2002; Hoskins et al., 2015). However, the suitability of plasmodia as food has been studied in only a few Neanuridae species (Hoskins et al., 2015). The effects of Collembola food preferences on plasmodia and plasmodium responses to consumption by Collembola have not been studied.
The objective of the present study was to determine whether (1) Collembola food preferences for myxomycete plasmodia differ among Collembola species and (2) plasmodium responses to Collembola differ among species. To address these questions, we prepared cultures of two plasmodium and two Collembola species, pairing one species of each taxon in each experiment. We observed body length increase, egg numbers, and survival rates in Collembola species, and quantified myxomycete sclerotium formation and plasmodium fragmentation in myxomycete species.
Section snippets
Collembola species
In this study, we used two Collembola species: Vitronura pygmaea (Neanuridae) and Ceratophysella denticulata (Hypogastruridae). Vitronura pygmaea was selected because it has been observed to consume plasmodia in the field (19 July 2017, on dead tree bark, Yokohama National University [Kataoka et al., in press]). Ceratophysella denticulata was selected as a fungivorous species for comparison. Initial populations of V. pygmaea and C. denticulata were obtained from Yokohama National University (
Collembola
In V. pygmaea, body length increases were significantly greater in treatments with plasmodia than in those with dry yeast and no food (Fig. 1; PERMANOVA followed by pairwise permutation t-test with BH correction, P < 0.05); egg numbers were significantly larger in treatments with plasmodia than in those with dry yeast and no food (Fig. 2; PERMANOVA followed by pairwise permutation t-test with BH correction, P < 0.05). Consumption of waste slime sheaths was not observed in V. pygmaea during the
Discussion
The greatest body length increase and egg numbers under treatments with plasmodia were observed in V. pygmaea. These results suggest that V. pygmaea can use plasmodia as food and that it has adapted to consume plasmodia. Plasmodium consumption has also been observed in other members of Neanuridae (Greenslade et al., 2002; Hoskins et al., 2015); their mouth part structures, lacking a molar plate, may be suitable for consuming plasmodia with liquid bodies.
Ceratophysella denticulata was observed
Acknowledgements
This work was supported by a Japan Society for the Promotion of Science Grant-in-Aid for Scientific Research B (no. 17H037321). We are grateful to Dr. Yosuke Degawa at Tsukuba University and Prof. Nobuhiro Kaneko at Fukushima University for their helpful suggestions.
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