Is the gut content ofMilnesium(Eutardigrada) related to buccal tube size?

Abstract

Milnesium, with its relatively short and wide buccal tube, is considered carnivorous. Species in this genus exhibit differences in buccal tube length, standard buccal tube width, and the buccal tube length/width ratio. To determine whether buccal tube size is correlated with the type of prey,~4000 specimens of various Milnesium species were examined. Among those with identifiable gut contents,~97% contained tardigrades, rotifers, or both, whereas only~3% contained nematodes or amoebas. In total, 189 females with guts containing only tardigrades, only rotifers, or both were analysed with general linear model multivariate analysis. Milnesium specimens containing only tardigrade remnants were larger and had longer and wider buccal tubes than those containing only rotifers. Those with only tardigrades in the gut also had a significantly lower buccal tube length to width ratio than those with only rotifers in the gut. Specimens with a mixed diet (rotifers and tardigrades) had intermediate values of buccal tube width and length, and these differed significantly from individuals containing rotifers or tardigrades only. Variation in buccal tube dimensions was linked with interspecific and age (size)related factors, and differences in buccal tube dimensions associated with gut content remained significant, even when the analysis was controlled for the interspecific variation. No evidence of cannibalism was observed.

Tips and tricks how to culture water bears: simple protocols for culturing eutardigrades (Tardigrada) under laboratory conditions

“…or Chlorella vulgaris Beijerinck 1890; nematodes: Caenorhabditis elegans (Maupas, 1900) and rotifers: Lecane inermis (Bryce, 1892). Other types of food proposed for some tardigrade species were bacteria, diatoms, cyanobacteria, other tardigrades or even fungi (Nelson et al 2010;Guidetti et al 2012;Roszkowska et al 2016;Morek et al 2020;Bryndová et al 2020). Moreover, the same type of food (the same prey species or algae) has been proposed for different tardigrade taxa, which shows that tardigrades are not monophagous and some are even omnivorous, which was also previously suggested by several authors (e.g.…”

Desiccation risk favours prevalence and diversity of tardigrade communities and influences their trophic structure in alpine ephemeral rock pools

“…Instead, we account for potential sampling bias in determining the number of genera by using the number of individuals mounted on slides and taxonomically identified as a second covariate in the diversity analysis. For model estimates, the proportion of non-carnivorous individuals, tardigrade density and rotifer abundance were included as covariates, as both tardigrades and rotifers are known food items of carnivorous tardigrades (Kosztyła et al, 2016;Roszkowska et al, 2016;Bryndová et al, 2020), and thus could influence their proportion. Although the sampling in this study was performed on three different occasions, the sampling period was not considered in the analyses as only a few samples were collected in the first and second sampling events (11/56 and 2/56 respectively; SM.01) and in those two sampling trips only clusters A, C, D, E and K were sampled.…”

“…This reduction in carnivorous tardigrades is probably due to competition with other co-occurring invertebrate predators (chironomids and flatworms). Moreover, since predatory tardigrades (e.g., Paramacrobiotus and Milnesium) are usually larger than the herbivorous ones (e.g., Hypsibius and Grevenius) (Kosztyła et al, 2016;Roszkowska et al, 2016;Bryndová et al, 2020), they could also be more appealing prey for even larger predators (i.e., size-dependent predation, see for example Sprules, 1972 andHohberg &Traunspurger 2005). Both competition with, and preferential predation by, bigger predators could contribute to this extremely biased trophic structure in Holes compared to Pans and Intermediates.…”

“…It is possible that the larger surface area allows more solar radiation to be captured by algae and thus increases primary productivity, which would in turn support the growth and reproduction of algivorous taxa. Lastly, as rotifers are preyed on by carnivorous tardigrades (Roszkowska et al, 2016;Bryndová et al, 2020), it would be logical to predict a link between the two trophic level groups. In contrast, we found that rotifer abundance did not have a significant effect on the proportion of non-carnivorous tardigrades, which suggests that this type of prey availability is not a main factor influencing tardigrade community trophic structures.…”

Two new species of the genus Milnesium Doyère, 1840 (Tardigrada, Apochela, Milnesiidae) from Madagascar

“…Species of the genus Milnesium Doyère, 1840 are large and carnivorous, feeding mainly on rotifers, nematodes and other tardigrades, but single reports show that they can also feed on amoebas (Miller and Williams 2012; Roszkowska et al 2015, 2016). Species in this genus reproduce parthogenetically and/or bisexually, and are characterised by sexual dimorphism (e.g., Suzuki 2003; Ciobanu et al 2015).…”