![]() Importantly, however, none of the surveys tested what specific tardigrade feeding groups (proposed by Guidetti et al., 2012) may or may not eat. These feeding associations have been used in a couple of ecological surveys to study tardigrade distribution in the environment ( Guil & Sánchez-Moreno, 2013 Vonnahme et al., 2016 Zawierucha et al., 2019). In spite of our limited knowledge on foraging preferences of individual species, tardigrades are traditionally classified into specialized groups according to the type of their feeding apparatus ( Guidetti et al., 2012). Feeding on plant cells had been disputed repeatedly ( Baumann, 1966 Hallas & Yeates, 1972), but feeding on mosses was recently documented molecularly in some Macrobiotidae ( Schill et al., 2011) and moss carotenoids were also detected in the body of the tardigrade Echiniscus blumi ( Bonifacio et al., 2012). Altiero & Rebecchi, 2001) and also by gut content analysis and laboratory observations ( Hyvőnen & Persson, 1996 Altiero & Rebecchi, 2001 McInnes et al., 2001 Hohberg & Traunspurger, 2005 Sánchez-Moreno et al., 2008 Schill et al., 2011). Feeding on algae and micrometazoans is well documented by direct observations in cultures (e.g. The best-described food sources of tardigrades are algae and micrometazoans. ![]() Protozoa, on the other hand, are reported mainly as occasionally observed remnants of testate amoebas in the gut of tardigrades ( Hallas & Yeates, 1972 Roszkowska et al., 2016). Interestingly, fungi are often mentioned as tardigrade food items but with no reference to original information sources ( Ramazzotti & Maucci, 1983 Sánchez-Moreno et al., 2008 Guidetti et al., 2012). Feeding on bacteria and detritus is known only from anecdotal observations of grazing on bacterial films or detritus ( Hallas & Yeates, 1972 Hohberg & Traunspurger, 2005 Hohberg, 2006). However, there are no studies that have tested the significance of bacteria, detritus, fungi or protozoa as a tardigrade food source. Tardigrades are known to feed on bacteria, detritus, algae, contents of plant cells, fungi, protozoans and micrometazoans, such as rotifers, nematodes and other tardigrades ( Ramazzotti & Maucci, 1983 Nelson et al., 2015). Moreover, feeding behaviour is also of vital importance in successful laboratory tardigrade culturing. For example, without understanding tardigrade dietary preferences, we fail to explain the role of tardigrades in food webs, their ability to influence other organisms and the distribution of tardigrades themselves, since abiotic factors seem to be inconclusive determinants of water bear communities ( Hohberg, 2006 Hohberg et al., 2011 Zawierucha et al., 2019). Despite their cosmopolitan distribution, basic knowledge of their biology, such as feeding behaviour and effect of diet on survival and reproduction, is limited. Limnoterrestrial species are most often found on mosses and lichens, but also in leaf litter and soil ( Ramazzotti & Maucci, 1983 Nelson et al., 2015). They are found in all climate zones and from ocean depths to mountain peaks. Tardigrades (water bears) are a phylum of microscopic metazoans that inhabit a wide variety of environments throughout the world. Thus, gut content analysis may be misleading as a method of studying tardigrade feeding habits.įeeding traits, gut contents, Hypsibius exemplaris, LHT, Milnesium inceptum, Paramacrobiotus fairbanksi, reproductive success, starvation resistance, survival, Tardigrada, water bears INTRODUCTION Finally, we demonstrate that tardigrades may ingest food types that they are not able to digest. Reproduction was strongly affected by food type. In some cases, juveniles preferred different types of food than adults. Paramacrobiotus fairbanksi, on the other hand, is demonstrated to be an omnivore, feeding on cyanobacteria, algae, fungi and animals. We also show that Hypsibius exemplaris is a herbivore, feeding on cyanobacteria, algae and fungi. In our experiments, Milnesium inceptum is confirmed to be a carnivore, being able to reproduce only on animal prey. We also tested for differences in preferences between juveniles and adults, and differences in survival between two age groups: one that started the experiment as juveniles and the other as adults. Here, we used a number of laboratory experiments with 18 potential food sources, representing a wide variety of organisms, to test feeding preferences, survival and fecundity of three tardigrade species, representing different feeding modes. However, little is known about their specific feeding preferences. Tardigrades may be divided into the following feeding groups: herbivores, carnivores and omnivores.
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