Buccal tube dimensions and prey preferences in predatory tardigrades

Tardigrades are ubiquitous microfauna that act as consumers and predators in soil food webs. Several studies have suggested that tardigrades have great potential to control nematode populations. However, the regulatory function of tardigrades depends on many factors, including their feeding preferences. Yet, tardigrade feeding preferences remain largely unresolved. Therefore, in our experiment, nine predatory tardigrade species were tested for their preferences for three types of microfauna prey (nematodes, rotifers and tardigrades) under controlled laboratory conditions. We also tested whether tardigrade prey preferences can be predicted by selected functional traits (body length and buccal tube dimensions), because such traits are known to be a powerful tool in determining ecological links between organisms. We observed overall avoidance of tardigrades as prey along with preference for nematode prey. The difference in the total consumed number of the three types of prey were attributable to predator species identity, whereas proportional differences in the three types of prey in the diet were attributable to buccal tube length. Buccal tube width, buccal tube width to length ratio and body length lacked the predictive power for feeding preferences of predatory tardigrades. Our results showed that buccal tube length is more informative of tardigrade prey preference than predator species identity and can be used to predict tardigrade feeding preferences. The knowledge of tardigrade feeding preferences is crucial for understanding the role of tardigrades in soil food web.