Mysterious Moss Piglet: Researchers discover new tardigrade species

Mysterious Moss Piglet: Researchers discover new tardigrade species

Tardigrades, also known as water bears or moss piglets, are microscopic animals that previous research has shown can survive extreme conditions. Researchers recently identified a new tardigrade species in Japan, Macrobiotus shonaicus, and describe its distinctive characteristics as well as how it relates to other known tardigrade species in their new PLOS ONE study. I discussed this finding, as well as its broader implications, with lead author Daniel Stec.


What drew you to studying tardigrades?

DS: I started working with tardigrades as an undergrad in the team of Łukasz Michalczyk, who is now my Ph.D. supervisor. I got drawn into tardigrade research very quickly since so many things about these amazing and beautiful creatures are yet to be uncovered, no matter whether it’s their taxonomy, phylogeny, evolution, ecology, behavior, physiology, or any other aspect of their biology. Everything about tardigrades is simply super thrilling to me.

Why study tardigrades in Japan specifically?

DS: Even though the number of tardigrade species recorded from Japan is not particularly low compared to other regions of the world, the majority of Japanese records are old and are based on outdated descriptions. In other words, the identity of many of Japanese tardigrades cannot be trusted. Thus, in the end, we cannot confidently say what tardigrade species diversity there is in Japan. There is no other way to fix this but study Japanese tardigrades with the use of the tools offered by integrative taxonomy.

Why did you think tardigrades would be present in the moss from a car park?

DS: Tardigradologists are very often asked this kind of questions and they are not easy to answer. Most of tardigrade species were described from mosses and lichens, thus any cushion of moss seems to be interesting for people working on tardigrades. If the moss cushion comes from an unusual habitat and looks very fresh and greenish, you can almost smell the new water bears and you basically cannot resist collecting the sample and examining the micro life that it harbors. Apparently, the same instinct was triggered when my colleague Kazuharu Arakawa spotted a patch of moss on a carpark outside his apartment. The identification of a new species in the sample confirms that Arakawa’s instinct was right.

What makes this tardigrade species different from previously known species?

DS: The species belongs to the Macrobiotus hufelandi group, a group of nearly fifty species that for decades used to be considered a single cosmopolitan species, M. hufelandi. Species within the group are characterised by conserved animal morphology and much for variable egg shell appearance. Nevertheless, characteristics of both animals and eggs have to be taken into consideration to correctly identify species in this group. The main characters that make M. shonaicus different from other congeners are those of egg ornamentation, such as solid egg surface between processes (i.e., without reticulation or pores) or flexible filaments at the end of egg processes (that are known only in two other species of the group, one from Africa and the other from South America).

SEM images of the new tardigrade species’ eggs.

Do we know the purpose of the variations in egg appearance found in different species?

DS: The variation in egg ornamentation compared to rather stable animal morphology in many tardigrade groups could be explained by either strong or relaxed natural selection. Generally, rapid evolutionary changes are known to be driven by unstable and/or heterogeneous environmental conditions. Thus, it could be hypothesized that different egg morphotypes are adaptations to egg laying in specific microhabitats that require different shapes and sizes of egg processes. However, the alternative explanation could be that water bears don’t show strong egg laying preferences and the morphological diversity of egg shells is evidence that the strict shape of processes is not crucial for maintaining protection and attachment properties of eggs. If this alternative scenario was true, it would mean that relaxed natural selection allows departures from ancestral egg morphotype and results in such a great diversity of egg ornamentation. Nevertheless, it remains to be tested which of these is a true explanation.

Why is our understanding of tardigrades important?

DS: The most basic reason is human curiosity and once you fall in love with tardigrades you only want to know more, especially since there is still so much to discover about them. However, there are also other reasons. Recently, tardigrades started to be used as model organisms in a variety of studies ranging from astrobiology, developmental and cell biology, physiology, evolutionary ecology and many other disciplines, in hope to address more general questions. Tardigrades became very famous in popular culture thanks not only to their undeniable cuteness, but mostly because of their ability to enter into cryptobiosis, a latent state in which virtually no metabolic activity can be detected. Yet, when dried or frozen tardigrades are provided with liquid water they come back to life as if nothing had ever happened. This ability to withstand harsh conditions and to suspend their lives inspired researchers to produce dry vaccines that don’t require refrigeration or create transgenic human cells that are more resistant to irradiation. Who knows, maybe someday, thanks to tardigrades, we will be able to preserve organs for transplantation, extend our lifespan, or travel to other planets and stars, not worrying about detrimental effects of cosmic radiation.

Reference: Stec D, Arakawa K, Michalczyk Ł (2018) An integrative description of Macrobiotus shonaicus sp. nov. (Tardigrada: Macrobiotidae) from Japan with notes on its phylogenetic position within the hufelandi group. PLoS ONE 13(2): e0192210.

Image Credit: Tardigrade and tardigrade egg images: Stec et al (2018); Daniel Stec


Tessa is the Journal Media Manager at PLOS. She graduated from the University of California, Berkeley with degrees in Rhetoric and Music. She can be reached by email at and on Twitter at @tessagregs.

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