The taxa used in this study are tardigrades, nematodes, and rotifers, all of which are able to achieve a state of cryptobiosis when environments are temporarily unfit. These taxa can be found in moss and lichen on trees. The goal of this study is to evaluate how moss and lichen environments affect cryptobiosis survival rates of tardigrades, nematodes, and rotifers in order to find out how environment affects cryptobiosis overall. Moss is a much damper plant than lichen, and this difference in environment could play a role in how well the taxa can achieve and survive cryptobiosis. Due to lichen being a drier environment, it is possible that the taxa found in lichen could be better adapted to this environment, and therefore better able to survive the dry state that is experienced in cryptobiosis.

Our research question shifted to: Does substrate type affect composition rates of tardigrades, rotifers, and nematodes? Originally, it we planned to investigate survival rates, but did not acquire enough survival rate data to accomplish this.

The Chi Square Goodness of Fit Test for Moss about Taxa Composition had a significant difference among the taxa, meaning the null hypothesis was rejected. The Chi Square Goodness of Fit Test for Lichen about Taxa Composition did not have a significant difference among the taxa, so the null hypothesis failed to be rejected. Because of this it's clear to see there is a significant difference between the two substrates.

Research Question: Does substrate type affect taxa composition?

Discussion:

Substrate type does affect taxa composition of tardigrades, rotifers, and nematodes (χ2=14.53, p<0.0007, df=2, Figure 3).

This can be observed through the abundance of rotifers and complete lack of tardigrades in moss (Figure 2) (χ2=23.69, p<0.0001, df=2), in comparison to the almost equally split composition of lichen (χ2=0.33, p=0.8479, df=2, Figure 1).

This shows that some taxa are better adapted to different substrates. For example, rotifers appear to be better suited to moss (Figure 3) and tardigrades appear to be better suited to lichen (Figure 3).

This could be because tardigrades are more suited to cryptobiosis, so they thrive better in an environment with less moisture.

For future work, survival rates of taxa from different substrates could be studied to investigate whether or not substrate type affects cryptobiosis, because cryptobiosis is a result of a lack of moisture.

Understanding what selective pressures in an environment/substrate make cryptobiosis adaptive could help reveal its evolutionary history.

Figure 1: Variations in composition of the different taxa between the two substrates, moss and lichen.

References:

Boothby, T.C., 2018. Molecular Biology in Tardigrades. In Water Bears: The Biology of Tardigrades (pp. 331-347). Springer, Cham.

Crowe, J.H. and Madin, K.A., 1974. Anhydrobiosis in tardigrades and nematodes. Transactions of the American Microscopical Society, pp.513-524.

Degma, P., Katina, S. and Sabatovičová, L., 2011. Horizontal distribution of moisture and Tardigrada in a single moss cushion. Journal of Zoological Systematics and Evolutionary Research, 49, pp.71-77.

Jönsson, K.I., 2007. Long-term experimental manipulation of moisture conditions and its impact on moss-living tardigrades. Journal of limnology, pp.119-125.