What's inside a spore?

Moss spores are small single celled packages that play a crucial role in establishing new populations. These tiny units are blown by the wind and then landing somewhere suitable, grow into a new moss plant. They enable mosses to spread far and wide across the globe. 

There are two strategies for releasing spores. 

Xerochastic = capsules are open and spores are released when conditions are dry.

Hygrochastic = capsules are open and spores are released when conditions are wet.

We might expect to that plants with different strategies for spore release also have different types of spores. Maybe those that are released during wet conditions are primed to develop more quickly and those released when it is dry have more long-term energy storage to increase their survival until conditions are good for growth. 

In a recent study, Nagore Medina explored the question of whether spores have different characteristics between those that have xerochastic vs. hygrochastic dispersal in seven closely related Orthotrichum species. She used Transmission Electron Microscopy to examine the spore ultrastructure to determine if there were any differences between the species.

She found that the two hygrochastic species that disperse when conditions are wet have slightly smaller amounts of lipids inside. Think of the lipids as fat storage that helps the spores make it through tough times when they are not producing new food. This points toward these spores being less prepared to survive long-term out in the world prior to growing. 

Also the hygrochastic species have higher proportions of bicellular spores. Usually spores are just a single cell, as I mentioned earlier, but of course in biology there are always exceptions to the rule. Life is gloriously messy like that! They interpret the bicellular spores as a sign of early germination. Think of these spores being ready to hit the ground growing. They are so prepared that they already started dividing to produce more cells. 

Examples of this spore difference are visible in the images below. The two on the left have bicellular spores. There is a thin line running through the middle of the spore labeled "CW" indicating where a new cell wall has formed separating the two cells on either side. The spores on the right are each composed of only a single cell.

From Medina & Estébanez 2014. Transverse sections through the spores.
Two hygrochastic species on the left. Two xerochastic species on the right.
Upper Left: Figure 1C.  Lower Left: Figure 4C. Upper Right: Figure 6D. Lower Right: Figure 7D.

These are the main differences that they found between the spores of hygrochastic and xerochastic species. Unfortunately no other significant differences were found between the spores. But that is how it sometimes goes with science. Scientists come up with an interesting hypothesis that predicts a particular pattern and you find a bit of data supporting your prediction, but not nearly as much as you had hoped to make a very strong conclusion. Instead there is a bit of evidence supporting your idea, which may be just enough to keep you trying out the next experiment to see where the explorations will take you. 

Nagore G. Medina & Belén Estébanez. 2014. Does spore ultrastructure mirror different dispersal strategies in mosses? A study of seven iberianOrthotrichum species. 9 (11): e112867.

A Science Communication Activity on Birds and Bryophytes

Have you ever played the telephone game? In this game a phrase is whispered from one person to another with the players trying to repeat the phrase exactly the same. By the time the phrase makes it to the other end of the line it is often altered, sometimes dramatically so. The same can also happen to research as it is transmitted from a peer-reviewed scientific article to the popular media, such as a magazine or newspaper. One explanation for alterations to the research story is that scientists use language with lots of jargon and scientists often use many words that are qualifiers. Qualifiers are words that limit or enhance the meaning of another word. Most often when scientists use them it is to explain the scope and limits of their findings. All-in-all the language of science is significantly different from the language the news media uses to communicate with the public and the weight that is given to different terms and phrases varies between the two.

I think that science communication is an important concept for students who are training to be scientists to both ponder and explore. Thus I developed a team-based learning activity to walk students through the exploration of a scientific research article and the news media reporting on the findings. The main learning objectives of this exercise are for students to: 

-   Analyze the transmission of information from scientific publication to news media.

-   Identify absolute versus qualified statements.

-   Differentiate different organisms from bryophytes.

An additional goal of this exercise was to introduce students, potentially for the first time, to a scientific research article. Reading peer-reviewed research from beginning to end can be intimidating for science students. This activity has students explore the research article for information to compare to the news articles, resulting in students both learning how to find information in scientific papers and how to ground-truth science that is reported in the media.  

If you are interested in trying out this activity with your students I posted the materials that you will need online, via Google Drive. Included in the materials is a detailed lesson plan, as well as a pre- and post- assessment (with a key) to measure student learning from the activity. Alternatively this activity can be modified to focus on any scientific paper from your field that has been covered in multiple news articles. 

The article that I used for this exercise was a publication studying whether migrating birds may be responsible for moving pieces of bryophytes from northern arctic regions to the far southern reaches of South America. 

The research article can be downloaded for free at the link below. 

Lily R. Lewis, Emily Behling, Hannah Gousse, Emily Qian, Chris S. Elphick, Jean-Francois Lamarre, Joel Bety, Joe Liebezeit, Ricardo Rozzi, and Bernard Goffinet. 2014. First evidence of bryophyte diaspores in the plumage of transequatorial migrant birds. PeerJ 2:e424; DOI 10.7717/peerj.424

The news articles covering this research are at BBC Nature News, Audubon Magazine, Science Magazine, UConn Today, and Alaska Dispatch News.

If you use this activity with your students, it would be great to hear your thoughts about the exercise in the comments section below the post!