An international team of researchers led in part by Texas Tech assistant biology professor Matt Johnson used a large amount of DNA data from each of mosses’ three genomes. Those genomes exist in the mosses’ mitochondria, the chromosomes of cell’s nucleus, and in the plant’s chloroplasts.
The study was funded by the National Science Foundation and was based on comparisons of 142 species of moss from 29 of the 30 orders of mosses in existence. It was published in 2019 in Nature Communication.
Johnson says there’s a misconception that organisms gain complexity as they evolve.
“The major lesson that mosses can teach us is about some of the misconceptions about evolution and how it’s shaped our world. Sometimes you’ll look at a moss and think ‘oh, it’s primitive, it doesn’t have roots, it doesn’t have seeds, it doesn’t have ways to transport water,’ but that doesn’t mean it’s primitive. Organisms’ populations are always evolving and even though they look simple, simple doesn’t mean that they stopped evolving. It just means that evolution has shaped them in a different way than the complexity that seems to accumulate in other groups.”
Johnson says the study’s findings showed a major theme in moss evolution is changes to the way a moss releases its spores.
In all, there are 13,000 species of mosses across the globe, more than the number of either mammals or birds. The study had representatives from each of the major moss groups.
Mosses are highly resilient, Johnson says, and like all species of plants and animals, subject to Darwin’s theory of survival of the fittest.
“Everything does fit under that survival of the fittest, but the survival is different for different organisms. So for one species it may be easier to survive by getting more complex and trying to attract pollinators and other species, the survival may come from living in the shadows on the edge of a tree, and so how can an organism best adapt to that low-light condition?”
He says that mosses are critical to ecosystems.
“They provide quite a resource for cycling of both carbon and nitrogen, and that’s true of the largest group of mosses, the group of mosses that might grow on rocks and trees. These are early colonizers of bare soils and will quickly turn over soils so that other organisms can grow. And then of course, you have my favorite, the peat mosses that essentially engineer their own ecosystem by creating an environment where nothing else can grow except the peat mosses, and they can totally change not just the environment, but the whole landscape.”
Critical to the study were contributions from herbaria, which are collections of dried plants mounted, labeled, and systematically arranged for use in scientific study, in Europe and the US
Johnson says the study is not the first to construct a tree of mosses. But this research, which took several years and was international in scope, is the first of its kind and produced the largest genome data set for mosses.
The study’s results, he says, helped build a well-nuanced data framework for additional research into which smaller moss groups can be fit. Another study is ongoing that is also funded by the National Science Foundation. The data analysis work done by Johnson and colleagues on this study will benefit the ongoing work with 430 moss species representing every genus of a major group.
“The same national science foundation grant that funded this research is also funding a larger project that focuses on one specific group of mosses. It’s a group that has about half of the species of mosses, and kind of with the theme that mosses did not stop evolving, this particular group originated only 90 million years ago, so on the scale of mosses, it’s relatively new.”