Off with the Wind: The Reproduction Story of Antarctic Lichens

How do organisms begin new life at the bare surfaces exposed by glacier retreat? A team of researchers from the Czech Republic recently published a paper on the spread of one organism, a lichen, across James Ross Island near the Antarctic Peninsula. The study found that lichens can disperse over long distances, likely by means of aerial transport. Increasing warming trends on James Ross Island will likely result in more deglaciation, providing species like lichens with the opportunity to colonize new areas.

Usnea sp Lichen on James Ross Island (Source: Elster Josef)
Usnea sp Lichen on James Ross Island (Source: Elster Josef).

There has previously been considerable debate on the reproductive and dispersal mechanisms of lichens, especially in the polar regions. The study’s findings on lichen reproduction is promising, given the important role lichens play as primary successors, contributing to soil development and the establishment of ecosystems with greater biomass and biodiversity. Combining an alga and a fungus, the lichen can grow on almost any surface, from sea level or high altitudes to the side of trees or on rocks. Lichens are also able to reproduce both sexually (through propagules, which are small, vegetative structures that get detached from the parent plant) or asexually (mini-lichens), and are transported by wind, sea currents or birds.

GlacierHub spoke with lead author Elster Josef from the Center of Polar Ecology about the study. He asserts that one of the most distinctive features of James Ross Island is the island’s so-called volcanic mesas, which are favorable locations for biomass growth. Volcanic mesas originate from superimposed subglacial volcanic eruptions and are characterized by a relatively flat highland with steep edges. Usnea sp., a lichen commonly known as the old man’s beard, is the most important lichen in this system. “It produces dense carpets in the oldest volcanic mesas. This species has many advantages in respect of dry local climate,” Josef said.

Overview of James Ross Island with its volcanic mesas (Source: Elster Josef)
Overview of James Ross Island with its volcanic mesas (Source: Elster Josef).

There is a clear gradient of lichen cover and diversity from north to south on James Ross Island, according to Josef. One important question of the research was how this lichen carpet advances with glacier retreat. Josef stated that his team was able to successfully develop a non-invasive method to measure lichen carpet diversity and biomass. Traps in the form of petri dishes fixed to rock surfaces with stick tape were the simplest and most effective way for the team to measure lichen dispersal across the island, according to Josef. A total of 100 traps were placed during the summer season of January/February 2008 and left exposed for a year. In the end, only 60 traps were found due to snow cover and strong wind disturbance.

For the Antarctic lichens, vegetative asexual reproduction was found to be more dominant due to environmental stresses. While the old man’s beard and the Leptogium fungus (Leptogium puberulum) were the two most common local species on the island, their frequency of occurrence in the traps was unrelated to local species dominance. Long-distance dispersal of vegetative parts occurs more frequently on the larger scale as a result of wind conditions.

Lichen Spore/Fragment trap designed for the research using sticky tape in a petri dish(Source: Elster Josef)
Lichen Spore/Fragment trap designed for the research using sticky tape in a petri dish (Source: Elster Josef).

Surface wind speeds on the mesas are often higher than 6m/s (roughly 12 mi/hr) on average, with extremes reaching up to 30m/s (60 mi/hr). Larger amounts of lichen spores and fragments were found in the traps located along the prevailing wind direction. Overall, the highest occurring species in the traps were of foliose and fruticose growth types, which favored wind dispersals.

The main difficulty of the research method was that the dispersal of lichens is influenced by many abiotic and also biotic factors, according to Josef. These include distance from glaciers and elevation to existing lichen diversity and cover on site. The method was also limited because it did not involve measurements of what is viably ready (in-situ) to start growth and only measured what types of lichens were dispersed.

A team member collecting the samples on the sticky tape after the trap was exposed for a year (Source: Elster Josef)
A team member collecting the samples on the sticky tape after the trap was exposed for a year (Source: Elster Josef).

The greatest confirmation to the team’s hypothesis was the strong positive correlation between the size of clast, or rock fragment, and the dispersed species assembly. Clast size is determined based on the average diameter of rocks in the area. Often, areas with larger clast size are characterized by a thriving diversity of lichen communities. They represent more stable locations for growth since larger stones shield the newly-trapped lichen fragments from being uprooted by the wind again.

Still, according to Josef, lichen development is rather rare despite the large numbers of reproductive fragments dispersed. The growth of a lichen community is a long-term process, and Josef hopes to continue to evaluate the reaction of lichens to climate change in polar regions to shed light on the colonization mechanism of pioneer species in newly-exposed surfaces.

On Glaciers, Moss Become Asexual

A recent study from the journal Czech Polar Reports presents interesting findings about a rarity on glaciers: moss.

Glacier Mosses(Credit: Flickr)
Glacier Mosses(Credit: Flickr)

When glaciers have a certain amount of moisture and cryoconite—a base layer that consists of small rock particles, soot, and microbes that have accumulated on glaciers— sometimes mosses can grow on them. While it is not common to see moss on glaciers, according to a paper by Olga Belkina, a researcher at the Institute of the Kola Science Centre of the Russian Academy of Sciences, they have been found on a few glaciers in Alaska, Iceland, and Svalbard, Norway.

There are some moss attributes that contribute to the mosses’ tolerance of the brutal living conditions found on glaciers. First, moss do not absorb nutrients from the substrate, the layer to which they are attached, since mosses do not have roots. They absorb water and nutrients directly through their leaves. Mosses only have rhizoids–threadlike tissues which look like roots, but function only to attach to the surface they grow on and can’t absorb water or nutrients from soil or any other substrate.

Second, mosses have have the ability to adapt to a wide range of light levels, which means some types of mosses can survive under massive exposure to sunlight. Some mosses are found in the desert, and some can survive with the low intensity of sunlight found in polar areas.

Glacier Mosses(Credit: Flickr)
Glacier Mosses(Credit: Flickr)

Although glacial areas aren’t the ideal living conditions for mosses, there are still the minimum living requirements for them to grow. There is enough moisture and little competition from other plants, allowing them to survive.

One mystery of the development of mosses found on ice is that how they reproduce in such cold areas. “Failure of sex reproduction of many mosses is widespread in the high polar regions,” the study reports.

The alternative is asexual reproduction. Reproduction strategies for most species fall into two categories, sexual reproduction and asexual reproduction. The offspring of the asexual reproduction process are identical to a single parent, while the offspring from sexual reproduction received genetic information from both parents.

An interesting finding, according to Belkina’s study, is that Schistidium abrupticostatum, a type of moss found on the ice of Bertilbreen, Svalbard, produces gametangia–an organ which produces gametes that can fuse with another cell during fertilization to sexually reproduce. However, the mosses do not evolve into sporophytes, or the non-sexual phase of a plant.

 

Glacier mice(Credit: Wikimedia)
Glacier mice(Credit: Mental_Floss)

Normally plants would alternate between a sexual phase (gametangia) and a non-sexual phase (sporophyte). During the non-sexual phase, plants grow larger and taller to produce spores through meiosis. Then the spores divide into gametes, or sex cells. A gamete from one plant can merge with another gamete, completing a set of chromosomes to start the next round of reproduction.

Generally, mosses do not develop into gametophytes in harsh conditions like glaciers, even though they do in areas that are near the glaciers. Many mosses can be brought to the glaciers by wind and then settle on surface and substratum, yet only a few have the chance to create long-lived populations in such cold conditions.
Each clump of moss on glaciers consists of genetically identical individuals, and the populations grow by the asexual method, which means new mosses can regenerate from a small section of existing moss plants.