Growing up in Canada, our culture has always praised the pioneers who colonized what we call home. Lichens, in the way the first settlers tell us about a community, tell us a lot about an ecosystem. They are bioindicators for air quality and perhaps even cardinal direction. Join us in our investigation as we discuss our interest in the latter myth.
A Little History
In 1867, Simon Schwendener proposed that lichens were composed of two organisms (Honegger, 2000). A study was conducted by Bässler et al (2015) just last year focusing on one lichen specie over 16 countries showing that fungi can select for specific photobionts which is likely a driving factor for such immense lichen diversity. Though lichens are known to be pioneer species, the first colonizers of a disturbed environment, they’re also quite sensitive to changes in temperature and levels of precipitation (Bässler et al, 2015). Some scientists are looking at lichens to predict the effects of climate change in certain ecosystems. Most recently, a paper was published by Spribille et al (2016) proving that many species of lichens have a third symbiotic partner: yeast. Even with this sink of knowledge the most experienced lichenologists must admit defeat when it comes to surveying lichens in large plots. The problem is they can be virtually anywhere. In a study by Vondrák, J., et al. (2016), it is explained that many species are very specialized and are found only in one place, for example, high in the forest canopy . Their canopy sampling was mostly from fallen twigs; clearly there were missed opportunities to complete their species list. In our own research we have a similar problem since our sampling was only at breast height and not the entire height of our tree replicates.
Symbiosis in lichens involve a mycobiont (fungus), and a photobiont (photosynthetic agent, usually algae), in one structural unit. The fungi provides a comfortable habitat for the algae and the algae provides food from photosynthesis. Lichens are distinguished by the shape, size, colour and specific combinations of mycobiont and photobiont; classification is based on their fungal component. Lichens generally assume one of four morphologies: foliose, fruticose, crustose and squamulose. The differentiation is usually made by examining the thallus, the main body (Shukla, Upreti et al. 2013).
Figure 1a) Blue green foliose lichen with two-dimensional lobes. b) Fruticose lichen with an erect and shrubby thallus. c) Green cup-like erect thallus of a fruticose lichen. d) Crustose lichen with an irregular-crack shape, seen through a magnifying glass.
The foliose growth form is one that we came across very often in the field. It’s characterized by a leafy two-dimensional thallus, more or less flattened, that remains attached to the substrate by adherent rhizines, which act as anchors rather than roots since they don’t take up nutrients (Brodo, Sharnoff et al. 2001). This wavy sheet-like structure usually gives rise to circular lobes (Figure 1a). A fruticose lichen presents a three-dimensional thallus that can be either erect (Figure 1b, c) or pendant. Its tangled appearance and the absence of rhizines leads to instability (Brodo, Sharnoff et al. 2001, Lepp 2011). Crustose lichens, as their name suggests, are crusty-looking and firmly attached to their substrate. They can be smooth or broken forming cracks that divides the lichen in patches (Figure 1d) (Brodo, Sharnoff et al. 2001).
Reproduction can either be sexual, meaning both parents contribute genes to the progeny, or asexual, the progeny is identical to one parent, or both, depending on the species (Lepp 2011). In sexual reproduction of lichen the fungal partner produces two kinds of reproductive structures, or fruiting bodies, resembling tiny button mushrooms (Brodo, Sharnoff et al. 2001, Lepp 2011). The first, apothecia, has a bowl shape with spores on the inside surface as shown in Figure 2a.
The other, perithecia, is shaped like a fig and has an internal spore producing layer hidden inside the thallus that releases spores by an opening on the top where the fig’s stem would be (Figure 2b) (Brodo, Sharnoff et al. 2001).
Figure 2 a) Black apothesia with a cup shape. b) Perithesia shown here as small black dots .
Those spores, once released, will need to land on the right photobiont, in the right habitat to be able to produce viable lichen, a challenging feat. Vegetative, or asexual, reproduction is when lichen grows from a broken fragment of the thallus. In this case the lichen is a clone of its parent; this is the most efficient way of reproducing (Lepp 2011).
Distribution of lichen is strongly correlated with its status of pioneer species. Lichens can survive surrounded by a thick layer of snow in Antarctica and extended periods of drought in the McMurdo valleys (Australian Government, 2016), conditions that would annihilate many other fierce species, even us. They grow on lots of surfaces like tree bark, rocks, and even on the outside walls of McGill’s Macdonald Campus.
Our Research Question
Is there any correlation of lichen abundance and diversity with cardinal direction on tree bark?
Step 0: We call this step zero because it must be completed before going into the field. Create a data sheet to record all data.
Step 1: Select an open area with several trees that appear to have even sun exposure on all sides.
Step 2: Tag trees that have been quickly inspected to see if they have equal exposure to the sun on each cardinal direction. In other words, walk around the tree and look.
Step 3: Stand by the tree. Use the compass to identify which side of the tree faces north. Imagine the tree as the center of the compass.
Step 4: Accurately measure Breast Height (1.3m) from the ground to the bottom of the grid square. Place the grid up against the tree following the direction previously determined.
Step 5: Observing the grid, use one grid square equals to 0.5%. Estimate approximately the amount of lichen coverage and identify the species involved; indicate the dominant specie. For identification, refer to Lichen Structure mentioned above. Record results.
See our video explaining our methods!
We observed lichens on every cardinal side of the tree but it remains to be seen if some lichen species prefer a specific cardinal side. We will need to revisit the number of visible species on many replicates since our identification techniques have broadened since the beginning of our research.
Stay tuned and follow us on twitter (@ImLichenIt16) to see how the cardinal direction myth pans out.
Figure 3. The lichen team
1- Australian Government, D. o. t. E. a. E., Australian Antarctic Division (2016). “Lichens.” from http://www.antarctica.gov.au/about-antarctica/wildlife/plants/lichens.
2- Bässler, C., et al. (2016). “Contrasting patterns of lichen functional diversity and species richness across an elevation gradient.” ECOG Ecography 39(7): 689-698.
3- Brodo, I. M., et al. (2001). Lichens of North America. New Haven, Yale University Press.
4- Duketoday (2011). “Lichen evolved on two tracks, like mammals and marsupials.” from https://today.duke.edu/2011/05/lichen.
5- Honegger, R. (2000). “Simon Schwendener (1829-1919) and the Dual Hypothesis of Lichens.” The Bryologist 103(2): 307-313.
6- Lawrey, J. D. (1994). Lichen Allelopathy: A Review. Allelopathy, American Chemical Society. 582: 26-38.
7- Lepp, H. (2011, 24 December, 2015). “Lichen.” from http://www.cpbr.gov.au/lichen/index.html.
8- Lutsak, T., et al. (2016). “Mycobiont-photobiont interactions of the lichen Cetraria aculeata in high alpine regions of East Africa and South America.” Symbiosis Symbiosis 68(1-3): 25-37.
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10-Seneviratne, G. and I. K. Indrasena (2006). “Nitrogen fixation in lichens is important for improved rock weathering.” J Biosci Journal of Biosciences 31(5): 639-643.
11- Shukla, V., et al. (2013). “Lichens to biomonitor the environment.”
12- Spribille, T., et al. (2016). “Basidiomycete yeasts in the cortex of ascomycete macrolichens.” Science 353(6298): 488-492.
13- Vondrák, J., et al. (2016). “Methods for obtaining more complete species lists in surveys of lichen biodiversity.” NJB Nordic Journal of Botany 34(5): 619-626.
14- Yahr, R., et al. (2006). “Geographic variation in algal partners of Cladonia subtenuis (Cladoniaceae) highlights the dynamic nature of a lichen symbiosis.” New Phytologist 171(4): 847-860.