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Solving a Myth: Do Lichens Know What Direction They’re Growing In?

Introduction

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.

Structure

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).

picture1Figure 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

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).

picture2Figure 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

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?

Methods

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!

Conclusion

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-14Figure 3. The lichen team

Bibliography

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.

9- Moore, T. R. (1981). “CONTROLS ON THE DECOMPOSITION OF ORGANIC MATTER IN SUBARCTIC SPRUCE-LICHEN WOODLAND SOILS.” Soil Science Soil Science 131(2): 107-113.

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.

 

 

 

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7 comments on “Solving a Myth: Do Lichens Know What Direction They’re Growing In?

  1. Great post guys!! Learned lots of neat things! This is such a neat natural history project because Lichens are just not that popular in the science community, but they are so important. So thank you for exploring such a lesser-well known topic!
    Your promo was excellent, and the blog post was just as great!

    Question for you now; Do you think that the cardinal direction of lichen growth could be used as bio-indicators of climate change and pollution levels?

    I’d be curious to see if certain species are more influenced to grow in the opposite direction of air currents (where air-borne pollutants are carried by the wind).

    Great job guys!

    • Thanks for taking an interest, Gaby! To answer your first question, certainly lichens can be used as bio-indicators for air quality, they already are; Liking Lichens 16’s project is based on this. Some lichens are intolerant to even small amounts of sulfur dioxide, for example, so they’re found more in rural areas rather than cities.

      As a bio-indicator for climate change, though, would be more difficult since lichens grow so slowly. Also, lichens that are dead stay attached to their substrate. So we wouldn’t see any change fast enough to use it as a bio-indicator for climate change.

      Thirdly, that’s a very interesting notion that lichens would grow on the side of the tree opposite to wind currents to avoid pollutants but it would take a very VERY long time to observe this growth. It would certainly be a great survival mechanism for them though!

      ImLichenIt Crew

      • All makes sense! And yup! I know they’re bio-indicators for contaminants and pollutants (so neat). But yea! You bring up a fair point about their slow growth (didn’t even consider it cause their little leaf-things are small in comparison to a normal plant). But it makes loads of sense.

        And yea, since they have a thallus and no roots, I suppose it would make sense for them to stay attached to their substrates!

        All very fair points! Such interesting creatures!
        Thanks for answering my question!
        Gaby

  2. Hey guys! Lichen pollution group here. Cool research project! Did you identify all your lichens to the species level? Just out of curiosity, how many different species did you find? It would be interesting to compare notes as to what we both found! We found a total of 19 species (specifics are posted on twitter). How many did you guys find?

  3. Hello fellow lichen colleagues!

    No, we couldn’t identify all of our lichens to the species level (but I’m sure Catherine won’t rest until she has). Did you run any tests to ID yours? Because we identified them by eye only and there are many that resemble each other. We looked at geography, size, color etc. to give us the best answer.

    We found about a dozen species. These were dominant on at least one cardinal side at least once in the Blossom Corner and at the entrance (near the hut) of the Arboretum:
    Beige crustose
    Parmelia sulcata
    Candelaria fibrosa
    Leprose Green
    Phaeophyscia adiastola
    Graphis Scripta
    Buellia [species]
    Physcia Stellaris
    Black
    Physcia Millegrana
    Evernia Mesomorpha (not part of data)
    Stubble lichen (not part of data)

    If were able to identify all 19 of your to the species level, kudos, that is not an easy task! We’d love to see you’re list as well! And we’re very excited to see on Wednesday if you found a difference between the Arboretum and Mac Campus.

    ImLichenIt Crew

    • Cool! We had a lot of species in common with you. We used the same ID methods as you, relying on reference materials with data on habitat and range. Some of the ID was quite difficult. Here’s what we saw at the arboretum (in order of declining abundance):
      Vulpicidia pinastri
      Physcia dubia
      Candelaria concolor
      Hyperphyscia adglutinata
      Phaeophyscia rubropulchra
      Physcia millegrana
      Phaeophyscia adiastola
      Lepraria lobificans
      Graphis scripta
      Lepraria incana
      Buellia stillingiana
      Parmelia sulcata
      Flavoparmelia caperata
      Candelariella efflorescent
      Hypogymnia physodes
      Physconia detersa

      We sampled at Mac Campus, too, where we also saw Xanthoria fallax, Physcia aipolia/stellaris (not sure which), and Physciella chlorantha.

      Looking forward to hearing your presentation on Wednesday!

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