*note -this post originally appeared on the Applied Ecologist's blog
Like canaries in coal mines, species can provide important
information about deteriorating environmental conditions. A whole
sub-discipline of environmental biomonitoring has emerged to provide the
necessary tools to evaluate biological responses to changes in environmental
conditions. While historically biomonitoring focused on contaminant
concentrations in sentinel species –such as heavy metals in clams; modern
biomonitoring uses information across multiple biological levels of
organisation, from tissues, to organism behaviour, to the abundances and
distributions of species. Since it is impossible to assess every aspect of an
ecosystem’s response to pollution, scientists and practitioners still need to
make decisions about which elements of an ecosystem should be monitored.
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| A coal miner with a canary –the classic sentinel species (url for photo: http://www.academia.dk/Blog/wp-content/uploads/CanaryInACoalMine_2.jpg) |
In freshwater systems, diatoms are often the preferred
organisms for monitoring since they have high diversity and diatom communities
are structured strongly by local environmental conditions. Because of their
long use in biomonitoring, freshwater biologists have sensitivity and indicator values for thousands of diatom species.
Thus, in principle, you should be able to sample diatom communities in lakes
and rivers of interest, and then assess the water quality based on the presence
and abundance of different diatom species. While such proxies should always be
validated and interpreted carefully (Stephens et al. 2015), there is a long and
successful history of using diatoms for environmental monitoring.
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| Image of diatoms from a scanning electron microscope. (By Kostas Tsobanoglou - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45315566) |
The difficulty in practice is to identify diatom species,
which requires expert training and can be time consuming. A number of
researchers have pursued proxies and surrogates, for example using life form
(e.g., diatom shape) or higher taxonomic groupings, instead of identifying
species (Wunsam, Cattaneo & Bourassa 2002). In a recent article in the
Journal of Applied Ecology, Francois Keck and colleagues (Keck et al. 2016) take this one step further,
by using diatom evolutionary relationships as the biomonitoring tool.
Keck et al. employ novel statistical methods to create
clusters of species based on their evolutionary relatedness from a phylogenetic
tree and species’ sensitivity to pollution and show that these clusters, when
delineated by short to moderate phylogenetic distances, do a good job of
replicating species-level community pollution sensitivity indices.
This may seem like a onerous task, to assign diatoms to a
correct position on a phylogenetic tree, but with the availability and now
widespread use of DNA barcoding techniques, it is becoming easier to get
genetic data for microscopic assemblages than to identify cells to species.
This means that samples can be fit to the phylogenetic clusters without needing
to shift through samples. Further, if species are observed, which have not been
properly assessed for their sensitivity, they can be assigned an expected
sensitivity value based on their relatedness to assessed species.
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| The phylogenetic tree and species’ sensitivities (Fig. 2 in Keck et al.). |
While diatom evolutionary history may not have been strongly
influenced by environmental pollutants in the past –because they are relatively
recent stressors; it is clear from Keck et al.’s results that closely related
species are similarly sensitive to pollution. Other fields of applied
management have also begun to incorporate evolutionary history in the design
and assessment of applied actions –for example, restoration (Hipp et al. 2015). Evolutionary history can
provide important insights and management tools for dealing with the
consequences of environmental change.
References
Hipp, A.L., Larkin, D.J., Barak, R.S., Bowles, M.L.,
Cadotte, M.W., Jacobi, S.K., Lonsdorf, E., Scharenbroch, B.C., Williams, E.
& Weiher, E. (2015) Phylogeny in the Service of Ecological Restoration. American Journal of Botany, 102, 647-648.
Keck, F., Bouchez, A., Franc, A. &
Rimet, F. (2016) Linking phylogenetic similarity and pollution sensitivity to
develop ecological assessment methods: a test with river diatoms (microalgae). Journal of Applied Ecology.
Stephens, P.A., Pettorelli, N., Barlow, J.,
Whittingham, M.J. & Cadotte, M.W. (2015) Management by proxy? The use of
indices in applied ecology. Journal of
Applied Ecology, 52, 1-6.
Wunsam, S., Cattaneo, A. & Bourassa, N.
(2002) Comparing diatom species, genera and size in biomonitoring: a case study
from streams in the Laurentians (Quebec, Canada). Freshwater Biology, 47,
325-340.
