Scanning the genetic barcode of plant-pollinator interactions

Tracking changes in ecosystems is both vital and extremely difficult. We need to know how differences in climate and land use will affect the success of different species, and what impacts this will have on the wider environment. Plant-pollinator interactions are particularly important for the stability of ecological communities, but how will these relationships be affected in the future and what will happen to the ecosystem services they provide?

A better understanding of dynamic plant-pollinator mutualisms is therefore critical, but monitoring these interactions has historically been extremely demanding, requiring hours of observations followed by the intricate taxonomic identification of pollinators that can look very much alike.

Image: These hoverflies mimic bumblebees, making their quick on-the-wing identification even more tricky! Image credit: S. Rae. Used under licence: CC BY 2.0.
These hoverflies mimic bumblebees, making their quick on-the-wing identification even more tricky! Image credit: S. Rae. Used under licence: CC BY 2.0.

Increasingly, ecologists are turning to molecular techniques for a community-level look at plant-pollinator interactions. One such approach is DNA barcoding, which can be used to quickly and accurately identify plants and their pollinators. This technique involves the sequencing of particular sections of DNA selected for their variability between species and relative similarity within a species. Researchers can then identify the sample by comparing its DNA sequence to a library of known species.

In their viewpoint article, published in New Phytologist, Jana Vamosi and colleagues discuss the new opportunities for exploring plant-pollinator interactions that DNA barcoding provides, and explain how it can be used to predict future declines in their ecosystem services.

Scanning multiple barcodes

New molecular techniques have made a dramatic improvement in the ease of identifying plants and their pollinators. Metabarcoding allows DNA barcoding to be performed on a sample containing many different species, for example pollen grains collected from a pollinator, without spending hours separating pollen grains. This technique is much faster than running separate DNA barcoding reactions, and much cheaper when labour costs are considered. Vamosi and colleagues highlight the need for an investment in the development of barcoding libraries, which will further increase the precision and accuracy of species-level identifications through this methodology.

Image: Identifying separate pollen grains on a generalist pollinator can be tricky. Image credit: Smudge. Used under licence: CC BY-SA 2.0.
Identifying separate pollen grains on a generalist pollinator can be tricky. Image credit: Smudge. Used under licence: CC BY-SA 2.0.

Another exciting development is the ability to detect and sequence trace amounts of DNA left on flowers by visiting pollinators. This environmental DNA can be tricky to obtain, but can highlight potential pollinators that were not identified by other means.

Reconstructing plant-pollinator interactions

The improvements in DNA barcoding and associated techniques mean that field-scale studies of plant-pollinator interactions are now far more practical, cost-effective and accurate, particularly in the identification of cryptic (morphologically identical) species. These data have opened up new opportunities for further research into a number of ecologically important topics, including the key area of pollinator specialisation.

When considering a specialised pollination mutualism, you may think of examples like figs and wasps, which have interacted for over 60 million years. In contrast, Vamosi et al. describe how most specialisations are dynamic and change depending on the relative abundances of the partner species in a particular habitat. Specialisation is generally considered to be risky for plants as they receive more variable amounts of pollen, but some studies have found that seed production may be increased overall due to a decrease in the deposition of pollen from other plant species.

Image: DNA barcoding can be used to identify the pollen of a wide variety of plant species, as well as the pollinators that visit them. Image credit: Joe Mabel. Image credit: CC BY-SA 2.0.
DNA barcoding can be used to identify the pollen of a wide variety of plant species, as well as the pollinators that visit them. Image credit: Joe Mabel. Used under licence: CC BY-SA 2.0.

Metabarcoding of pollen on the stigmas of plants in herbaria, or on pollinators stored in museums, can be compared with data on modern plant-pollinator interactions to investigate how these relationships may have changed over time, indicating how rapidly specialist pollinators may have been lost as human activities increased. The loss of specialists tends to reduce the stability of ecosystems. Recent phylogenetic studies have suggested that specialist lineages are more ephemeral over evolutionary timescales, with higher rates of speciation and extinction over evolutionary timescales. These patterns indicate that their disappearance may be a natural phenomenon, with further work needed to more accurately understand these transitions.

Consequences for conservation

These new molecular techniques highlight how pollinator and plant species can influence the sustainability of the ecosystem as a whole. Vamosi and colleagues explain that pollination is typically a community-level process and it can be difficult to prioritise particular species for a focussed conservation effort, but one group to target would be efficient pollinators with declining populations. Understanding how plant-pollinator interactions and communities may change in the future provides data for the prediction of how their associated ecosystem services may be affected, and the problems that this might present.

Read the paper:

Vamosi, J.C., Gong, Y-B., Adamowicz, S.J. and Packer, L. (2016). Forecasting pollination declines through DNA barcoding: the potential contributions of macroecological and macroevolutionary scales of inquiry. New Phytologist. doi: 10.1111/nph.14356


 

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Sarah Jose
@JoseSci