Environmental DNA Technique Sheds New Light on Pollinator Monitoring

Keeping track of pollinators is more important than ever, but traditional techniques can be inaccurate. A study by Newton and colleagues, recently published in the journal Environmental DNA, employs a method called environmental DNA (eDNA) metabarcoding to detect the presence of flower-visiting pollinators. This technique holds the potential to revolutionize how we monitor and conserve these essential species.

Pollinators are the unsung heroes of the natural world, responsible for the reproduction of approximately 90% of flowering plants. These creatures, including bees, butterflies, birds, and even some mammals, ensure the survival of countless plant species, ultimately contributing to the food we eat and the ecosystems that support life on Earth. However, many pollinating species are experiencing alarming declines globally, prompting scientists to develop more effective ways to monitor their populations and interactions with plants.

Finding out what pollinators are interacting with plants can be difficult. Traditional methods use traps, netting or cameras to see what is visiting a plant, but some ways are better with some animals and worse with others. For example, camera traps work best when your visitor is large. As an alternative, Newton and colleagues asked if animals were leaving a ‘calling card’ on flowers in the form of eDNA.

The term eDNA refers to the genetic material that organisms leave behind in their environment, such as skin cells, faeces, or pollen. Metabarcoding is a method that combines DNA barcoding and high-throughput sequencing to identify multiple species present in an eDNA sample. In this study, the researchers collected flowers from seven plant species with diverse floral morphologies and analyzed them for eDNA traces left by pollinators.

Newton and colleagues tested this technique using flowers from seven plant species with diverse flower shapes. Their site was within the Helena and Aurora Range (Kalamaia name: “Bungalbin”) in the Goldfields-Esperance region of Western Australia. The survey took two trips. In the spring, they studied six species, Acacia adinophylla, Eremophila clarkei, Eremophila oppositifolia, Grevillea georgeana, Leucopogon spectabilis and Tetratheca aphylla subsp. aphylla. After the survey, they collected flowers for eDNA analysis. In the autumn, they returned for one more plant, Banksia arborea, which wasn’t flowering for the first visit. Newton and colleagues write in their article:

These plants represented a range of species with different flower morphologies and different assumed pollinators. Furthermore, many of the plant species sampled are of conservation concern, with little information on pollinating taxa currently available.

Newton et al. 2023

The results of the study were revealing. The eDNA metabarcoding technique, using three different assays, detected more animal species visiting flowers than traditional visual surveys conducted at the same time. This included birds, bees, and other pollinator species. Among the discoveries was the presence of a western pygmy possum visiting a flower, marking the first eDNA metabarcoding study to simultaneously identify the interaction of insect, mammal, and bird species with flowers. This finding underscores the power and versatility of eDNA metabarcoding in capturing the complex relationships between pollinators and plants.

Interestingly, the highest diversity of taxa – or groups of related organisms – was found on large inflorescence flower types, specifically those of Banksia arborea and Grevillea georgeana. This highlights the importance of these plants in supporting a wide range of pollinator species.

The study’s implications extend far beyond simply detecting the presence of pollinators. The ease of sample collection and the robustness of the eDNA metabarcoding methodology can revolutionize the management of biodiversity. This technique allows for the monitoring of not only plants but also their cohort of potential pollinators, opening up opportunities for rapid and efficient comparison of biodiversity and ecosystem health between different sites.

Moreover, eDNA metabarcoding may provide valuable insights into surrogate pollinators in the event of pollinator declines. Surrogate pollinators are alternative species that can step in and perform the same pollination services when the primary pollinators are in decline. Identifying and understanding these surrogates can help scientists develop targeted conservation strategies to maintain ecosystem health and stability.

The innovative eDNA metabarcoding method developed by Newton and colleagues offers a promising new approach to pollinator monitoring and conservation. By providing a more comprehensive understanding of the intricate relationships between pollinators and plants, this technique can help researchers and conservationists identify potential threats and develop effective strategies to safeguard these vital species. As pollinator populations continue to decline worldwide, the importance of innovative tools like eDNA metabarcoding cannot be overstated. However, the technique still needs some refining. Newton and colleagues conclude:

Further baseline studies are necessary to establish eDNA metabarcoding of flowers as a robust tool for assessing flower-visiting animals. To date, few studies have examined the relevant factors (i.e., temperature, UV, and rainfall) that may influence DNA degradation on plant material (although see Valentin et al., 2021), with no studies, to the best of our knowledge, examining the factors that influence deposition of eDNA on flowers. Therefore, it is currently impossible to determine if relatively low flower-visiting animal diversity is a result of few visitations (as suggested by visual surveys in our study) or DNA degradation due to environmental factors (Evans & Kitson, 2020; Goldberg et al., 2018).

Newton et al. 2023

READ THE ARTICLE

Newton, J.P., Bateman, P.W., Heydenrych, M.J., Kestel, J.H., Dixon, K.W., Prendergast, K.S., White, N.E. and Nevill, P. (2023) “Monitoring the birds and the bees: Environmental DNA metabarcoding of flowers detects plant–animal interactions,” Environmental DNA. Available at: https://doi.org/10.1002/edn3.399.