Spring into action: Life in Earth’s rarest soils under threat

Spring into action: Life in Earth’s rarest soils under threat

Spring into action: Life in Earth’s rarest soils under threat

Springtails (Collembola) in the Antarctic indicate that unique soil biodiversity in the region faces biotic homogenization due to increased human activity

Invasive springtail (Collembola) in sub-Antarctic soil.

PHOTO CREDIT: Laura Phillips

Efforts to understand and protect Earth’s biodiversity have largely overlooked life present in the soil. However, soil biodiversity is critical to ecosystem health, playing an integral role in nutrient cycling, carbon storage, water filtration, and food production1.

The Antarctic, once a pristine wilderness, is undergoing rapid environmental change and increased human pressures. Yet the true diversity, uniqueness, and vulnerability of its soil communities are only beginning to be revealed. As tourism and science expeditions bring ever more passengers and cargo to Antarctica, human-induced transport of species (‘biological invasion’) – both into and throughout the region – presents a growing threat to soil biodiversity, as highlighted recently in our study.

The Antarctic terrestrial biome near McMurdo station. PHOTO CREDIT: Helena Baird

In the Antarctic region, which broadly covers approximately 30% of the planet’s surface, soil organisms represent the vast majority of terrestrial life. Antarctic soil organisms, which include nematodes, mites, springtails, fungi, and tardigrades, have eked out a largely isolated existence over millions of years in fragmented patches of ice-free land on the continent, or on the sub-Antarctic islands.

On the Antarctic continent, ice-free soil represents <1% of the total land area and can be found on mountain tops, scree slopes, valleys, and the coast. The sub-Antarctic islands encircle the continent, located in the frigid waters of the Southern Ocean and each is separated by up to thousands of kilometres of open ocean. Antarctic soil species are therefore highly isolated and possess unique adaptations to their harsh environment. They are at risk of being outcompeted, or ultimately even replaced, by invasive species as the climate warms2.

LEFT: Helena Baird and colleagues busy with sub-Antarctic fieldwork on Marion Island while king penguins watch in the background. RIGHT: Soil sampling with the use of a soil core – an undisturbed cylindrical sample.
PHOTO CREDIT: Charlene Janion-Scheepers

In our study, we used DNA barcoding to investigate the spread of an invasive springtail species, known to adversely affect native soil species, across the sub-Antarctic islands. Identification of numerous divergent barcode sequences revealed that the invasive has been introduced to Antarctica several times.

By comparing barcodes from Antarctic specimens in BOLD to those found elsewhere in the world, we could identify genetic lineages shared across countries which aligned with known shipping routes to the Southern Ocean, highlighting the utility of molecular tools in tracking invasion. For example, a shared barcode haplotype between Norway and the sub-Antarctic island of South Georgia accords directly with Norway’s long history of whaling on this island. That a well-known invasive species has been introduced on multiple occasions to such a remote region emphasises the importance of ongoing biosecurity monitoring, even for invasive species that have already established, since multiple invasions can introduce more genetic resilience and enable the invasive species to spread.

Research vessel as it approaches Possession island, Crozet archipelago, one of the sub-Antarctic islands in the region. PHOTO CREDIT: Helena Baird

Charlene Janion-Scheepers (left) and Helena Baird (right) sort soil species at sea using Berlese funnels.
PHOTO CREDIT: Steven Chown

Our study also explored the consequences of intra-regional human transport on native soil species. Antarctic soil organisms are typically highly endemic, even to local patches within the region. This raises the concern that increased human traffic throughout Antarctica could transport and ultimately homogenise soil populations, altering the region’s unique biogeography. Using genome-wide SNPs, we showed that a widespread native springtail species is indeed so distinct between sub-Antarctic islands that it is likely in the process of speciating. Clearly, future exchange of individuals among islands could possibly disrupt this biodiversity process, diluting the specific adaptations each population has evolved over millennia. Potential evolutionary consequences include a decrease in the fitness of island-specific populations, lineage extinction, or the loss of biodiversity by ‘reverse speciation’3.

Regardless of the outcome, the threat of disrupting biodiversity processes among these unique and fragile islands emphasises the importance of biosecurity for ships travelling throughout the Southern Ocean, particularly when passengers embark and disembark at multiple locations.

Taking a break to enjoy the view in the sub-Antarctic. PHOTO CREDIT: Helena Baird

One of the main hurdles to accurately predicting future changes to soil communities is a lack of basic biodiversity knowledge. In the Antarctic, molecular work such as metabarcoding continues to reveal far more soil diversity – most of which is locally endemic – than previously recognised4,5. This situation echoes worldwide, with biodiversity and biogeography patterns constantly revised as we probe the soil biome deeper. Fortunately, schemes such as the Global Soil Biodiversity Initiative are bringing fragile soil ecosystems under the spotlight, where we will be better served to protect them.

References:

1. Bardgett RD & van der Putten WH (2014) Belowground biodiversity and ecosystem functioning. Nature, 515. 2. Janion-Scheepers C, Phillips L, Sgrò CM, Duffy GA, Hallas R & Chown SL (2018) Basal resistance enhances warming tolerance of alien over indigenous species across latitude. Proceedings of the National Academy of Sciences, 115. 3. Seehausen O (2006) Conservation: losing biodiversity by reverse speciation. Current Biology, 16. 4. Czechowski P, Clarke LJ, Cooper A & Stevens MI (2016) A primer to metabarcoding surveys of Antarctic terrestrial biodiversity. Antarctic Science, 1-13. 5. Velasco-Castrillón A, McInnes SJ, Schultz MB, Arróniz-Crespo M, D’Haese CA, Gibson JAE, . . . Stevens MI (2015) Mitochondrial DNA analyses reveal widespread tardigrade diversity in Antarctica. Invertebrate Systematics, 29.

Read the complete manuscript in Evolutionary Applications.

Read more news about the Antarctic:

NEW AUSTRALIAN PROGRAM TO SECURE FUTURE FOR ANTARCTICA’S ENVIRONMENT AND BIODIVERSITY

The Australian Government has awarded $36 million to a new research program led by Monash University, Securing Antarctica’s Environmental Future (SAEF).

Written by

Helena Baird

Helena Baird

Monash University, School of Biological Sciences, Melbourne, Australia

June 4, 2020

doi: 10.21083/ibol.v10i1.6180

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Resident or invasive species? Environmental DNA can provide reliable answers

Resident or invasive species? Environmental DNA can provide reliable answers

Resident or invasive species? Environmental DNA can provide reliable answers

Environmental DNA can be successfully applied to identify vertebrates in a tropical lake improving our capacity to map and monitor species.
Panoramic view of Bacalar Lake including the 40-m deep Esmeralda sinkhole. PHOTO CREDIT: Manuel Elías-Gutiérrez

Monitoring life within large bodies of water – those species that should and shouldn’t live there – can be very expensive and time consuming. To overcome these limitations, efforts in many temperate regions employ methods that use environmental DNA (eDNA), enabling effective and targeted detection of invasive and resident endangered species.

Our study is the first to demonstrate that eDNA-based monitoring can be successfully applied to target the whole fish community in a tropical freshwater system and its adjacent wetlands.

Between 1980 -1990, eDNA was the term introduced to define particulate DNA and it was used to detect and describe microbial communities in marine sediments and phytoplankton communities in the water column1. However, eDNA is presently defined as the genetic material left behind by eukaryotic organisms in the environment, reflecting a rise in the use of eDNA for the detection of vertebrate and invertebrate species in aquatic systems1. The popularity of using eDNA has increased following the development of next-generation sequencing, advances in quantitative PCR (qPCR), and the growth of DNA barcodes libraries such as the Barcode of Life Data System (BOLD), providing a quicker and more taxonomically comprehensive tool for biodiversity assessments.

 

South end of lake Bacalar with the sinkhole Cenote Azul.
PHOTO CREDIT: Manuel Elías-Gutiérrez

Lake Bacalar is the largest epicontinental habitat in Mexico’s Yucatan Peninsula, and it is renowned for its striking blue color, clarity of the water, and for the world’s largest occurrence of living stromatolites, a calcareous mound built up of layers of lime-secreting cyanobacteria. Due to the presence of sediments derived from karst limestone, it represents the world’s largest fresh groundwater-feed ecosystem. The northern part of Lake Bacalar is connected to a complex system of lagoons and the southern part has an indirect connection to the sea via a wetland system that connects with Hondo River and enters Chetumal Bay. This river has been heavily impacted by the discharge of organic waste and pesticides, by vegetation clearing, and by the introduction of invasive fish such as tilapia and the Amazon sailfin catfish (Pterygoplichthys pardalis) 2-4, first detected in 2013 4. The Amazon sailfin catfish is a serious threat to the fragile stromatolite ecosystem due to its burrowing habits and competition with local fish. The impact of declining water quality and the rise of invasive species on the native fish fauna needs to be carefully monitored in aid of conservation efforts of Lake Bacalar.

A team of researchers from the Instituto Tecnológico de Chetumal and El Colegio de la Frontera Sur sampled eight localities in December 2015, and January and April 2016. After each of 14 sampling events, water and sediment samples were immediately placed on ice before transportation to the lab in Chetumal. To minimize eDNA degradation, we filtered water samples within seven hours of collection. All filters and sediments were stored at -18°C before being transported on ice from Chetumal to the Centre for Biodiversity Genomics in Guelph, Canada, where DNA extraction was undertaken.

 

Water sampling between stromatolites.
PHOTO CREDIT: Miguel Valadez

We sequenced short fragments (<200 bp) of the cytochrome c oxidase I (COI) gene on Ion Torrent PGM or S5 platforms. In total, we recovered eDNA sequences from 75 species of vertebrates including 47 fishes, 15 birds, seven mammals, five reptiles, and one amphibian. Although all species are known from this region, six fish species represent new records for the study area, while two require verification (Vieja fenestrata and Cyprinodon beltrani /simus), because their presence is unlikely in this ecosystem. While there were species (two birds, two mammals, one reptile) only detected from sediments, water samples recovered a much higher diversity (52 species), indicating better eDNA preservation in the slightly alkaline Bacalar water.  Because DNA from the Amazon sailfin catfish was not detected, we used a mock eDNA experiment that confirmed our methods were effective.

Interesting findings include the detection of rare species, such as an anteater Tamandua mexicana, which was detected by both PGM and S5 instruments from a river sample (Juan Sarabia), and migratory birds, such as warbler Oreothlypis peregrina known to overwinter in the Yucatan Peninsula.

Docks in front of Bacalar town
PHOTO CREDIT: Miguel Valadez

Our study indicates that eDNA can be successfully applied to monitor vertebrates in a tropical oligotrophic lake as well as more eutrophic (higher primary production) wetlands and can aid conservation and monitoring programs in tropical areas by improving our capacity to map occurrence records for resident and invasive species.

Our next step is to convince Mexican and international stakeholders to implement these methodologies and establish a permanent biomonitoring system for this and other pristine freshwater ecosystems found in Yucatan Peninsula. This work is necessary to detect effects of climate change, declining water quality, and the increasing tourism activities in this region.

References:

1. Díaz-Ferguson EE, Moyer GR (2014) History, applications, methodological issues and perspectives for the use of environmental DNA (eDNA) in marine and freshwater environments. Revista de Biología Tropical 62: 1273-1284. DOI: 10.15517/RBT.V62I4.13231

2. Wakida-Kusunoki AT, Luis Enrique Amador-del Ángel (2011) Aspectos biológicos del pleco invasor Pterygoplichthys pardalis (Teleostei : Loricariidae) en el río Palizada, Campeche, México. Revista Mexicana de Biodiversidad 82: 870-878

3. Alfaro REM, Fisher JP, Courtenay W, Ramírez Martínez C, Orbe-Mendoza A, Escalera Gallardo C, et al. (2009) Armored catfish (Loricariidae) trinational risk assessment guidlines for aquatic alien invasive species. Test cases for the snakeheads (Channidae) and armored catfishes (Loricariidae) in North American inland waters. Montreal, Canada: Commission for Environmental Cooperation. pp. 25-49.

4. Schmitter-Soto JJ, Quintana R, Valdéz-Moreno ME, Herrera-Pavón RL, Esselman PC (2015) Armoured catfish (Pterygoplichthys pardalis) in the Hondo River basin, Mexico-Belize. Mesoamericana 19: 9-19.

Written by

Natalia V. Ivanova

Natalia V. Ivanova

Centre for Biodiversity Genomics, Guelph, ON, Canada

Martha Valdez-Moreno

Martha Valdez-Moreno

El Colegio de la Frontera Sur, Unidad Chetumal, Chetumal, Mexico

Manuel Elías-Gutiérrez

Manuel Elías-Gutiérrez

El Colegio de la Frontera Sur, Unidad Chetumal, Chetumal, Mexico

May 15, 2019
doi: 10.21083/ibol.v9i1.5474

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