Discovering a resilient and hyperdiverse midge fly fauna in a Singaporean swamp forest

Nee Soon Swamp Forest, Singapore

PHOTO CREDIT: Wang Luan Keng

Benthic macroinvertebrates – those animals that live at the bottoms of water bodies – are abundant, diverse, relatively immobile, and responsive to environmental stresses, and these traits make them ideal indicators of the quality of aquatic ecosystems. Our study demonstrates the utility of Next-Generation Sequencing (NGS) platforms as an efficient and rapid tool for monitoring efforts.

In freshwater ecosystems, non-biting midges (Diptera: Chironomidae) often constitute the majority of diversity and biomass with different chironomid species varying in their sensitivity to environmental changes. But, when monitoring these habitats, chironomids are either ignored entirely or not studied at a species-level because morphological assessments are expensive and laborious, and the identification literature is based on adults while larvae are most often collected.

Chironomid adults collected from Nee Soon Swamp Forest. Different chironomid species vary in their sensitivity to environmental parameters. PHOTO CREDIT: Bilgenur Baloglu

The solution? NGS platforms. They allow for fast and effective species-level assessments of large-scale samples at low cost (less than $0.40 USD/specimen). Moreover, there is a high congruence between molecular and morphological identification, enabling a detailed examination of the composition of taxonomically complex communities^1,2. Freshwater swamp forests – the forested wetlands occurring along rivers and lakes – are home to various endemic and endangered species with 33% of birds and 45% of mammals either threatened or endangered on the IUCN Red List³, and with most of the insect fauna unknown. These ecosystems are under threat worldwide from habitat destruction, pollution, and climate crisis. Most of the world’s tropical swamp forests are found in Southeast Asia’s Indo-Malayan region collectively occupying more than 13 million ha⁴ among many geographically separated peninsulas and islands. Nee Soon swamp forest is the largest remnant (90 ha) of its kind in Singapore and thus of high national conservation value.

Bilge Baloglu sampling water DNA from Singapore’s largest swamp forest remnant.
PHOTO CREDIT: Dickson Ng

We generated DNA barcodes using NGS to study chironomids among the natural swamp forest Nee Soon and three adjacent man-made reservoirs. We wanted to understand the effects of urbanization and to know whether the chironomid fauna of Nee Soon is resistant to, that is, minimally impacted by, the adjacent reservoirs. We sampled >14,000 chironomid specimens (both adults and larvae) as part of a freshwater quality monitoring program, and quantified species richness and compositional changes using NGS and DNA barcoding.

Our study showed that Singapore’s biggest swamp forest remnant maintains a rich and largely unique fauna of about 350 species. The minimal species overlap between sites indicated that the Nee Soon swamp forest is resistant against the invasion of species from surrounding artificial reservoirs.

These findings suggest that even small or fragmented swamp forests can be suitable habitats for chironomids, shedding light on many other swamp forests in Southeast Asia that collectively occupy a much larger area and that are threatened by destruction for oil palm plantations and paper pulp production. Overall, our study exposes the enormous power of NGS and DNA barcoding in ecological research to study ecosystem health, biological diversity, and habitat conservation.

References:

1. Brodin Y, Ejdung G, Strandberg J, Lyrholm T (2013) Improving environmental and biodiversity monitoring in the Baltic Sea using DNA barcoding of Chironomidae (Diptera). Molecular Ecology Resources 13:996–1004.

2. Montagna M, Mereghetti V, Lencioni V, Rossaro B (2016) Integrated taxonomy and DNA barcoding of alpine midges (Diptera: Chironomidae). PLoS One 11:e0149673

3. Posa MR (2011) Peat swamp forest avifauna of Central Kalimantan, Indonesia: Effects of habitat loss and degradation. Biological Conservation 144(10):2548-2556.

4. Hooijer A, Page S, Canadell JG, Silvius M, Kwadijk J, Wösten H, Jauhiainen J (2010) Current and future CO2 emissions from drained peatlands in Southeast Asia. Biogeosciences 7:1505–1514

For full details, please refer to the publication in Frontiers in Zoology.

Written by

Bilgenur Baloğlu

Centre for Biodiversity Genomics, Guelph, ON, Canada

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doi: 10.21083/ibol.v9i1.5525

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