Research Article |
Corresponding author: Dirk Steinke ( dsteinke@uoguelph.ca ) Academic editor: Dmitry Schigel
© 2021 Dirk Steinke, Thomas WA Braukmann, Laura Manerus, Allan Woodhouse, Vasco Elbrecht.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Steinke D, Braukmann TWA, Manerus L, Woodhouse A, Elbrecht V (2021) Effects of Malaise trap spacing on species richness and composition of terrestrial arthropod bulk samples. Metabarcoding and Metagenomics 5: e59201. https://doi.org/10.3897/mbmg.5.59201
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The Malaise trap is a popular device for assessing diverse terrestrial arthropod communities because it collects large samples with modest effort. A number of factors influence its collection efficiency, placement being one of them. For instance, when designing larger biotic surveys using arrays of Malaise traps we need to know the optimal distance between individual traps that maximises observable species richness and community composition. We examined the influence of spacing between Malaise traps by metabarcoding samples from two field experiments at a site in Waterloo, Ontario, Canada. For one experiment, we used two trap pairs deployed at weekly increasing distances (3 m increments from 3 to 30 m). The second experiment involved a total of 10 traps set up in a row at 3 m distance intervals for three consecutive weeks.
Results show that community similarity of samples decreases over distance between traps. The amount of species shared between trap pairs drops considerably at about 18 m trap-to-trap distance. This change can be observed across all major taxonomic groups and for two different habitat types (grassland and forest). Large numbers of OTUs found only once within samples cause rather large dissimilarity between distance pairs even at close proximity. This could be caused by a large number of transient species from adjacent habitats which arrive at the trap through passive transport, as well as capture of rare taxa, which end up in different traps by chance.
Biodiversity, biomonitoring, experimental design, insects, metabarcoding
“During my extensive travels I have repeatedly found that insects happened to enter my tent, and that they always accumulated at the ceiling-corners in vain efforts to escape at that place without paying any attention to the open tent-door. On one occasion one of the upper tent-corners happened to have a small hole torn in the fabric, and through this hole all the insects pressed their way and escaped. Later on the idea occurred to me, that, if insects could enter a tent and not find their way out, and always persistently tried to reach the ceiling, a trap, made as invisible as possible and put up at a place where insects are wont to patrol back and forth, might catch them much better than any tent and perhaps better than a man with a net…”
Rene Malaise 1937
The inclusion of terrestrial invertebrates in biodiversity inventories and surveys has increased substantially over the past years (
Initially Malaise traps were considered of limited use in conservation evaluation and bio-surveillance because of the huge size of their catch (
There are various factors that influence the efficiency of Malaise traps. Temperature, precipitation, and wind are considered important as largest catches generally occur on hot, dry, and still days (
The main objective of this study was to examine the effects of spacing between traps on species richness and composition of Malaise trap samples. Bulk samples from two field experiments at a site in Waterloo, Ontario, Canada were assessed using metabarcoding to determine if (1) there is a critical distance between traps at which species overlap drops significantly and if (2) structural composition of habitats has an influence on such a distance.
Arthropod bulk samples were collected using ez-Malaise traps (Bugdorm, Taiwan). Traps for the first experiments (Fig.
All samples were dried at room temperature for three days in a disposable grinding chamber. Each sample was ground to fine powder using an IKA Tube Mill control (IKA, Breisgau, Germany) at 25,000 rpm for 2 × 3 min. DNA was extracted from approximately 20 mg of ground tissue using the DNeasy Blood & Tissue kit (Qiagen, Venlo, Netherlands) in line with the manufacturer’s protocols.
Metabarcoding was carried out using a two-step fusion primer PCR protocol (
Initial quality control of raw sequence data was done using FastQC v0.11.8. Subsequently, sequence data were processed using the JAMP pipeline v0.69 (github.com/VascoElbrecht/JAMP) starting with demultiplexing, followed by paired-end merging using Usearch v11.0.667 with fastq_pctid=75 (
OTU tables (Suppl. material
We were able to extract high quality DNA from all samples, and obtained strong bands for all 70 samples after the second PCR step. Illumina sequencing generated 13,910,614 reads (partial run shared with other projects), with the raw data being available on NCBI SRA with the accession number SRP200574. About 27% of the reads were filtered during data processing, leaving an average of about 137,181 sequences per sample. In total, 10,151,381 post-filtering reads could be used for clustering with Usearch.
Our analysis shows a total of 2,315 OTUs for the grassland site and 2,804 OTUs for the forest pond site in experiment 1 (Fig.
Results for experiment 1. (a) OTU accumulation curves for both sites by sample, (b) Dot plot of Sørensen’s similarity coefficient between samples of distance pairs for both sites. Percentage of shared OTUs per trap distance pair for the top five arthropod orders (representing 90% and 96% of all OTUs, respectively) at grassland (c) and forest pond (d) site.
The total OTU count for the grassland site comprised 21 orders with six orders (Coleoptera, Diptera, Hemiptera, Hymenoptera, Lepidoptera, Orthoptera) representing 97% of all OTUs (Suppl. material
For experiment 2 we found totals of 1,017 for week 1, 662 for week 2, and 738 OTUs for week 3 (Fig.
Results for experiment 2. (a) OTU accumulation curves for each sampling week by trap (b) Dot plot of Sørensen’s similarity coefficient between samples of all possible distance pairs for all weeks, (c) percentage of shared OTUs by trap distance for the top five arthropod orders (representing 90% of all OTUs) for each week.
OTUs found during experiment 2 comprised 15–18 orders with the five orders Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera representing between 85–95% of all specimens (Suppl. material
Malaise traps as sampling method for terrestrial arthropod communities represent a rather efficient and economical means for obtaining comprehensive samples with minimal effort (
The small similarity values observed in both our experiments (Figs
Malaise trapping with only a few traps at a single site over a short timescale always provides an incomplete species list. That is no different for our study which suggests that additional trapping efforts by increasing the number of traps or by enlarging the trapping surface (e.g.
In conclusion, our results suggest the following recommendations for sampling and monitoring terrestrial invertebrate communities with Malaise traps: (a) within a temperate and uniform habitat a number of traps equally spaced at >18 m will likely sample more of the local diversity while at the same time reduce the extend of repetitive sampling, (b) longer trapping duration can help to reach asymptotic species richness and lead to more complete species lists, and (c) future work should include research on the origin and the role of singletons. Are they in fact transient species passively dispersed towards the trap or low abundant resident core species that are not efficiently detected?
DS developed the concept, DS and VE designed the experiments and carried out the sampling, VE and LM did the laboratory work, DS and VE analysed the data, DS wrote the paper, VE, AW, and TB revised the paper and provided input throughout the study.
This study was supported by funding through the Canada First Research Excellence Fund. It represents a contribution to the University of Guelph Food From Thought research program. We thank the Optimist Club of Kitchener-Waterloo for access to their site at Camp Heidelberg. We are grateful to peer reviewers and editors who provided comments that improved the manuscript.
Figure S1
Data type: histogram
Explanation note: Histogram of OTU richness per trap (corresponding trap shown in photograph below) per week of experiment 2.
Figure S2
Data type: histogram
Explanation note: Histogram showing Number of OTU occurrences in traps of experiment 2.
Table S1
Data type: lab protocol information
Explanation note: Tagging layout.
Table S2
Data type: OTU list
Explanation note: OTU table (FC, FM, PC, PM – Experiment 1; A, B, F – Experiment 2; C – Controls).
Table S3
Data type: taxonomic
Explanation note: Taxonomic breakdown by order for both experiments and sites.