Money spider dietary choice in pre‐ and post‐harvest cereal crops using metabarcoding

Abstract

1. Money spiders (Linyphiidae) are an important component of conservation biological control in cereal crops, but they rely on alternative prey when pests are not abundant, such as between cropping cycles. To optimally benefit from these generalist predators, prey choice dynamics must first be understood. 2. Money spiders and their locally available prey were collected from cereal crops 2 weeks pre-and post-harvest. Spider gut DNA was amplified with two novel metabarcoding primer pairs designed for spider dietary analysis, and sequenced. 3. The combined general and spider-exclusion primers successfully identified prey from 15 families in the guts of the 46 linyphiid spiders screened, whilst avoiding amplification of Erigone spp. The primers show promise for application to the diets of other spider families such as Agelenidae and Pholcidae. 4. Distinct invertebrate communities were identified pre-and post-harvest, and changes in spider diet and, to a lesser extent, prey choice reflected this. Spiders were found to consume one another more than expected, indicating their propensity towards intraguild predation, but also consumed common pest families. 5. Changes in spider prey choice may redress prey community changes to maintain a consistent dietary intake. Consistent provision of alternative prey via permanent refugia should be considered to sustain effective conservation biocontrol.

The problem of omnivory: A synthesis on omnivory and DNA metabarcoding

“…This is especially true of invertebrate predators and/or prey, where microscopic identification is frequently impossible. Metabarcoding can resolve prey taxa to species level in systems where this would be otherwise impossible, e.g., in fluid‐feeding invertebrates such as spiders (Cuff et al, 2020; Krehenwinkel et al, 2017), most insects (Pompanon et al, 2012), and centipedes (Eitzinger et al, 2018). Similarly, there are many prey species that do not possess morphologically identifiable structures that resist digestion, such as earthworms (Brown et al, 2012).…”

“…These short, degraded sections of DNA are, however, often outcompeted during amplification by the fresh and abundant DNA of the focal consumer where the PCR primers used amplify both. This can, however, be circumvented by using primers that amplify a broad taxonomic range of consumed species but do not also amplify host DNA (Cuff et al, 2020; Lafage et al, 2020; Piñol et al, 2014; Vestheim & Jarman, 2008) or by using blocking probes (Vestheim & Jarman, 2008), both of which can introduce taxonomic biases to those prey detected (Murray et al, 2011; Piñol et al, 2015, 2019). For analysing omnivorous diets, using multiple HTS markers is optimal to determine the complete range of consumed prey given few options are currently available for the adequate amplification of animals and plants with a single primer pair.…”

“…By limiting amplification of the host, however, a greater read depth is ensured which is increasingly likely to accurately capture the true diversity of consumed species. This choice of method can be most acute when the predator is closely related to its prey, for example, when a spider is eating other spiders (Cuff et al, 2020), requiring a fine balance between taxonomic bias and loss of sequencing depth. Few problems are encountered where the consumer is distantly related, such as an herbivore ingesting plant material.…”

“…Alternatively, some studies accept amplification of host DNA and remove reads conspecific with the host post-bioinformatics (Piñol et al, 2014); in such studies over 95% of the sample read depths can be lost to host DNA (Cuff et al, 2020). By limiting amplification of the host, however, a greater read depth is ensured which is increasingly likely to accurately capture the true diversity of consumed species.…”

Exploratory analysis reveals arthropod consumption in 10 lemur species using DNA metabarcoding

“…DNA was dried and stored in preservation plates (Ivanova & Kuzmina, 2013) and shipped to Queen Mary University of London for polymerase chain reaction (PCR) and sequencing. PCR was conducted using two different primer sets, targeting separate regions of the F I G U R E 1 Location of sample collection sites in Madagascar mitochondrial cytochrome c oxidase subunit 1 gene (CO1), one of 157 bp (Zeale et al, 2011) and the other 312 bp (Cuff et al, 2020). The mitochondrial cytochrome c oxidase subunit 1 gene has been recognized as a particularly useful metabarcoding gene, as it is nearly universal across animals, but substitutions allow for species-level differentiation (Hebert et al, 2003).…”