A DNA Barcode Library for North American Ephemeroptera: Progress and Prospects

Abstract

DNA barcoding of aquatic macroinvertebrates holds much promise as a tool for taxonomic research and for providing the reliable identifications needed for water quality assessment programs. A prerequisite for identification using barcodes is a reliable reference library. We gathered 4165 sequences from the barcode region of the mitochondrial cytochrome c oxidase subunit I gene representing 264 nominal and 90 provisional species of mayflies (Insecta: Ephemeroptera) from Canada, Mexico, and the United States. No species shared barcode sequences and all can be identified with barcodes with the possible exception of some Caenis. Minimum interspecific distances ranged from 0.3–24.7% (mean: 12.5%), while the average intraspecific divergence was 1.97%. The latter value was inflated by the presence of very high divergences in some taxa. In fact, nearly 20% of the species included two or three haplotype clusters showing greater than 5.0% sequence divergence and some values are as high as 26.7%. Many of the species with high divergences are polyphyletic and likely represent species complexes. Indeed, many of these polyphyletic species have numerous synonyms and individuals in some barcode clusters show morphological attributes characteristic of the synonymized species. In light of our findings, it is imperative that type or topotype specimens be sequenced to correctly associate barcode clusters with morphological species concepts and to determine the status of currently synonymized species.

DNA barcodes and morphology reveal unrecognized species in Chironomidae (Diptera)

“…However, a fixed threshold of COI sequences is not appropriate for all taxonomic groups. In insects for instance, a 2% threshold provides effective identification at the species level of Ephemeroptera (Schmidt et al 2015;Webb et al 2012;Zhou et al 2010), Lepidoptera (Zahiri et al 2014) and Trichoptera (Zhou et al 2016), while a 2.2% threshold appears appropriate for Heteroptera (Knebelsberger et al 2014), 2.5% for aquatic beetles (Monaghan et al 2005), and >3% for various dipteran groups (Nzelu et al 2015;Renaud et al 2012). Furthermore, an average threshold of 4-5% appears appropriate for most Chironomidae (Lin et al 2015;Meier et al 2015), even if a 7% threshold has been reported for closely related species in this family (Carew & Hoffmann 2015).…”

Extensive cryptic diversity in the cosmopolitan sludge worm Limnodrilus hoffmeisteri (Clitellata, Naididae)

“…Thus, it cannot be automatically assumed that COI lineages, which are that far apart, represent different species, without testing this with nuclear data. This again illustrates how problematic it is to delimit species with a DNA-barcoding gap as the sole criterion, in Clitellata (e.g., Achurra and Erséus 2013;Martinsson et al 2013Martinsson et al , 2015Martinsson and Erséus 2017) as well as in other animal groups (e.g., Munoz et al 2011;Webb et al 2012;Hogner et al 2012) …”

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“…The use of molecular marker sequences to assist in determining species has been a positive step toward addressing the problems of identifying species from life stages and material for which there are no useful traditional taxonomic keys. Webb et al (2012) used the COI marker sequence to confirm the co-occurrence of P. midas and P. chelifer in samples from Churchill, Manitoba. Their consensus analysis of sequence divergence values also showed a strong association of samples of P. midas from Manitoba and New Brunswick with clear separation from samples of P. chelifer.…”