Abstract
DNA barcoding identification needs a good characterization of intraspecific genetic divergence to establish the limits between species. Yet, the number of barcodes per species is many times low and geographically restricted. A poor coverage of the species distribution range may hamper identification, especially when undersampled areas host genetically distinct lineages. If so, the genetic distance between some query sequences and reference barcodes may exceed the maximum intraspecific threshold for unequivocal species assignation. Taking a group of Quercus herbivores (moths) in Europe as model system, we found that the number of DNA barcodes from southern Europe is proportionally very low in the Barcoding of Life Data Systems. This geographical bias complicates the identification of southern query sequences, due to their high intraspecific genetic distance with respect to barcodes from higher latitudes. Pairwise intraspecific genetic divergence increased along with spatial distance, but was higher when at least one of the sampling sites was in southern Europe. Accordingly, GMYC (General Mixed Yule Coalescent) single‐threshold model retrieved clusters constituted exclusively by Iberian haplotypes, some of which could correspond to cryptic species. The number of putative species retrieved was more reliable than that of multiple‐threshold GMYC but very similar to results from ABGD and jMOTU. Our results support GMYC as a key resource for species delimitation within poorly inventoried biogeographic regions in Europe, where historical factors (e.g., glaciations) have promoted genetic diversity and singularity. Future European DNA barcoding initiatives should be preferentially performed along latitudinal gradients, with special focus on southern peninsulas.
Highlights
A decade and a half ago, DNA barcoding was presented as a novel system to provide wide-scale and quick species identification using certain gene sequences as molecular species-specific tags (Hebert, Cywinska, Ball, & de Waard, 2003)
For the data downloaded from BOLD, we considered two sequences to come from the same locality when the name for that field site was identical in the database or when the coordinates showed that the specimens had been collected within a distance lower than 5 km
The rest correspond to Iberian haplotype clusters classified as independent operational taxonomic units (OTUs) mostly within those species with a maximum intraspecific genetic divergence over 2% (Table 1), namely C. nymphagoga, C. pennaria, T. alternella, and W. uncinula
Summary
A decade and a half ago, DNA barcoding was presented as a novel system to provide wide-scale and quick species identification using certain gene sequences as molecular species-specific tags (Hebert, Cywinska, Ball, & de Waard, 2003). DNA barcoding often allows for the identification of morphologically cryptic species and individuals at life stages difficult to determine morphologically (e.g., insect larvae) (Ahrens, Fabrizi, Šípek, & Lago, 2013; Bonal, Muñoz, & Vogler, 2011). We analyzed the geographical scale effect on intraspecific genetic distance using as study model a group of Heteroceran Lepidoptera (i.e., moths) whose caterpillars feed on oak (Quercus spp.) leaves. These moth species are widely distributed over most parts of Europe (Camus, 1936–1954). | 10756 monophyletic clades (intraspecific distinct lineages and potential cryptic species) exclusive of southern Europe
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