Marko Mutanen is an enthusiastic entomologist and molecular taxonomist who has expertise on North European Lepidoptera and sawfly diversity. His research focuses broadly on insect biodiversity, but in particular he is interested in finding efficient solutions to our current inefficiency to understand the bewildering biological diversity surrounding us. He is a strong proponent of both DNA barcoding and DNA taxonomy. He is convinced that overcoming the so-called taxonomic impediment and achieving global bio-literacy requires wide-scale adoption of genetics and genomics each in species identification, species delimitation and biomonitoring. Mutanen leads the Finnish Barcode of Life (FinBOL) project, which is building a DNA barcode reference library for the multicellular species occurring in Finland. He also is leading several research projects that focus on finding ways to make us more bio-literate. Furthermore, he presently directs the Biodiverse Anthropocenes (2021-2026), an 8M-Euro multidisciplinary university research profiling programme. Mutanen has published ca 120 peer-reviewed scientific articles.
What do unexpected patterns in DNA barcodes indicate? Insights from genomics
Many national initiatives and individual researchers are working hard to build DNA barcode reference libraries covering geographic regions and taxonomic groups. Lepidoptera researchers across the world have been particularly active on this front. Presently, DNA barcodes are available for over 100,000 species of Lepidoptera. While DNA barcoding was originally designed to facilitate specimen identification into respective species, they have also turned out to be efficient in revealing cryptic diversity and speeding up taxonomic workflows. Consequently, new species have been revealed even in regions that have been subjected to thorough taxonomic scrutiny. Several newly discovered species from North Europe provide examples of usefulness of barcoding in unmasking cryptic diversity.
Ideally, DNA barcodes would show little variability within species and a plenty between them as this would ensure the efficiency of the approach. Unfortunately, it is not always that straightforward. Basically, barcoding may reveal two kinds of patterns that complicate their use in identification. First, DNA barcodes may differ only little, or not at all, between species. Second, they may show extraordinary variability within species that may even exceed that usually observed between species. Furthermore, it is not unusual to find two or more highly distinct clusters of barcodes within a single species.
Such unexpected patterns in DNA barcodes may result from either ‘operational’ or biological causes. A ‘wrongly’ placed barcode raises a question: Is this specimen misidentified, or did contamination take place? Ruling out such operational causes may require analysis of additional genetic markers or detailed morphological study. Barcode sharing may be due to taxonomic over-splitting. Alternatively, extraordinary levels of intraspecific variability may have resulted from amplification of pseudogene instead of the true barcode. In addition to such operational causes, mitonuclear discordance may result from biological causes. Two species may share the same barcode because their recent speciation. Similarly, high intraspecific variation may result from other biological processes, such as retained genetic polymorphism or introgression.
In order to understand the numerous observed cases of unexpected patterns observed in DNA barcodes of European Lepidoptera, we studied a number of cases using genomic approaches, including ddRAD sequencing and Target Capture, under various setting, including sympatry, parapatry and allopatry. These studies have revealed a variety of patterns and likely explanations, suggesting that patterns of variability in mitochondrial DNA is shaped by several biological processes, and their elucidation may require insights from nuclear genome. These studies have also revealed evident cases of cryptic diversity and taxonomic over-splitting.
Keywords: Bioliteracy, DNA barcoding, genomics, mitochondrial DNA, mitonuclear discordance
