Introduction
The maintenance of biodiversity, as the sum of all “plants, animals, fungi, and microorganisms on Earth, their genotypic and phenotypic variation, and the communities and ecosystems of which they are a part” (Dirzo & Raven, 2003), is one of the most important current concerns of humankind, as wild species are decreasing at an alarming rate, and an inversion of this trend requires an anthropic intervention to guarantee their survival (Frankham et al., 2002). Biodiversity is composed by multiple dimensions, and no single measure of biodiversity can capture all its dimensions (Carpenter et al., 2009): Genetic diversity is essential in order to develop an evolutionary potential for species to be able to react to environmental changes (Toro & Cabarello, 2005). However, very little is known on trends in genetic diversity, particularly in wild species (Pereira et al., 2012). While taxonomic coverage with indicator taxa and diversity assessments is very limited, the extinction risk of the vast majority of biodiversity is not known (Pereira et al., 2012). Thus, a characterization and management of genetic diversity seems necessary considering idiosyncratic population structures, as well as to choose the correct way and the proper resolution power to estimate it (Storfen et al., 2010).
Mitochondrial DNA (mtDNA) has been a marker of choice for reconstructing historical patterns of population demography, admixture, biogeography, and speciation (Castro et al., 1998; Hull & Jiggins, 2005). Mitochondrial DNA (mtDNA) is maternally inherited and generally a non-recombinant marker. Variation in mtDNA is assessable by DNA sequencing in a cost-effective way which are exactly the properties that make mtDNA marker suitable for the large-scale assessment of species boundaries through its variation being used in rapid assessment approaches for biodiversity research (Ratnasingham & Hebert, 2007), such as barcoding studies. Barcoding uses a single gene fragment (COI ) and, thus, through large scale barcoding universal data of intraspecific genetic variation became available over a wide range of organisms.
Ecological studies typically require a determination of the species involved. Acquisition of such biodiversity data for plants and animals using morphological characteristics to identify field collected samples requires both a significant time effort for identification based on morphology and sufficient taxonomic expertise that is rarely available for a vast variety of organism groups. Therefore, many ecological studies lack taxonomic information while ecological data for many species are rare. The recent development of DNA-based methods for species identification, known as DNA barcoding (Hebert et al., 2003a), has drastically simplified this identification step (Coissac et al., 2012) and might help to overcome the gap between taxonomy and ecology.
Using a standardized genetic marker in DNA barcoding allows connecting the identities of different life stages such as eggs, larvae, or adults – often a major difficulty in morphology-based taxonomy and cryptic species (e.g., Ahrens et al., 2007; Šipek & Ahrens, 2011; García-Robledo et al., 2013; Etzler et al., 2014; Köhler et al., 2022) and to trace in the environment remnants of organismal DNA (Taberlet et al., 2012; Yu et al., 2012). Barcoding has been successfully applied to a vast number of taxa in many different geographic regions (www.boldsystems.org). It has become obvious that validated, comprehensive species libraries are the most fundamental basis for optimal barcode-based taxon identification (Kvist, 2013). The huge amount of barcode data with large number of already collected, identified and barcoded specimens opens up to ecologists to use these data of biodiversity in a vast geographic scale. They enhance a fast and clear overview on the biodiversity. Indeed, population genetic analysis of ecological communities with COI sequences extends the value of the DNA barcode employed as identification and taxonomic tool. Whereas barcoding for taxonomic purposes was in past often limited by economic constraints to a very few individuals per species, larger comprehensive studies becoming more and more available (e.g., Dincă et al., 2011; Bergsten et al., 2012; Hendrich et al., 2015; Rulik et al., 2017). These data-rich studies with multiple sampling sites may provide useful population genetic information with a link to the entire species distribution range applicable to a range of ecological and historical questions (Craft et al., 2010; Baselga et al., 2013, 2015).
DNA metabarcoding, which couples the principles of DNA barcoding with next generation sequencing technology, provides an opportunity to easily produce large amounts of data on biodiversity. Microbiologists have long used metabarcoding approaches, but use of this technique in the assessment of biodiversity in plant and animal communities is under-explored. DNA metabarcoding, which couples the principles of DNA barcoding with next generation sequencing technology, provides an opportunity to easily produce large amounts of data on biodiversity. Microbiologists have long used metabarcoding approaches, but use of this technique in the assessment of biodiversity in plant and animal communities is underexplored.
In this study, we analyze random samples from different Central European beetle metapopulations in order to provide a first meta-analysis of data generated in a large-scale barcoding project (GBOL; Hendrich et al., 2015; Rulik et al., 2017) with focus on their intraspecific degree of genetic divergence compared to their spatial and ecological properties. We collected all the available metadata information about Central European beetles contained in the BOLD data base in order to provide a rapid, and as complete as possible, survey about the beetle biodiversity to explore patterns of genetic differentiation among different ecological guilds considering the spatial scale to investigate circumstances driving the intraspecific mtDNA divergence in beetle species (Coleoptera). We were interested whether the relation of intraspecific genetic distances and geographic distances differed between ecological guilds. Finally, we aimed to provide a new and complete all-fauna phylogeographical overview on middle European beetle biodiversity.