*1.1. Accurate and Reliable Identification of Species in Taxonomy, Ecology, Evolution,and Conservation*

Hypothesis testing is at the heart of the biological sciences and is the standard for how we understand the complexity of the natural world. For most biodiversity research, the reliability and repeatability of hypothesis testing is dependent on accurate identifications of the species under investigation. Faulty identifications can result in faulty hypotheses. A fundamental challenge for any biologist, therefore, is to determine in a reliable and repeatable fashion the correct identification of any given biological sample. "DNA barcodes," i.e., standardized short sequences of DNA between 400 and 800 base pairs long, which in

**Citation:** Gostel, M.R.; Kress, W.J. The Expanding Role of DNA Barcodes: Indispensable Tools for Ecology, Evolution, and Conservation. *Diversity* **2022**, *14*, 213.https://doi.org/10.3390/d14030213

Academic Editor: Mario A. Pagnotta

Received: 19 February 2022 Accepted: 7 March 2022 Published: 13 March 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

theory can be easily isolated and characterized for all species on the planet, were originally conceived to facilitate this task [1]. By combining the strengths of molecular biology, sequencing technology, and bioinformatics, DNA barcodes offer a quick and accurate means to recognize previously known, described, and named species and to retrieve information about them.

**Table 1.** Diversity and number of barcode sequences available in the Barcode of Life Data System (BOLD) database, taxon labels follow the BOLD format.


1 Data accessed from https://www.boldsystems.org/index.php/TaxBrowser\_Home, accessed on 26 January 2022.

For plants, DNA barcoding has truly become a universal tool for hypothesis testing by expanding the ability to identify a species at all stages of its life history (i.e., fruits, seeds, seedlings, mature individuals both fertile and sterile) from damaged or preserved

specimens, as well as environmental samples with multiple species. Accordingly, DNA barcodes have been applied to address fundamental questions in ecology, evolution, and conservation biology, such as: how are species assembled in communities; what is the extent and specificity of multispecies interactions in well-studied and previously poorly known environments; and where are the most evolutionarily rich habitats for priority conservation and natural area protection in this age of habitat degradation [4,5]. With regard to the applied users of taxonomy, DNA barcodes also serve as a means to identify regulated species, invasive species, and endangered species.

### *1.2. Generating, Applying, and Sharing DNA Barcodes*
