Integrative taxonomy for Biodiversity Exploration in the XXI century
Accelerating the pace of biodiversity description is a major challenge as extinction rate increases. The onset of the 21st century has seen the development of technological advances that can increase the description of biodiversity, including the DNA-barcoding initiatives, which attempt to identify specimens at the species level using single-gene libraries. The modern DNA-taxonomy strategies, include multistep procedures starting with exploratory surveys (usually morphologically based, for approximating species dlimitations), then followed by the genetic characterization of the taxa (to define the taxa), and finally by the establishment of molecular databases. However, morphology based investigations usually proceed at a very slow rate, and are particularly problematic with hyperdiverse groups, such as arthropods and molluscs, due to the large numbers of taxa to be analysed, and to the high percentages of morphologically cryptic diversity.
DNA-barcoding data can be used as an exploratory tool for approximating species delimitations, and subesequently combined with other evidences in an integrative taxonomic framework.
Classic molluscantaxonomic methodology proposes primary species hypotheses (PSHs) based on shellmorphology. However, in groups where most of the species remain unknown and for which homoplasy and plasticity ofmorphological characters is common, shell-based PSHs can be arduous to define.
A four-prongedapproach was recently developed by our team and tested to generate robust species hypotheses on a dataset of 1000 specimens of South-West Pacific Turridae (a hyperdiverse family of predatory neogastropods) in which: (i) analysis of COI DNA Barcode gene is coupledwith (ii) species delimitation tools GMYC (General Mixed Yule Coalescence Method)and ABGD (Automatic Barcode Gap Discovery) to propose PSHs that are then (iii)visualized using Klee diagrams and (iv) evaluated with additional evidence, such asnuclear gene rRNA 28S, morphological characters, geographical and bathymetricaldistribution to determine conclusive secondary species hypotheses (SSHs). The integrative taxonomy approach applied identified 87 Turridae species, more than doubling the amount previously known in theGemmulagenus. In contrast to a predominantly shell-based morphological approach, which over the last 30 years proposed only 13 newspecies names for the Turridae genusGemmula, the integrative approach described identified 27 novel species hypotheses not linked to available species names in theliterature. This formalized strategy outlines an effective and reproducibleprotocol for large-scale species delimitation of hyperdiverse groups. We are currently extending its use to several unrelated families of gastropods such as Cerithiopsidae, Muricidae, Cancellariidae, Trochidae, and to faunistic inventories (Mediterranean gastropods, Antarctic mollusca etc….).
Our aims are to test the hypothesis that with such strategy, the exploratory step will provide in a short time the specialist with a reduced package of extremely selected samples, which need his/her taxonomic expertise, shortening the time for biodiversity exploration, and the cost of the steps propedaeutic to alpha taxonomic.