Morphological and Molecular Assessments of Bobtail Squids (Cephalopoda: Sepiolidae) Reveal a Hidden History of Biodiversity

Fernando Á Fernández-Álvarez,Pilar Sánchez,Roger Villanueva

doi:10.3389/fmars.2020.632261

Abstract

Molecular species delimitation assists taxonomic decisions for challenging species, like cryptic species complexes. Bobtail squids (Family Sepiolidae Leach, 1817) are a very diverse group of benthic and nektonic small to medium size cephalopods with many taxonomic questions to solve. In this study we provided new sequence data for 12 out 17 Mediterranean bobtail squid species including all the genera present i n the area. Other relevant species from other parts of the world were used as comparison. The combined use of several molecular species delimitation methods consistently showed a picture of hidden biodiversity within this family which hinders the use of molecular data isolated from morphological characters. On the one hand, those methods provided contrasting results for the number of recognized species of some morphologically well-defined species. We suggest this can be an effect of recent speciation phenomena followed by an intense morphological drift. On the other hand, cryptic biodiversity was detected among members of several monophyletic clades assigned to the same nominal species, pointing to recent speciation phenomena without a parallel morphological evolution. Although Mediterranean bobtail diversity has been extensively studied for more than a century, a new species ofStoloteuthisVerrill (1881) was discovered and described here, both using molecular and morphological methods. This new research stresses the necessity of combined morphological and molecular studies to correctly assess cephalopod diversity. urn:lsid:zoobank.org:act:57AFBB38-18EA-4F80-B1D4-73519C12694F.

Highlights

The use of molecular species delimitation methods is widespread in modern systematics and taxonomic research
The individuals examined in the present study and identified based on morphological characters always clustered together in a single clade, but some inconsistencies were detected on previously published sequences
As we showed with S. affinis, S. atlantica and S. intermedia, as well as the molecular data provided for the descriptions of Sl. japonica and Sp. nipponensis, these situations are likely to be frequent in bobtail squids

Summary

Introduction

The use of molecular species delimitation methods is widespread in modern systematics and taxonomic research. Methods such as the Automatic Barcode Gap Discovery (ABGD, Puillandre et al, 2012), the statistical parsimony networks (e.g., Pons et al, 2006), the Bayesian Poisson Tree Processes model (bPTP, Zhang et al, 2013) and the Generalized Mixed Yule Coalescent approach (Fujisawa and Barraclough, 2013) assist in taking taxonomic decisions for challenging species, like cryptic species complexes (e.g., Fernández-Álvarez et al, 2020) or other morphologically challenging organisms. Even though hectocotylus morphology is a reliable character, recently it was discovered that the previously recognized intraspecific variability in one species undercovered pseudocryptic biodiversity (Groenenberg et al, 2009; de Heij and Goud, 2010). Identifications based on early life stages and females are challenging and misidentifications are abundant on GenBank (Groenenberg et al, 2009), hindering identification based only on DNA barcoding

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Conclusion