Is Cryptic Biodiversity a Common Phenomenon among Atlantic Oceanic Squids?

Abstract

Historically, marine oceanic open environments have been considered without barriers to dispersal, and the subsequent speciation of lineages from distant areas. As a consequence, many marine pelagic invertebrates are considered as monotypic cosmopolitan taxa, sometimes even including divergent geographic morphotypes. However, this view has been consistently challenged in the last decades by the discovery of many cryptic species complexes among pelagic marine “cosmopolitan” invertebrates. Despite their vast ecological importance, oceanic squids of the orders Oegopsida Orbigny, 1845 and Bathyteuthida Lindgren, 2010 are seldomly molecularly tested for cryptic biodiversity covering wide areas. Here, we barcoded specimens belonging to 12 oceanic squid species sampled during several Atlantic oceanic cruises covering waters from Brazil to Iceland, and the Mediterranean Sea. For assessing the presence of cryptic lineages, we studied the uncorrected p-distances at the intra- and interclade level and performed molecular species delimitation methods, such as the Poisson Tree Processes and the Generalized Mixed Yule Coalescent approach. Within Atlantic waters, we found cryptic biodiversity in five species: Abraliopsis morisii (Verany, 1839), Ancistrocheirus lessueuri (Orbigny 1842), Chtenopteryx sicula (Verany 1851), Galiteuthis armata Joubin, 1898 and Helicocranchia pfefferi Massy 1907. Atlantic individuals of Pterygioteuthis gemmata Chun, 1908 represent a divergent lineage of those from New Zealand. The divergence values among cryptic lineages of individuals of the same nominal species range from 2.2 to 17%, likely representing different stages of divergence since each putative speciation phenomena. In total, 50% of the tested species revealed cryptic lineages, which indicates that oceanic squid biodiversity is underestimated and it is necessary to develop more studies to assess the diversity of these animals at a global scale