Barcoding and morphometry to identify and assess genetic population differentiation and size variability in loliginid squid paralarvae from NE Atlantic (Spain)

Abstract

Accurate species classification is essential to understand complete life cycles of cephalopods. Identifying freshly caught or fixed loliginid paralarvae to species level with the traditional taxonomic guides is challenging. Therefore, the aim of this work was to identify genetically loliginid paralarvae captured in NW Spain (a region where at least three loliginid species are known to coexist) during 2012, 2013, and 2014, and to seek a means to distinguish the species from each other based on their morphometry. First, the barcoding region (COI gene) was amplified to identify each paralarva, and to obtain population molecular diversity indices and genetic structure for the different species. Afterwards, discriminant analysis (DA) was used to evaluate the performance of the selected morphometric measurements to distinguish among the species previously identified. Molecular analyses revealed three loliginid species (Alloteuthis media, A. subulata, and Loligo vulgaris), with different patterns of molecular diversity. DAs based on body morphometrics correctly categorised 75% of paralarvae to genus (Loligo and Alloteuthis) and 72% of Alloteuthis individuals to species level (A. media and A. subulata). When statolith measurements were included in the morphometric analysis, successful classification increased to 94 and 82%, respectively. The most useful variables for the discrimination of genus were hatching ring length and head width, while tentacle length helped to differentiate A. media from A. subulata. These discriminant functions should be tested with more paralarvae from different origins and seasons to account for body shape plasticity, but suggest a promising result to facilitate loliginid paralarvae identification for future research.