Not as clear as expected: what genetic data tell about Southern Hemisphere corellids (Ascidiacea: Phlebobranchia)

Abstract

The morphology of corellids (Ascidiacea) has led to numerous misidentifications and wrong taxonomic decisions over the last century. Paradoxically, the morphology has also enabled new species to be identified and ancient entities to be re-established in the Southern Hemisphere. There are many examples of the integration of morphological and molecular data leading to the same taxonomic conclusions, and therefore we aimed to analyse DNA sequences of the gene cytochrome oxidase subunit I of currently accepted species within Corellidae occurring in the Southern Hemisphere. Haplotype networks along with phylogenetic trees and genetic distances not only corroborate the distinction between Corella eumyota and Corella antarctica, but also separate the latter into two potential groups, one located in Terre Adélie and the other in the Antarctic Peninsula (AP). Furthermore, the C. antarctica group from the AP was closely related to the allied abyssal species, Corynascidia suhmi from Terre Adélie. Although the number of new sequences is reduced, our results are congruent with a long record of suspicion on the matter and stress the need for deeper and more extensive investigation of this ascidian family.

Morphology, genetics, and historical records support the synonymy of two ascidian species and suggest their spread throughout areas of the Southern Hemisphere

“…These values fall within the range of intraspecific genetic distances of COI in other ascidians (0.88-3%, e.g. Lambert et al 2010;Alurralde et al 2018;Rocha et al 2019;Viard et al 2019). In a study within the Pyura stolonifera species complex, after a morphological and mitonuclear genetic analysis, a genetic distance of 10% for COI was found to differentiate the sibling species Pyura praeputialis and P. doppelgangera (Rius and Teske 2013).…”

“…For phylogenetic reconstruction, four stolidobranch sequences obtained from GenBank database were included in the analyses for comparison: Cnemidocarpa verrucosa (GenBank accession number: KU299764, Turon et al 2016b); Styela paessleri (GenBank: KU299779, Turon et al 2016b); Pyura legumen (GenBank: KU299778, Turon et al 2016b); and Paramolgula gregaria (GenBank: KU299769, Turon et al 2016a). We also included two phlebobranch ascidian sequences as an outgroup, corresponding to the species Corella eumyota and Corella antarctica (GenBank: MG877558 and GenBank: MG877561 respectively, Alurralde et al 2018; the alignment is available in the supplementary file S1).…”

A long and winding but exciting road: Biodiversity, phylogenetic, and biogeographic relationships of ascidians in the Southwest Atlantic

“…I stepped into the picture, eager to leverage my expertise in genetics and molecular markers to advance and deepen our understanding of ascidian biodiversity. We have focused on systematic aspects, identifying species and defining the biogeographic status of cryptogenic species identified in the area (e.g., Alurralde et al, 2018;Taverna et al, 2021). A crucial aspect of our investigation involves tracing the origins of these species, discerning their invasion pathways, the timing of their arrival, and their dispersion patterns.…”