Species delimitation in Amblyosyllis (Annelida, Syllidae)

Abstract

Amblyosyllis is a worldwide distributed group of annelids mainly found in coastal environments. It is well known among the polychaete specialists mostly because of its notable beauty, showing bright colourful patterns and outstanding long and coiled appendices. Amblyosyllis is a monophyletic genus easy to identify due to its distinct diagnostic features; however, the species and their boundaries are, in most cases, not well defined. Herein, we provide an extensive sample of Amblyosyllis material (115 specimens) from several world geographic areas. We have studied the morphological features of each specimen and photographed them alive. Two mitochondrial DNA markers (COI and 16S) and one nuclear gene fragment (28S, D1 region) were sequenced. We performed phylogenetic analyses based on each DNA partition, as well as the combined data sets, obtaining congruent results. Species delimitation methods such as distance analyses, statistical parsimony networks and multi-rate Poisson tree processes were also applied. The combined results obtained from different methodologies and data sets are used to differentiate between, at least, 19 lineages compatible with the separately evolving meta-populations species concept. Four of these lineages are identified as nominal species, including the type species of Amblyosyllis , A . rhombeata . For three other lineages previously synonymized names are recovered, and seven lineages are described as new species. All of these species are described and supported by appropriate iconography. We recognize several morphological characters useful to identify species of Amblyosyllis , which in some cases should also be combined with molecular methods for species delineation. The genetic divergence in the genus is high, contrary to the morphological homogeneity observed. Two species show a wide geographical distribution, while the rest have a more restricted distribution. There are several examples of species with overlapping distribution patterns.

A complex species complex: The controversial role of ecology and biogeography in the evolutionary history of Syllis gracilis Grube, 1840 (Annelida, Syllidae)

“…In order to maintain a conservative approach, we adopted the interpretation proposed by more than one method (BI species tree, TCS, and NDT) which converged in indicating the occurrence of four entities. Accordingly, distances retrieved between different lineages are slightly higher than those retrieved in 16S sequences between different species of Amblyosyllis (Aguado et al, ), thus supporting the hypothesis of four cryptic species.…”

“…Moreover, different Mediterranean lineages were indistinguishable on the basis of the shape of modified chaetae and the live color (Álvarez‐Campos, Riesgo, et al, ). Lastly, Aguado et al () highlighted a previously overlooked pseudocryptic diversity within the genus Amblyosyllis Grube & Ørsted in Grube, 1857, combining two mitochondrial and one nuclear gene with morphological data.…”

“…The occurrence of cryptic species in polychaetes has been verified with molecular techniques for 86 nominal species, belonging to 30 families (Nygren, ). Among polychaetes, Syllidae represent the most numerous family, with approximately 700 described species within a wide range of morphological and ecological diversity (Musco & Giangrande, ), and some documented instances of cryptic speciation (Aguado et al, ; Álvarez‐Campos, Giribet, San Martín, Rouse, & Riesgo, ; Álvarez‐Campos, Riesgo, & Giribet, ; Maltagliati et al, ; Westheide & Schmidt, ). In the majority of cases, however, evolutionary processes underlying cryptic speciation are still poorly known, and complexity of differentiation patterns is expected.…”

To name but a few: descriptions of five new species of Terebellides (Annelida, Trichobranchidae) from the North East Atlantic

“…The most informative markers in previous studies are COI and ITS (Nygren et al 2018;Lavesque et al 2019). In the present study, analyses have been mainly based on mitochondrial COI, the universal barcoding gene, because it offers no ambiguities in the alignment process, and is the most commonly used in molecular taxonomy in annelids (e.g., Borda et al 2013;Tomioka et al 2016;Álvarez-Campos et al 2017;Aguado et al 2019;Grosse et al 2020) and other taxa (e.g., Kekkonen and Hebert 2014). After species delimitation, identification to the correct nominal species level is ideal, as species names allow the communication, study, quantification, classification, use and management of life on the planet.…”

Atypical reproduction in a syllid worm: the stolon ofSyllis rosea(Annelida, Syllidae) takes care of its offspring

“…This similarity is clearly due to convergent evolution, mirroring similar adaptive strategies between S. rosea and the subfamily Autolytinae. Also the period within the cocoon of S. rosea larvae is similar to that reported for some Autolytinae (e.g Proceraea fasciata (Bosc, 1902) – see Allen, 1964), and shorter than that reported for Amblyosyllis anae Aguado, Capa, Lago-Barcia, Gil, Pleijel & Nygren 2019 (Pernet, 1998 – as Amblyosyllis speciosa Izuka, 1912: see Aguado et al ., 2019). However, contrary to what was observed for S. rosea , Autolytinae generally have free-swimming larval stages, as reported in Epigamia alexandri (Qian & Chia, 1989).…”