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

Abstract

The cryptic diversity in the polychaete Syllis gracilis Grube, 1840, in the Mediterranean Sea was examined with an integrative morpho-molecular approach. Individuals of S. gracilis were collected at eleven Mediterranean localities to provide an insight into the role of brackish environments in inducing cryptic speciation. The examination of morphological features combined with a molecular genetic analysis based on a partial sequence of the 16S rRNA gene highlighted discrepancies between morphological and molecular diversity. Morphological data allowed to identify a morphotype with short appendages occurring in coralline algae communities and another one with long appendages observed in brackish-water environments and Sabellaria reefs. Multivariate analyses showed that sampling localities were the greatest source of morphological divergence, suggesting that phenotypic plasticity may play a role in local adaptations of S. gracilis populations. Molecular data showed the occurrence of four divergent lineages not corresponding to morphological clusters. Different species delimitation tests gave conflicting results, retrieving, however, at least four separated entities. Some lineages occurred in sympatry and were equally distributed in marine and brackish-water environments, excluding a biogeographic or ecological explanation of the observed pattern and suggesting instead ancient separation between lineages and secondary contact. The co-occurrence of different lineages hindered the identification of the lineage corresponding to S. gracilis sensu stricto. The discrepancy between morphological and molecular diversity suggests that different environmental and biogeographic features may interact in a complex and unpredictable way in shaping diversity patterns. An integrative approach is needed to provide a satisfactory insight on evolutionary processes in marine invertebrates. K E Y W O R D SMediterranean Sea, mitochondrial DNA, phenotypic plasticity, polychaetes, species complex | 67 LANGENECK Et AL.

Taxonomical and functional analyses of epifaunal polychaetes associated with Mussismilia spp.: the effects of coral growth morphology

“…The material identified as Syllis gracilis may correspond to a different related species because there are increasing evidence that this species complex includes several cryptic and pseudo-cryptic lineages ( e.g. , Álvarez Campos, Giribet & Riesgo, 2017 ; Langeneck et al, 2020 ). Sphaerosyllis brasiliensis was originally described from colonies of M. hispida from islands off the coast of São Paulo southeastern Brazil ( Nogueira, San Martín & Amaral, 2001 ).…”

Morphological and molecular study of Syllinae (Annelida, Syllidae) from Bermuda, with the description of five new species

“…Nevertheless, the current molecular information available for O. brunnea comes from an Australian individual (electronic supplementary material, table S2), and thus, we decide not to take any taxonomic action until new fresh material can be collected from the type locality in Madeira. Given the amount of putative worldwide distributed species in the subfamily Syllinae that have resulted to be a complex of different species with restricted geographical distributions [ 10 , 20 , 55 ], any taxonomic action in this group should always be based in analyses that include material from the type locality. Finally, our phylogenetic results place the species Syllis laiae n. sp.…”

From 13 to 22 in a second stroke: revisiting the European Eumida sanguinea (Phyllodocidae: Annelida) species complex

“…Environmental features could be an explanation for this variation. In the Syllis gracilis Grube, 1840 complex (Langeneck et al, 2020), a univariate analysis of morphological characters showed that marine specimens sampled on intertidal algal communities are differentiated from brackish-water and Sabellaria-associated individuals.…”