A molecular phylogeny of Rissoidae (Caenogastropoda: Rissooidea) allows testing the diagnostic utility of morphological traits

Description of Alvaniawangi Xu, Qi & Kong, sp. nov. (Mollusca, Gastropoda, Littorinimorpha, Rissoidae) from the East China Sea

Alvaniawangi Xu, Qi & Kong, sp. nov. (Mollusca, Gastropoda, Littorinimorpha, Rissoidae) was discovered within the intertidal zone in the Nanji Islands and Zhoushan Islands, Zhejiang Province, China. It has a radula characteristic of Alvania Risso, 1826, a protoconch sculptured with micro pits and lamellae between spiral lirae, and a teleoconch with growth lines and subobsolete cords. Specimens were examined using an integrative taxonomic approach incorporating morphological observations and phylogenetic analyses of concatenated mitochondrial 16S rRNA and nuclear 28S rRNA gene sequences. The findings suggest that the new species is sister to Alvaniacircinata A. Adams, 1861 and is probably endemic to the shallow waters of the East China Sea.

Dispersal ability, habitat characteristics, and sea-surface circulation shape population structure of Cingula trifasciata (Gastropoda: Rissoidae) in the remote Azores Archipelago

Background

In the marine realm, dispersal ability is among the major factors shaping the distribution of species. In the Northeast Atlantic Ocean, the Azores Archipelago is home to a multitude of marine invertebrates which, despite their dispersal limitations, maintain gene flow among distant populations, with complex evolutionary and biogeographic implications. The mechanisms and factors underlying the population dynamics and genetic structure of non-planktotrophic gastropods within the Azores Archipelago and related mainland populations are still poorly understood. The rissoid Cingula trifasciata is herewith studied to clarify its population structure in the Northeast Atlantic Ocean and factors shaping it, with a special focus in intra-archipelagic dynamics.

Results

Coupling microsatellite genotyping by amplicon sequencing (SSR-GBAS) and mitochondrial datasets, our results suggest the differentiation between insular and continental populations of Cingula trifasciata, supporting previously raised classification issues and detecting potential cryptic diversity. The finding of connectivity between widely separated populations was startling. In unique ways, dispersal ability, habitat type, and small-scale oceanographic currents appear to be the key drivers of C. trifasciata’s population structure in the remote Azores Archipelago. Dispersal as non-planktotrophic larvae is unlikely, but its small-size adults easily engage in rafting. Although the typical habitat of C. trifasciata, with low hydrodynamics, reduces the likelihood of rafting, individuals inhabiting algal mats are more prone to dispersal. Sea-surface circulation might create dispersal pathways for rafts, even between widely separated populations/islands.

Conclusions

Our results show that gene flow of a marine non-planktotrophic gastropod within a remote archipelago can reveal unanticipated patterns, such that the understanding of life in such areas is far from well-understood. We expect this work to be the starting of the application of SSR-GBAS in other non-model marine invertebrates, providing insights on their population dynamics at distinct geographical scales and on hidden diversity. How transversal is the role played by the complex interaction between functional traits, ecological features, and sea-surface circulation in the population structure of marine invertebrates can be further addressed by expanding this approach to more taxa.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01862-1.