Cryptic diversity within the harmful dinoflagellate Akashiwo sanguinea in coastal Chinese waters is related to differentiated ecological niches

Abstract

Blooms of the harmful dinoflagellate Akashiwo sanguinea are responsible for the mass mortality of fish and invertebrates in coastal waters. This cosmopolitan species includes several genetically differentiated clades. Four clonal cultures were established by isolating single cells from Xiamen Harbour (the East China Sea) for morphological and genetic analyses. The cultures displayed identical morphology but were genetically different, thus revealing presence of cryptic diversity in the study area. New details of the apical structure complex of Akashiwo sanguinea were also found. To investigate whether the observed cryptic diversity was related to environmental differentiation, 634 cells were obtained from seasonal water samples collected from 2008 to 2012. These cells were sequenced by single-cell PCR. For comparison with Chinese material, additional large subunit ribosomal DNA sequences were obtained for three established strains from Malaysian and French waters. To examine potential ecological differentiation of the distinct genotypes, growth responses of the studied strains were tested under laboratory conditions at temperatures of 12°C to 33°C. These experiments showed four distinct ribotypes of A. sanguinea globally, with the ribotypes A and B co-occuring in Xiamen Harbour. Ribotype A of A. sanguinea was present year-round in Xiamen Harbour, but it only bloomed in the winter and spring, thus corresponding to the winter type. In contrast, A. sanguinea ribotype B bloomed only in the summer, corresponding to the summer type. This differentiation supports the temperature optimum conditions that were established for these two ribotypes in the laboratory. Ribotype A grew better at lower temperatures compared to ribotype B which preferred higher temperatures. These findings support the idea that various ribotypes of A. sanguinea correspond to distinct ecotypes and allopatric speciation occurred in different climatic regions followed by dispersal.

Characterization of the Parasitic Dinoflagellate Amoebophrya sp. Infecting Akashiwo sanguinea in Coastal Waters of China

“…One well‐defined subclade included all sequences from the east coast of the USA, and the other comprised those sequences from Korea, Japan, and China (Ribotype A in Luo et al. ).…”

“…Except for the sequence AY421770 identified as the isolate GSW0207 from Korea, the other 13 sequences formed two sister subclades. One welldefined subclade included all sequences from the east coast of the USA, and the other comprised those sequences from Korea, Japan, and China (Ribotype A in Luo et al 2017).…”

Morphological and molecular variability of Peridinium volzii Lemmerm. (Peridiniaceae, Dinophyceae) and its relevance for infraspecific taxonomy

“…However, no unequivocal or operable correlations between certain ribotypes, diagnostic traits, ecological preferences and/or geographic occurrence can be drawn. Cryptic speciation (Fenchel, 2005) can certainly not be excluded as it has been shown for other dinophytes (Lajeunesse et al, 2012;Luo et al, 2017;Montresor et al, 2003;Wang et al, 2019), but a single, variable species P. volzii is more likely at this moment in time, as it was worked out also for P. cinctum of the same phylogenetic group (Izquierdo López et al, 2018).…”

Cryptic speciation in Protoceratium reticulatum (Dinophyceae): Evidence from morphological, molecular and ecophysiological data

“…Multiple evidence for the presence of cryptic species have been reported in a few dinoflagellates such as Scrippsiella acuminata (Ehrenberg) Kretschmann, Elbrächter, Zinssmeister, S.Soehner, Kirsch, Kusber & Gottschling and Akashiwo sanguinea (Hirasaka) G. Hansen & Moestrup (Montresor et al, 2003;Luo et al, 2017). The Alexandrium tamarense species complex comprises several morphologically indistinguishable but genetically differentiated species, which now are even formally designated as five species (John et al, 2014), and this was the first case where dinoflagellate species are defined by sequence differences only.…”