Amini Omar Juma (MSc Thesis 2022)

Molecular and morphological characterization of cryptophytes of the Teleaulax amphioxeia/Plagioselmis prolonga complex and their salinity preferences.
Supervisor: Aitor Laza (UPV/EHU)
Cryptophytes of the Teleaulax/Plagioselmis/Geminigera (TPG) clade are the most prominent plastid donors to the toxic bloom forming dinoflagellates of the genus Dinophysis. These blooms lead to the outbreak of diarrhetic shellfish poisoning (DSP) and the temporary closure of shellfish fisheries and aquaculture, which affect the economy. The challenges in predicting blooms from novel means divert the focus to ecological modelling of the responsible species. As the link between Dinophysis and the TPG clade has recently been discovered, a gap in ecological and physiological information about these cryptophytes challenges the modelling studies. Some studies suggest that Teleaulax amphioxeia and Plagioselmis prolonga are haploid and diploid morphotypes of the same species that have different environmental preferences. In this study, the molecular approach using plastidial 23S rDNA, scanning electron microscopy, together with laboratory culture assays, were employed to characterize their molecular diversity, morphotypes, and growth response to salinity. The molecular analyses revealed the pseudo-cryptic diversity within the T. amphioxeia and P. prolonga species in which two major ribotypes (1A and 1B) that differed by three base pairs were delineated and each ribotype comprised both morphotypes. A less represented third ribotype (1C) differed by only one nucleotide from ribotype 1A and only included Plagioselmis-morphotype strains. No sequences from the databases representing Dinophysis and/or Mesodinium environmental samples clustered together with ribotype 1B. Apart from that, some strains that were originally classified as cf. Plagioselmis clustered with other related Teleaulax spp. in the phylogenetic analysis. No evident morphological differences were observed between strains of the same morphotype of different ribotype. Although ribotype 1A grew at a significantly faster rate than ribotype 1B, both ribotypes were capable of growing over a wide salinity range. Further molecular markers should be studied to resolve whether the ribotypes 1A and 1B are different species or a lineage of the same species. In addition, further ecophysiological studies are needed to reveal the environmental preferences of ribotypes and morphotypes in terms of temperature, nutrients and light conditions. These studies at the base of the food chain cryptophyte-Mesodinium-Dinophysis will help enhance the predictability of the harmful Dinophysis blooms. Key words: Cryptophytes, dimorphism, Dinophysis, Mesodinium, morphotype, ribotype, Teleaulax amphioxeia, Plagioselmis prolonga.

Molecular and morphological characterization of cryptophytes of the Teleaulax amphioxeia/Plagioselmis prolonga complex and their salinity preferences.

Supervisor: Aitor Laza (UPV/EHU)

Cryptophytes of the Teleaulax/Plagioselmis/Geminigera (TPG) clade are the most prominent plastid donors to the toxic bloom forming dinoflagellates of the genus Dinophysis. These blooms lead to the outbreak of diarrhetic shellfish poisoning (DSP) and the temporary closure of shellfish fisheries and aquaculture, which affect the economy. The challenges in predicting blooms from novel means divert the focus to ecological modelling of the responsible species. As the link between Dinophysis and the TPG clade has recently been discovered, a gap in ecological and physiological information about these cryptophytes challenges the modelling studies. Some studies suggest that Teleaulax amphioxeia and Plagioselmis prolonga are haploid and diploid morphotypes of the same species that have different environmental preferences. In this study, the molecular approach using plastidial 23S rDNA, scanning electron microscopy, together with laboratory culture assays, were employed to characterize their molecular diversity, morphotypes, and growth response to salinity. The molecular analyses revealed the pseudo-cryptic diversity within the T. amphioxeia and P. prolonga species in which two major ribotypes (1A and 1B) that differed by three base pairs were delineated and each ribotype comprised both morphotypes. A less represented third ribotype (1C) differed by only one nucleotide from ribotype 1A and only included Plagioselmis-morphotype strains. No sequences from the databases representing Dinophysis and/or Mesodinium environmental samples clustered together with ribotype 1B. Apart from that, some strains that were originally classified as cf. Plagioselmis clustered with other related Teleaulax spp. in the phylogenetic analysis. No evident morphological differences were observed between strains of the same morphotype of different ribotype. Although ribotype 1A grew at a significantly faster rate than ribotype 1B, both ribotypes were capable of growing over a wide salinity range. Further molecular markers should be studied to resolve whether the ribotypes 1A and 1B are different species or a lineage of the same species. In addition, further ecophysiological studies are needed to reveal the environmental preferences of ribotypes and morphotypes in terms of temperature, nutrients and light conditions. These studies at the base of the food chain cryptophyte-Mesodinium-Dinophysis will help enhance the predictability of the harmful Dinophysis blooms.

Key words: Cryptophytes, dimorphism, Dinophysis, Mesodinium, morphotype, ribotype, Teleaulax amphioxeia, Plagioselmis prolonga.

Amini Omar Juma (MSc Thesis 2022)

Molecular and morphological characterization of cryptophytes of the Teleaulax amphioxeia/Plagioselmis prolonga complex and their salinity preferences.

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