Sexual reproduction and genetic polymorphism within the cosmopolitan marine diatom Pseudo-nitzschia pungens

Jin Ho Kim,Bum Soo Park,Hong Chang Lim,Myung-Soo Han,Sing Tung Teng,Shauna A Murray,Po Teen Lim,Joo-Hwan Kim,Penelope Ajani

doi:10.1038/s41598-020-67547-9

Abstract

Different clades belonging to the cosmopolitan marine diatom Pseudo-nitzschia pungens appear to be present in different oceanic environments, however, a ‘hybrid zone’, where populations of different clades interbreed, has also been reported. Many studies have investigated the sexual reproduction of P. pungens, focused on morphology and life cycle, rather than the role of sexual reproduction in mixing the genomes of their parents. We carried out crossing experiments to determine the sexual compatibility/incompatibility between different clades of P. pungens, and examined the genetic polymorphism in the ITS2 region. Sexual reproduction did not occur only between clades II and III under any of experimental temperature conditions. Four offspring strains were established between clade I and III successfully. Strains established from offspring were found interbreed with other offspring strains as well as viable with their parental strains. We confirmed the hybrid sequence patterns between clades I and III and found novel sequence types including polymorphic single nucleotide polymorphisms (SNPs) in the offspring strains. Our results implicate that gene exchange and mixing between different clades are still possible, and that sexual reproduction is a significant ecological strategy to maintain the genetic diversity within this diatom species.

Highlights

Different clades belonging to the cosmopolitan marine diatom Pseudo-nitzschia pungens appear to be present in different oceanic environments, a ‘hybrid zone’, where populations of different clades interbreed, has been reported
Strain bearing auxospores were assigned to mating type PNp−, while strains successfully mating with a PNp− were assigned to mating type PNp+
Successful mating results were observed within same clades, and between clades I and III and clades I and II strains without exception, but not between clades II and III strains belong to opposite mating-types (Table 1)

Summary

Introduction

Different clades belonging to the cosmopolitan marine diatom Pseudo-nitzschia pungens appear to be present in different oceanic environments, a ‘hybrid zone’, where populations of different clades interbreed, has been reported. The cosmopolitan diatom Pseudo-nitzschia pungens, is a good model organism to examine the evolution and species concept in marine diatoms This diatom is distributed globally and is highly d iverse[35,36,37,38,39]. This species contains three genetically distinct groups (clade I, II and III), based on sequences of ribosomal DNA (rDNA) internal transcribed spacers (ITS) region[35], and three clades of P. pungens characterized into three morphological varieties according to its differences of the cingular band structure. Their distinct physiological characteristics formed by specific habitat environments have been r eported[42]

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