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Harmful algal blooms: mechanisms, monitoring, and prevention in a rapidly changing world
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An assessment on the intrapopulational and intraindividual genetic diversity in LSU rDNA in the harmful algal bloom-forming dinoflagellate Margalefidinium (= Cochlodinium) fulvescens based on clonal cultures and bloom samples from Jiaozhou Bay, China
P-B1-21-S
Siheng Lin* , Institute of Oceanology Chinese Academy of Sciences
Zhangxi Hu, Institute of Oceanology Chinese Academy of Sciences
Ying Zhong Tang, Institute of Oceanology Chinese Academy of Sciences
Presenter Email: linsiheng@qq.com |
| Large subunit ribosomal DNA (LSU rDNA) sequences have been increasingly used to infer the phylogeny and species identity of organisms including microalgae because LSU rDNA are considered to be more suitable for discriminating closely related species or identifying intraspecific genetic variability. Previous studies have observed high intraspecific and even intraindividual variability in LSU rDNA in a number of dinoflagellates due to large copy numbers of LSU rDNA in dinoflagellates. Since the number of copies in LSU rDNA varies tremendously among different species of dinoflagellates, the intraspecific and intraindividual diversity for a species of particular interest thus needs to be investigated individually. As a toxic and rapidly expanding harmful algal blooms (HABs)-forming dinoflagellate, Margalefidinium (= Cochlodinium) fulvescens has been observed to reach blooming density in Jiaozhou Bay, China since 2015 after numerous blooms of the species have been reported from many other countries. In trying to identify the source of this newly observed HABs-forming species in China by sequencing the LSU rDNA for both field samples and clonal cultures, we noticed and thus further investigated high intrapopulational and intraindividual genetic diversities of the dinoflagellate. The D1-D6 region of the LSU rDNA (1435bp) were amplified using universal primers from 7 field samples (assemblages of many cells of M. fulvesens picked up and pooled under microscope from bloom water) and 11 clonal cultures, cloned, sequenced, and further analyzed using DnaSP v5 for 2304 sequences obtained. We found high intrapopulational and intraindividual genetic diversity in M. fulvescens as reflected in pairwise differences between sequences and the mean nucleotide differences in the clone library for different field samples and clonal cultures. Based on that the mean and overall intrapopulational genetic diversity (based on the 7 field samples) was almost equal to the mean and overall intraindividual variability (based on the 11 clonal cultures) in all indices of genetic diversity, together with the result of AMOVA analysis, it was inferred that the sequence variability within individual cells (i.e. variability among polymorphic copies of LSU rDNA) caused both the observed intraindividual and intrapopulational genetic diversities of the Jiaozhou Bay population of M. fulvescens. It was thus assumed that a higher interpopulational diversity would be observed when different geographic populations (e.g. the west coast of Canada and USA, that from Spain, Japan and Korea, and Indonesia) are compared. We believe the results as presented will provide an insightful basis for this comprehensive survey. |
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