Genetic Diversity and Population Dynamics of Invasive Ascidiella aspersa: Insights from Cytochrome Oxidase Subunit I and 18S rDNA Analyses in Korean and Global Populations

Round 1

Reviewer 1 Report (Previous Reviewer 4)

Comments and Suggestions for Authors

-      The author should correct the fonts in the body to be consistent across the board. Also, the content of the legend should be centered or left-aligned.

-      The authors should add information on creating the TCS network and the software used in the materials and methods section.

-      The authors should include citations for Figure 2, 3, Tables S4, S7, and S10-S15. The authors should also add the explanations of Tables S4, S7, and S10-S15 in the manuscript.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

     The author should correct the fonts in the body to be consistent across the board. Also, the content of the legend should be centered or left-aligned.

-      The authors should add information on creating the TCS network and the software used in the materials and methods section.

-      The authors should include citations for Figure 2, 3, Tables S4, S7, and S10-S15. The authors should also add the explanations of Tables S4, S7, and S10-S15 in the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

In the manuscript by Lee at al., the authors aim to characterize the population of invasive species Ascidiella aspersa based on the genetic diversity of its cytochrome oxidase subunit I gene and its 18S-rDNA gene. In the study samples from 80 (more or less) sea squirts were sequenced, sorted in haplotypes and compared. Although results bring in new information about this invasive species they fail to “provide valuable insights into the species' colonization history and adaptation mechanisms, shedding light on the factors shaping its genetic structure” as the authors proposed.

In order to improve the manuscript for publication I suggest the following major revisions:

11.       The introduction is very brief and general, more detailed information is needed about previous studies on this topic:

- what is known about the diversity of this species, has its spread from Norway to other countries been monitored/investigated previously, what were the findings,

 

-          what is its rate of mutation and would the authors expect to find a single haplotype in Korea or multiple given the mutation rate and time it has colonized these shores?

2.       Materials and methods are lacking a lot of details and are sometimes misleading.

-          The map showing the location of the sampling sites suggests the authors collected samples from several location around the world, however I believe this is not the case. Samples were only collected from the coast of Korea, the rest of the sequences were acquired from a database. This should be more clearly explained and the two presented separately, samples that were actually collected and analyzed by the authors versus sequences that were taken from databases.

-          There is no information about how sequencing was done. We are only told the genes were amplified by PCR but there are no details about how their sequence was determined

-          Table 2 should be labeled table 1 and vice versa as that is the order in which they appear in the manuscript

-          Why in one section of the materials and methods there are 82 and 83 sea squirts and in the next section only 80 and 79? Why aren’t there the same number of sequences for COI and 18S-rDNA? I believe the sequences were obtained from the same samples so they should both be the same number.

3.       The results of the study are purely descriptive with no real insight into the origin of this invasive species, its spread strategy in Korea, and so on.

4.       The discussion section fails to compare the results of the current study with the results from the literature and integrate this study into the knowledge base already in existence.

Comments on the Quality of English Language

The English is fine, only needs minor spell check.

Author Response

The introduction is very brief and general, more detailed information is needed about previous studies on this topic:

- what is known about the diversity of this species, has its spread from Norway to other countries been monitored/investigated previously, what were the findings,

-  what is its rate of mutation and would the authors expect to find a single haplotype in Korea or multiple given the mutation rate and time it has colonized these shores?

 

2. Materials and methods are lacking a lot of details and are sometimes misleading.

-  The map showing the location of the sampling sites suggests the authors collected samples from several location around the world, however I believe this is not the case. Samples were only collected from the coast of Korea; the rest of the sequences were acquired from a database. This should be more clearly explained and the two presented separately, samples that were actually collected and analyzed by the authors versus sequences that were taken from databases.

- There is no information about how sequencing was done. We are only told the genes were amplified by PCR but there are no details about how their sequence was determined

- Table 2 should be labeled table 1 and vice versa as that is the order in which they appear in the manuscript

- Why in one section of the materials and methods there are 82 and 83 sea squirts and in the next section only 80 and 79? Why aren’t there the same number of sequences for COI and 18S-rDNA? I believe the sequences were obtained from the same samples so they should both be the same number.

 

3. The results of the study are purely descriptive with no real insight into the origin of this invasive species, its spread strategy in Korea, and so on.

 

4. The discussion section fails to compare the results of the current study with the results from the literature and integrate this study into the knowledge base already in existence.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

Please read the manuscript again for a final editing check before submitting the final version for publication, there still are some minor errors.

Comments on the Quality of English Language

A final spell check is needed.

Author Response

Comments 1: Please read the manuscript again for a final editing check before submitting the final version for publication, there still are some minor errors.

Response 1: Thank you for pointing this out. We have performed a final check on the grammar and language of the manuscript. Minor grammatical errors in the text have been corrected.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

No comments

Comments on the Quality of English Language

It is necessary to conduct a comprehensive review of the English language and grammar, as well as make structural enhancements.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript by Lee et al. compared the genetic diversity of COI sequences of Ascidiella aspersa between Korean and global populations, and suggested that the species was able to maintain genetic diversity during invasion. There is no doubt that the present study could provide important information for its management and control in invasive ecosystem. However, my major concerns of this manuscript are as following.

1. Only COI sequences were included in the genetic diversity analysis. Is there any possibility to include a nuclear marker as well?

2. In the 10 Korean population, only 80 individuals were selected. The sampling was quite inadequate, and may attribute to inaccurate results. Therefore I strongly recommend the authors to increase the number of individuals for each population. 

Some minor points are as following：

1. The citation format of references needs to be unified. In the Material and Method part, some references were cited as author name and publishing date (e.g., Kearse et al., 2012; Thompson et al., 2003). Please refer to the instructions of the journal and also include them in the reference list.

2. In Phylogenetic analyses and genetic diversity of Material and Method part, "Phylogenetic tree by" should be removed.

3. The description of phylogenetic reconstruction should be improved. For example, please mention the evolutionary model, the number of generations for Mrbayes.

Reviewer 3 Report

Comments and Suggestions for Authors

General comments

The manuscript addresses an interesting problem of the increase of exotic species around the world, in this case, Ascidiella aspersa in W Asia, a species that seems to be expanding throughout all temperate regions. The work seems well structured and the results are interesting from the point of genetic variability. However, from the formal point of view, the figures must be improved, and the Discussion should be improved.

Specific comments:  Only some observations are in the bibliography (see attached text). 

The manuscript could be published in 'Water' if the Discussion is improved

Comments for author File: Comments.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

 

-      In the third paragraph of the Introduction, the gene abbreviation such as COI is used for the firth time. Therefore, the full name must be written with abbreviated one in the parenthesis.

-      The author said that various studies have been conducted on A. aspersa. It is necessary to describe in the Introduction whether a study similar to this study has never been conducted and, if there was similar study, the difference of the previous study and present study should be written.

-      In the Materials and Methods, haplotype analysis results included tables 1 and 2. It is recommended that the haplotype analysis should be described in the paragraph of the Results.

-      " Phylogenetic tree were generated by Bayesian inference (BI) using MrBayes ver. 3.2.” in the Materials and Methods is ambiguous. The authors should add the detailed conditions and parameters for the analysis.

-      In the Materials and Methods “Phylogenetic analyses and genetic diversity”, the authors analyze the phylogenetic tree, however, there are no results of the phylogenetic tree.

-      The citation format is not consistent throughout the manuscript. The authors should revise the format of citation.

-      The author said in the Introduction that this had conducted research to evaluate the population genetic structure, but in the Discussion, the authors said: "aimed to uncover genetic signatures of natural selection at both the population and genomic levels." The purpose of the discussion does not match the overall content of this manuscript. Authors should correct this.

-      There are several sentences in the Discussion explaining the results, but none of these are cited. Authors should add citations to support.

-      In the manuscript, figure and fig. are used inconsistently. The authors should correct these consistently.

-      In table 2, location abbreviation is described, while table 4 is not. The authors should correct these consistently.

-      The Materials and methods do not include all methods using in this study such as Haplotype network. The authors should write all methods with the details such as parameters.

-      The resolution of the figure should be improved.

Comments on the Quality of English Language

Minor editing of English language required