Morphological and Molecular Characters Differentiate Common Morphotypes of Atlantic Holopelagic Sargassum

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

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Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is very well written, based on extensive bibliographical references and based on recent approaches that analyzed morphological and molecular data. But before the manuscript is recommended for publication in Phycology, small clarifications and/or corrections are needed:

 

Title: I don't understand why the authors restricted it only to the common morphotypes of the North Atlantic holopelagic Sargassum, if the collections were more extensive, as shown in figure 1, which included the Caribbean expedition and Transatlatic expedition. Furthermore, holopelagic Sargassum is also very common in the Caribbean region up to northern Brazil, although in the latter region the occurrence is sporadic.

 

Suggestion: still in the title, replace North Atlantic to Tropical Atlantic Ocean

 

Abstract, lines 27 to 29: "Without additional molecular characterization, these morophotypes cannot be classified as three distinct species."

Could it be that if more genomic analyzes were carried out, these three common morphotypes (S. fluitans III, S. natans I, and S. natans VIII) could be classified into three distinct species?

In the information presented in lines 87 to 94 (page 2), even in comparisons of full-length mitogenomes the divergences between these three morphotypes are low.

Thus, I suggest replacing distinct species to distinct taxa.

 

Line 97: Replace tropical North Atlantic to tropical Atlantic Ocean

 

Line 431, please include reference to International Code of Nomenclature of the algae, fungi and plants.

 

In conclusion: Although morphological analyzes of 54 characters have revealed no intermediate form between the three morphotypes, the genetic divergence to differentiate the three taxa is very low. I believe that the proposition of these three morphotypes as a single species of Sargassum, S. natans with its varieties (var. typica or natans; var. wingei and var. fluitans) would make the issue simpler and more uniform in the treatment of this complex.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This very interesting study helps to clarify the taxonomic status of holopelagic Sargassum morphotypes found in the tropical North Atlantic Ocean. 

No comments or suggestions

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has substantially improved. I think this manuscript will be largely cited, and provides a guide that is very needed, independently if the final conclusion with time will come to understand the taxonomy of species of the genus Sargassum . something that has proved to be a real challenge.

Before fully accepting the manuscript, and concerned with the potential creation of confusion, the discussion needs to clarify several strong statements made by the authors. First, I think the discussion on whether there is several species or one species is still open and this manuscripts does not solve the issue, what authors clearly state.

I think this manuscript opens a very important discussion about the value of other than molecular data to define a species. I applaud their courage. I would add that point to their conclusion. It will be a strong debate as studies following populations of Sargassum show incredible morphological variation.

I think the key provided will be the major contribution of this paper and therefore it needs to be very clear and friendly use. The issue with Sargasso is quite beyond taxonomists, many non-phycologists and conducting monitoring programs and this key will be essential.

Some observations:

1-      Clarify what is a branch, and how that differs from previous understanding of steam/stipe and the branch is clear for a phycologist/botanist. However, this paper will be used by many non-phycologist. Within your diagnosis and description, you do not use steam to describe if the morphotype has or not spines in the steam and is OK. Am I trying to avoid confusion, some monitoring programs might not have people that understand the difference. Perhaps they might interpret that you use branches for leaves… I mention this because that happens with some volunteers during their training session.

 

2-       This might create confusion to the community. I think using steam/instead of stipe is correct as they are floating, but branches can have steam and blade, and the presence/absence of spines is used to make a difference with S. fluitans. Please revise your diagnosis and the key provided. Perhaps just provide a small figure with the different parts.

 

3-       clarify why you mention that Figure 4D in Gonzalez-Nieto et al. paper is wrong, it is hard from a dry specimen and herbarium specimen to detect the spines in the branches or other characteristics.

 

4-      The link provided in the diagnosis is not working please check it out.

 

5-      Please revisit your guide, you mention that S. fluitans do not have spines on their bladders line 587, but your figure for a non-phycologist can interpret that is has spines, please clarify in the legend of the figure that each morphotype has different pedicels, just add an arrow or something that will be properly interpreted. I am trying here to see all potential problems from non-phycologists. 

Author Response

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Author Response File: Author Response.pdf