Footprints of Natural Selection in North Atlantic Eels: A Review

Round 1

Reviewer 1 Report

In this manuscript entitled “Footprints of natural selection in North Atlantic eels: a review”, authors review the studies of natural selection and local adaptation on North Atlantic eels, European eel and American eel. In addition, authors discuss genome architecture in relation to local adaptation in North Atlantic eels and the role of both genetic and non-genetic on the survival of eels across their distribution range.

This manuscript is concise with respect to the subject area and there are no serious problems. Thus, it is considered worthy of publication in Fishes. However, the following points need to be improved.

Major comments

Temperate eel such as, A. japonica and A. asustralis, are also panmictic and are characterized by their distribution in a variety of habitats. On the other hand, some tropical eels are locally distributed. These characteristics make them suitable for the study of footprints of natural selection not only for North Atlantic eels, but also for all eel species.

Minor comments

Different fonts can be seen where the intent is not clear in some places. The fonts should be unified. i.e. L135 “Evidence for”, L143-144 ”The Environmental variable showing the highest association was temperature”

The number written at the beginning of the citation should be deleted.

L359 : Gray highlighted should be deleted.

Author Response

Major comments

Temperate eel such as, A. japonica and A. asustralis, are also panmictic and are characterized by their distribution in a variety of habitats. On the other hand, some tropical eels are locally distributed. These characteristics make them suitable for the study of footprints of natural selection not only for North Atlantic eels, but also for all eel species.

Agree with the point made by the reviewer and we have added a line in the 2nd section of the review stating that besides North Atlantic eels the rest of species of the genus are also adequate for selection studies.

Minor comments

Different fonts can be seen where the intent is not clear in some places. The fonts should be unified. i.e. L135 “Evidence for”, L143-144 ”The Environmental variable showing the highest association was temperature”

The number written at the beginning of the citation should be deleted.

L359 : Gray highlighted should be deleted.

We apologise for the issues, but those were not present in our Word document and must have only appeared when generating the PDF.

Reviewer 2 Report

In this manuscript, Jose Martin Pujolar and colleagues reviewed selective signatures of Atlantic eels (European and American eels). The review first highlighted the species’ excellent role in studying footprints of selection, despite panmixia, and then reviewed empirical studies on signatures of selections within respective species, between life-cycle stages, and between the two species. In the end, the papers discussed genomic islands of divergence and their insights.

This review of Atlantic eels is timely, covering comprehensive studies in the recent 20 years, and being structured well, as demonstrated by its subtitles. Overall, this manuscript is well written and of significant general interest to eel/fish researchers, geneticists and evolutionary researchers. I recommend the acceptance of this review in Fishes.

I have only two suggestions:

1-   As a review paper, it would be helpful to add a figure showing European and American eels. Readers might be interested in their morphology and differences. The figure could go along with the existing Figure 1, enriching its information, or as a separate figure.

2-   It would be good to provide a table specifying the selective signatures identified in the past literature reviewed in the paper. The following information could be listed: sequencing technology used/types of loci, sample sizes, focal phenotypes, number of signatures/loci identified, paper information, etc. This is just a suggestion from my side and would not discriminate against the quality of this review paper.

Author Response

Thanks very much for the nice words and good suggestions in regards to the manuscript. 

1-   As a review paper, it would be helpful to add a figure showing European and American eels. Readers might be interested in their morphology and differences. The figure could go along with the existing Figure 1, enriching its information, or as a separate figure.

We agree with the reviewer that a Figure would help readers interested in morphology and differences between species. But actually we believe showing a picture of each species would be of no interest as both species are identical. Instead we have re-analyzed the data from Avise et al. (1990) in regards to the overlap in vertebrae counts between European and American eel and made a new figure (Figure 1) showing the geographic distribution of both species in the background and the overlap in vertebrae counts between species. We believe this figure will be interesting for the reader. 

2-   It would be good to provide a table specifying the selective signatures identified in the past literature reviewed in the paper. The following information could be listed: sequencing technology used/types of loci, sample sizes, focal phenotypes, number of signatures/loci identified, paper information, etc. This is just a suggestion from my side and would not discriminate against the quality of this review paper.

We have now added a table (Table 1) providing all the information suggested by the referee.