The Centre–Periphery Model, a Possible Explanation for the Distribution of Some Pinus spp. in the Sierra Madre Occidental, Mexico

Round 1

Reviewer 1 Report

This is a very nice article, a significant update of the previous version that I reviewed. My previous comments were adequately reflected in this version.

I have two additional recommendations.

1. The abstract mentions 'criterion 2', but only the Material and Methods section explains what it is. If there is no space to explain this in the abstract, it might be better to replace 'for criterion 2' with 'in respect to elevation' or something similar.
2. In Conclusions, line 549, shouldn't it be 'genetically peripheral populations were not found'? In my understanding, geographically central/peripheral populations are defined by the sampling sites and distribution ranges, which are known a priori. Genetically central/peripheral populations are defined by their diversity and differentiation, according to the theoretical expectations and the results of the performed tests. Saying that 'peripheral populations were not found' or 'most populations are central' (abstract) without making this distinction is therefore confusing. It might be helpful to define and distinguish these terms in the text. 

Author Response

Dear Reviewer 1,

 

Thank you very much for helping us to improve this manuscript. I attended all your observations and comments.

 

Sincerely yours,

 

Claudia Bailón Soto

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript ID: forests-1543672

Title: The entre-periphery model, a possible explanation for the distribution of some Pinus spp. in the Sierra Madre Occidental, Mexico

General comments

This is a very interesting, important, and original genetic study that tested the theory that peripheral and central Pine species populations geographic distribution may presented different levels of genetic diversity. The studied was caried out for six Pine species along its geographic distribution in the Sierra Madre Occidental, Mexico, on based in a great sample population and individual sample sizes, using dominant AFLP genetic markers. The main goal of the study was to determine whether the centre-periphery population theory could explain the distribution of the species, for the purposes of conservation and subsequent sustainable use. The mains result was that in general centre-periphery model only explained the genetic diversity in one species, elevation gradient was an important factor that influenced genetic diversity and most species populations are central. In general the results of the present study indicated that both central or peripheral populations from the six pine species studied may be useful for regarding the collection of seeds for genetic conservation.

 

However, I have some suggestions to improve the manuscript, as show bellow.

 

Best regards,

The reviewer

 

Minor corrections

The terms genetic variability, variation, and diversity are used throughout the manuscript for the same purpose. I suggest using the term genetic diversity instead of genetic variability and variability (i.e. lines 21, 36, 117, 181, 349, 364, 373, 375, 416, 437, and 470) throughout the manuscript.  

 

Lines 163-178. This part is very confused.

Where you read ….to estimate genetic differentiation by analysis of the average genetic distances among populations (GD) and ….. by generating several matrices with the genetic distances among pairs of populations. Thus, paired combinations of all populations were run for all species. In addition, the AFLP binary data matrix was used to conduct Principal Coordinate Analysis (PCoA). The analysis was conducted, along with graphical representation of individual species and populations of species……….. according to the protocol described ……. Simpson's diversity [54]………. Higher DW values

…. I suggest ….…

to estimate the mean pairwise genetic distances between populations (GD) …. by generating several matrices with the genetic distances between pairs of populations. Thus, paired combinations of all populations were run for all species. In addition, AFLP matrix was used to conduct Principal Coordinate Analysis (PCoA). The analysis was conducted, along with graphical representation of individual species and populations of species…. according to the protocol described….. Simpson's diversity [54]. ……where higher values…..

 

Lines 202-207. Where you read ….location, along with the genetic diversity and differentiation indexes calculated for each population are shown in Table S1. The findings are shown and listed according to the first criterion. The elevation partitioning criterion (2nd criterion) and the indices of genetic diversity and differentiation calculated for each population are shown in Table S8. See relevant results in subsection 3.3 and thereafter with the genetic diversity and differentiation indices calculated for each population are shown in Table S1… I thing that the correc is….. location, genetic diversity and differentiation indexes calculated for each population to the first criterion are shown in Table A1 and the elevation partitioning criterion (2nd criterion) and the indices of genetic diversity and differentiation are shown in Table A2.….

 

Lines 208-220. Where you read …., measured according to Gregorius [52] and Wehenkel et al. [53], was generally similar in all the populations analysed; the lowest ?2 value of 1.250 corresponded to a central population of Pinus arizonica, while the highest ?2 value of 1.414 corresponded to a peripheral population of P. durangensis. The %Poly varied from 57.8% in a central population of P. arizonica to 87.3% in a central population of P. durangensis. The rarity index (DW), calculated according to Schönswetter and Tribsch [56], reached values ranging from 0.051 in a peripheral population of P. durangensis to 0.426 in a peripheral P. cembroides population. The PopGD varied from 66.677 to 93.638 in central populations of P. herrerae and P. cembroides, respectively. The lowest and highest GD values of 52.027 and 89.388....

....I suggest.... measured (?2) was generally similar in all the populations analysed; the lowest ?2 value of 1.25 corresponded to a central population of P. arizonica, while the highest ?2 value of 1.414 corresponded to a peripheral population of P. durangensis. The % Poly varied from 57.8% in a central population of P. arizonica to 87.3% in a central population of P. durangensis. The rarity index (DW) reached values ranging from 0.051 in a peripheral population of P. durangensis to 0.426 in a peripheral P. cembroides population. The PopGD varied from 66.7 to 93.6 in central populations of P. herrerae and P. cembroides, respectively. The lowest and highest GD values of 52 and 89.4....

 

Lines 219-221. Where you read …. from 0.057 km to 31.45 km in peripheral populations of P. arizonica and P. durangensis, respectively. ……….. highest (3,062 m)....I suggest.... from 0.06 to 31.45 km in peripheral populations of P. arizonica and P. durangensis, respectively…… highest (3062 m)…..

 

Lines 248-253. Where you read …. for the AFLP fragments evaluated in the six Pinus spp. showed higher levels of variation within populations than between populations. The FST values ranged from 0.0191 for P. cembroides to 0.0667 for P. herrerae, with values of 0.0501 for P. arizonica, 0.0541 for P. durangensis, 0.0472 for P. engelmannii and 0.0409 for P. leiophylla.....I suggest.... evaluated in the six species showed higher levels of variation within than between populations (FST ranged from 0.019 for P. cembroides to 0.067 for P. herrerae, with values of 0.05 for P. arizonica, 0.054 for P. durangensis, 0.047 for P. engelmannii and 0.041 for P. leiophylla…….

 

Lines 255-258. Where you read ….Several significant correlations between different diversity indexes were detected in the six Pinus spp. studied (Tables 2-7). However, in Pinus arizonica, P. cembroides, P. durangensis and P. engelmannii, …..(Tables 2-5). ....I suggest.... Significant correlations between different diversity indices were detected in the six Pinus spp. studied (Please, look my suggestion for tables 2 to 7). However, in P. arizonica, P. cembroides, P. durangensis and P. engelmannii, ……(Table 2)….

 

Lines 285-287. Where you read …. for Pinus herrerae.... I suggest.... for P. herrerae…

 

Lines 295-299. Where you read …. of Pinus leiophylla and its different peripheral and central populations, the differences might not be statistically significant due to the small number of populations sampled; ....I suggest.... of P. leiophylla and its different peripheral and central populations, the differences might not be statistically significant due to the small number of populations sampled….. But the differences were statistic significant (0.945*)!!!!! I am wrong!! Please, verified.

 

Lines 307-309. Where you read ….The results obtained for elevation as a partitioning criterion along with the genetic diversity and differentiation indexes calculated for each population are shown in Table S2. (I suggest delete this sentence).

 

Lines 310-324. Where you read ….genetic diversity measured according to Gregorius [52], and Wehenkel et al. [53], in all the analysed populations was similar; the lowest ?2 value of 1.3015 corresponded to peripheral populations of Pinus arizonica, while the highest ?2 value of 1.3760 corresponded to peripheral populations of P. cembroides. The %Poly varied from 69.4% in central populations of P. engelmannii to 81.60% in peripheral populations of P. cembroides. The rarity index, DW, calculated according to Schönswetter and Tribsch [56], reached values varying from 0.051 in peripheral populations of P. durangensis to 0.426 in peripheral P. cembroides populations. The PopGD varied from 69.326 to 91.778 in peripheral populations of P. arizonica and P. cembroides, respectively. The lowest (64.097) and highest (81.666) GD values corresponded to peripheral populations of P. arizonica and P. cembroides respectively (Table 8). The geographic distance varied from 3.720 km to 12.522 km in peripheral populations of P. engelmannii and P. arizonica, respectively. The lowest recorded elevation (1,820 m) corresponded to a peripheral population of P. engelmannii, and the highest (3,062 m)….

....I suggest....

genetic diversity (?2), in all the analyzed populations was similar; the lowest ?2 value (1.3015) corresponded to peripheral populations of P. arizonica (the correct is P. engelmannii, please confirm), while the highest value (1.376) corresponded to peripheral populations of P. cembroides (Table 8). The % Poly varied from 69.4% in central populations of P. engelmannii to 81.6% in peripheral populations of P. cembroides. The rarity index (DW) ranged from 0.051 in peripheral populations of P. durangensis to 0.426 in peripheral P. cembroides populations. The PopGD varied from 69.3 to 91.8 in peripheral populations of P. arizonica and P. cembroides, respectively. The lowest (64.1) and highest (81.7) GD values corresponded to peripheral populations of P. arizonica and P. cembroides, respectively. The geographic distance varied from 3,72 to 12,522 km in peripheral populations of P. engelmannii and P. arizonica, respectively. The lowest recorded elevation (1820 m) corresponded to a peripheral population of P. engelmannii, and the highest (3062 m)........

 

Lines 335-339, 344-347. Please, confer these results. Please, tried be simple.

 

Lines 362, 464, 469, 473, 513, 519, 529, 523, 548. Where you read ….diversity…. I suggest.... genetic diversity....

 

Lines 441-442 Where you read …. from self-fertiliza tion, affecting….. I suggest.... from self-fertilization and biparental inbreeding, affecting....

 

Line 492. Pinus leiophylla, ….. I suggest... P. leiophylla,….

 

I suggest joint the tables 2 to 7, due to the fact there are too much tables (8) and figures (3), total 11. Furthermore, the values between upper and lower diagonal are the same, so it is redundant to present both.  Please, verified the values un yellow, because these values are high (0r lower, small negatives), maybe they are significant different from zero (higher or lower) at 5% (P< 0.05) or 1% (P= 0.01) of probability.

 

Table 2. Correlations between genetic and geographical indecies of six Pinus spp. and the different peripheral and central populations of these species.

	% Poly	DW	GD	PopGD	Elevation	DGEO
P. arizonica
??	0.878*	0.849*	0.996*	0.945*	0.016	0.046
% Poly		0.936*	0.911*	0.84*	0.027	0.046
DW			0.88*	0.862*	0.085	-0.007
GD				0.948*	0.041	0.065
PopGD					0.055	0.025
Elevation						0.655
P. cembroides
??	0.574	0.443	0.978*	-0.112	-0.274	0.632
% Poly		0.891*	0.665	-0.589	0.069	0.747
DW			0.458	-0.877	0.368	0.449
GD				-0.070	-0.325	0.757
PopGD					-0.724	-0.125
Elevation						-0.018
P. durangensis
??	0.914*	0.775	0.997*	0.618	-0.238	-0.111
% Poly		0.867*	0.93*	0.499	-0.111	-0.040
DW			0.785	0.460	0.016	-0.156
GD				0.609	-0.238	-0.109
PopGD					-0.046	0.022
Elevation						0.156
P. engelmannii
??	0.907*	0.849*	0.990*	0.936*	0.434	0.107
% Poly		0.967*	0.913*	0.897*	0.316	0.079
DW			0.861*	0.849*	0.265	0.274
GD				0.898*	0.331	0.120
PopGD					0.602	0.092
Elevation						0.076
P. herrerae
??	0.938*	0.919*	0.994*	0.761	0.895*	-0.281
% Poly		0.922*	0.958*	0.855*	0.791	-0.076
DW			0.944*	0.898*	0.663	0.099
GD				0.799	0.853*	-0.202
PopGD					0.474	0.316
Elevation						-0.594
P. leiophylla
??	0.78*	0.195	0.999*	0.956*	0.616	-0.088
% Poly		0.478	0.793	0.921*	0.455	0.167
DW			0.207	0.262	0.753	0.945*
GD				0.962*	0.615	-0.079
PopGD					0.510	-0.057
Elevation						0.657

Note: ?2= genetic diversity measured through the effective number of variants; % Poly= percentage of polymorphic fragments; DW= frequency down-weighted marker; GD= average genetic distance between populations; PopGD= average genetic distance within populations; Elevation in metres above sea level (a.s.i.); DGEO= distance to the nearest edge (km); *P< 0.005.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 2,

Thank you very much for your help in the improvement of this manuscript.

I attended all your observations, comments and suggestions.

Sincerely yours,

Claudia Bailón Soto

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Nothing to declare.

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

I’m sorry this manuscript is not acceptable for publication in its current form. The English needs to be edited by a professional or native English speaker. I think it is largely the need for collaboration with a native English speaker or help with English translation that unfortunately makes the paper too difficult to understand. Whilst I can largely work out what has been done, and some of the points being made, generally the work is confusing, and the writing is almost impossible, for me, to follow in some places. Often multiple ideas and concepts are lumped into sentences or paragraphs with no clear focus and, in the Discussion, with no clear links to the results obtained here. I really have little idea of what the relevance of the outcomes of the work are. I’m sorry I can’t give a better response to the authors, but can see the merit in the work and would encourage them to rewrite with clearer focus and the help of a translator. I have tried to provide a good overview of the kinds of problems with the confusion of ideas presented in the Discussion and elsewhere. I’ve also shown a number of examples of text editing which of course relates primarily back to English translation. I have made many, but not in any way comprehensive edits, and questions/comments that would require clarification, directly on the pdf.

Comments for author File: Comments.pdf

Author Response

We are grateful for the comments and suggestions from the reviewer 1 to this manuscript. The current form was changed. As suggested, the style from the entire manuscript was corrected by a professional translator who is a native speaker. We think the manuscript is easier to understand with these new changes. Also, we gave a more logical order of different sentences.

In the title we changed one word to make it easier to understand, line 2.

In the abstract, lines 20 to 39 were corrected.

In the introduction, lines 42 to 59 were rearranged. Lines 65 to 74, lines 78 to 118 were also changed; and finally, lines 126 to 141 were changed to make the introduction more readable.

In the Materials and Methods, Part 2.1 was totally rewritten, while in Part 2.2 lines 166 to 177 were changed. Part 2.3 was mostly changed from line 183 to 197. In Part 2.4, lines 215, 225, 229 and 242 were corrected. From Part 2.5, lines 246, 247 and 252 were changed.

The results part was largely rewritten for better comprehension.

As recommended the discussion section was reorganized and rewritten for better understanding and easier reading.

In the discussion we tried to link better the results obtained from the study.

We highlighted the relevance of the outcomes of the work.

Finally, the conclusions were also rewritten for better comprehesion.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript by Ramirez-Orozco et al. examines genetic variation in Mexican populations of several Pinus species in order to test a theoretical concept in ecology called the central-peripheral theory.

 

Although I cannot evaluate this manuscript from the perspective of theoretical ecology, I am experienced in analyses of genetic diversity and involved in guiding strategies for ex situ conservation of plant genetic resources. From this perspective, the manuscript is sound and well-written, its objective is clearly presented, uses appropriate methodology, and the interpretation of results appears adequate. In general, I greatly support efforts to test predictions coming from theoretical concepts or modeling against empirical evidence.

 

I only identified one potentially contentious issue.

One of the crucial factors for a meaningful test of the genetic expectations of the central-peripheral theory is the definition of ‘central’ and ‘peripheral’ ecological niches. If populations identified as peripheral do not actually come from an ecological periphery, the test becomes invalid. I suppose it is difficult to define an ecological periphery, because limiting factors can be complex and unknown. Then it may be reasonable to define the center and the periphery in respect to the species’ geographic distribution. However, here it appears that the center and the periphery are defined in respect to the sampling sites (lines 157-169), which may not reflect the natural geographic distribution. In my view, the natural geographic distribution needs to be known a priori, and serve to define the center and the periphery. This should then guide the sampling. It is not clear whether this logic was followed, and it may appear that sampling was conducted first, and the periphery was defined from the sampling sites… This needs to be clarified, and implied limitations discussed.

 

Also, related to this issue is the question whether it is appropriate to define a ‘distribution zone’ in respect to a two-dimensional geographic area, or to take elevation into account and define 3D distribution zones. In such a case, there may be multiple ‘islands’ of periphery within a wider distribution zone, making the testing of the central-peripheral theory more complex.

 

Additional minor points that the authors may wish to consider:

line 22: The aim is better expressed on lines 136-137.

 

line 33 and other instances thereafter: ‘Behavior’ is not the best expression.

 

lines 75-78: This is confusing. If it refers to the neutral theory of evolution, and drift is limited in the core area, why is the core population more diverse? (Absence of drift prevents new neutral mutations from rising to viable frequencies.) Besides, the previous sentence mentions balancing selection in the core populations as a source of diversity, but selection is not a neutral force. Perhaps it would make sense if balancing selection (a non-neutral process) explains the diversity in the core, and drift explains genetic differentiation at the peripheries.

 

lines 86-89: Because of the overproduction of offspring, each species is expected to fill its ecological niche (which is subject to change in time). Accordingly, there is a continual supply of individuals pushed towards the periphery. Therefore in my view, gene flow from the core towards the periphery could be a rule rather than an exception. Is that a part of Mayr’s hypothesis?

 

lines 103-105: What is most relevant from a conservationist perspective (but not mentioned here) is whether peripheral populations contain unique variants (worth protecting/conserving). High genetic differentiation at the peripheries is not so relevant if all that variation is present in the core. Therefore, screening of diversity should focus on identification of unique variants, not just diversity or differentiation.

 

Finally, I am not much in favor of using the buzzword ‘climate change’ too liberally. Here, it appears five times, but without specific context. Is there any concrete evidence that the populations under investigation are currently endangered by climate change? If not, I would limit the use of the phrase.

 

28/05/2021

Author Response

Please see the atachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have not addressed any of the comments I provided to improve the manuscript.

Author Response

Dear Reviewer 1.

Thank you for revising this manuscript and for all your comments and suggestions.

The manuscript now has been extensively revised by a professional translator and native speaker who made major changes to the style and editing.

I hope this version is more readable.

Again, thank you very much for all your suggestions. They have helped us to improve this manuscript.

 

Sincerely,

 

Claudia Bailón Soto