Anomalous Coloration of Indo-Pacific Humpback Dolphins off Southern China

Round 1

Reviewer 1 Report

The paper is well written and presented. The photographs are very clear and very well laid out. The methods are clearly presented. 

However: one nearly fatal flaw is that the paper states it own weakness, in lines 163-164. All this could be a natural process and the authors could be biased. This concept should be emphasized more and explained in greater detail as a source of error or misunderstanding of the importance of these findings. 

As part of this, recommend authors do a statistical test even if only chi-square vs presenting percentages throughout. Run tests on the findings given in line 160. Is the 3.3% difference meaningful statistically? They also would need to run a power analyses on the sample sizes in Table 1 in order to determine the above test as well. 

English issues throughout. 

In line 175 remove "besides".

line 180, fix English. Is it a mice model or many mice models? 

Author Response

The paper is well written and presented. The photographs are very clear and very well laid out. The methods are clearly presented. 

However: one nearly fatal flaw is that the paper states it own weakness, in lines 163-164. All this could be a natural process and the authors could be biased. This concept should be emphasized more and explained in greater detail as a source of error or misunderstanding of the importance of these findings. 

Reply: Thanks for this comment. In the revised section 2.2, we make a clear definition of anomalous color pattern for humpback dolphin. To better illustrate the difference between anomalous and normal color patterns, we now include examples of normal juvenile, spotted adult and unspotted adult in revised figure 2.

“Since the Indo-Pacific humpback dolphins go through a discoloration process, they naturally exhibit color spots (Fig. 2A). The color spots are generally occurred in regular dot, spindle or oval shape with varying, yet highly comparable, sizes (Table 1). In the present study, anomalous pigmentation was defined as a lack or an excess of melanin in part of the dolphin body, including either localized hypo- or hyperpigmentation which differ substantially from the rest of the body of the same individual (Fig. 2B). (De-)pigment spots with unusual large size (e.g., > 5 cm but < 10 cm in length), which generally still have a smooth shape, were taken as merged/overlapping spots or ex-treme cases of normal discoloration spotting pattern due to individual variation but not included as anomalous pigmentation (Fig. 2C-D). Hypopigmentation associated with physical scars (such as rope scar, propeller trauma, biting scar, etc., Fig. 2E) was also excluded from the analysis (Table 1).”

As part of this, recommend authors do a statistical test even if only chi-square vs presenting percentages throughout. Run tests on the findings given in line 160. Is the 3.3% difference meaningful statistically? They also would need to run a power analyses on the sample sizes in Table 1 in order to determine the above test as well. 

Reply: Added as listed below.

“representing 3.3% of the individuals recorded in this area (χ² = 21.0, p < 0.001). Unlike for mid-PRD, the proportion of hypopigmentation at the two flanking zones of PRD was low and highly comparable to other conspecific populations (West-PRD: χ² = 1.1, p =0.29; East-PRD: χ² = 1.5, p = 0.21).”

English issues throughout. 

In line 175 remove "besides".

Reply: revised as suggested.

line 180, fix English. Is it a mice model or many mice models? 

Reply: “Mice model” was revised to “mice models”.

 

Reviewer 2 Report

This is an interesting analysis of coloration/discoloration patterns in Indo-Pacific humpback dolphins. Overall the data is good, and an important contribution to the literature to better understand the morphology of humpback dolphins. However, clarity can be improved throughout. My biggest concern is the use of melanistic and hypopigmentation terms. These are normally associated with animals that are all (or almost all) dark or light, like Migallo mentioned in the introduction. This led me to think the anomalies presented here would be similarly strikingly different. However, since this is such a color species with such variation in color, the anomalies presented look more like color morphs or just animals with odd dark or light patches, rather than anomalies like Migallo. Part of this may be not being as familiar with what is ‘normal’ for this species, but for example the pictures in Fig 2 don’t really look that drastically different to be outside of some normal variation in this colorful species.  I suggest that the authors better define what is considered an anomaly for this species. I think a description of the size of these patches compared to normal discoloration spots/patterns would be helpful in understanding why these are so different from normal patterns (i.e. there must be some threshold that is used to say that this patch is an anomalous pattern, vs. just a small blemish. It seems like the anomalies are large patches of light or dark skin, compared to small spots that develop with age). And again, I would hesitate in saying these are melanistic or hypopigmented animals, rather there are melanistic or hypopigmented patches (and then what is the difference between that and pale patch). Overall I think the authors need to clarify what is normal vs. anomaly (including having a figure for ‘normal’ animals, and a different one for the 3 categories of anomalies), and differentiate these from the discoloration process. See specific line notes below.

 

Abstract

Line 16 – How prevalent? Can you provide some reference or number here?

Line 27 – Please describe what a discoloration process is in this sentence, instead of the next one.

Line 32-36 – Although interesting, I am not sure how this relates to the study. Is this information necessary, or contributes to the paper?

Line 42 – It is unclear how renaming it mottled has to do with this uncertainty, can you clarify?

Line 57-58 – reference for the humpback dolphin please. Also, Herzing (I think 1997) described color/spotting patterns for Atlantic spotted dolphins through life that you might want to reference as well (unless this is already covered in the references of general spotted dolphins).

Overall the introduction focuses on the variation in discoloration between populations, which I think is important to understand in the context of anomalies, but I think there needs to be more connection between this variation and the anomalies (i.e. how why do we need to understand the variations in order to discuss the anomalies). How are you defining an anomaly if there is so much variation? If they are the most colorful cetacean, and have so much variation in color in general, are these really anomalies? Emphasize why it is important to look at many different locations to be able to describe the variation and what constitutes anomalies.

 

Methods

Line 78 – was should be were (photographs were collected)

Line 70 – year round (remove all)

Line 80 – Please also describe the cameras/lens you used

Line 87 – this is a definition I was looking for in the introduction (or at least discussion around it to give context in relation to the discoloration and variation in coloration seen in this species), particularly the part about how you are differentiating between discoloration process and anomalies.

Line 98 – State in the caption here that A are considered anomalies and B/C are regular patterns (as stated in the text, it is unclear just looking at the pictures that those are two different categories).

In addition, looking at the photos in figure 2, won’t hypopigmentation be prevalent in calves, but much reduced in adults since they lose their color as they age (so older adults will have much lower hypopigmentation rates)? And vice versa with melanism (in adults but not calves?). This should be discussed either way.

In looking at these pictures, I would not call these anomalies, but rather variations in pigmentation. For example, the panels 2A and B/C aren’t strikingly different as I would expect for an anomaly (like Migallo), but rather just variations in coloration. In the introduction you note Migallo, and other drastically melanistic or leucistic animals. Those are very different than what is seen here with this species. Given that they are the most colorful, and have such a wide variation in coloration within and between stocks, I would describe these more as color variations or morphs rather than anomalies. It seems there is some ‘normal’ level of variation in the populations more than that these are striking outliers. Alternatively, as there does seem to be few animals with these types of pigmentation, if you keep the anomaly description, I would suggest using different terms than hypopigmentation or melanism because these usually referred to the whole animal, not just in patches.

Results

Line 111 – what is pale morph vs. hypopigmentation? Please have all categories either described in the text, or in a table. This would be helpful in the introduction or methods so readers can better compare what is normal vs. anomaly.

Line 115 – this doesn’t make sense to say mid twice, should it be that there was a high level in the PRD, with most of the hypopigmentation cases being in the mid-PRD (so going specific from the general). Where does 3.3% come from? 20 out of how many?

Line 123 – how is continuous depigmentation different from discoloration?

Line 143 – Example of constant hypopigmentation observed for most of the individuals.

Discussion

Line 167 – this is what I was looking for earlier about the age classes, so perhaps mention this in the introduction or methods.

Line 177-178 – As such, the hypopigmentation of humpback dolphins resembles congenital leukoderma..

Line 180 – Mice models… is regulated

Line 202 – Fitness in regards to reproduction/social relationships may be important, depending on how they choose mates/associates. There are some studies on other species about anomalous pigmentation and effects on social associations and/or reproduction that would be good to reference here.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have significantly improved the paper. I appreciate the change of wording, adding measurements and the additions of the tables and pictures in the figures to showcase normal vs. abnormal pigmentation for this color species. It is much more clear what is being considered anomalous and why. The introduction is much clearer about how this all fits within the other species, and intraspecies variation.  I just have a few points where things could be a little clearer (see below). My only big question is how 44% show anomously pigmentation overall, if most of the %s are less than 1% for the different populations.  With a couple more minor edits, I look forward to seeing it published.

Intro

·         Line 70 – changes in body color through life cycles are not rare, there are quite a few species and references (which are given). I would change to: “Changes in body color through life cycles have been reported for some cetaceans (refs).”  Then go into the next part, “In addition, anomalous body color is not unusual…”

·         Line 85 – it isn’t clear that you are talking about different species here, so add, “….documented during fieldwork on a variety of cetacean species (refs).” I would also say that you should put e.g. references, as you certainly do not have all the anomously pigmented examples here, as there are many (including other species of dolphins and porpoises).

·         Around line 90-93 I would also perhaps put in a sentence of the uniqueness of this data set, as you have BOTH changing colors through the life cycle AND anomously pigmented individuals. That is something that hasn’t been published as much.

 

Methods

·         Line 117 – have the #cm here too as you have in the table, since you have it for the spots you are not calling anomalous.

·         Line 126 – I think this figure shouldn’t be here??

·         Line 132-136 – the figure caption needs to be looked at, it is very confusing as to which is typical vs. not vs. variations in normal coloration and not as clear as the text. I think hypopigmentation is B1? I would change it to something like (if I have it right):

o   Typical and atypical patterns of the Indo-Pacific humpback dolphins. Typical color patterns: A) life cycle discoloration from calf to adult. Atypical color patterns: B1) hypopigmentation, B2) hyperpigmentation. Unusual, but not considered anomalous color patterns (part of normal interindividual varation): C) unusual white or dark spots, D) merging dots, E) depigmentation due to physical trauma.  ***note I left out large in panel C – those aren’t as large as what you are calling hyper/hypopigmentation so I would be careful, they are larger than normal spots, so you could say that, but just saying large is strange because the anomalous patches are bigger***

Results

·          Line 144 – I wouldn’t say only here, 44% is a large number; also how is it 44% if it was less than 1% in most of the populations?

 

Author Response

Dear reviewer, we thank you for your comprehensive and constructive comments. First re your biggest concer, the "44" in line 144 represents the number of anomalies rather than percentage. To avoid misunderstanding, we changed "44 presented anomalous pigmentation" to "42 individuals presented anomalous pigmentation" (note the number was change as we omitted the records with pale patch). All the other suggestions were accepted and the manuscript was revised accordingly. The English writing was also improved by a native English speaker (coauthor of the present study). Again we thank you for reviewing our manuscript and happy the year of rabbit.   

Best regards

WZ Lin