Peer review of: The evolution of parental care diversity in amphibians (2019)


Reviewers' Comments:  
 
Reviewer #1:  
Remarks to the Author:  
The authors have adequately addressed my previous comments in their revision.  
 
 
 
Reviewer #2:  
Remarks to the Author:  
I was a previous reviewer of this MS and the authors have done a great job of addressing my previous 
concerns regarding the MS and adding some additional focus and content to really emphasise the 
novel components of the MS. I do have a number of minor concerns still regarding this MS which i 
detail below. If they can be addressed then I believe that this MS will make a valuable contribution to 
our understanding of how parental care evolves.  
 
1. One thing that I think might help the interpretability of the MS overall is if there was a diagram 
indicating how the different care/developmental periods overlap. That is eggs, viviparity, brooding 
with direct development, tadpoles, juveniles, ect - perhaps indicating the number of species with each 
form of developmental trajectory. This would really help the reader interpret the sequence of caring 
periods for each developmental sequence and thus visualize how care types at early stages of 
development actually correspond with later development for each of the different developmental 
trajectories observed in this group. Of course this, may not be possible if the diversity of 
developmental trajectories that occur across amphibians is extremely high - but to some degree it 
must not be if you want to make generalizations across these different forms of development.  
 
Page 11, Lines 3 - 5: I am not convinced that this is a particularly unexpected result - i would expect 
that egg attendance is the easiest trait to evolve - because parents are most likely to be present at 
the production of eggs - but less likely to be present at the hatching of those eggs. Thus, attendance 
of the eggs simply requires parents to hang around immediately after there production - but 
attendance at the tadpole and juvenile stage requires prolonged association (either via initial egg 
attendance - or via other processes like viviparity - see Halliwell et al., 2017 for similar arguments). In 
this context you dont necessarily need an explanation that invokes differential selective pressures 
(lines 8 - 9) - its all about opportunity (which is kind of inferred on lines 10 - 14).  
 
Page 14, Lines 6 - 8: I found it interesting that egg brooding and viviparity were did not facility 
prolonged care post birth/brooding. It seems like these traits would pose an as likely scenario as egg 
attendance for facilitating prolonged care. I wonder if this should be discussed a little more.  
 
Page 14, Lines 12 - 15: Minor point but following on from a point above - I am not sure that it 
immediately follows that parent-offspring conflict and sibling competition facilitate increases in care 
complexity - instead the reduction of conflict and the increase in competition is likely to stabilize the 
associations which then set the stage for the further elaboration of care. Fundamental to this, to my 
interpretation, would simply be the presence of offspring and parents together in some form and that 
itself provides a novel selective environment for promoting either even more prolonged associations 
(e.g., care at other stages of development) or for the evolution of more complex forms of care within 
that developmental stage (e.g., via the emergence of novel behaviours or the co-option of behaviours 
that function in novel social scenarios). This will of course only occur if the mediation of conflict and 
cooperation allows associations to be stabilized - but that conflict and cooperation does not necessarily 
lead to the emergence of those extended forms of parental care per se.  
 

Page 16, lines 15 - 23: How much actual data is there available to actually study transitions between 
uni and bi-parental care at the level of individual care traits? From the the next page it appears as if 
there are only 31 species that exhibit bi-parental care - does that really supply the requisite diversity 
across specific care types to allow for examining transitions for specific care types (e.g., tadpole 
transport). I realise that you note that these analyses are only undertaken on traits for which you 
have sufficiently large sample sizes but I was still not clear whether we can be confident in drawing 
any strong conclusions from trait specific examinations of biparental care.  
 
Page 18, lines 7 - 23: Following on from the above I thought some of your final conclusions are 
slightly overstated given what your data suggested. Specifically, your data did not allow you to infer 
anything about relative costs and benefits of different traits nor anything about the extent of parent vs 
offspring control. While these things can be discussed in the main body of the discussion, with 
additional suggestions with respect to moving forward with research to test these ideas, I was not 
convinced they should be coaxed as major conclusions per se. Furthermore, could some of these ideas 
be tested, particularly the latter idea, by examining whether the evolution of parental care has 
resulted in a change in offspring phenotype in the direction expected if parental and offspring traits 
were co-evolving? Do offspring of species with strong prolonged care show evidence of shifts towards 
more altricial offspring?  
 
 
 
Reviewer #3:  
Remarks to the Author:  
I appreciate the author's responses and revisions to the manuscript. This is a very nice paper and I 
have just a couple of minor text edits to suggest.  
 
line 16: "...are more common because they are easier to evolve;"  
 
page 21, line 22: Clarify that scaling is to a mean branch length - the current wording is ambiguous 
since rescaling is usually to a set tree height (root to tip distance)  
 
Signed  
Gavin Thomas