Show me the data!

My 1st peer-review published paper

August 11th, 2011 | Posted by rmounce in Palaeontology | phdchat | Phylogenetics

After more than 6 months of waiting, my long overdue first paper has finally been published in Nature

Why do I say ‘long overdue’?
Doesn’t it usually take a long time for academic papers to get published?

Well… if you read it here [paywalled], you’ll see it’s only 600 words and 1 figure (at the absolute limit allowed by Nature’s editorial policy). It’s not really a full and lengthy contribution to science, just a simple “this previous paper is significantly wrong, and this is why”. I would have gone into greater depth of analysis had I been allowed to, but the strict word-limit rather prohibits this. I have no idea quite why it took so long to get accepted and published. I suspect Nature isn’t to blame. Politeness dictates that the original study authors can take a certain amount of time to reply to such letters, fair’s fair – but 6 months? Hmmm…

Anyway, some background and context:

My entire research thesis relies on re-analysing other people’s data. I have no access to specimens, I’m not a field palaeontologist, my research angle is ‘palaeoinformatics’ – large-scale re-analyses of hundreds if not thousands of palaeontological datasets. So naturally, when a new fossil specimen (reconstruction below) with novel phylogenetic data gets published in Nature I justifiably take a keen interest.

Artistic reconstruction of Diania cactiformis by Mingguang Chi as first published in Nature

Using the freely-available software program TNT, one can quickly and easily re-analyse the data matrix given in the Liu et al 2011 supplementary materials in a matter of seconds with any desktop computer. Any such reasonably informed parsimony analysis of this data (there are numerous parameters and settings one could specify), does NOT generate the consensus phylogeny they depict and furthermore the ‘real’ result generates cladograms in which the position of Diania cactiformis is significantly different.

It took several different re-analyses to be sure that I was onto something interesting. Frustratingly in phylogenetics, authors aren’t always as explicit in their methods sections as I’d like them to be. In this instance, it was not stated (as is true of most papers) what branch collapsing rules were followed. Is it safe to assume that they used the default setting? I think not!

So, once I was sure there was a problem, I emailed the corresponding author with my concerns. This was her reply in verbatim:

Hello, Ross, thank you for your attention, now I am very busy with writing an application (the deadline is March 10th), could you wait me for few days, I will show you all the phylogeny tree which I got, the methods, the rules and so on. Thank you very much!
All best regards!

I never did get a follow-up email. [I assume because I submitted a formal reply to Nature which Jianni will have been notified of]. As a lowly grad student I’m sadly used to getting fobbed-off all the time…
Good thing I didn’t wait too long to formally reply either. It soon became apparent via Facebook that another research group intended to challenge this paper too. Well done to David Legg et al for their successful reply, also published in Nature.

Finally, I’d like to thank my supervisor Matthew Wills for helping me appropriately word my submission. I may have had the idea, and done the analyses, but it might not have been published without his excellent editorial input into the wording of the piece. We tried very hard to be polite and maintain the importance of the specimen, whilst necessarily pointing out the flaws of the analysis given.

I’ve been in Nature two times now in 2011! I didn’t write the first piece though. Can I make it a hat-trick? Time will tell…

As for the Liu et al. counter-reply which I’ve only just been allowed to see like the rest of the world – I’m surprised certain bits of it made it past peer-review. Their use of the PTP test is particularly intriguing and defies current scientific consensus on the validity of the usage of this test:

“Additionally, a significant value of the partitioning tail permutation (PTP) test (P = 0.01) suggests the presence of a clear phylogenetic signal in the morphological data, also strongly supporting the topology shown.”

First of all, I’ll generously assume they intended to refer to the permutation tail probability test not the “partitioning tail permutation” [sic] test. I don’t doubt the numerical result of the PTP test they present – it’s the inference they make from that result that I find illogical and unjustified given the numerous papers that have critically examined the PTP test – that this result somehow “strongly support[s] the topology shown” well; it doesn’t!!! One only has to look at the titles of numerous papers on the PTP test (although, please by all means read them!) to see that few if any can recommend it’s use for the purpose of supporting particular topologies:

  • Swofford et al (1996) The Topology-Dependent permutation test for monophyly does not test for monophyly.
  • Slowinski & Crother (1998) Is the PTP test useful? [Barely; only to determine if data has 'signal']
  • Peres-Neto & Marques (2000) When are random data not random, or is the PTP test useful? [Largely, no]
  • Harshman (2001) Does the T-PTP test tell us anything we want to know? [Largely, no]
  • Wilkinson, M. et al (2002) Type 1 error rates of the parsimony permutation tail probability test. [Points out errors in the Peres-Neto & Marques 2000 analysis, but still agrees that "the parsimony PTP cannot generally be assumed to guarantee well-supported phylogenetic hypotheses."]

FYI the original papers describing the PTP test are Archie, 1989; Faith 1991; and Faith & Cranston 1991 [full citations and links given at the bottom]

There are other problems with the Liu et al reply which I hope others may be able to see for themselves but I’ll leave it at that for now. I perceive this statement for instance:

In this context, Mounce and Wills seem to have overlooked the potential significance of their reanalysis of our data.

to be a bit of a ‘cheap shot’ especially considering the extremely short word-limit enforced on our comment by Nature. Of course we would have loved to have described the implications of the reanalysis for each and every character – but this simply wasn’t relevant enough to the criticism we were presenting. How this was deemed relevant to the rebuttal of our valid and justified points in the Mounce & Wills comment I leave up to you to decide

I’d also like to say how much I admire the work of many of the scientists on the Liu et al paper. I think they produce some excellent work, and I’ve met Jason Dunlop in particular many times – he’s a nice guy and an excellent scientist. As a middle author I’m pretty confident he has little to do with the problems inherent in the original Liu et al Nature paper and the subsequent Liu et al counter-reply. My own objections to both papers are nothing personal – just an obsession with good science and logical reasoning!

Welcome to the world of academia…

    References & Links:

Archie, J. W. A randomization test for phylogenetic information in systematic data. Systematic Biology 38, 239-252 (1989). URL

Callaway, E. Fossil data enter the web period : Nature news. Nature (2011). URL

Coddington, J. & Scharff, N. Problems with zero-length branches. Cladistics 10, 415-423 (1994). URL

Faith, D. P. Cladistic permutation tests for monophyly and nonmonophyly. Systematic Zoology 40, 366-375 (1991). URL

Faith, D. P. & Cranston, P. S. Could a cladogram this short have arisen by chance alone?: On permutation tests for cladistic structure. Cladistics 7, 1-28 (1991). URL

Harshman, J. Does the T-PTP test tell us anything we want to know? Systematic Biology 50 (2001). URL

Legg, D. A. et al. Lobopodian phylogeny reanalysed. Nature 476, E1 (2011). URL

Liu, J., Steiner, M., Dunlop, J., Keupp, H., Shu, D., Ou, Q., Han, J., Zhang, Z., & Zhang, X. (2011). An armoured Cambrian lobopodian from China with arthropod-like appendages Nature, 470 (7335), 526-530 DOI: 10.1038/nature09704

Liu, J. et al. Liu et al. reply. Nature 476, E1 (2011). URL

Mounce, R., & Wills, M. (2011). Phylogenetic position of Diania challenged Nature, 476 (7359) DOI: 10.1038/nature10266

Peres-Neto, P. R. & Marques, F. When are random data not random, or is the PTP test useful? Cladistics 16, 420-424 (2000). URL

Slowinski, J. B. & Crother, B. I. Is the PTP test useful? Cladistics 14, 297-302 (1998). URL

Swofford, D. L., Thorne, J. L., Felsenstein, J. & Wiegmann, B. M. The Topology-Dependent permutation test for monophyly does not test for monophyly. Syst Biol 45, 575-579 (1996). URL

Wilkinson, M., Peres Neto, P. R., Foster, P. G. & Moncrieff, C. B. Type 1 error rates of the parsimony permutation tail probability test. Systematic Biology 51, 524-527 (2002). URL