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Opinion Article
Revised

Animating and exploring phylogenies with fibre plots

[version 2; peer review: 3 approved with reservations]
PUBLISHED 25 Jan 2017
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This article is included in the Phylogenetics collection.

Abstract

Despite the progress that has been made in the visualisation of information since Haeckel's time, phylogenetic visualisation has moved forward remarkably little. In this brief essay, I give a short review of what I consider to be some recent major advances, and outline a new kind of phylogenetic visualisation. This new graphic, the fibre plot, uses the metaphor of sections through a tree to describe change in a phylogeny. As an animation, I suggest it is a powerful method to help interpret large phylogenetic hypotheses, although snapshots of it can also be displayed. As we enter the Anthropocene, I argue there has never been a greater need to know humanity's true place in the world, as depicted in the tree of life.

Keywords

phylogeny, visualisation, 3D, fractal, animation, tree of life

Revised Amendments from Version 1

A new version of this article has been published to correct the author’s affiliation to: Department of Biology & Ecology Center, Utah State University, Logan, UT, USA.

See the author's detailed response to the review by Stephen A. Smith
See the author's detailed response to the review by Rafael Zardoya
See the author's detailed response to the review by Diego San Mauro and Ainhoa Agorreta

A new generation of phylogeneticists are piecing together the entire tree of life, making vast phylogenies of millions of taxa1,2. Many have produced tree-like depictions of the relationships among species, both before and after Darwin described the origin of species3,4, but Haeckel’s drawings are perhaps the most well-known. As our phylogenies become larger, a problem has emerged: humans cannot easily interpret phylogenies with millions of tips. In this brief essay, I will describe recent progress in the visualisation of phylogenies, and outline a new kind of plot in development (the fibre plot). My aim is not to write a review [c.f. 5], but rather to provide an opinionated commentary on some major milestones in the progress of phylogenetic visualisation.

Haeckel’s phylogenies are beautiful to look at, and convey the overall structure of a phylogeny well. Each minor branch rarely maps onto a particular species, but their presence reminds the reader of the ever-changing nature of diversification. Both Haeckel and Darwin convey two kinds of information in their visualisations: time through depth on the page, and relatedness through the branching structure itself. Haeckel is also notable for producing a series of phylogenies, each examining a finer phylogenetic scale. Haeckel grasped that humans cannot process the fine details of all species without becoming lost, and that a series of phylogenies provides the same information in a more digestible format than a single, large, fully-resolved tree.

The last one hundred years have seen transformative changes to phylogenetic inference [see 6, but the same is not true of phylogenetic visualisation. The pace of change of phylogenetic visualisation has not matched that of other aspects of statistical visualisation. A time-traveller from 1859 could decipher a phylogeny from 2016 with On the Origin of Species3 as a guide, but the box-plots7 and histograms8 we rely on today would be foreign to them. Circular (“radial”) phylogenies are sometimes preferred when space is limited, and “magnifiers” in some computer programs highlight certain parts of the tree in more detail [e.g. 9], but for the most part any advances have been relatively minor.

To my knowledge, Paloverde10 was the first openly-released 3D phylogeny viewer. While it offered the user the ability to explore the most tree-like phylogenetic depiction to date, it also permitted the user to fly around a circular phylogeny rendered in a virtual space. Paloverde is notable for its claim that phylogeny is something to be explored, not merely viewed, and that “a 3D world, offers visual cues that aid in navigation and display that is unavailable in strictly 2D versions of the same layout.”10 The author of Paloverde, like Haeckel, recognised that scientists need to shift between finer and coarser phylogenetic scales when examining data, and so allowed users to collapse nodes at will. The program was a major advance in helping phylogeneticists conceptualise their own phylogenetic hypotheses. At least as transformative was the release of OneZoom11: a fractal phylogeny representation capable (theoretically) of displaying the entire tree of life on one page. OneZoom also requires the user to explore the tree, scanning up and down between finer and coarser details to make sense of the entire tree. Critically, OneZoom’s authors recognised that we are reaching the limits of what can be displayed in books: “[w]e now need to take the next step with a transition to data visualization that is optimized for interactive displays rather than printed paper.”11 They suggest that the way to display the next generation of data is to use the next generation of technology. A common thread running through these developments is their capacity to change the information displayed to the viewer, to better emphasise difference in structure across different phylogenetic depths. Consequently, I suggest the use of a new visualisation, the “fibre plot”, which is intended to leverage our natural ability to detect visual change through time. The fibre plot may be considered a horizontal slice through the tree of life, taken at whatever height (depth) the viewer requires (Figure 1). By moving along the tree, from the root to the tip, viewers will see the relative width of each fibre, and so gauge the number of terminal tips subtending that clade. I suggest an animation, with frames recorded at equal intervals along that trunk, which will provide the viewer with an intuitive sense of the timing of the diversification of major clades. I emphasise that, while Figure 1 shows the underlying logic behind the plot, the “plot” should really be called an animation - it is most readily interpretable when the user watches a video composed of successive slices through the trunk of the tree. I have included a toy implementation of this preliminary idea in R (Supplementary File 1), and an example of how it can be used to visualise the entire mammal tree of life12 (Supplementary File 2). Picking an ideal layout of the tips in the two-dimensional plane at the top of the tree is complex; a colleague has suggested using Hilbert curves based on the phylogeny’s distance matrix as an alternate solution to the one I have implemented.

e33080bb-50cf-473e-ad74-c03fc92e333c_figure1.gif

Figure 1. An explanation of a fibre plot.

On the left, I show a phylogeny (in grey) with a series of slices cut through it (in black). To the right, I show views through those slices surrounded in black outlines: each of these slices forms the basis of a fibre plot. Within each slice, a square represents descendent tips, and colours of those squares represent the composition of clades within a particular time slice. Squares of the same colour form a “fibre” in the tree of life. A true fibre plot would be an animation of the transition between these slices, showing how the clades (fibres) that make up the tree split as diversification takes place. Alternate colouring schemes are possible for the fibres (e.g., representing clade age), and I suggest displaying the age of each slice as the animation progresses (see Supplementary files for examples).

Despite humanity being closer than ever to a true tree of all life on Earth1,2, phylogenetic visualisation may seem like a niche topic. I strongly feel that phylogenetic visualisation is critical to grasp the full extent of our planet’s biodiversity. Human activity has carelessly altered almost every aspect of our planet, and we must now live with the shame and hubris of a geologic age we named after ourselves13. There has never been a greater need to find a way to show humanity our true place in the world. In whatever sense a phylogeneticist can have a duty, I believe it is ours to show the world that we are nothing more than a twig on a tree that we are cutting down.

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Version 3
VERSION 3 PUBLISHED 29 Nov 2016
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Pearse WD. Animating and exploring phylogenies with fibre plots [version 2; peer review: 3 approved with reservations]. F1000Research 2017, 5:2790 (https://doi.org/10.12688/f1000research.10274.2)
NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Open Peer Review

Current Reviewer Status: ?
Key to Reviewer Statuses VIEW
ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 2
VERSION 2
PUBLISHED 25 Jan 2017
Revised
Views
13
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Reviewer Report 17 Feb 2017
Diego San Mauro, Department of Zoology and Physical Anthropology, Complutense University of Madrid, Madrid, Spain 
Ainhoa Agorreta, Department of Zoology and Physical Anthropology, Complutense University of Madrid, Madrid, Spain 
Approved with Reservations
VIEWS 13
This paper presents a brief overview on phylogenetic visualization and introduces a novel approach for visualizing phylogenies (timetrees) using fibre plots. Given the rapid accumulation of phylogenetic information over the last years that has enabled the construction of massive trees ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
San Mauro D and Agorreta A. Reviewer Report For: Animating and exploring phylogenies with fibre plots [version 2; peer review: 3 approved with reservations]. F1000Research 2017, 5:2790 (https://doi.org/10.5256/f1000research.11550.r19938)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 05 Apr 2017
    Will Pearse, Department of Biology & Ecology Center, Utah State University, Logan, USA
    05 Apr 2017
    Author Response
    I thank you both for your comments, which have greatly improved the article. I'm particularly grateful that you mentioned Walrus; this was a huge oversight on my part, and I'm ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 05 Apr 2017
    Will Pearse, Department of Biology & Ecology Center, Utah State University, Logan, USA
    05 Apr 2017
    Author Response
    I thank you both for your comments, which have greatly improved the article. I'm particularly grateful that you mentioned Walrus; this was a huge oversight on my part, and I'm ... Continue reading
Views
15
Cite
Reviewer Report 13 Feb 2017
Stephen A. Smith, Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA 
Approved with Reservations
VIEWS 15
Pearse presents a new means for visualizing large phylogenies called the fibre plot. The purpose of this plot is to better represent splits by different colors and shades. This is an interesting idea and is demonstrated with an accompanying animated ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Smith SA. Reviewer Report For: Animating and exploring phylogenies with fibre plots [version 2; peer review: 3 approved with reservations]. F1000Research 2017, 5:2790 (https://doi.org/10.5256/f1000research.11550.r19876)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 05 Apr 2017
    Will Pearse, Department of Biology & Ecology Center, Utah State University, Logan, USA
    05 Apr 2017
    Author Response
    Thank you for these suggestions. I have now altered the fibre plot code in exactly the way you suggested, adding a traditional phylogeny to the right-hand side of the animation ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 05 Apr 2017
    Will Pearse, Department of Biology & Ecology Center, Utah State University, Logan, USA
    05 Apr 2017
    Author Response
    Thank you for these suggestions. I have now altered the fibre plot code in exactly the way you suggested, adding a traditional phylogeny to the right-hand side of the animation ... Continue reading
Views
20
Cite
Reviewer Report 10 Feb 2017
Rafael Zardoya, Department of Biodiversity and Evolutionary Biology, Museo Nacional de Ciencias Naturales, Madrid, 28006, Spain 
Approved with Reservations
VIEWS 20
The paper entitled  “Animating and exploring phylogenies with fibre plots” by Pearse is an interesting contribution that proposes a new and distinct way to visualize phylogenetic trees. The new method propose by the author uses fibre plots to slice a ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Zardoya R. Reviewer Report For: Animating and exploring phylogenies with fibre plots [version 2; peer review: 3 approved with reservations]. F1000Research 2017, 5:2790 (https://doi.org/10.5256/f1000research.11550.r19939)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 05 Apr 2017
    Will Pearse, Department of Biology & Ecology Center, Utah State University, Logan, USA
    05 Apr 2017
    Author Response
    Thank you for these comments. I hope the changes I have made address some of your concerns about interpretation, all of which I think are legitimate. I have added the ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 05 Apr 2017
    Will Pearse, Department of Biology & Ecology Center, Utah State University, Logan, USA
    05 Apr 2017
    Author Response
    Thank you for these comments. I hope the changes I have made address some of your concerns about interpretation, all of which I think are legitimate. I have added the ... Continue reading

Comments on this article Comments (0)

Version 3
VERSION 3 PUBLISHED 29 Nov 2016
Comment
Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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