Agent skill

bio-phylo-tree-visualization

Draw and export phylogenetic trees using Biopython Bio.Phylo with matplotlib. Use when creating publication-quality tree figures, customizing colors and labels, or exporting to image formats.

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npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/data/tree-visualization

SKILL.md

Tree Visualization

Draw phylogenetic trees using matplotlib integration.

Required Import

python
from Bio import Phylo
import matplotlib.pyplot as plt

ASCII Tree Display

python
tree = Phylo.read('tree.nwk', 'newick')

# Quick text representation
print(tree)

# ASCII art diagram
Phylo.draw_ascii(tree)

Basic Tree Drawing

python
tree = Phylo.read('tree.nwk', 'newick')

# Simple plot (opens interactive window)
Phylo.draw(tree)
plt.show()

# Save to file
fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax)
plt.savefig('tree.png', dpi=300, bbox_inches='tight')
plt.close()

Customizing Tree Appearance

python
fig, ax = plt.subplots(figsize=(12, 10))
Phylo.draw(tree, axes=ax, do_show=False,
           branch_labels=lambda c: f'{c.branch_length:.2f}' if c.branch_length else '',
           label_func=lambda c: c.name if c.is_terminal() else '')

ax.set_title('Phylogenetic Tree')
plt.savefig('custom_tree.png', dpi=300, bbox_inches='tight')
plt.close()

Label Customization

python
# Custom label function
def custom_labels(clade):
    if clade.is_terminal():
        return clade.name
    elif clade.confidence:
        return f'{clade.confidence:.0f}'
    return ''

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax, label_func=custom_labels)
plt.savefig('labeled_tree.png', dpi=300)
plt.close()

Branch Labels (Bootstrap, Lengths)

python
# Show branch lengths
def branch_length_labels(clade):
    if clade.branch_length:
        return f'{clade.branch_length:.3f}'
    return ''

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax, branch_labels=branch_length_labels)
plt.savefig('with_lengths.png', dpi=300)
plt.close()

# Show bootstrap values (stored in clade.confidence or clade.name for internal nodes)
def bootstrap_labels(clade):
    if not clade.is_terminal() and clade.confidence:
        return f'{clade.confidence:.0f}'
    return ''

Phylo.draw(tree, axes=ax, branch_labels=bootstrap_labels)

Coloring Trees

python
# Color specific clades before drawing
tree = Phylo.read('tree.nwk', 'newick')

# Set colors for specific clades (PhyloXML trees support this natively)
for clade in tree.find_clades():
    if clade.name and 'Human' in clade.name:
        clade.color = 'red'
    elif clade.name and 'Mouse' in clade.name:
        clade.color = 'blue'

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax)
plt.savefig('colored_tree.png', dpi=300)
plt.close()

Highlighting Clades

python
from Bio.Phylo.PhyloXML import BranchColor

# Convert to PhyloXML for color support
phyloxml_tree = tree.as_phyloxml()

# Color a clade and its descendants
target = phyloxml_tree.find_any(name='Human')
if target:
    target.color = BranchColor.from_name('red')

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(phyloxml_tree, axes=ax)
plt.savefig('highlighted.png', dpi=300)
plt.close()

Multiple Output Formats

python
tree = Phylo.read('tree.nwk', 'newick')
tree.ladderize()

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax, do_show=False)

# PNG (raster, good for presentations)
plt.savefig('tree.png', dpi=300, bbox_inches='tight')

# PDF (vector, good for publications)
plt.savefig('tree.pdf', bbox_inches='tight')

# SVG (vector, good for web)
plt.savefig('tree.svg', bbox_inches='tight')

plt.close()

Figure Size and Layout

python
# Adjust figure size based on tree size
n_taxa = len(tree.get_terminals())
height = max(8, n_taxa * 0.3)  # Scale with number of taxa

fig, ax = plt.subplots(figsize=(10, height))
Phylo.draw(tree, axes=ax, do_show=False)
plt.tight_layout()
plt.savefig('scaled_tree.png', dpi=300)
plt.close()

Phylo.draw() Parameters

Parameter Type Description
tree Tree Tree object to draw
axes Axes Matplotlib axes (optional)
label_func callable Function to generate tip labels
branch_labels callable/dict Function or dict for branch labels
do_show bool Call plt.show() automatically (default True)

Pre-Processing for Better Visualization

python
tree = Phylo.read('tree.nwk', 'newick')

# Ladderize for cleaner appearance
tree.ladderize(reverse=True)

# Set missing branch lengths to small value
for clade in tree.find_clades():
    if clade.branch_length is None:
        clade.branch_length = 0.001

fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax)
plt.savefig('clean_tree.png', dpi=300)
plt.close()

Side-by-Side Tree Comparison

python
tree1 = Phylo.read('tree1.nwk', 'newick')
tree2 = Phylo.read('tree2.nwk', 'newick')

fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(16, 8))

Phylo.draw(tree1, axes=ax1, do_show=False)
ax1.set_title('Tree 1')

Phylo.draw(tree2, axes=ax2, do_show=False)
ax2.set_title('Tree 2')

plt.tight_layout()
plt.savefig('comparison.png', dpi=300)
plt.close()

Hide Axis and Frame

python
fig, ax = plt.subplots(figsize=(10, 8))
Phylo.draw(tree, axes=ax, do_show=False)

ax.axis('off')  # Remove axis
ax.set_frame_on(False)  # Remove frame

plt.savefig('clean_tree.png', dpi=300, bbox_inches='tight', transparent=True)
plt.close()

Deprecated Functions

Function Status Alternative
draw_graphviz() Removed (1.79) Use Phylo.draw() for rectangular trees

For radial (circular) tree layouts, use external tools like ETE3 or DendroPy.

Common Issues

Issue Cause Solution
Labels overlap Too many taxa Increase figure height
No branch lengths Missing in file Set defaults or use cladogram
Colors not showing Wrong tree format Convert to PhyloXML first
Figure not saving do_show=True Set do_show=False before savefig

Related Skills

  • tree-io - Read and write tree files
  • tree-manipulation - Ladderize and reroot before visualization
  • distance-calculations - Build trees from alignments for visualization

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