Evolutionary bursts drive morphological novelty in the world's largest skinks

Area of Science:

• Evolutionary biology
• Macroevolutionary patterns
• Phylogenetics

Background:

• Animal phenotypes diverge due to selective pressures and genetic drift.
• Understanding the tempo and mode of morphological evolution is crucial for macroevolutionary studies.
• The relative contributions of gradual versus episodic change to novel morphologies remain debated.

Purpose of the Study:

• To investigate the tempo and mode of morphological evolution in Australo-Melanesian Tiliquini skinks.
• To resolve the rapid Miocene diversification of these lizards.
• To identify evolutionary pathways toward new morphologies.

Main Methods:

• Generated a time-calibrated phylogenomic tree using ~400 nuclear markers from over 100 specimens.
• Collected linear morphological data for 19 traits across the head, body, limb, and tail.
• Analyzed trait evolution patterns to identify rate shifts and evolutionary modes.

Main Results:

• Unprecedented resolution of the rapid Miocene diversification of Tiliquini skinks.
• Identified that most traits evolve conservatively, punctuated by infrequent evolutionary bursts.
• Phenotypic discontinuities arise from rapid rate increases along individual branches, termed 'punctuated gradualism'.

Conclusions:

• The evolution of novel morphologies in skinks is characterized by 'punctuated gradualism', a mode distinct from traditional gradualism and punctuated equilibrium.
• This mode has led to rapid diversification, producing forms like 'blue-tongued giants and armored dwarves'.
• Highlights the heterogeneity of evolutionary tempo and mode, even within individual traits.