Fluctuations in Evolutionary Integration Allow for Big Brains and Disparate Faces

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Morphological evolution

Background:

• Evolutionary modularity proposes that distinct anatomical structures can evolve independently.
• This modularity can drive morphological diversification by allowing different rates and directions of phenotypic evolution.
• Craniofacial diversity is substantial in both teleost fishes (Gymnotiformes) and mammals (Carnivora).

Purpose of the Study:

• To compare rates of craniofacial evolution and estimate evolvability in face and braincase modules.
• To investigate how phylogenetic integration influences skull-shape evolution in diverse clades.
• To test the theoretical framework of evolutionary modularity in empirical systems.

Main Methods:

• Geometric morphometrics was employed to analyze craniofacial shape.
• Phenotypic matrix statistics were used to assess integration and evolvability.
• Comparative analysis was conducted on two distinct clades: teleost fishes (Gymnotiformes) and mammals (Carnivora).

Main Results:

• The face and braincase modules exhibit varying degrees of integration within both clades.
• In Gymnotiformes, the face and braincase evolved at similar rates.
• In Carnivora, the braincase evolved twice as fast as the face, indicating differential evolutionary rates.

Conclusions:

• Differential responses to selection, influenced by fluctuating phylogenetic integration, affect skull-shape evolution.
• Evolvability and constraints within facial and braincase modules contribute to observed patterns of morphological diversification.
• The study supports the role of modularity in shaping evolutionary trajectories of complex anatomical structures.