Macroevolutionary integration of phenotypes within and across ant worker castes

Area of Science:

• Evolutionary biology
• Macroevolutionary patterns
• Social insect evolution

Background:

• Phenotypic traits in social insects often form integrated evolutionary modules within and across castes.
• Understanding integration and modularity patterns across castes provides insights into evolutionary and diversification factors.

Purpose of the Study:

• To develop and test hypotheses on contrasting patterns of worker integration.
• To analyze major and minor worker evolution in the ant genus *Pheidole*.

Main Methods:

• Comparative analysis of 246 *Pheidole* species.
• Geometric morphometrics applied within a phylogenetic framework.

Main Results:

• Fast and tightly integrated evolution of mesosoma shape between major and minor workers.
• Slower and more independent evolution of head shape between the two worker castes.
• *Pheidole* workers exhibit both intracaste and intercaste integration with rate heterogeneity.

Conclusions:

• Decoupling of homologous traits across worker castes is observed.
• This modular evolution may facilitate the development of social complexity in ants.