Modularity underlies the morphological evolution of Appalachian salamanders

Area of Science:

• Evolutionary biology
• Macroevolutionary patterns
• Speciation and diversification

Background:

• Modularity describes how traits evolve as interconnected systems, potentially facilitating adaptation and diversification.
• The Appalachian Mountains are a rich biodiversity hotspot for lungless salamanders (Plethodontidae), yet the drivers of their radiation are unclear.
• Understanding evolutionary modularity in Plethodontidae can illuminate mechanisms of diversification in this group.

Purpose of the Study:

• To investigate the presence and extent of modularity in functional and morphological traits of Appalachian salamanders.
• To determine if evolutionary rates differ across identified modules.
• To assess the correlation between the rates of evolution in different modules.

Main Methods:

• Analysis of functional and morphological characters to identify distinct evolutionary modules (e.g., head, trunk, limbs, tail).
• Comparative analysis of evolutionary rates across modules within major salamander clades (Plethodon, Eurycea, Desmognathus).
• Statistical assessment of correlations between module evolutionary rates.

Main Results:

• Appalachian salamanders exhibit significant modularity, with distinct modules identified under different analytical models.
• Evolutionary rates among modules showed non-significant differences, with the trunk evolving slowest and the tail fastest.
• Rates of modular evolution were often highly correlated, indicating coordinated responses.

Conclusions:

• Modularity plays a role in the morphological diversity of Appalachian salamanders by enabling independent phenotypic responses to selection.
• Despite modularity, evolutionary rates across modules are not significantly different, suggesting integrated responses to ecological opportunity.
• The findings highlight how modularity can facilitate diversification while maintaining coordinated evolutionary trajectories.