Quercus species divergence is driven by natural selection on evolutionarily less integrated traits

Area of Science:

• Ecology
• Evolutionary Biology
• Plant Morphology

Background:

• Functional traits influence ecological functions and adaptation potential.
• Phenotypic integration and modularity determine evolutionary constraints versus adaptive capacity.
• Leaf morphology in European white oaks (Quercus petraea and Quercus robur) varies and can distinguish species.

Purpose of the Study:

• To investigate in situ heritability, genetic correlation, and trait integration in leaf morphology of sympatric oaks.
• To test for differential evolutionary responses to selection among Quercus species.
• To understand the role of trait modularity in ecological divergence.

Main Methods:

• Sampled 2098 individuals of Quercus petraea and Quercus robur across their distribution.
• Estimated in situ heritability and genetic correlations for leaf morphological traits.
• Applied Selection Response Decomposition to analyze evolutionary responses.

Main Results:

• Identified a 'leaf size gradient' as a functionally integrated module under global regulation in both oak species.
• Found that lamina basal shape and intercalary vein number were less integrated, suggesting multiple trait modules.
• These less integrated traits, showing high species discriminatory power, likely experienced differential selection, driving ecological divergence.

Conclusions:

• Leaf morphology in sympatric oaks is modular, with distinct evolutionary trajectories for different trait groups.
• The 'leaf size gradient' module is conserved, while other traits like lamina basal shape and vein number are key drivers of adaptation.
• Differential selection on specific leaf traits has shaped the ecological preferences of Quercus petraea and Quercus robur in varying microclimates.