Evolution at the tips: Asclepias phylogenomics and new perspectives on leaf surfaces

Area of Science:

• Evolutionary Biology
• Plant Science
• Phylogenetics

Background:

• Leaf surface traits like trichome density and epicuticular waxes are crucial for plant ecology, influencing herbivory defense and water balance.
• Understanding the evolutionary history of these traits in diverse plant lineages is essential for ecological and evolutionary studies.

Purpose of the Study:

• To construct a robust phylogenetic framework for the genus Asclepias using plastome data.
• To analyze the evolutionary history of leaf surface traits, specifically trichome density and epicuticular wax presence, within Asclepias.

Main Methods:

• Generated a maximum-likelihood phylogeny for 103 Asclepias species utilizing their plastomes.
• Reconstructed ancestral states for leaf surface traits.
• Employed model comparisons within a likelihood framework to study character evolution.

Main Results:

• Resolved the backbone phylogeny of Asclepias, identifying key clades.
• Reconstructed the ancestral state as lacking epicuticular waxes and possessing sparse trichomes.
• Supported a macroevolutionary optimum for trichome density and detected an accelerated rate of its evolution.

Conclusions:

• Enhanced phylogenetic resolution and character evolution estimates were achieved through increased sampling and rigorous model selection.
• Character coding proved more influential on evolutionary inferences than model selection.
• The study provides a resolved phylogeny and novel insights into the evolution of leaf surface traits in Asclepias.