Are Ophiolitic Substrates Drivers for Reticulate Evolution in Armeria (Plumbaginaceae)?

Area of Science:

• Ecology
• Evolutionary Biology
• Genomics

Background:

• Ultramafic substrates influence plant adaptation and microevolution.
• The Armeria denticulata complex includes species with distinct substrate preferences: A. denticulata (serpentinophyte), A. saviana (limestone/jasper), A. arenaria subsp. praecox (ophiolites), and A. gracilis (limestone).
• Understanding speciation drivers in this complex is crucial, especially given similar ecological conditions did not induce speciation in related Armeria arenaria.

Purpose of the Study:

• To investigate whether substrate specificity and/or hybridization promoted speciation within the Armeria denticulata complex.
• To determine the evolutionary origins of Armeria saviana and specific populations of Armeria denticulata.
• To evaluate reticulate evolution scenarios using phylogenomic and morphometric data.

Main Methods:

• Genome skimming and Illumina sequencing to assemble plastomes.
• Analysis of nuclear genome data (ribosomal DNA, single-copy markers) for phylogenetic inference.
• Phylogenomic analyses incorporating the Coalescent model to assess gene tree probabilities and reticulate evolution.
• Complementary morphometric analyses using Gaussian Mixture Models, Neighbor-Net networks, and linear discriminant analysis.

Main Results:

• Phylogenomic and morphometric data indicate Armeria saviana is of homoploid hybrid origin, with Armeria denticulata s.str. as the ovule donor and Armeria gracilis as the pollen donor.
• A distinct population of Armeria denticulata (Monte Ferrato) likely arose from introgression between Armeria denticulata s.str. (pollen donor) and Armeria arenaria subsp. praecox (ovule donor).
• Substrate specificity and hybridization/introgression are identified as key drivers of microevolutionary processes in the Armeria denticulata complex.

Conclusions:

• Substrate specificity and hybridization have played significant roles in the speciation of the Armeria denticulata complex.
• Hybridization events, including homoploid and introgression, are critical mechanisms shaping the evolutionary trajectory of these plant species.
• The study highlights the interplay between geological substrates and genetic exchange in driving plant diversification.