Chloroplast evolution in the Pinus montezumae complex: a coalescent approach to hybridization

Area of Science:

• Botany and Evolutionary Biology
• Plant Genomics and Phylogenetics
• Conservation Genetics

Background:

• Pinus hartwegii and P. montezumae are closely related pine species within the Ponderosae subsection, endemic to Mexico and Central America.
• These species inhabit different elevations but frequently co-occur on the same mountain ranges, presenting opportunities for gene flow and hybridization.
• Understanding their evolutionary history is crucial for conservation efforts and clarifying their taxonomic relationships.

Purpose of the Study:

• To elucidate the evolutionary history and genetic structure of the chloroplast genomes of Pinus hartwegii and P. montezumae.
• To investigate patterns of haplotype distribution and infer potential hybridization events using coalescent theory.
• To assess the degree of genetic differentiation and shared evolutionary history between these two pine species.

Main Methods:

• Collected 350 individuals of Pinus hartwegii and P. montezumae from four distinct mountain locations in Mexico.
• Mapped the chloroplast genomes using eight restriction enzymes and characterized 51 distinct haplotypes.
• Analyzed 38 polymorphic restriction sites out of 160 to reconstruct phylogenetic relationships using parsimony.

Main Results:

• Identified geographically localized clades of chloroplast haplotypes that do not overlap in distribution.
• Observed that these localized clades contain haplotypes exclusive to one species as well as those shared between Pinus hartwegii and P. montezumae.
• Found evidence of 38 polymorphic restriction sites among 160 analyzed sites, indicating genetic variation.

Conclusions:

• The observed haplotype distribution strongly suggests ancient and/or ongoing hybridization between Pinus hartwegii and P. montezumae.
• The data indicate a shared chloroplast genome history within specific geographic regions of Mexico for these two species.
• These findings highlight the complex evolutionary dynamics and potential reticulation between closely related pine taxa.