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Reticulate evolution and incomplete lineage sorting among the ponderosa pines
Ann Willyard1, Richard Cronn, Aaron Liston
1Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA. Ann.Willyard@USD.edu
Molecular Phylogenetics and Evolution
|March 3, 2009
Summary
Hybridization drives reticulate evolution in pine species, challenging traditional hierarchical lineage models. Gene flow via introgression, not just incomplete lineage sorting, shapes pine evolutionary history.
Area of Science:
- Evolutionary biology
- Plant genetics
- Phylogenetics
Background:
- Interspecific gene flow through hybridization can create reticulate evolutionary patterns in plants.
- Detecting reticulation is challenging in pines due to shared ancestral polymorphism across species.
- Diploid pine hybrids suggest potential for introgression, but evidence remains elusive.
Purpose of the Study:
- To investigate evidence of reticulate evolution within the subsection Ponderosae (Pinus).
- To differentiate between introgression and incomplete lineage sorting as causes of incongruence in gene trees.
- To understand the role of hybridization in shaping pine species divergence.
Main Methods:
- Analysis of nucleotide sequences from 53 accessions across 17 species in subsection Ponderosae.
- Construction and comparison of low-copy nuclear gene trees.
- Phylogenetic analysis of chloroplast haplotypes.
Main Results:
- Discordant patterns in nuclear gene trees and chloroplast haplotype data support introgression.
- Ancient introgression followed by a genetic bottleneck explains conflicting resolution in Pinus coulteri.
- Recent hybridization resulted in chloroplast transfer from Pinus jeffreyi to Pinus washoensis.
Conclusions:
- Reticulate evolution, driven by introgression, is a significant factor in the evolution of subsection Ponderosae pines.
- Incomplete lineage sorting can explain some non-monophyletic patterns but introgression provides a better explanation for observed discordance.
- Caution is advised against single-accession or single-locus sampling in phylogenetic analyses of Pinus due to reticulation.
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