Abstract Detail

Systematics

Rose, Jeff [1], Sytsma, Kenneth J. [2].

Testing the relative contribution of incomplete lineage sorting and reticulate evolution in the evolutionary history of flowering plants: Polemonium (Polemoniaceae) as a case study.

Polemonium is comprised of at least 27 species and is most diverse in montane and arctic-alpine areas of western North America. Past phylogenetic studies based on nrITS or AFLPs provide few insights into backbone relationships within the genus. In addition, previous analyses of a handful of low-copy nuclear genes and a large segment of the chloroplast genome suggest the presence of high amounts of genealogical discordance. We utilize an anchored phylogenomics approach to generate sequences for 360 nuclear genes as well as complete nuclear ribosomal and chloroplast genomes. We use these data to generate better-supported phylogenetic hypotheses of relationships in Polemonium and to investigate the contribution of incomplete lineage sorting and reticulation in its evolutionary history. We then use this new phylogenetic framework to examine the impact of changes in altitude and geographic space on species formation in Polemonium. This phylogenomics approach clearly demonstrates that incomplete lineage sorting and reticulate evolution have significantly contributed to the evolutionary history of Polemonium and also uncovers several previously unknown lineages. Analysis of the nuclear genome confirms rampant genealogical discordance, but does suggest that a dominant, underlying tree-like structure exists. Furthermore, three major reticulation events have contributed to extant diversity in Polemonium. The chloroplast genome shows strong discordance with the inferred nuclear DNA species trees. Discordance in the nuclear ribosomal genome is similar to that expected based on a combination of incomplete lineage sorting and reticulate evolution, but the plastome genealogy is extremely discordant and irreconcilable by invoking incomplete lineage sorting and the inferred reticulation events. Overall, the history of the genus implied by the nuclear and nuclear ribosomal genomes are consistent with each other and consistent with species circumscription based on morphology, but the plastome history is strongly inconsistent with these other lines of evidence. The main driver of speciation in Polemonium is allopatric in nature, with altitude showing strong phylogenetic conservatism. Speciation in Polemonium has primarily proceeded horizontally in geographic space, whereas species in sympatry represent secondary contact. Current barriers to reproduction appear to be maintained by both spatial isolation and chromosomal rearrangements. Our study of the Polemonium system provides insights into to evolution of plant groups in the Cordillera of western North America and provides methodological and conceptual insights to guide the study of phylogenetic relationships in plants in the era of next-generation sequencing.

1 - The University of Wisconsin-Madison, Botany, 430 Lincoln Dr., Madison, WI
2 - University Of Wisconsin, Department Of Botany, Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, United States

Keywords:
allopatric speciation
genealogical discordance
phylogenetic network
Polemoniaceae
Incomplete Lineage Sorting
reticulate evolution.

Presentation Type: Oral Paper
Session: 19, ASPT Cooley Awards I
Location: 110/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 11:30 AM
Number: 19014
Abstract ID:453
Candidate for Awards:George R. Cooley Award