Less Pollen-Mediated Gene Flow for More Signatures of Glacial Lineages: Congruent Evidence from Balsam Fir cpDNA and mtDNA for Multiple Refugia in Eastern and Central North America

Benjamin Cinget,Jean Bousquet,Jean Beaulieu,Sébastien Gérardi,Tzen-Yuh Chiang

doi:10.1371/journal.pone.0122815

Benjamin Cinget, Jean Bousquet + Show 3 more

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https://doi.org/10.1371/journal.pone.0122815

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Journal: PloS one	Publication Date: Apr 7, 2015
Citations: 16	License type: CC BY 4.0

Affiliation: Université Laval, Natural Resources Canada

Abstract

The phylogeographic structure and postglacial history of balsam fir (Abies balsamea), a transcontinental North American boreal conifer, was inferred using mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) markers. Genetic structure among 107 populations (mtDNA data) and 75 populations (cpDNA data) was analyzed using Bayesian and genetic distance approaches. Population differentiation was high for mtDNA (dispersed by seeds only), but also for cpDNA (dispersed by seeds and pollen), indicating that pollen gene flow is more restricted in balsam fir than in other boreal conifers. Low cpDNA gene flow in balsam fir may relate to low pollen production due to the inherent biology of the species and populations being decimated by recurrent spruce budworm epidemics, and/or to low dispersal of pollen grains due to their peculiar structural properties. Accordingly, a phylogeographic structure was detected using both mtDNA and cpDNA markers and population structure analyses supported the existence of at least five genetically distinct glacial lineages in central and eastern North America. Four of these would originate from glacial refugia located south of the Laurentide ice sheet, while the last one would have persisted in the northern Labrador region. As expected due to reduced pollen-mediated gene flow, congruence between the geographic distribution of mtDNA and cpDNA lineages was higher than in other North American conifers. However, concordance was not complete, reflecting that restricted but nonetheless detectable cpDNA gene flow among glacial lineages occurred during the Holocene. As a result, new cpDNA and mtDNA genome combinations indicative of cytoplasmic genome capture were observed.

Highlights

During the last two decades, haploid cytoplasmic genomes have proven useful to infer phylogeographic structures of tree species because of their relative lack of recombination and small population size relative to nuclear genes [1]
FSCcp and FSTcp were equivalent since no population structure was detected using cpSSRs, as in the present study. These results suggest that A. balsamea experiences substantially less pollen gene flow than any other sympatric North American conifer for which data were available
CpDNA gene flow appeared limited in balsam fir, presumably owing to its low pollen production and dispersal, and to the potential negative impact of recurrent spruce budworm outbreaks on the reproductive effort of balsam fir

Summary

Introduction

During the last two decades, haploid cytoplasmic genomes have proven useful to infer phylogeographic structures of tree species because of their relative lack of recombination and small population size relative to nuclear genes [1]. These genomes allow to compare the extent of seed and pollen gene flow in the Pinaceae [1], for which mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) are maternally and paternally inherited, respectively [2,3]. This approach allows to detect putative cytoplasmic capture events (e.g. at the intraspecific level, [6,10]), which can lead to erroneous phylogeographic inferences when overlooked

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