Gene flow between diploid and tetraploid junipers - two contrasting evolutionary pathways in two Juniperus populations

Perla Farhat,Carlos Salazar-Mendias,Robert P Adams,Carlos Fabregat,Joaquín Altarejos,Sonja Siljak-Yakovlev,Silvia Lopez-Udias,Nicolas Valentin

doi:10.1186/s12862-020-01688-3

Abstract

BackgroundGene flow and polyploidy have been found to be important in Juniperus evolution. However, little evidence has been published elucidating the association of both phenomena in juniper taxa in the wild. Two main areas were studied in Spain (Eastern Iberian Range and Sierra de Baza) with both diploid and tetraploid taxa present in sympatry. Gene flow and ploidy level were assessed for these taxa and the resulted offspring.ResultsTwenty-two allo-triploid hybrids between J. sabina var. sabina and J. thurifera were found in the Eastern Iberian Range population. However, in the Sierra de Baza population no triploids were found. Instead, 18 allo-tetraploid hybrids between two tetraploid taxa: J. sabina var. balkanensis and J. thurifera were discovered. High genetic diversity was exhibited among the tetraploid hybrids at Sierra de Baza, in contrast to the genetically identical triploid hybrids at the Eastern Iberian Range; this suggests meiotic difficulties within the triploid hybrids. In addition, unidirectional gene flow was observed in both studied areas.ConclusionPolyploidy and hybridization can be complementary partners in the evolution of Juniperus taxa in sympatric occurrences. Juniperus was shown to be an ideal coniferous model to study these two phenomena, independently or in concert.

Highlights

Gene flow and polyploidy have been found to be important in Juniperus evolution
In the E Iberian Eastern Iberian range (Range), J. thurifera showed a genome size ranging from 41.79 pg to 44.84 pg with a mean of 42.55 pg (σ =0.86 pg)
Juniperus sabina sampled from this population hold a genome size of 20.79 pg to 22.51 pg with a mean of 21.83 pg (σ =0.41 pg)

Summary

Introduction

Gene flow and polyploidy have been found to be important in Juniperus evolution. little evidence has been published elucidating the association of both phenomena in juniper taxa in the wild. The evolutionary impact of hybridization coupled with polyploidy through allopolyploidy has not been very well elaborated to date in Juniperus. A potential allo-tetraploid taxon, Juniperus sabina var. Tashev has been discovered [15, 16] This variety was described principally based on the DNA sequence differences with only a few morphological differences with its sister variety, J. sabina var. Sabina (2n = 2x), first evidence of allo-triploid hybrids between those two taxa have been recently discovered in the French Alps, where the taxa occur in sympatry [18]. Sabina and J. thurifera are occasionally sympatric and a putative hybrid has been described as Juniperus x cerropastorensis J.M. Aparicio & P.M. Uribe-Echebarria, based on their intermediate morphology [19]

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