First evidence for allotriploid hybrids between Juniperus thurifera and J. sabina in a sympatric area in the French Alps

Abstract

Key message Discovery of the first case of allotriploid juniper in a wild population in the French Alps where the parental species occurs in sympatry. ContextInterspecific hybridization and polyploidy are important evolutionary phenomena in vascular plants. Natural hybridization between species living in sympatry can sometimes occur. Less frequent are successful hybridizations between species having different ploidy levels. At Saint Crépin location (French Alps), where sympatry between the tetraploid Juniperus thurifera and the diploid Juniperus sabina occurs, three individuals with an atypical morphology have been observed.AimsProspect interspecific hybrids and interspecific genetic introgression occurrence.MethodsFlow cytometry was employed to screen ploidy levels. Four chloroplast markers, nrDNA (ITS), and AFLP markers were used to unravel hybridization and potential introgression events. Variability of pollen size and morphology was assessed to have a first insight on the regularity of microsporogenesis in hybrids.ResultsThe three putative hybrids were shown to be triploids. Molecular data demonstrated that these individuals were hybrids originated from a cross between J. sabina and J. thurifera and suggested that a backcross at least with J. thurifera is possible. Male triploid hybrids produced heterogeneous pollen and displayed evidence of irregularity in the microsporogenesis.ConclusionThis study sheds light on a rare case of hybridization in a natural sympatric population of two Juniperus species with different ploidy levels. This mechanism might have been an important driver for the evolution and diversification of this coniferous genus.