Asymmetric Reproductive Barriers and Gene Flow Promote the Rise of a Stable Hybrid Zone in the Mediterranean High Mountain
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AuthorAbdelaziz Mohamed, Mohamed; Muñoz Pajares, Antonio Jesús; Berbel, Modesto; García Muñoz, Ana; Gómez, José M.; Perfectti Álvarez, Francisco
Frontiers Research Foundation
HybridizationErysimum mediohispanicumErysimum nevadenseSierra NevadaPhenotypeReproductive isolation
Abdelaziz M... [et al.] (2021) Asymmetric Reproductive Barriers and Gene Flow Promote the Rise of a Stable Hybrid Zone in the Mediterranean High Mountain. Front. Plant Sci. 12:687094. doi: [10.3389/fpls.2021.687094]
SponsorshipSpanish Ministry of Economy and Competitiveness CGL2014-59886JIN; Organismo Autonomo de Parques Nacionales 2415/2017; Spanish Government PID2019-111294GB-I00/SRA/10.13039/501100011033; FEDER/Junta de Andalucia-Consejeria de Economia y Conocimiento A.RNM.505.UGR18; Spanish Ministry of Science and Competitiveness CGL201679950-R CGL2017-86626-C2-2-P; TransSpeciation project CGL2014-59886JIN; European Commission under the Marie Sklodowska-Curie Action 754446; UGR Research and knowledge TransferAthenea3i global Hybrids project 2415/2017; OUTevolution project PID2019-111294GB-I00/SRA/10.13039/501100011033
Hybrid zones have the potential to shed light on evolutionary processes driving adaptation and speciation. Secondary contact hybrid zones are particularly powerful natural systems for studying the interaction between divergent genomes to understand the mode and rate at which reproductive isolation accumulates during speciation. We have studied a total of 720 plants belonging to five populations from two Erysimum (Brassicaceae) species presenting a contact zone in the Sierra Nevada mountains (SE Spain). The plants were phenotyped in 2007 and 2017, and most of them were genotyped the first year using 10 microsatellite markers. Plants coming from natural populations were grown in a common garden to evaluate the reproductive barriers between both species bymeans of controlled crosses. All the plants used for the field and greenhouse study were characterized by measuring traits related to plant size and flower size. We estimated the genetic molecular variances, the genetic differentiation, and the genetic structure by means of the F-statistic and Bayesian inference. We also estimated the amount of recent gene flow between populations.We found a narrow unimodal hybrid zone where the hybrid genotypes appear to have been maintained by significant levels of a unidirectional gene flow coming from parental populations and from weak reproductive isolation between them. Hybrid plants exhibited intermediate or vigorous phenotypes depending on the analyzed trait. The phenotypic differences between the hybrid and the parental plants were highly coherent between the field and controlled cross experiments and through time. The highly coherent results obtained by combining field, experimental, and genetic data demonstrate the existence of a stable and narrow unimodal hybrid zone between Erysimum mediohispanicum and Erysimum nevadense at the high elevation of the Sierra Nevada mountains.