Genomic data supportBetula halophilaandBetula microphyllaas one species and reveal unidirectional introgression fromBetula pendulatoBetula microphylla

Abstract

AbstractConservation of rare species faces challenges arising from uncertainties in species recognition, interspecific gene flow and global climate change.Betula microphyllaandBetula halophilaare endangered species in Xinjiang province, Northwest China, where they occur with the abundantBetula pendula. The species status ofB. halophilaremains dubious. The extent of gene flow between B.microphyllaandB. pendularemain unexplored. Here, we first resolve the identity ofB. halophilaand then assess the extent of gene flow betweenB. microphyllaandB. pendulausing restriction-site associated DNA sequencing (RADseq). We sequenced 40B. pendulaindividuals, 40B. microphyllaindividuals, oneB. halophilaindividual and sevenB. tianshanicaindividuals. Our molecular analyses show thatB. halophilaandB. microphyllarefer to the same species. STRUCTURE analyses show unidirectional genetic admixture fromB. pendulatoB. microphylla. The ABBA-BABA test indicates that the genetic admixture reflects introgression rather than incomplete lineage sorting. Furthermore, we identified 233 functional genes within the introgressed regions with eight genes related to salt-tolerance, suggesting the possibility of potential adaptive introgression. Our study shows an urgent need to conserve the genetically pure populations ofB. microphyllaand to shift conservation efforts fromB. halophilatoB. microphylla. In addition, ex-situ conservation of B. microphylla and conservation strategies to avoid genetic swamping byB. pendulaandB. tianshanicashould be implemented.