PJB-2023-522
Natural hybridization between anciently divergent Hippophae tibetana and H.neurocarpa (Elaeagnaceae) in the eastern margin of the
Hui Zhang
Abstract
It is well-regarded that young species are apt to mix their genomes through natural hybridization, whereas the hybridization of old species is rare due to acquired intrinsic reproductive isolation, and alternatively the challenges in detection. In the present study, we identified a hybrid zone of the basal taxon Hippophae tibetana mating with H. neurocarpa based on morphological and molecular evidence in Hippophae. The putative hybrid plants were first discriminated from the sympatric congeneric populations in a field survey, relying on their morphological intermediates of fruit and leaf between the putative parents. Then additivity of the biparental distinctive nucleotide signals of ITS and CHSi, as well as the intermediate features of SSR markers and cpDNA trnS-trnG detected in putative hybrid individuals subsequently, comprehensively support the natural hybridization event that historically occurred. We further estimated that H. tibetana and H. neurocarpa had diverged 26~27 MYA and hybridization occurred 0.1~0.2 MYA, far from the widely reviewed 5-10 MYA to waiting for hybrid sterility. This is the deepest hybridization event in seed plants studied so far. We speculate that both perennial woody trees and abiotic pollination mechanisms are mainly responsible for the slow evolution of reproductive incompatibility in the genus. Our findings shed light on the incomplete reproductive isolation barriers between members of Hippophae, facilitating frequent hybridization and hybrid speciation in the margins of the Qinghai-Tibet Plateau.
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