Natural hybridization and introgression in sympatricLigulariaspecies (Asteraceae, Senecioneae)

Abstract

The difficulty in clarifying species of genus Ligularia Cass. has been attributed to rapid and continuous allopatric speciation in small and isolated populations, combined with interspecific diploid hybridization in the Qinghai‐Tibetan Plateau and adjacent areas. However, no concrete example has been reported to prove this hypothesis. We studied a natural mixed population of six species of Ligularia in which some individuals were morphologically intermediate between L. subspicata and L. nelumbifolia. Based on DNA sequences (trnC‐F, trnL‐rpL32, trnQ‐5′rps16, trnK‐rps16, and internal transcribed spacer) and inter‐simple sequence repeat data, we concluded that putative hybrids are primarily products of hybridization between L. nelumbifolia and L. subspicata. The other four species or additional, unknown species may also be involved in hybridization. This hybridization is bidirectional but asymmetrical. Hybrid individuals were mostly the first generation, but F2 and later‐generation hybrids were also present. Moreover, the backcrossed individuals detected indicate that natural gene flow occurs among at least three Ligularia species. Hybrids may become stabilized to form new species or may function as intermediates in evolutionary diversification.

Chemical Constituents in Hybrids of Ligularia tongolensis and L. cymbulifera: Chemical Introgression in L. tongolensis

“…Several cases have been reported where hybrids inherit compounds from both parents [b]. We also reported that hybrids of L. nelumbifolia and L. subspicata produced compounds of both parents additively . In the present case of hybrids of L. cymbulifera and L. tongolensis , the chemical outcome was variable.…”

“…Hand .‐ Mazz . . Furanoeremophilanes were detected in L. subspicata but not in L. nelumbifolia ; they were detected in the hybrids.…”

Phylogeography of an alpine plant Ligularia vellerea (Asteraceae) in the Hengduan Mountains

“…It is endemic to the HMR, with a distribution in northwestern Yunnan and southwestern Sichuan provinces. It usually grows in grasslands, alpine meadows, and forest understories of various environments at altitudes of approximately 2100–4600 m. Ligularia vellerea occurs with a few other congeneric species in some regions, however, no obvious hybridization or introgression has been detected between this species and other co‐occurring species (Yu et al, 2011). Thus, this species is suitable for studying intraspecific diversification in the HMR.…”

Homoploid hybridization of plants in the Hengduan mountains region

“…Similarly, shared pollinators are observed in sympatric Primula ( P. secundiflora × P. poissonii ), Roscoe ( R. humeana × R. cautleoides ) (Du et al, ; Zhu et al, ). Generalist pollination syndromes are thought in particular to be a key feature for hybridization in Ligularia (Cao, Ma, & Wang, ; Yu, Kuroda, & Gong, ; Yu, Kuroda, et al, ). Therefore, these prerequisites may reduce reproductive barriers and increase the probability for occurrence of hybridization in regions of sympatry for these taxa.…”

“…Moreover, difference in competition of the pollen at the stigmatic surface may facilitate asymmetrical hybridization. The bidirectional and asymmetrical hybridization are suggested in the case of L. subspicata and L. nelumbifolia (Yu et al, ). One of the parents is five times more prevalent than the other in a sympatric zone of Ligularia .…”