Pollination biology of two Chinese endemic and sympatric Impatiens (Balsaminaceae) species

Abstract

The genus Impatiens exhibits some varied floral features with a dichogamous reproductive system, in which pollination biology plays a key role in speciation and adaptive evolution. China is one of the centers of Impatiens species, including a large number of endemic and sympatric distributions, but there are few data on their pollination biology. Comparative pollination biology of two Chinese endemic and sympatric species, Impatiens corchorifolia and I. cyathiflora, were investigated, including flowering phenology, floral features, pollinators, behavior of pollinators, and as well as breeding systems. The results were as follows: (1) Morphology of spur was varied in two species, which played a key role in different floral syndromes. The spurs in I. corchorifolia and I. cyathiflora could produced a similar nectar sugar content, (45.48 ± 2.28)% and (46.12 ± 1.48)%, respectively. They could share two pollinators, Apis cerana and Vespa. However, the short spur in I. corchorifolia produced less amount of (4.57 ± 1.43) μL nectar while the long spur in I. cyathiflora yielded more nectar content of (10.15 ± 3.28) μL. And then, the latter also could be pollinated by the other insects including one species of Macroglossum and two species of Bombus. (2) The behavior of the common pollinators shared in I. corchorifolia and I. cyathiflora were obviously distinguished by their staggered flower visits and differential sizes of flower channels for visitors with inconsistent positions of pollens carried. (3) Breeding system experiments showed that species possessed obvious hybridization barriers and obvious cross-pollination. Thus, significant differences in spur morphology lead to distinct pollination syndrome differentiation and different pollinator behavior. Both species prefer cross-pollination to self-fertiliation, which greatly depend on the effective pollinators. Reproductive isolation could be maintained by different flower visiting behavior of shared pollinators, differences in floral morphology, and heterozygous discordance. It provides new evidence for a better understanding the relationships between pollination syndrome, pollinators behavior, and cross-breeding stystem in Impatiens.

Keywords

• impatiens corchorifolia
• impatiens cyathiflora
• pollination biology
• sympatric distribution
• breeding system
• pollination syndromes