Effective hawkmoth pollination in the primarily bee‐pollinated Salvia daiguii—an example of adaptive generalization

Abstract

Many plants exhibit floral traits that are directed to specific pollinator groups. Nevertheless, they can also attract less‐adapted pollinators and gain benefits under certain conditions, resulting in adapted generalization. This may be the case in Salvia daiguii (Lamiaceae), an endangered, bee‐pollinated species native to the Tianmenshan National Forest Park, China. The flower appears phenotypically specialized to bees but is also visited by Macroglossum bombylans. In the present study, we test whether the moth is an effective pollinator of S. daiguii. We quantified and compared the frequency of flower visits by bees and moths and the number of pollen grains deposited on the stigma after a single visit. We also recorded the movements of pistils and stamens of S. daiguii and the behavior of the hawkmoth at the flowers. We found that Apis cerana was the predominant pollinator, depositing an average of 4.74 pollen grains on the stigma after a single visit. However, as the style bends downward during anthesis and reaches the same level as the anthers, Macroglossum individuals hovering around the flowers were also able to effectively transfer pollen to the stigma. On average, 1.38 pollen grains were deposited on the stigma during a single visit. We demonstrate for the first time that the hawkmoth is an effective secondary pollinator in the primarily bee‐pollinated S. daiguii. Style bending allows a nectar thief to become a secondary pollinator. The extent of pollinator generalization is thus increased without affecting the fundamental phenotype adapted to bees as the main pollinators.

Endangered status and threatened population ecological factors in Salvia daiguii, an endemic species from Hunan, China

“…Xiao, Huang, and Wei ( 2022 ) and Xiao, Liu, et al. ( 2023 ) conducted extensive surveys in more than 25 provinces and cities during 2011–2021 and also found this species only in the vicinity of Tianmenshan National Forest Park, Zhangjiajie City, Hunan Province, China (Figure 1 ‐TNFP 2 and ZEFR 1). In the present study, although we found the largest point ZEFR 2 to date, with 274 individuals, it was still restricted to the vicinity of Tianmenshan National Forest Park.…”

“…Salvia daiguii has four ovules per flower and produces a small amount of nectar at the base of the corolla tube. Previous studies found that Apis cerana is the primary pollinator of S. daiguii , but its curved style allows the nectar thief Macroglossum bombylan s to become a secondary pollinator (Xiao, Liu, et al., 2023 ).…”

“…Researchers from the Shanghai National Labiatae Germplasm Resource Bank over 25 provinces and cities extensively surveyed between 2011 and 2021, and S. daiguii was found at only three sites in Zhangjiajie City (Wei et al., 2019 ; Xiao, Liu, et al., 2023 ; see Figure 1 , TNFP [TNFP 1 and 2], ZEFR 1, and TGM). To investigate the distribution of S. daiguii , we re‐surveyed the three previous locations.…”

“…The genus Salvia includes about 1000 species, making the genus widely distributed worldwide; various species are widely used in ornamental, culinary, and medicinal fields due to their beautiful plant forms, diverse flower shapes and colors, and richness in many aromatic substances and medicinal ingredients (Hu et al., 2023 ; Xiao et al., 2021 ; Xiao, Huang, et al., 2023 ; Xiao, Huang, Wang, et al., 2022 ; Xiao, Liu, et al., 2023 ; Zheng et al., 2013 ). Forty‐five of these are classified as threatened species by the International Union for Conservation of Nature (IUCN; https://www.iucnredlist.org/ ).…”