Temporal variation in floral scent emission of a woody plant and flower visiting behaviour of male and female flies

Most flowering plants rely on insects for pollination and flowers are
advertised using odor and visual cues. Flower scent consists of a complex
blend of volatile compounds of which the emission can vary over time (and
space) within species. Pollinator foraging behaviour, such as the choice
for flowers and the time spent gathering nectar and/or pollen, can also
show significant intraspecific variation. Underlying variation in
pollinator behaviour can be sensory or foraging-related biases among sexes
or individuals. Investigating the role of temporal variation in floral
volatiles on visitation behaviour of male and female pollinators is
largely unexplored. We examined temporal variation in the emission of
scent of yellowhorn Xanthoceras sorbifolium flowers, visitation behaviour
of its main pollinators, male and female Bibio rufiventris flies, and
their responses to floral volatile compounds using field experiments and
controlled bioassays. Our results show significant daily fluctuations in
floral volatile emission of X. sorbifolium in the field. The relative
emission of 1-octen-3-ol, 1-octanol, benzaldehyde, and α-farnesene
increased from 9:00 to 15:00 h, while (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol,
(E)-2-hexenal, 2-methyl-6-hepten-1-ol, (E)-2-nonenal,
2,6,6-trimethyl-2-cyclohexene-1-methanol, (E)-2-nonenal, and
(E,Z)-2,6-nonadienal decreased. In concert, we observed an increase in
visits and visitation duration for male pollinators, but a decrease for
female visitation duration. Pollinators exhibited sex-specific responses
to floral volatiles, with attraction to 1-octen-3-ol and 1-octanol for B.
rufiventris males, while (E)-2-nonenal, (E,Z)-2,6-nonadienal, and
(E)-2-hexenal attracted females. Our study shows that temporal variation
in floral scent may explain differences in flower visitation by male and
female pollinators through sex-specific responses to floral volatiles.
Investigating sex-based differences exhibited by pollinators and temporal
variation in floral scent emission will help understand the dynamic nature
of plant–pollinator interactions.

大多数开花植物依赖昆虫进行授粉（pollination），花朵通过气味和视觉信号吸引传粉者。花香由复杂的挥发性化合物（volatile compounds）混合物组成，其释放量在物种内会随时间（及空间）发生变化。传粉者的觅食行为（如花朵选择、采集花蜜（nectar）和/或花粉（pollen）所花费的时间）也存在显著的种内变异（intraspecific variation）。传粉者行为变异的潜在原因可能是不同性别或个体间的感官偏差或与觅食相关的偏好。关于花挥发性物质（floral volatiles）时间变异对雌雄传粉者访问行为的作用，目前研究尚浅。我们通过田间实验和受控生物测定（controlled bioassays），研究了文冠果（Xanthoceras sorbifolium）花香释放的时间变异、其主要传粉者——雌雄 Bibio rufiventris 蝇的访问行为，以及它们对花挥发性物质的响应。结果表明，田间条件下文冠果的花挥发性物质释放存在显著的日波动：1-辛烯-3-醇（1-octen-3-ol）、1-辛醇（1-octanol）、苯甲醛（benzaldehyde）和 α-法尼烯（α-farnesene）的相对释放量从9:00到15:00增加，而（Z）-3-己烯-1-醇、（E）-2-己烯-1-醇、（E）-2-己烯醛、2-甲基-6-庚烯-1-醇、（E）-2-壬烯醛、2,6,6-三甲基-2-环己烯-1-甲醇、（E）-2-壬烯醛和（E,Z）-2,6-壬二烯醛的相对释放量则减少。与此同时，我们观察到雄性传粉者的访问次数和访问时长增加，而雌性的访问时长减少。传粉者对花挥发性物质表现出性别特异性响应（sex-specific responses）：雄性 Bibio rufiventris 被1-辛烯-3-醇和1-辛醇吸引，而雌性则被（E）-2-壬烯醛、（E,Z）-2,6-壬二烯醛和（E）-2-己烯醛吸引。本研究表明，花香的时间变异可通过传粉者对花挥发性物质的性别特异性响应，解释雌雄传粉者访问花朵的差异。研究传粉者表现出的性别差异以及花香释放的时间变异，有助于理解植物-传粉者互作（plant-pollinator interactions）的动态本质。