Floral Reward, Advertisement and Attractiveness to Honey Bees in Dioecious Salix caprea

Abstract

In dioecious, zoophilous plants potential pollinators have to be attracted to both sexes and switch between individuals of both sexes for pollination to occur. It often has been suggested that males and females require different numbers of visits for maximum reproductive success because male fertility is more likely limited by access to mates, whereas female fertility is rather limited by resource availability. According to sexual selection theory, males therefore should invest more in pollinator attraction (advertisement, reward) than females. However, our knowledge on the sex specific investment in floral rewards and advertisement, and its effects on pollinator behaviour is limited. Here, we use an approach that includes chemical, spectrophotometric, and behavioural studies i) to elucidate differences in floral nectar reward and advertisement (visual, olfactory cues) in dioecious sallow, Salix caprea, ii) to determine the relative importance of visual and olfactory floral cues in attracting honey bee pollinators, and iii) to test for differential attractiveness of female and male inflorescence cues to honey bees. Nectar amount and sugar concentration are comparable, but sugar composition varies between the sexes. Olfactory sallow cues are more attractive to honey bees than visual cues; however, a combination of both cues elicits the strongest behavioural responses in bees. Male flowers are due to the yellow pollen more colourful and emit a higher amount of scent than females. Honey bees prefer the visual but not the olfactory display of males over those of females. In all, the data of our multifaceted study are consistent with the sexual selection theory and provide novel insights on how the model organism honey bee uses visual and olfactory floral cues for locating host plants.

Spatiotemporal Floral Scent Variation of Penstemon digitalis

“…1a). Typically, plants with diurnal pollinators show stronger volatile emissions during the day than at night (Balao et al 2011;Borges et al 2013;Jürgens et al 2014;Morinaga et al 2009) as we observed in this study (Fig. 2), further suggesting their function in attracting day-active bee pollinators.…”

Early spring floral foraging resources for pollinators in wet heathlands in Belgium

“…Sugar ratios also differed between flower sexes, with nectar of male flowers being sucrose-dominant, whereas the nectar of female flowers was hexose-dominant. Sexual differences in nectar composition have been observed in other species such as Salix myrsinifolia x phylicifolia or Salix caprea (Katoh et al 1985;Elmqvist et al 1988;Dötterl et al 2014). The consequences of such differences in sugar proportions for pollinator foraging remain to be elucidated.…”

Plant‐sex‐biased tritrophic interactions on dioecious willow

“…The paucity of studies is surprising given the emerging consensus that herbivore populations are often as strongly controlled by predators in a top-down manner as by host plant quality via bottom-up factors (e.g., Hairston et al 1960, Oksanen et al 1981, Halaj and Wise 2001, Terborgh et al 2006. Dioecious plants express intersexual differences in several traits that are utilized by predators, not least nectar composition (Dö tterl et al 2014) and pollen availability. Differences in such plant-based resources can potentially affect both predator population dynamics (Å gren et al 2012) and their willingness to consume animal food (Stenberg et al 2011b).…”