The role of ultraviolet reflectance and pattern in the pollination system of Hypoxis camerooniana (Hypoxidaceae)

Abstract

Apart from floral morphology and colours perceived by the human eye, ultraviolet (UV) reflectance acts as an important visual advertisement of numerous flowering plant species for pollinators. However, the effect of UV signalling on attracting pollinators of particular plant species is still insufficiently studied, especially in the Afrotropics. Therefore, we studied the pollination system of Hypoxis camerooniana in montane grasslands of Mount Cameroon, West/Central Africa. We focused mainly on the effects of the flowers’ UV reflectance on its visitors. We experimentally removed UV reflection from petals either completely or partially. Thereafter, flower visitors were recorded and pistils were collected post-flowering to quantify germinated pollen tubes per treatments. The most important visitors were bees, followed by flies. Due to their contacts with reproductive organs bees are considered as the primary pollinators. Visitation rates were lower when UV reflectance was completely removed, whereas the decrease of frequency on half-treated flowers did not differ significantly from control treatments. The complete removal of UV also affected bees’ landing behaviour, but not that of flies. We showed that the presence of UV reflectance is more important than UV pattern for bees visiting flowers of H. camerooniana. We hypothesize that exploiting all flowers irrespective of their pattern can be more efficient for pollinators in the open grasslands of high altitudes to spot these relatively scarce flowers by their UV reflectance. Furthermore, we highlight the necessity of both experimental and natural controls in similar studies to control for additional effects of the used UV manipulations.Many plants advertise their flowers with UV reflectance visible to their insect visitors. By manipulating the UV reflectance and pattern of Hypoxis camerooniana in the Afromontane grasslands of Mount Cameroon, we have shown how crucial it is for the predominant visitor, bees. Both bees' preferences for flowers and their behaviour during visits are influenced by changes in UV reflectance. However, the presence of some UV signal is more important than the specific pattern. Especially in montane grasslands with higher UV irradiation, the UV floral colours are important for recognition of flowers by potential pollinators.

Floral UV Features of Plant Species From a Neotropical Savanna

“…On the other hand, even with an unclear colour preference, flies are usually related to yellowish flowers (Lunau, 2014), such as the (EC) fly-pollinated species registered in our study. The absence of UV reflectance does not discourage fly-pollination of the tropical Hypoxis camerooniana (Klomberg et al, 2019) but the presence of UV pattern favoured fly visitation of the temperate Argentina anserina flowers. Flies are sensitive to UV (Chittka and Briscoe, 2001;Cronin et al, 2014;Lunau, 2014) and maybe tuned to yellow UV-patterned flowers (An et al, 2018), similar to Cissus erosa, the fly-pollinated species sampled here.…”

“…In general, it has been shown that conspicuous flowers can receive more pollinator visits , which might represent selection pressures toward more contrasting and distinguished visual features. Indeed, floral UV-patterns may favour bee attraction (Rae and Vamosi, 2013;Klomberg et al, 2019) and may increase the probability of the pollinator reaching floral resources, reducing handling time (Dinkel and Lunau, 2001;Leonard and Papaj, 2011). In spite of the predominance of UV-patternless flowers in butterfly-, hummingbird-, beetle-, bat-, and hawkmothpollinated species, we cannot disregard the importance of UV patterns for these pollinators until there are experimental evidences.…”

Bracts and basal leaves in Hacquetia epipactis differ in their spectral signatures

“…In addition to all this, bracts are also extremely important for attraction of pollinators in some species (Bertechine Gagliardi et al 2018), as might also be the case with H. epipactis (Bavcon 2013). In 25% of angiosperm flowers, the reflection of ultraviolet light represents an important visual information for pollinators (Klomberg et al 2019). Based on all this, we presumed that bracts might differ from basal leaves regarding their biochemical structure and optical properties, especially in the UV range.…”

Spatiotemporal shifts in the role of floral traits in shaping tropical plant-pollinator interactions

“…The flowering plant species along the set transects were recorded for a 24-hour period using security cameras (VIVOTEK IB8367T with IR night vision; for more information on the methodology see Klomberg et al, 2019;Mertens et al, 2020Mertens et al, , 2018 to detect and identify flower visitors to 13 functional groups of pollinators. We recorded flowers at all vegetation strata from understory to canopies (reached using tree climbing methods).…”