Floral UV Features of Plant Species From a Neotropical Savanna

Abstract

Despite the wide interest in flower colours, only after the end of the nineteenth-century studies started to comprise floral UV reflection, which is invisible to humans but visible to the major groups of pollinators. Many flowers and inflorescences display colour patterns, an important signal for pollinators, promoted by the presence of at least two different colours within flowers or inflorescences, including colours in the UV waveband. For Neotropical savanna plant species, we characterised floral UV features using UV-photography and reflectance measurements. We tested (i) whether floral UV features were constrained by their shared ancestry, (ii) whether floral UV features were associated with pollinators, and (iii) whether floral UV features were associated with floral traits mediating these interactions, including floral resource, type of attraction unit and presence/absence of non-UV colour patterns. Of 80 plant species, ca. 70% were UV-patternless, most of them UV-absorbing. Approximately 30% presented one of three types of UV-patterns: bullseye, contrasting corolla markings oriented toward floral resources or contrasting reproductive structures, which were all considered as floral guides. Floral UV features were phylogenetically constrained and were associated with pollinators, floral resources and attraction unit, but not with non-UV colour patterns. UV-patternless flowers were associated with most of the pollination systems, while UV-patterned flowers were mainly associated with bee-pollination. UV-absorbing flowers comprised the only category with hawkmoth- and butterfly-pollinated flowers, and a high percentage of hummingbird-pollinated species. Nocturnal pollinated species were also commonly UV-absorbing, except for one UV-reflecting bat-pollinated species and one beetle-pollinated species with UV-reflecting stigmas. All types of floral UV features were associated with nectar; however, flowers with contrasting reproductive structures were mainly associated with pollen. There was an association between UV-absorbing species and the presence of inflorescences and intermediate attraction units. Our results evince that phylogenetic relatedness can constraint floral UV features’ diversification, but combinations of evolutionary and ecological processes may be expected in this scenario.

Heteromorphic stamens are differentially attractive in Swartzia (Fabaceae)

“…However, for S. simplex flowers, we realized a general UV pattern similar to the ‘bull’s eye’ pattern, as seen for some bee-pollinated flowers (e.g. Lunau et al 2021 ; Tunes et al 2021 ). This pattern refers to flowers displaying a UV-reflecting periphery but a UV-absorbing centre.…”

1080. Coreopsis lanceolata L.: Compositae

“…UV‐patterning is not just restricted to the Compositae (where anthochlor pigments are common), but is relatively widespread with varying degrees of UV‐patterning present in several other families. Whilst UV‐patternless floral structures in the savanna plants studies were the most common, about a third of the taxa examined by Tunes et al (2021) show both UV‐reflecting and UV‐absorption areas creating different patterns, and these are visible to many pollinators. All UV features were associated with nectar, although those with contrasting reproductive structures were often associated with pollen.…”

Major Flower Pigments Originate Different Colour Signals to Pollinators

“…Petals may advertise with simple homogenous colours in some species, through to extremely complex colour patterns in other plant species. Our ability to interpret such complex signals is just starting to emerge (Lunau et al, 2021;Tunes et al, 2021). Even in petals or petal parts with homogeneous colour, one or several types of major pigment classes may be accumulated to generate a unique colour (Kay et al, 1981;Grotewold, 2006;Davies, 2009).…”