Pollen and stamen mimicry: the alpine flora as a case study

Abstract

Many melittophilous flowers display yellow and UV-absorbing floral guides that resemble the most common colour of pollen and anthers. The yellow coloured anthers and pollen and the similarly coloured flower guides are described as key features of a pollen and stamen mimicry system. In this study, we investigated the entire angiosperm flora of the Alps with regard to visually displayed pollen and floral guides. All species were checked for the presence of pollen-and stamen-imitating structures using colour photographs. Most flowering plants of the Alps display yellow pollen and at least 28% of the species display pollen-or stamen-imitating structures. The most frequent types of pollen and stamen imitations were (mostly yellow and UV-absorbing) colour patches on petals (65% of species displaying imitations), patterns of inflorescences (18%), stamen-like pistils (10%), and staminodes (6%), as well as three-dimensional structures such as convex lower lips and filamental hairs (\5%). Dichogamous and diclinous species display pollen-and stamen-imitating structures more often than non-dichogamous and non-diclinous species, respectively. The visual similarity between the androecium and other floral organs is attributed to mimicry, i.e. deception caused by the flower visitor's inability to discriminate between model and mimic, sensory exploitation, and signal standardisation among floral morphs, flowering phases, and co-flowering species. We critically discuss deviant pollen and stamen mimicry concepts and evaluate the frequent evolution of pollen-imitating structures in view of the conflicting use of pollen for pollination in flowering plants and provision of pollen for offspring in bees.

How flower colour signals allure bees and hummingbirds: a community‐level test of the bee avoidance hypothesis

“…We surveyed categorical and quantitative variables previously described as important visual signals for target detection and discrimination by bees and birds (Spaethe et al ., ; Cazetta et al ., ; Dyer et al ., ; Bukovac et al ., ; Lunau et al ., ; van der Kooi et al ., ). We considered as categorical variables the presence of colour patterns, floral guides and UV patterns (Fig.…”

“…These colour patterns are generally composed of a predominant colour located peripherally and small colourful structures found in the central part of the flower that act as floral guides, improving flower detection and resource location (Lunau et al ., , ; de Ibarra et al ., ). A recurrent floral signal is a yellow UV‐absorbing area in the centre of the flower, which corresponds to the colour of anthers and pollen or to pollen/anther‐mimicking structures (Heuschen et al ., ; Lunau et al ., ). Such yellow UV‐absorbing colour plays a major role in attracting bees, as they innately respond to this stimulus (Lunau et al ., ).…”

“…According to bees’ preferences, flowers primarily pollinated by bees (hereafter bee‐flowers) reflect mainly in one or two of the three relevant ranges of wavelengths (ultraviolet, blue, green) and commonly present more than one colour (colour pattern) (Chittka et al ., ; Lunau et al ., ; Dyer et al ., ; Papiorek et al ., ). These colour patterns are generally composed of a predominant colour located peripherally and small colourful structures found in the central part of the flower that act as floral guides, improving flower detection and resource location (Lunau et al ., , ; de Ibarra et al ., ). A recurrent floral signal is a yellow UV‐absorbing area in the centre of the flower, which corresponds to the colour of anthers and pollen or to pollen/anther‐mimicking structures (Heuschen et al ., ; Lunau et al ., ).…”

“…Flower colour is a major communication trait between plants and their pollinators which promotes flower detection and signals the availability of resources to potential pollinators (Shrestha et al ., ; Lunau et al ., ). Owing to the diversity of colour vision systems caused by sensitivity or insensitivity to ultraviolet and red light, members of different groups of pollinators perceive and select flowers differently (Briscoe & Chittka, ; Wester & Lunau, ).…”

“…A recurrent floral signal is a yellow UV‐absorbing area in the centre of the flower, which corresponds to the colour of anthers and pollen or to pollen/anther‐mimicking structures (Heuschen et al ., ; Lunau et al ., ). Such yellow UV‐absorbing colour plays a major role in attracting bees, as they innately respond to this stimulus (Lunau et al ., ).…”