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Visual and Olfactory Floral Cues of Campanula (Campanulaceae) and Their Significance for Host Recognition by an Oligolectic Bee Pollinator.

Milet-Pinheiro P, Ayasse M, Dötterl S - PLoS ONE (2015)

Bottom Line: Spiroacetals, rarely found as floral scent constituents but quite common among Campanula species, were recently shown to play a key function for host-flower recognition by Ch. rapunculi.We conclude that Campanula species share some visual and olfactory floral cues, and that neurological adaptations (i.e. vision and olfaction) of Ch. rapunculi innately drive their foraging flights toward host flowers.The significance of our findings for the evolution of pollen diet breadth in bees is discussed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Experimental Ecology, University of Ulm, Ulm, Germany.

ABSTRACT
Oligolectic bees collect pollen from a few plants within a genus or family to rear their offspring, and are known to rely on visual and olfactory floral cues to recognize host plants. However, studies investigating whether oligolectic bees recognize distinct host plants by using shared floral cues are scarce. In the present study, we investigated in a comparative approach the visual and olfactory floral cues of six Campanula species, of which only Campanula lactiflora has never been reported as a pollen source of the oligolectic bee Ch. rapunculi. We hypothesized that the flowers of Campanula species visited by Ch. rapunculi share visual (i.e. color) and/or olfactory cues (scents) that give them a host-specific signature. To test this hypothesis, floral color and scent were studied by spectrophotometric and chemical analyses, respectively. Additionally, we performed bioassays within a flight cage to test the innate color preference of Ch. rapunculi. Our results show that Campanula flowers reflect the light predominantly in the UV-blue/blue bee-color space and that Ch. rapunculi displays a strong innate preference for these two colors. Furthermore, we recorded spiroacetals in the floral scent of all Campanula species, but Ca. lactiflora. Spiroacetals, rarely found as floral scent constituents but quite common among Campanula species, were recently shown to play a key function for host-flower recognition by Ch. rapunculi. We conclude that Campanula species share some visual and olfactory floral cues, and that neurological adaptations (i.e. vision and olfaction) of Ch. rapunculi innately drive their foraging flights toward host flowers. The significance of our findings for the evolution of pollen diet breadth in bees is discussed.

No MeSH data available.


Flowers of Campanula species used for the study and their oligolectic pollinator Chelostoma rapunculi.(A) Ca. glomerata, (B) Ca. lactiflora (C) Ca. persicifolia alba, (D) Ca. persicifolia, (E) Ca. rapunculoides, (F) Ca. rotundifolia, and (G) Ca. trachelium. (G, H) Females of Ch. rapunculi gathering pollen on Ca. trachelium and Ca. glomerata, respectively. All photos by Paulo Milet-Pinheiro.
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pone.0128577.g001: Flowers of Campanula species used for the study and their oligolectic pollinator Chelostoma rapunculi.(A) Ca. glomerata, (B) Ca. lactiflora (C) Ca. persicifolia alba, (D) Ca. persicifolia, (E) Ca. rapunculoides, (F) Ca. rotundifolia, and (G) Ca. trachelium. (G, H) Females of Ch. rapunculi gathering pollen on Ca. trachelium and Ca. glomerata, respectively. All photos by Paulo Milet-Pinheiro.

Mentions: Chelostoma rapunculi (Lepeletier 1841) (Fig 1) is a European oligolectic bee that collects pollen on several Campanula species [30, 31], and in the presence of host plants, both males and females restrict nectar gathering to these plants. The genus Campanula L. (Campanulaceae) comprises about 400 species of bellflowers, harebells, and starbells, whose flowers are predominantly violet-blue to the human eyes [32, 33]. In spite of its remarkable diversity, floral scent composition in the genus Campanula has been chemically characterized only in a single species, namely Ca. trachelium [34]. Recently, we showed that Ch. rapunculi innately prefers both visual and olfactory floral cues of Ca. trachelium over those of two other co-flowering non-host plants [20]. The exact cues involved in the innate visual preference by Ch. rapunculi remain unknown, even if some evidence point to color as important visual dimension [35]. In terms of olfactory cues, however, newly-emerged bees of Ch. rapunculi were shown to rely on spiroacetals to discriminate host from non-host flowers [34]. Spiroacetals form a distinct group of natural volatiles that are rarely encountered in floral scents [24]. In the floral scent bouquet of Ca. trachelium, however, six spiroacetals were found, some of them recorded for the first time as floral scent constituents [34].


Visual and Olfactory Floral Cues of Campanula (Campanulaceae) and Their Significance for Host Recognition by an Oligolectic Bee Pollinator.

Milet-Pinheiro P, Ayasse M, Dötterl S - PLoS ONE (2015)

Flowers of Campanula species used for the study and their oligolectic pollinator Chelostoma rapunculi.(A) Ca. glomerata, (B) Ca. lactiflora (C) Ca. persicifolia alba, (D) Ca. persicifolia, (E) Ca. rapunculoides, (F) Ca. rotundifolia, and (G) Ca. trachelium. (G, H) Females of Ch. rapunculi gathering pollen on Ca. trachelium and Ca. glomerata, respectively. All photos by Paulo Milet-Pinheiro.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465695&req=5

pone.0128577.g001: Flowers of Campanula species used for the study and their oligolectic pollinator Chelostoma rapunculi.(A) Ca. glomerata, (B) Ca. lactiflora (C) Ca. persicifolia alba, (D) Ca. persicifolia, (E) Ca. rapunculoides, (F) Ca. rotundifolia, and (G) Ca. trachelium. (G, H) Females of Ch. rapunculi gathering pollen on Ca. trachelium and Ca. glomerata, respectively. All photos by Paulo Milet-Pinheiro.
Mentions: Chelostoma rapunculi (Lepeletier 1841) (Fig 1) is a European oligolectic bee that collects pollen on several Campanula species [30, 31], and in the presence of host plants, both males and females restrict nectar gathering to these plants. The genus Campanula L. (Campanulaceae) comprises about 400 species of bellflowers, harebells, and starbells, whose flowers are predominantly violet-blue to the human eyes [32, 33]. In spite of its remarkable diversity, floral scent composition in the genus Campanula has been chemically characterized only in a single species, namely Ca. trachelium [34]. Recently, we showed that Ch. rapunculi innately prefers both visual and olfactory floral cues of Ca. trachelium over those of two other co-flowering non-host plants [20]. The exact cues involved in the innate visual preference by Ch. rapunculi remain unknown, even if some evidence point to color as important visual dimension [35]. In terms of olfactory cues, however, newly-emerged bees of Ch. rapunculi were shown to rely on spiroacetals to discriminate host from non-host flowers [34]. Spiroacetals form a distinct group of natural volatiles that are rarely encountered in floral scents [24]. In the floral scent bouquet of Ca. trachelium, however, six spiroacetals were found, some of them recorded for the first time as floral scent constituents [34].

Bottom Line: Spiroacetals, rarely found as floral scent constituents but quite common among Campanula species, were recently shown to play a key function for host-flower recognition by Ch. rapunculi.We conclude that Campanula species share some visual and olfactory floral cues, and that neurological adaptations (i.e. vision and olfaction) of Ch. rapunculi innately drive their foraging flights toward host flowers.The significance of our findings for the evolution of pollen diet breadth in bees is discussed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Experimental Ecology, University of Ulm, Ulm, Germany.

ABSTRACT
Oligolectic bees collect pollen from a few plants within a genus or family to rear their offspring, and are known to rely on visual and olfactory floral cues to recognize host plants. However, studies investigating whether oligolectic bees recognize distinct host plants by using shared floral cues are scarce. In the present study, we investigated in a comparative approach the visual and olfactory floral cues of six Campanula species, of which only Campanula lactiflora has never been reported as a pollen source of the oligolectic bee Ch. rapunculi. We hypothesized that the flowers of Campanula species visited by Ch. rapunculi share visual (i.e. color) and/or olfactory cues (scents) that give them a host-specific signature. To test this hypothesis, floral color and scent were studied by spectrophotometric and chemical analyses, respectively. Additionally, we performed bioassays within a flight cage to test the innate color preference of Ch. rapunculi. Our results show that Campanula flowers reflect the light predominantly in the UV-blue/blue bee-color space and that Ch. rapunculi displays a strong innate preference for these two colors. Furthermore, we recorded spiroacetals in the floral scent of all Campanula species, but Ca. lactiflora. Spiroacetals, rarely found as floral scent constituents but quite common among Campanula species, were recently shown to play a key function for host-flower recognition by Ch. rapunculi. We conclude that Campanula species share some visual and olfactory floral cues, and that neurological adaptations (i.e. vision and olfaction) of Ch. rapunculi innately drive their foraging flights toward host flowers. The significance of our findings for the evolution of pollen diet breadth in bees is discussed.

No MeSH data available.