Abstract
BackgroundMany insects have multiple generations per year and cohorts emerging in different seasons may evolve their own phenotypes if they are subjected to different selection regimes. The bivoltine bee Andrena bicolor is reported to be polylectic and oligolectic (on Campanula) in the spring and summer generations, respectively. Neurological constraints are assumed to govern pollen diet in bees. However, evidence comes predominantly from studies with oligolectic bees. We have investigated how sensory constraints influence the innate foraging behavior of A. bicolor and have tested whether bees of different generations evolved behavioral and sensory polyphenism to cope better with the host flowers available in nature when they are active.ResultsBehavioral and sensory polyphenisms were tested in choice assays and electroantennographic analyses, respectively. In the bioassays, we found that females of both generations (1) displayed a similar innate relative reliance on visual and olfactory floral cues irrespective of the host plants tested; (2) did not prefer floral cues of Campanula to those of Taraxacum (or vice versa) and (3) did not display an innate preference for yellow and lilac colors. In the electroantennographic analyses, we found that bees of both generations responded to the same set of compounds.ConclusionOverall, we did not detect seasonal polyphenism in any trait examined. The finding that bees of both generations are not sensory constrained to visit a specific host flower, which is in strict contrast to results from studies with oligolectic bees, suggest that also bees of the second generation have a flexibility in innate foraging behavior and that this is an adaptive trait in A. bicolor. We discuss the significance of our findings in context of the natural history of A. bicolor and in the broader context of host-range evolution in bees.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0074-z) contains supplementary material, which is available to authorized users.
Highlights
Many insects have multiple generations per year and cohorts emerging in different seasons may evolve their own phenotypes if they are subjected to different selection regimes
We have investigated the innate responses of A. bicolor females to visual and olfactory floral cues of two common host plants, namely Taraxacum officinale (Fig. 1a) and Campanula trachelium (Fig. 1b), whose blooming peaks coincide with the flight activity of the first and second generation, respectively
Relative importance of visual and olfactory floral cues When testing the relative importance of floral cues, we found that bees of the first and second generation responded to the floral cues, irrespective of the host plants tested
Summary
Many insects have multiple generations per year and cohorts emerging in different seasons may evolve their own phenotypes if they are subjected to different selection regimes. The bivoltine bee Andrena bicolor is reported to be polylectic and oligolectic (on Campanula) in the spring and summer generations, respectively. We have investigated how sensory constraints influence the innate foraging behavior of A. bicolor and have tested whether bees of different generations evolved behavioral and sensory polyphenism to cope better with the host flowers available in nature when they are active. Bees visit flowers mainly to collect nectar and pollen. These floral rewards are essential for both their own nutritional requirements and brood provision [1]. Whereas the basal state of oligolecty is well acknowledged, the ecological and physiological aspects governing host choice in bees remain poorly investigated. In addition to being pollinators, bees can be seen as herbivores and plants might be under selective pressure to reduce pollen harvesting
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