Pollen, anther, stamen, and androecium mimicry

Floral colours represent a highly diverse communication signal mainly involved in flower visitors' attraction and guidance, but also flower discrimination, filtering non-pollinators and discouraging floral antagonists. The divergent visual systems and colour preferences of flower visitors, as well as the necessity of cues for flower detection and discrimination, foster the diversity of floral colours and colour patterns. Despite the bewildering diversity of floral colour patterns, a recurrent component is a yellow UV-absorbing floral centre, and it is still not clear why this pattern is so frequent in angiosperms. The pollen, anther, stamen, and androecium mimicry (PASAM) hypothesis suggests that the system composed of the flowers possessing such yellow UV-absorbing floral reproductive structures, the flowers displaying central yellow UV-absorbing structures as floral guides, and the pollen-collecting, as well as pollen-eating, flower visitors responding to such signals constitute the world's most speciose mimicry system. In this review, we call the attention of researchers to some hypothetical PASAM systems around the globe, presenting some fascinating examples that illustrate their huge diversity. We will also present new and published data on pollen-eating and pollen-collecting pollinators' responses to PASAM structures supporting the PASAM hypothesis and will discuss how widespread these systems are around the globe. Ultimately, our goal is to promote the idea that PASAM is a plausible first approach to understanding floral colour patterns in angiosperms.

Honey bee colonies change their foraging decisions after in-hive experiences with unsuitable pollen

Pollen is the protein resource for Apis mellifera and its selection affects colony development and productivity. Honey bee foragers mainly lose their capacity to digest pollen, so we expect that those pollen constituents that can only be evaluated after ingestion will not influence their initial foraging preferences at food sources. We predicted that pollen composition may be evaluated in a delayed manner within the nest, for example, through the effects that the pollen causes on the colony according to its suitability after being used by in-hive bees. To address whether pollen foraging is mediated by in-hive experiences, we conducted dual-choice experiments to test the avoidance of pollen adulterated with amygdalin, a deterrent that causes post-ingestion malaise. In addition, we recorded pollen selection in colonies foraging in the field after being supplied or not with amygdalin-adulterated pollen from one of the dominant flowering plants (Diplotaxis tenuifolia). Dual-choice experiments revealed that foragers did not avoid adulterated pollens at the foraging site; however, they avoided pollen that had been offered adulterated within the nest on the previous days. In field experiments, pollen samples from colonies supplied with amygdalin-adulterated pollen were more diverse than controls, suggesting that pollen foraging was biased towards novel sources. Our findings support the hypothesis that pollen assessment relies on in-hive experiences mediated by pollen that causes post-ingestive malaise.

Do honeybees (Apis mellifera) differentiate between different pollen types?

Bees receive nectar and pollen as reward for pollinating plants. Pollen of different plant species varies widely in nutritional composition. In order to select pollen of appropriate nutritional quality, bees would benefit if they could distinguish different pollen types. Whether they rely on visual, olfactory and/or chemotactile cues to distinguish between different pollen types, has however been little studied. In this study, we examined whether and how Apis mellifera workers differentiate between almond and apple pollen. We used differential proboscis extension response conditioning with olfactory and chemotactile stimulation, in light and darkness, and in summer and winter bees. We found that honeybees were only able to differentiate between different pollen types, when they could use both chemotactile and olfactory cues. Visual cues further improved learning performance. Summer bees learned faster than winter bees. Our results thus highlight the importance of multisensory information for pollen discrimination.

Bumble bee ecophysiology: integrating the changing environment and the organism

Bumble bees are among the most ecologically and economically important pollinators worldwide, yet many of their populations are being threatened by a suite of interrelated, human-mediated environmental changes. Here, I discuss recent progress in our understanding of bumble bee ecophysiology, including advances related to thermal biology in light of global warming; nutritional biology in the context of declining food resources; and the capacity for bumble bees to exhibit physiological plasticity or adaptations to novel or extreme environments, with reference to their evolutionary history and current biogeography.