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Females and males often face different sources of selection, resulting in dimorphism in morphological, physiological, and even cognitive traits. Sex differences are often studied in respect to spatial cognition, yet the different ecological roles of males and females might shape cognition in multiple ways. For example, in dietary generalist bumblebees (Bombus), the ability to learn associations is critical to female workers, who face informationally rich foraging scenarios as they collect nectar and pollen from thousands of flowers over a period of weeks to months to feed the colony. While male bumblebees likely need to learn associations as well, they only forage for themselves while searching for potential mates. It is thus less clear whether foraging males would benefit from the same associative learning performance as foraging females. In this system, as in others, cognitive performance is typically studied in lab-reared animals under captive conditions, which may not be representative of patterns in the wild. In the first test of sex and species differences in cognition using wild bumblebees, we compared the performance of Bombus vancouverensis nearcticus (formerly bifarius) and Bombus vosnesenskii of both sexes on an associative learning task at Sierra Nevada (CA) field sites. Across both species, we found that males and females did not differ in their ability to learn, although males were slower to respond to the sucrose reward. These results offer the first evidence from natural populations that male bumblebees may be equally as able to learn associations as females, supporting findings from captive colonies of commercial bees. The observed interspecific variation in learning ability opens the door to using the Bombus system to test hypotheses about comparative cognition. [ABSTRACT FROM AUTHOR]

Learning associations between food-related stimuli and nutrients allows foragers to collect resources efficiently. In turn, the nutrients that foragers consume can themselves affect learning performance, through innate preferences for pre-ingestive stimuli, as well as post-ingestive reinforcement. Bees are insect models of learning and memory, yet the vast majority of this research concerns nectar (carbohydrate) rather than pollen (protein/lipid) rewards, despite the fact that many bees collect both simultaneously. We asked how one component of pollen surface chemistry, a free fatty acid (oleic acid), affected bees' performance in a nectar-learning task. We found that ingestion of oleic acid enhanced visual learning, likely through positive post-ingestive reinforcement. This was supported by our finding that although bees did not prefer to consume the oleic acid solution, its ingestion both decreased motor activity and increased survival. These results are a step towards understanding how nutritionally complex floral rewards may affect cognitive processes that underlie pollination mutualisms. [ABSTRACT FROM AUTHOR]

Foraging theory assumes that animals assess value based on objective payoffs; however, animals often evaluate rewards comparatively, forming expectations based on recent experience. This form of evaluation may be particularly relevant for nectar foragers such as bumblebees, where individuals can visit thousands of flowers daily that vary in nectar quality. While many animals, including bees, demonstrate reference-based evaluation in experimental contexts, it is unclear whether this occurs in the wild. Here, we asked how daily experience with wildflower nectar influenced wild bumblebees' reward evaluation. We measured the daily nectar concentration of bee-visited wildflowers (Penstemon spp.), before presenting foragers with conspecific flowers filled with a range of artificial nectar concentrations. We recorded bees' acceptance of artificial nectar, the probability of subsequent visits to flowers on the same plant, and residence time. While bees had a minimum threshold of nectar acceptability that was unaffected by experience, when there was higher-concentration environmental nectar, they were less likely to accept lower-quality rewards on manipulated plants. Bees also visited more flowers and stayed longer on plants with higher-concentration nectar. This study shows evidence for both absolute and reference-based evaluation in wild bees and points towards differences between bees' behavior in lab- and wild-foraging contexts. [ABSTRACT FROM AUTHOR]

How foragers cope with complexity in both needs and resources is a major question in behavioral ecology. When faced with nutritionally diverse resources, or when foraging for offspring with divergent nutritional needs, animals must meet the challenge of how to structure their foraging bouts, including what resources to forage for and in what order (how) to collect them. We investigated how nutritional variation in resources and requirements shapes the structure of bumble bee foraging bouts. Bumble bee workers collect 2 nutritionally distinct resources for consumers with different nutritional needs, floral nectar (largely carbohydrates) for their own needs and that of larvae, and pollen (largely protein) that is used primarily by larvae. We maintained colonies of the Eastern Bumble Bee (Bombus impatiens) in the laboratory on either protein-rich or protein-limited diets and assessed bees' foraging bout structure on artificial flowers that offered low, medium, or high ratios of pollen to nectar. We analyzed bout structure using both traditional floral constancy metrics as well as hierarchical Bayesian analyses. Bees from pollen-satiated colonies responded to variation in floral pollen:nectar ratios, tending to collect pollen consecutively when nectar volumes were high. In contrast, foragers from pollen-limited colonies were relatively insensitive to floral reward ratio, tending to collect pollen in long runs regardless of nectar volume. We discuss the implications of these findings for the pollination services that bees provide plants. [ABSTRACT FROM AUTHOR]