Bee Brains: Dissecting pollinator behavior and the importance of plasticity in the face of changing environments

All organisms face environmental variability, and much of contemporary biological research aims to understand the mechanisms allowing organisms to adapt and survive in the face of change. Animals residing in urban habitats face particularly high levels of unpredictability and environmental fluctuation due to changes based upon human desire. Though urban areas are considered relatively novel habitats, numerous species have adapted to city life, mediated through behavioral and physiological plasticity. Native bee species show particularly high species richness and abundance in urban settings, but the mechanisms driving this pattern are poorly understood. In this dissertation, I explore how bees employ plasticity to cope with environmental variation. I approach this aim by evaluating behavioral, physiological, and genetic plasticity of two native bee species first in the wild, and then in a controlled laboratory setting. First, I review urban bee research, highlighting studies that document plasticity and flexibility, as well as provide a list of testable predictions for future study (Chapter 1). I then concentrate on the foraging flexibility of a facultatively eusocial bee species, Halictus ligatus (Halictidae: Halictus) residing across an urban-rural habitat gradient (Chapter 2), as well as assess brain differential gene expression (Chapter 3). I find that the frequency, duration, and sequential pattern of pollen collecting behaviors performed by H. ligatus vary significantly across habitats, and discover a potentially novel behavior performed by sweat bees. Additionally, I find brain differential gene expression is highly conserved for most behaviors. However, genes important for physiological processes and immune response are differentially expressed, with significant upregulation of vision and photoreceptor genes in suburban bees compared to both urban and exurban areas. Lastly, I utilize a classical two arm bandit experimental design to determine how resource reward persistence impact the risk sensitivity of foraging eusocial bumble bees (Bombus impatiens). I find that persistence of resource quality, resource color, and experience gained by the forager affect bee risk sensitivity. As rewards become more or less predictable, individuals shift their foraging strategy. In summation, this dissertation provides evidence of important mechanisms allowing pollinating bees to successfully forage and survive in highly variable, ever-changing environments