Abstract
The ecological success of social insects is frequently ascribed to improvements in task performance due to division of labour amongst workers. While much research has focused on improvements associated with lifetime task specialization, members of colonies can specialize on a given task over shorter time periods. Eusocial bees in particular must collect pollen and nectar rewards to survive, but most workers appear to mix collection of both rewards over their lifetimes. We asked whether bumblebees specialize over timescales shorter than their lifetime. We also explored factors that govern such patterns, and asked whether reward specialists made more foraging bouts than generalists. In particular, we described antennal morphology and size of all foragers in a single colony and related these factors to each forager’s complete foraging history, obtained using radio frequency identification (RFID). Only a small proportion of foragers were lifetime specialists; nevertheless, >50% of foragers specialized daily on a given reward. Contrary to expectations, daily and lifetime reward specialists were not better foragers (being neither larger nor making more bouts); larger bees with more antennal olfactory sensilla made more bouts, but were not more specialized. We discuss causes and functions of short and long-term patterns of specialization for bumblebee colonies.
Highlights
Source of carbohydrates and pollen as their primary source of protein and lipids[15,16]
According to the well-supported response threshold model (RTM), reward specialization arises as a result of interindividual variation in sensitivity to cues that stimulate nectar or pollen foraging
We measured antennal sensory morphology and other morphological attributes which might be associated with different patterns of reward specialization and foraging effort
Summary
Source of carbohydrates and pollen as their primary source of protein and lipids[15,16]. We might expect that specialists on either reward would be larger and more effective foragers; olfactory sensilla number might instead relate more strongly to the degree to which a forager is specialized on a given reward To test these hypotheses, we compiled a complete lifetime record of pollen and nectar foraging activity for every bumblebee forager (Bombus impatiens) in a single colony and related these patterns to the sensory morphology and size of each forager. We measured antennal sensory morphology (sensilla placodea number or ‘pore plates’) and other morphological attributes (forewing length, head width, antennal length, and proboscis length) which might be associated with different patterns of reward specialization and foraging effort. This is the first study to our knowledge that examines patterns of reward specialization at multiple timescales and that connects them to forager size and sensory morphology
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