SR: Feeding Behaviour Flashcards
The honeybee dance language, in which foragers perform dances containing information about the distance and direction to food sources, is the quintessential example of symbolic communi- cation in non-primates1,2. The dance language has been the subject of controversy3,4, and of extensive research into the mechanisms of acquiring1,5,6, decoding7,8 and evaluating9 the information in the dance. The dance language has been hypoth- esized, but not shown, to increase colony food collection1,9,10.
Here we show that colonies with disoriented dances (lacking direction information) recruit less effectively to syrup feeders than do colonies with oriented dances. For colonies foraging at natural sources, the direction information sometimes increases food collected, but at other times it makes no difference. The food-location information in the dance is presumably important when food sources are hard to find, variable in richness and ephemeral. Recruitment based simply on arousal of foragers and communication of floral odour, as occurs in honeybees1, bumble bees11 and some stingless bees12, can be equally effective under other circumstances. Clarifying the condition-dependent payoffs of the dance language provides new insight into its function in honeybee ecology.
The dance resembles a miniaturized re-enactment of the flight to the food source. Elements of the dance (repeated waggle runs) encode the direction and distance to the food source.
The direction of the waggle run corresponds to the angle of the heading to the food source relative to the current sun azimuth, and is performed relative to a sensory reference.
In Apis mellifera the dances are usually done on a vertical comb in a dark nest cavity, and the reference is upward. In Apis florea and in some circumstances in other Apis species, the dance is performed on a horizontal surface with a reference to the sun azimuth, detected from a direct view of the sun, sky polarization patterns or landmarks13.
When on horizontal comb in the dark or in diffused light, bees still dance, but in random directions, and the indication of distance is also disrupted1. Bees will interpret spots of artificial light as the Sun or as particular regions of the polarized blue sky1,5,14
To test the effect of the dance language, we established a diffuse- light treatment in which bees performed completely disoriented dances, and an oriented-light treatment in which bees performed well-oriented dances.
Former studies comparing disoriented and oriented dances1,3,15 compared vertical and horizontal hives, which may differ in factors other than dance orientation. We used two- frame horizontal observation hives that could be illuminated with either treatment: light from three 25-W bulbs diffused through white translucent Plexiglas suspended above the colony, or uni- directional light from one 75-W bulb above a sheet of transparent Plexiglas plus a fluorescent ‘black light’ providing short wave- lengths.
The directions of waggle runs transcribed from videotapes of single dances in the diffuse-light treatment did not differ from a circular random distribution (mean vector length ^ s.e. in ten dances averaged 0.198 ^ 0.038, Rayleigh test (ref. 17), P . 0.5 for nine of the ten), as shown in Fig. 1a.
The dances in the oriented-light treatment were highly directionally oriented (mean vector length averaged 0.950 ^ 0.012, P , 0.001 for each of ten dances), similar to dances on vertical comb (where mean vector length averaged 0.984 ^ 0.004).
To verify that these light treatments affected recruitment, we compared the recruitment to feeders when colonies had disoriented and oriented dances in reciprocal-treatment experiments. This design provided tests for effects of light treatment, colony and time of day, as well as controlling for wind and the possibility of locale-specific odours3,4.
An equal number of foragers were trained from each colony to a feeder, and individually tagged for identifi- cation. Each colony’s feeder was in a different direction.
