The orientation flights of bees are lovely examples of behaviours structured to aid learning. The mushroom bodies of insects have long-been implicated in learning of all types. Here, evidence is presented to the genetic mechanisms related to learning in the MB following the orientation flights of naive bees as well as bees responding to the changes in the layout of the environment. Interestingly, the mechanisms respond to visual novelty and show deeply conserved mechanisms.
Abstract: “The natural history of adult worker honey bees (Apis mellifera) provides an opportunity to study the molecular basis of learning in an ecological context. Foragers must learn to navigate between the hive and floral locations that may be up to miles away. Young pre-foragers prepare for this task by performing orientation flights near the hive, during which they begin to learn navigational cues such as the appearance of the hive, the position of landmarks, and the movement of the sun. Despite well-described spatial learning and navigation behavior, there is currently limited information on the neural basis of insect spatial learning. We found that Egr, an insect homolog of Egr-1, is rapidly and transiently upregulated in the mushroom bodies in response to orientation. This result is the first example of an Egr-1 homolog acting as a learning-related immediate-early gene in an insect and also demonstrates that honey bee orientation uses a molecular mechanism that is known to be involved in many other forms of learning. This transcriptional response occurred both in na+»ve bees and in foragers induced to re-orient. Further experiments suggest that visual environmental novelty, rather than exercise or memorization of specific visual cues, acts as the stimulus for Egr upregulation. Our results implicate the mushroom bodies in spatial learning and emphasize the deep conservation of Egr-related pathways in experience-dependent plasticity.”
Lutz, C. C., Robinson, G. E. 2013 Activity-dependent gene expression in honey bee mushroom bodies in response to orientation flight.JEB. 216, 2031-2038.
Abstract: Honeybees have at least three compass mechanisms: a magnetic compass; a celestial or sun compass, based on the daily rotation of the sun and sun-linked skylight patterns; and a backup celestial compass based on a memory of the sun’s movements over time in relation to the landscape. The interactions of these compass systems have yet to be fully elucidated, but the celestial compass is primary in most contexts, the magnetic compass is a backup in certain contexts, and the bees’ memory of the sun’s course in relation to the landscape is a backup system for cloudy days. Here we ask whether bees have any further compass systems, for example a memory of the sun’s movements over time in relation to the magnetic field. To test this, we challenged bees to locate the sun when their known celestial compass systems were unavailable, that is, under overcast skies in unfamiliar landscapes. We measured the bees’ knowledge of the sun’s location by observing their waggle dances, by which foragers indicate the directions toward food sources in relation to the sun’s compass bearing. We found that bees have no celestial compass systems beyond those already known: under overcast skies in unfamiliar landscapes, bees attempt to use their landscape-based backup system to locate the sun, matching the landscapes or skylines at the test sites with those at their natal sites as best they can, even if the matches are poor and yield weak or inconsistent orientation.
Dovey, K. M., Kemfort, J. R., Towne, W. F. 2013 The depth of the honeybee’s backup sun-compass systems. JEB. 216, 2129-2139.
Bowens SR, Glatt DP, Pratt SC (2013) Visual Navigation during Colony Emigration by the Ant Temnothorax rugatulus. PLoS ONE 8(5): e64367.
This week’s Nature has an interesting bit of engineering inspired by insect eyes:
Young Min Song et al. (2013) Digital cameras with designs inspired by the arthropod eye. Nature 497, 95–99
Although many ant species have very neat recruitment systems, in the form of their pheromone trail networks, some ant species – notably desert ants – do not use pheromone trails. Whether these ants have any other form of directional recruitment is a fascinating question. From this study of the foraging ecology of the Australian desert ant Melophorus bagoti, we get a hint that pheromone-independent directional mass recruitment may exist. Nests of M. bagoti were surrounded by feeders with only one of them baited with protein. Ants that had discovered the protein feeder were temporarily captured and then released en masse. Subsequent arrivals at all feeders were recorded. Occasionally, very great numbers of recruits (a hundredfold more than at other feeders!) were observed at the target feeder specifically. Odour markings and plumes can be discounted, leaving us with a strangely evocative question about how directional information is transmitted from knowledgeable workers to recruits.
Patrick Schultheiss, Sabine S Nooten (2013) Foraging patterns and strategies in an Australian desert ant. Austral Ecology
For Cataglyphis ants, there are two particularly significant odours – are used to pinpoint food or nest. The nest is indicated by a Co2 plume, whereas food is indicated by complex molecules given off by recently dead insects. Before odour following can take place – guidance to the vicinity of food or nest is often driven by path integration. Here, Buehlman et al. show that ants will ignore Co2 plumes when they still have a large home vector, but are nevertheless attracted by food odours when a learnt food vector is still large. The pattern of results obviously reflects an adaptive solution, as you need to make sure you enter your own nest, though you don’t care whether the food you get is from the same patch as you have previously visited. The interesting question now is to ask whether this is driven by cognitive mechanisms are whether the simple sensori-motor ouptut of PI interacts differently with the potential plume following of different odours.
Buehlmann C, Hansson BS, Knaden M. (2013) Flexible weighing of olfactory and vector information in the desert ant, Cataglyphis fortis. Biol Lett 9: 20130070.
We know that plants and bees share a close relationship developed through their coevolution. This has been most closely studied in terms of colours and odours. This paper from Clarke et al. shows how another channel might also be used a signal between plant and bee. They showed that floral electric fields, which are impacted by visits from naturally charged bees, can be discriminated by bees, providing extra information about the shape and recent history of a flower. As the authors say “… our study provides a framework for exploring the function and adaptive value of the perception of weak electric fields by bees in nature.”