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Animal of the month: the evolution of the imperfect honeybee

Honey bee colonies have historically been considered as marvels of evolution resulting in perfectly cooperative and harmonious societies, and exemplars of what we humans might achieve. This is an appealing image to many, but it is of course a caricature. Nobody is perfect, not even honey bees. As with any complex social system, honey bee societies are prone to error, robbery and social parasitism. Although there is only a single queen, the honey bee colony is composed of many subfamilies as the queen can mate with over 50 drones, using the sperm from all to produce offspring. The resulting web of subfamilies facilitates worker specialization, but also provides huge potential for intracolonial conflict.

Although efficient mechanisms are in place to prevent overt conflict among the subfamilies in the hive this is far from being perfect, and the apparently harmonious, cooperative whole has a considerable dark side. It is full of individual mistakes, obvious maladaptations and evolutionary dead ends. There is conflict, cheating, worker inefficiency, and unfair reproduction strategies.

The fact that honey bee colonies get by remarkably well in spite of many seemingly odd biological features is surprising. However, these “aberrations” are central to fully understanding the social organization of the colony.

Image credit: ‘bee-bees-honey’ by dmohanna. CC0 via Pixabay.

Aberrations observed within colonies include:

  • Fierce competition among the colony members using both physical force and chemical signaling where individual interests are often pursued at the expense of the colony, in some cases resulting in social parasitism. For example, Cape honeybee workers can invade foreign colonies to replace the native queen and take over the host colony. As these workers can produce female offspring that are also parasitic, the colony will eventually die as there are no workers to take care of the brood. The parasites need to find new host colonies in order to maintain the parasitic lineage.
  • Honey bees have evolved risky, sub-optimal and seemingly maladaptive solutions to organizational problems compared to other closely related social bee species. Reproductive swarming behavior is an excellent example of such a high risk strategy. As the old queen swarms with half of the colony’s worker force she needs to stall egg laying well before the actual swarming. This is important as she needs to decrease her ovary size to regain flight ability. Thus the colony has to suffer from a huge brood gap in the middle of the season when it actually seems more efficient to invest in a bigger colony size. In addition the swarm sets off without any clue where to find a new nesting site. Instead they fly off to the nearest tree branch to bivouac for several days before an appropriate nesting site has been identified and agreed upon by all members of the colony. Stingless bees show us how efficient swarming can be organized. The old queen stays in the nest and reproductive colony fission only starts once a new nesting site has been established. Workers then guide the newly mated queen to the new site when all is in place.
  • Honey bees have a highly specific mode of sex determination controlled by a single gene (complementary sex determiner, or csd). When an individual is heterozygous at this locus it is a female, if it is hemizygous like the haploid drone it becomes a male. Diploid individuals that are homozygous at the sex allele become diploid males that are sterile and in honey bees cannibalized by the workers. This causes serious problems in inbred colonies as up to 50% of the brood will be diploid males if the queen mates with a drone that shares a sex allele with her. Clearly any genetic system with more than one locus would be much more adaptive since it would result in a much lower frequency of diploid drones.
  • A clear example of a foraging failure is the robbery of bird seed from a bird feeder that we observed a few years ago. Honey bee workers recruited their nestmates to the feeder and numerous foragers were frantically rolling in the seed grains to fill their pollen basket on the hind legs (corbicula) with one seed each. This was achieved much faster than flying from flower to flower slowly filling the corbiculae with a pollen pellet. At the same time the birds were chased away as they were loath to confront the bees. Eventually the dish was emptied. Yet in the hive the drama must have been great because the bees cannot use the seed grains as food. This is a lose-lose situation that is clearly maladaptive and one of the rare cases where innate behavior can result in the reduction of the fitness of all the parties involved.

Honey bees are an exceptionally successful species with the ability to survive in the wild, in cities, in habitats from deserts to rainforests and even in beekeepers’ boxes. They get by because they have adequate but not perfect skills, and as with all social insects, it is the large number of individuals in the colony that compensates for a lack of perfection.

Featured image credit: ‘lavender-bee-summer’ by castleguard. CC0 via Pixabay.

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