Bee shortage? What bee shortage?

An article in the New York Times this week suggests that the current scare over colony collapse disorder is nothing extraordinary. It has happened before and will probably happen again. What has been missing from the debate, some scientists say, is historical context. Records show that colonies were vanishing in the 19th century, when the cause was seen as lack of moral fibre. Bees that weren’t returning to their hives had “weak character”. And it happened in the late 1970s, when it was called “disappearing disease”. The disease too disappeared, and no cause was ever isolated.

One day we may know, and extra money for long-term monitoring (none has been forthcoming) may help. In the meantime, if the “crisis” has helped people appreciate the importance of bees as pollinators, and prompted deeper investigations, then that is surely A Good Thing. To prove the point, two deeply fascinating papers have been published in the past month showing that genetic diversity in honeybees and other social insects is also A Good Thing.

This is counterintuitive, because the reason social insects are social is that they are genetically uniform.

Most social insects have a system of sex determination called haplodiploidy. The queen stores sperm from the male she mates with and chooses whether to fertilize an egg or not. Fertilized eggs turn into females, while unfertilized eggs become males. The upshot is that a gene for altruism — helping your mother to raise more sisters, some of whom will become queens — is very likely to be shared by those sisters, and so to spread.

That’s a (very) simplified account, but it’ll do. Because if a queen mates with several males, then any randomly chosen pair of the queen’s daughters are less likely to share the altruism gene. So they shouldn’t be as social. And yet honeybees are among the most polyandrous and the most social of insects; each queen mates with several males. And they’re not the only ones. Leafcutter ants, harvester ants and very social wasps are all more polyandrous.

There are actually lots of ways in which the benefits of diversity might outweigh the costs of lower relatedness among sisters, and they’re not necessarily exclusive. Resistance to disease, for example, might be part of the reason while another might be that the queen does not want to risk getting duff sperm from just one male. Benjamin Oldroyd and Jennifer Fewell take an overview of them all, and conclude that an important reason is that genetic diversity allows different families of workers to be specialized for different tasks, and that this enables the colony to regulate things like the temperature in the nest, or food stores, more precisely. ((Benjamin P. Oldroyd and Jennifer H. Fewell (2007), Genetic diversity promotes homeostasis in insect colonies, Trends in Ecology & Evolution 22: 408-413))

There is good evidence of a genetic basis to task specialization in these very social insects. Analyze the DNA of workers keeping the nest cool by fanning with their wings, for example, and you discover that they belong primarily to one patriline, as the daughters of one male are known. Oldroyd and Fewell speculate that this is the result of different sensitivity to stimuli. Thus some bees will fan at a lower temperature than others. Their analogy will resonate with many students.

Imagine a shared house: as dishes accumulate in the sink, one person is likely to ‘notice’ first and to wash them. By doing so, they remove the visual stimuli for their house-mates to do the washing up. When dishes begin to accumulate, that person is likely to notice them first again, and so they become the dishwashing specialist. … Individuals differ in their thresholds for different chores, so that one person might wash dishes while another (hopefully) vacuums.

The result, one hopes, is a tidier house than if everyone washes dishes while nobody ever vacuums. Of course if a party results in a huge pile of dishes in the sink, even the vacuuming specialist might be stimulated to do some washing up. And so it is with social insects. The more males the queen mates with, the more stable the temperature within the nest, in real life and in theoretical models.

The other paper is direct practical proof that Genetic Diversity in Honey Bee Colonies Enhances Productivity and Fitness. ((Heather R. Mattila and Thomas D. Seeley (2007), Genetic Diversity in Honey Bee Colonies Enhances Productivity and Fitness. Science 317: 362 – 364.)) Heather Mattila and Thomas Seeley created swarms around queens that they had inseminated with sperm from 15 different males or one single male, then watched (and measured) what happened.

Swarming is a dangerous time in the life of a colony.

With limited resources and labor, a swarm must construct new comb, build a food reserve, and begin rearing workers to replace the aging work force. In temperate climates, newly founded colonies must operate efficiently because there is limited time to acquire the resources to support these activities. Colony founding is so difficult that only 20% of swarms survive their first year; most do not gather adequate food to fuel the colony throughout the winter and die of starvation.

As it happened, there was a cold snap in August last year that killed half of the genetically uniform colonies. All the diverse colonies survived it. None of the remaining uniform colonies had enough food to survive beyond mid-December. A quarter of the diverse colonies made it till Spring brought renewed resources.

I can’t really express how delightful both papers are. They’re not really difficult, both are full of insights, and details that I couldn’t hope to cover here. If you have access and the least interest in clear thinking on genetic diversity and just a few of the benefits it delivers, in some species that are very important to people, do give them a read.