新托福阅读：Bees Work Wonders When Babies Need Them

奇妙的生物钟

Although it is about bees, not humans, a paper just published in The Journal of Neuroscience will speak to anyone who has ever been up around the clock as a new parent, a medical resident, or any other type of caregiver. The findings by Guy Bloch and his Hebrew University of Jerusalem team suggest that our brains, our very body clocks, are capable of profound change when we get an all-important signal: Our care is needed.

Guy Bloch, a professor of animal behavior and evolution, spoke with Mind Matters co-editor Carey Goldberg from Jerusalem:

Q: Your work looked at “nurse bees” that care for the hive’s larvae through the day and night. How amazing are they? Do they truly work non-stop?

A: We discovered quite a while ago that they do stop but they don’t have circadian rhythms. Most of us, and most animals, are usually active during one phase of the day. For us, we are active during the day and we sleep at night. There are nocturnal animals that are active during the night and sleep during the day. But nurse bees switch between activity and inactivity all day long. And it’s not like they’re sleeping for two hours and waking up. The switch is much more frequent. From studies observing them in the lab, I’d say they sleep from five minutes to maybe thirty minutes. You can actually see very nicely when they sleep because their body position is totally different.

Q: So what did you set out to discover?

A:The nurse bees’ basic behavior was known, but we were trying in recent years to approach two important questions. One is: what is the mechanism underlying this activity? We know the circadian clock genes are very conserved and recent studies suggest that the clock proteins and organizational principles are more similar to mammals than to fruit flies. But usually if you try to induce a mammal or even fruit flies to work around the clock, it will cause deterioration in cognitive performance, and you’ll see increasing pathology. What we’re trying to do is to learn as much as we can about the molecular and neuronal mechanisms that allow the bee to show this remarkable pattern of activity.

And the other front is trying to understand what is the social regulation involved, because we know from previous studies that all this remarkable plasticity is regulated by social factors related to the division of labor. Some bees care for the young; others do foraging, other bees are guarding the colony and so forth. But around-the-clock activity is most typical to nurses. So we looked at what would happen when you remove the nurse bee from the hive.

Q: And what did you find?

A: What we showed in this study is that all this behavior, the ability of nurse bees to work around the clock, is very context-specific. The nurse bees care for the brood around the clock when in the hive, but show strong circadian rhythms in activity shortly after being removed from the hive to constant conditions in the lab. You can think about it like a mother caring for the baby. If the mother needs to care for the baby she will be active around the clock. Human babies, during the first three weeks or one month, have no circadian rhythm. The comparison is very interesting.

Q: So how do the social cues work?

A: In this study, we performed manipulations to try to understand the source of the social signals. First, we caged nurse-age bees on an empty comb inside the hive. So they were of a similar age and genotype as nurses in the colony and they could smell the brood pheromones inside the hive. They experienced a similar environment in terms of temperature, carbon-dioxide concentrations and humidity, but they couldn’t interact with the brood because there was no brood in these cages. We found that these bees had very strong circadian rhythms both in their activity and in their molecular clockwork functions. These nurse bees were more similar to foragers. So it’s not just something in the environment that induces nurse bees to work around the clock. It’s something in direct contact with the brood.

This experiment is very difficult to perform because you have to be active around the clock, and we repeated it with three colonies so it was huge work but provided a nice result.

Q: Can you go any farther and say what exactly it is about contact with the brood that affects the clockwork?

A: We’re exploring several lines of research on that. We know that in bees, pheromones are very important, and the chemical identity of brood pheromones is known. So we’re trying to manipulate them, and have some preliminary data on that.

The other line of research is to try to see what sensory modalities are involved. We know it’s not vision because the hive is dark. And probably not auditory because it’s so noisy in the hive. Chemical signals are very likely, and can be communicated in several ways. We think the antennae are one of the keys but there are also gustatory receptors in the mouth and legs. We’ll try to find the sensory modality, and try to find the link between it and the circadian system, which is currently unknown even in mammals and flies. The bee is a very powerful model: due to their social evolution they appear to be extremely sensitive to social signals,

Q: Just to enter science fiction for a moment: could we, many years down the line, figure out the mechanism that nurse bees use to lose their circadian rhythm and then simulate it in, say, soldiers?

A: In order to understand what could be done, we would also need to understand why it’s so unhealthy when you put a human on a schedule of, say, alternating one hour of sleep and one hour awake. The bees seem able to do it without damage. We need to progress in the research using various model animals. Activity around the clock is not common in the animal kingdom. Social insects such as honey bees and bumble bees can be active around the clock, and recently similar activity pattern was discovered in ants and termites. There was a very nice paper recently about reindeer and other deer during the polar summer. We have more and more evidence that animals can evolve to be active around the clock - it’s not just bees. But it’s not very common.