BEES HAVE THERMOSTATS

by Whit Gibbons

August 8, 2004

Honeybees are amazing creatures in many ways. We know this because of the excellent research by behavioral scientists and geneticists who have learned so much about them. Especially intriguing are the colonial attributes of honeybees, in which the workers, all females, will defend their colony to the death, communicate with each other about where the nearest pollen is, and tend the hive and developing young. Males (aka drones) are viewed almost as a by-product whose sole function is to mate with the queen. But a recent study in Australia (honey bees have been introduced on every warm continent) indicates that which particular males breed with the queen can make a difference in how hive temperature is controlled.

Being social insects, honeybees operate in a super-organism mode, each individual operating in the best interest of the hive. Thus, members of the colony operate in unison to maintain the hive as close to the preferred temperature of 95 degrees as possible. In hot weather the bees wave their wings to cool the hive. In cold weather they warm the hive by huddling together to generate heat from their bodies. As environmental temperatures may rise or fall slowly or rapidly, depending on the season and local weather conditions, honeybees must be in a constant state of readiness to act as a group to raise or lower the temperature in the hive.

The study by Julia C. Jones and colleagues at the University of Sydney was an impressive mix of behavioral observations and DNA analyses demonstrating that multiple matings by the queen, rather than the choice of only a single drone to mate with, are in the best interest of the hive. The experiments were conducted on pairs of hives having the same number of bees but differing genetically. One hive consisted of worker bees that were all the offspring of a single queen and single drone. The behavior of the hive with uniform genetic parentage was compared to that of another in which the queen had had multiple mates. Hence the workers in the second hive were of mixed genetic heritage.

What the researchers found in regard to temperature regulation was that worker bees in both hives maintained the hive temperature at the preferred temperature. However, they differed in that the temperature over time in the mixed genetic hive was relatively invariable compared to the uniform genetic hive. In other words, the uniformly genetic individuals eventually got the hive to the proper temperature but their response time lagged behind that of the genetically diverse hive.

The explanation for the differing responses is that individual bees, just like people, vary in their internal thermostats. That is, some individuals will take action to regulate their surrounding temperature when their body is slightly warmer or cooler than that to which another individual might respond. We see this all the time in office buildings and other places where groups congregate. Someone always thinks the room is too cold or too hot in contrast to another who thinks the opposite. Bees are apparently the same way, although their focus is on what is best for the hive, not themselves as individuals.

When honeybees are genetically similar, they are more likely to respond to a need to begin "regulating the thermostat of the hive" at the same temperature. This means they all begin to operate at about the same time. In the genetically diverse hive, individuals respond at different temperature levels. Thus some begin the cooling process of fanning the hive on a hot day at slightly lower temperatures than other individuals that pick up the call to duty a little later. The temperature of a hive is kept at a more uniform level because individual bees are responding across a wider gradient of temperatures. To confirm the relationship between genetics and behavior, the researchers did DNA tests in a mixed genetic hive. They removed some workers that began fanning at one temperature and some that began fanning at other temperatures. Sure enough, individuals that began fanning at a given temperature were more likely to have the same father than those fanning at other temperatures.

The honeybee findings are indeed captivating. But consider the scientific complexity involved in conducting such a study. The scientists are as impressive as the bees.



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