Old bees get a new lease on life (through glutamate!)
Have you ever heard a story about an elderly person who seems surprisingly fine and with it in the outside world, but is then transferred to a nursing home where they quickly slide from their mental peak? Have you ever stayed at home all day, playing video games (ahem) and feeling a bit sluggish only to go back to mentally stimulating work and feel more alert? No matter what people say, our work is our life.
Honeybees spend the first two or three weeks of their life as nurses, taking care of the young, tending to the queen, building out and cleaning the hive. When they get older, they get reassigned to a job outside the hive as a forager. Now they have to search out nectar and pollen and live in the dangerous outside world. They are quick to die off as the stress of the outside environment and downright intense physical work causes them to age. Not only are there physical effects, but mental ones, too: their ability to learn and associate is impaired.
But not all is lost for these bees! Sometimes disaster falls a hive and more nurses are needed. When this happens, some forager bees return to become nurses. Baker et al studied these bees to see how returning to the hive affected them. Although in some ways the returned bees looked like their foraging compatriots, in terms of learning and memory they were identical to their younger nursing brethren. They had a new lease on life!
Some of these returned nurses did better than others. Baker et al looked at what proteins were differentially expressed between these two groups, and the data pointed to proteins that affected physical structure (alpha-tubulins), stress and cell maintenance, and neuronal functioning and signaling. One of the most abundantly different proteins was the glutamate transporter homologous to EAAT2. Glutamate is the primary neurotransmitter in the brain, and is the basis for the most common form of long-term learning. The glutamate transporter will remove glutamate from the extracellular space, so different amounts of glutamate transporter will change the concentration. This means that cells will be generally more or less excitable and will have different levels of plasticity.
There are clearly a couple of problems with this study which can basically be labeled statistics. Do the bees learn better because they have returned to nursing? Or do they return to nursing because they are the better bees? This is selection bias. Also, if the bees are learning better, is it because of this change in proteins? Or were those differences in proteins there before they returned, and something totally different has changed?
What the paper may provide evidence for, though, is the social brain hypothesis. This hypothesis suggests that the reasons humans got smarter is because we lived in social groups, and the fittest individual was the one that was smartest at dealing with the social group. Perhaps the bees that return need to be the smartest because they have to return and deal with a social environment, a possibly more intellectually demanding environment. These bees have more to keep track of, a variety of other bees to placate. Not only does your job affect you, but so does your social environment.
Well, it’s something to think about at least.
Baker et al (2012). Age-related learning deficits can be reversible in honeybees Apis mellifera
Experimental Gerontology DOI: 10.1016/j.exger.2012.05.011