As we mentioned just the other day, studying animal behavior is tough as “animals do whatever they darned please“. Thus, making sure that everything is controlled for in an experimental setup is of paramount importance. Furthermore, for the studies to be replicable in other labs, it is always a good idea for experimental setups to be standardized. Even that is often not enough. I do not have access to Science but you may all recall a paper from several years ago in which two labs tried to simultaneously perform exactly the same experiment in mice, using all the standard equipment, exactly the same protocols, the same strain bought from the same supplier on the same date, the same mouse-feed, perhaps even the same colors of technicians’ uniforms and yet, they got some very different data!
The circadian behavior is, fortunately, not chaotic, but quite predictable, robust and easily replicable between labs in a number of standard model organisms. Part of the success of the Drosophila research program in chronobiology comes from the fact that for decades all the labs used exactly the same experimental apparatus, this one, produced by Trikinetics (Waltham, Massachusetts) and Carolina Biologicals (Burlington, North Carolina):
This is a series of glass tubes, each containing a single insect. An infrared beam crosses the middle of each tube and each time the fly breaks the beam, by walking or flying up and down the tube, the computer registers one “pen deflection”. All of those are subsequently put together into a form of an actograph, which is the standard format for the visual presentation of chronobiological data, which can be further statistically analyzed.
The early fruitfly work was done mainly in Drosophila pseudoobscura. Most of the subsequent work on fruitfly genetics used D.melanogaster instead. Recently, some researchers started using the same setup to do comparative studies of other Drosophila species. Many fruitfly clock labs have hundreds, even thousands, of such setups, each contained inside a “black box” which is essentially an environmental chamber in which the temperature and pressure are kept constant, noise is kept low and constant (“white noise”), and the lights are carefully controlled – exact timing of lights-on and lights-off as well as the light intensity and spectrum.
In such a setup, with a square-wave profile of light (abrupt on and off switches), every decent D.melanogaster in the world shows this kind of activity profile:
The activity is bimodal: there is a morning peak (thought to be associated with foraging in the wild) and an evening peak (thought to be associated with courtship and mating in the wild).
The importance of standardization is difficult to overemphasize – without it we would not be able to detect many of the subtler mutants, and all the data would be considered less trustworthy. Yet, there is something about standardization that is a negative – it is highly artificial. By controlling absolutely everything and making the setup as simple as possible, it becomes very un-representative of the natural environment of the animal. Thus, the measured behavior is also likely to be quite un-natural.
Unlike in the lab, the fruitflies out in nature do not live alone – they congregate with other members of the species. Unlike in a ‘black box’, the temperature fluctuates during the day and night in the real world. Also unlike the lab, the intensity and spectrum of light change gradually during the duration of the day while the nights are not pitch-black: there are stars and the Moon providing some low-level illumination as well. Thus, after decades of standardized work, it is ripe time to start investigating how the recorded behaviors match up with the reality of natural behavior in fruitflies.
Three recent papers address these questions by modifying the experimental conditions in one way or another, introducing additional environmental cues that are usually missing in the standard apparatus (and if you want to know what they found, follow me under the fold):
Continue reading →
Like this:
Like Loading...
A Blog Around The Clock 