Flies in Heat Part 1: Hot vs Cold

One of the themes of my research interests is understanding how organisms sense and adaptively respond to their environment.  While I am mainly interested in marine larvae, because their responses can have effects on dispersal and thus population connectivity and dynamics, these are not model organisms where the bulk of the progress is occurring.  So it is useful to keep up with some of the fascinating research that is being done on animals like flies, plants (see previous post) and worms (sorry Palin).

Two recent articles uncover some of the secrets of how flies sense temperature.  I'll comment on one article in this post and the second article in Part 2.

Zuker and colleages show that flies have separate neurons in their antennae to sense hot or cold.  The hot neurons and cold neurons project onto distinct but neighboring regions in the fly 'brain' to process this information.  So while hot and cold sensation are related, both use TRP channel receptors and project onto the same part of the brain, they have dedicated machinery (neurons) and processing areas.


While this work on the adult flies is fascinating and provides new mechanistic insight into the neural processing of temperature, it also leaves room for thought on how changes in ambient temperature (e.g. climate change) affect thermosensation.  Before learning anything on the subject, I would have guessed that temperature was sensed as a continuous variable - one set of one neuron type that sensed all temperatures (from hot to cold).  With a division of the work between hot neurons and cold neurons, I can't help but to wonder how the two temperature regimes are divided.  One organism's hot could be another's cold.  Ambient or optimal temperature should lie, I would hope, between the two temperature regimes.

What happens when ambient temperature shifts?  How is ambient temperature sensed? (Part 2 may have some clues to this second question.) Logic would then assume that there are then three types of neurons for temperature sensation - Hot, Cold, and Ambient.  Hot and Cold may be detected like pain stimuli (TRP channels are also involved in pain sensation), whereas Ambient may be more similar to my naive idea of a detecting a continuous gradient.  This would mean that now THREE sensory pathways must be selected upon to adapt to new environmental temperature regimes (climate change).  A tall order indeed.

Gallio, M., T.A. Ofstad, L.J. Macpherson, J.W. Wang, and C.S. Zuker. (2011) The Coding of Temperature in the Drosophila Brain. Cell. 144(4): 614-624.DOI 10.1016/j.cell.2011.01.028