The daily and seasonal rhythms of life are controlled by biological clocks. The circadian clock tells us when to sleep and wake up, and the photoperiodic clock tells many creatures how to behave in response to seasonal changes associated with changing day length. But no one knew whether components of the daily circadian system functioned in the insect's longer-term photoperiodic clock (p. 867).

Sakiko Shiga and Hideharu Numata from Osaka City University, Japan, decided to test the roles of circadian neurones in the photoperiodic clock by removing neurons that regulate the blow flies' circadian rhythms, and monitoring the blow flies' ability to become dormant in response to shorter days associated with the onset of winter.

The team found that flies lacking the circadian clock's small lateral ventral neurons were unable to distinguish between long and short days, with 48% of the insects going into diapause when the days were long (and they shouldn't have), while only 55% of the flies went into diapause when the days were short and all of them should have hunkered down.

So neurones involved in regulating daily rhythms also seem to be involved in regulating seasonal behaviours and the photoperiodic clock shares some of the circadian clock's neural elements.

Shiga, S. and Numata, H. (
). Roles of PER immunoreactive neurons in circadian rhythms and photoperiodism in the blow fly, Protophormia terraenovae.
J. Exp. Biol.