Neurospora Circadian Rhythms in Space: a Reexamination of the Endogenous-Exogenous Question

Abstract

To test the functioning of circadian rhythms removed from periodicities of the earth's 24-hour rotation, the conidiation rhythm of the fungus Neurospora crassa was monitored in constant darkness during spaceflight. The free-running period of the rhythm was the same in space as on the earth, but there was a marked reduction in the clarity of the rhythm, and apparent arrhythmicity in some tubes. At the current stage of analysis of our results there is insufficient evidence to determine whether the effect seen in space was related to removal from 24-hour periodicities and whether the circadian timekeeping mechanism, or merely its expression, was affected.

Comparative studies of tidal rhythms. VIII. A translocation experiment involving Circalunidian rhythms

“…Space-age versions of "translocation" experiments-not to a new time zone, but through all of them every 90 minutes-have now been carried out. Two circadian rhythms tested in Challenger space-shuttle flights did not alter their periods relative to earth-bound controls (Sulzman et al 1984;Mergenhagen and Mergenhagen, 1987).…”

Two sides of a coin: ecological and chronobiological perspectives of timing in the wild

“…In addition to the best-studied diel time scale ('circadian' clocks, with a period length of about: ('circa') 1 day ('dian')), similar rhythms were shown on circannual, circatidal and circalunar scales [4][5][6]. Nonetheless, only in the latter part of the twentieth century, when experiments including a space mission proved that no hidden earthly cues are needed to drive biological rhythms, was endogenous rhythm-generation fully accepted [7][8][9].…”

Plant Circadian Rhythms

“…Pfeffer himself extensively studied leaf movements and provided many examples of the free-running periods of leaf movement rhythms differing from 24 h (Pfeffer, 1915). That the rhythms were circadian and not exactly 24 h was an extremely important point because it was the best evidence, until experiments on the fungus Neurospora crassa were conducted in space (Sulzman et al, 1984), that these rhythms were truly endogenous and not driven by some subtle and undetected geophysical cue associated with the rotation of the earth on its axis.…”