THE INFLUENCE OF THE SLOWING OF EARTHS ROTATION - A HYPOTHESIS TO EXPLAIN CELL-DIVISION SYNCHRONY UNDER DIFFERENT DAY DURATION IN EARLIER AND LATER EVOLVED UNICELLULAR ALGAE

Every year the Earth's rotation period is reduced, mainly due to the t idal drag of the moon. The length of day increases continuously by abo ut 1 h every 200 million years. The period of rotation around the Sun remains constant; hence, the length of the year remains constant, so y ears acquire progressively fewer days. Many unicellular algae show rhy thmicity in their cell division cycle. If primitive algae evolved unde r a shorter day duration, then it is possible that the early-evolved a lgae had to synchronize their cell division cycle to shorter lengths o f day than did later-evolved algae. We tested this hypothesis by growi ng Cyanobacteria, Dinophyceae, Prasinophyceae, Bacillariophyceae and C onjugatophyceae (evolutionary appearance probably in this order) at 8: 8 h light-dark cycles (LD), 10:10 LD, and 12:12 LD, at 20 or 27 degree s C. Cyanobacteria synchronized their cell division cycles optimally a t 8:8 h LD, Dinophyceae and Prasinophyceae at 10:10 h LD, and Conjugat ophyceae and Bacillariophyceae at 12:12 h LD. The synchrony of cell di vision was scarcely affected by temperature. Results suggested that th e early evolved unicellular autotrophic organisms such as the Cyanobac teria synchronized their cell division cycle under a shorter day durat ion than later-evolved unicellular algae, and these traits may have be en conserved by quiescent genes up to the present day.