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From biological clocks to biological calendars

Here's an interesting unsolved problem in science: how can cellular biochemistry count how many years have passed?  Examples of biological clocks have been well-studied; not so for biological calendars.

Several species of cicada in the Eastern United States emerge to breed in huge numbers once every 17 years (others every 13, both prime numbers).  This has been thought to give them an advantage against predators, whose feeding capacity is overwhelmed in those rare intervals with no harmonics.  Other theories work from the idea that unstable paleoclimate conditions may have forced expensive breeding into a conservative temporal niche.

Juvenile cicadas suck sap from tree roots year upon year prior to emergence as adults.  To effectively emerge in the same year, a very reliable biological calendar is needed to count to 17 (with errors less than 1 in 100,000; see Hayes, American Scientist, 2004).  Recent evidence shows that biological cues from the tree sap are involved...trapping such insects among trees in greenhouses with two artificial winters per year results in cicadas emerging twice as quickly.

Effective counters need a 'forcing function', in this case provided by the tree and the chemistry of its sap.  However, they also need a base number system of some sort.  Those few cicadas that misstep in their counting tend to emerge with differences of one year, or four, from the canon (some at 9 years, for example).  This suggests a counting mechanism that combines base 4 with base 1.  A 13-year or a 17-year cicada would count by fours, then add one, under this scheme.

There are species of bamboo that also count years, flowering en masse every 120 years in one spectacular a display as the cicadas, but far more rare a sight.

How might this work, in terms of the regulation of proteins and genes?

The author's affiliation with The MITRE Corporation is provided for identification purposes only, and is not intended to convey or imply MITRE's concurrence with, or support for, the positions, opinions or viewpoints expressed by the author.

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