June 30, 2013
to be posted on nobabies.net

John Cooley
75 N. Eagleville Road
Unit 3043
Storrs, CT 06269-3040

Dear Dr. Cooley:
I enjoyed the article about you in NATURE (Richard Monastersky Long-lived Insects Raise Prime Riddle NATURE vol. 497 no. 7451 May 30, 2013 page 545).  I see that you are interested in speciation and mating system evolution.  The article mentioned just how dense cicadas are.  I was amazed. 

My own interest is in the mechanism for inbreeding depression and outbreeding depression.  My position is that the size of a mating pool has to be restricted or speciation effects will ultimately wipe the population out.
I put this to the test with fruit flies.  I attach the paper.  Sure enough a big population fluctuated in a fashion that suggests that there is a short term – presumably epigenetic – mechanism that keeps a population from getting to big or else eliminates it if it has exceeded a safe level.  In mammals or at least in humans this amounts to something like a hundred matings, give or take a factor of maybe three. 

My fruit flies seemed to equilibrate at about 20,000.  So when I saw that the population of cicadas is up to 350 per square meter my initial thought was, “Oh, no.  That must mean a gene pool on average in the millions if the bugs are flying around seeking mates over a range of only a thousand meters.  Something is terribly wrong here.”  And indeed something may be wrong.  I really hope so because reasoning from available data humans are taking the long walk.  On the other hand if they are that dense they really don’t have to travel far to find a mate. 

Assuming that the mechanism is fundamental and varies little from species to species, even if the numbers and mechanism seem quite different between mammals and insects, one might guess that the average distance traveled must be close to seven meters.  In other words the cicadas emerge, fly up into the trees and hardly budge thereafter. 

I am always looking for data and had the fantasy of waiting seventeen years and gong to where the bugs were coming up, collecting all within a square meter, painting their undersides (no need to draw predators) and then seeing how close to their starting point they were when they ultimately fell to earth.  It would make a good high school science project.  Of course such a study may already have been done; you would know and I don’t. 

If not, it works out as a nice clean study, taking only a few weeks and there would not even be the nuisance of getting a grant.  But two things come to mind.  One is that there are many broods of cicada so it shouldn’t be too long a wait before the study could be done.  The other is that if you are pursuing them anyway the added effort would be small.

What do you think? 


M. Linton Herbert MD 

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