Genetic bottlenecks (was: menstrual cycles)

Cameron Laird claird at sugar.NeoSoft.COM
Mon Feb 7 16:02:39 EST 1994

In article <2j1vfh$srh at hydra.unm.edu>,  <wtucker at unm.edu> wrote:
>It used to be widely believed that menstrual synchronization occured
>among women living in close quarters.  The original and widely cited
>work was done on women living in college dorms.  These studies and
>the effect have since proven to be unreproducible, and their 
>methodology is suspect.  Wenda Trevathen at New Mexico State University
>more detail.  When I was last up on this, no solid study was able
>to demonstrate synchronization, which is unfortunate because there
>were some interesting hypotheses kicking around to explain it.
Perhaps this is a good opportunity to draw attention to

	Caro, T. M., and M. Karen Laurenson
	1994	"Ecological and Genetic Factors in
		Conservation:  A Cautionary Tale",
		Science, volume 263, pages 485-486
		(28 January 1994),

where one reads

	The effects of inbreeding and loss of genetic
	diversity on the persistence of populations in
	the real world are, however, increasingly
	questionable.  . . .  One key example used in
	such arguments has been the cheetah because it
	is depauperate in genetic variation and has
	poor survival prospects in the wild.

	... [A] considerable secondary conservation
	and evolutionary literature, as well as the
	popular press, has uncritically assumed that
	lack of genetic variation is the cause of the
	cheetah's plight ...  Now, in light of new
	evidence ..., we re-examine the potential
	consequences of genetic homozygosity ...

	. . .  Predation on young cubs is therefore a
	strong candidate for explaining why cheetahs
	have low population densities ...

	These finds suggest that genetics may have
	been overemphasized in relation to the plight
	of the cheetahs.  . . .

	Genetic considerations ... may only be rele-
	vant ... in limited circumstances because
	they impact populations on a slower time
	scale than environmental or demographic
	problems.  . . .  Species that have undergone
	a demographic bottleneck such as the California
	sea otter or Great Indian rhinoceros do not
	necessarily show reduced genetic variation,
	and in those that do, the number of deleteri-
	ous recessives will depend on how fast the
	bottleneck occurred because they will have
	been purged not fixed if decline was slow.

Like menstrual synchronization, genetic bottlenecking is an
interesting theory, for which empirical justification simply
doesn't match intellectual attraction and popular reception.

The "... Cautionary Tale", incidentally, is a near-perfect
review of the facts, from the little I know.  The prose is
concise but lucid, the references accurate and apposite,
and the organization well matched to the format the pages
of *Science* offer.  The authors know cheetahs as well as
anyone in the world.  The largest flaw of which I'm aware
is that the last sentence cited above deserves a couple
more commas ("... purged, not fixed, ...").

I've narrowed follow-ups.

Cameron Laird
claird at Neosoft.com (claird%Neosoft.com at uunet.uu.net)	+1 713 267 7966
claird at litwin.com (claird%litwin.com at uunet.uu.net)  	+1 713 996 8546

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