Beneficial (?) fungus in D. pseudoobscura collection

[A.J. Davis]

In article <3.0.32.19970131164141.0068a624 at ucspop.byu.edu>,
   JLFarmer at bioag.byu.edu ("James L. Farmer") wrote:

>I collected D. pseudoobscura in the Abajo Mountains of Utah 
>last summer.  This fall, I noticed that some bottles 
>contained a fungus and others did not.  Flies in bottles 
>with fungus are uniformly healthy and vigorous,
>reproduce well, and live long.  Many of the bottles without 
>fungus were quite unhealthy.  The medium is Carolina blue 
>without added yeast.

It often seems a surprise to those working mainly or 
entirely in the lab that brewers' yeast S. cervisiae is not 
the most common, or even likely, food for Drosophila species 
in the wild.  This yeast species is absent even 
from many fermenting substrates in the field used by D. 
melanogaster and such substrates carry many more species of 
micro-organisms than just S.c.

For obscura group species, which use many non-fermenting 
substrates, substrates without microorganisms or those 
with mainly S.c. are very poor food sources indeed.  Your 
pseudoobscura are probably very happy to have the mould !  A 
similar phenomenon has been documented for D. immigrans 
(Atkinson 1983 i think).


Andrew

Andrew Davis
University of Leeds, Yorkshire
England, LS2 9JT   UK

a.j.davis at uk.ac.leeds