In article <18.104.22.16870131164141.0068a624 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).
University of Leeds, Yorkshire
England, LS2 9JT UK
a.j.davis at uk.ac.leeds