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[Drosophila] overseeding

Laurence Mueller via dros%40net.bio.net (by ldmuelle from uci.edu)
Thu Nov 15 15:24:45 EST 2012

It is actually impossible to diagnose your particular problem with the
information you have supplied. Female fecundity, and the resulting larval
viability will be a function of (i) the age of the females, (ii) the size of
the females (which depends on the larval density they were raised at), (iii)
the nutritional status of the females (e.g. were they well fed prior to
laying eggs, where well fed means given excess live yeast), (iv) were they
kept in a vials or bottles for several days prior to egg laying (the
presence of many larvae in the female's environment will cause them to
reduce egg laying and once they are given fresh food there will typically be
an explosion of egg laying), (v) the volume and quality of the food provided
for the larvae, (vi) the number of females laying eggs, and (vii) how long
you let the females lay eggs (if you have lots of eggs in a culture there is
no point to leaving adults in longer than one day since any eggs laid on
days 2, 3 etc will be buried and killed by the feeding larvae that hatch
from the first days egg laying). 

Finally it matters what your ultimate goal is. Do you want the largest
number of flies possible, even if they are small, or do you want many, very
large and therefore fecund flies. What's a worse outcome for you, occasional
cultures that have very few flies but others that have many flies or having
many cultures all with a moderate number of flies? 

It should be relatively easy to control the output of your cultures by
standardizing the conditions I mentioned above, and then varying them
systematically to find a set of conditions that works best for your goals.

Laurence Mueller
Professor and Chair
Department of Ecology & Evolutionary Biology
University of California, Irvine 92697
Phone: (949) 824-4744
FAX: (949) 824-2181
Web site: http://darwin.bio.uci.edu/~mueller

-----Original Message-----
From: dros-bounces from oat.bio.indiana.edu
[mailto:dros-bounces from oat.bio.indiana.edu] On Behalf Of Mark Thorson
Sent: Wednesday, November 14, 2012 4:55 PM
To: bionet-drosophila from magpie.bio.indiana.edu
Subject: [Drosophila] overseeding

I've noticed some of my cultures have a syndrome I think is caused by
seeding with too many adults.
The symptoms are many larvae, few pupae, and few adults; unusually flat
surface to the culture medium aside from sort of a pebble grain texture; and
most of all, when light reflects off the surface of the culture medium I can
see the whole thing is alive with motion.  It's that last one which makes me
suspect these cultures are suffering from larval crowding.  Does that sound
right, and if so, is overseeding the cause?

For the past few days I've been careful to limit the number of adults I use
to about 20-25 per culture.  I don't know what the optimal number is for my
culture system, but from experiments I did several months ago I know there
is no benefit from using more than 30.  I have probably been using closer to
50, and I think the improvement in my methods after adding calcium
propionate has brought out this new failure mode.  It'll be a week or two
before I know whether reducing the number of adults used to start a culture
eliminates the problem, but even then I might not be sure because it is a
sporadic problem -- usually only a few cultures are affected, though I did
have one batch in which all the cultures were affected.

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