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Re: Daphnia generations
I've noticed the same environmental changes you mention. If I put (indoor) Daphnia magna in a clay-lined pond, they get smaller and paler. Those I put in a 2000 gallon liner pond get huge and apple green. However after several season of reseeding the clay pond with Giant Russian Daphnia magna, they now retain the red color and most of the size.
It probably is response to environment when you see changes within days of getting a new daphnia or moina variety. I have experimented with inside cultures by adding a little peat moss. The more peat moss, the smaller the daphnia get. Too much, and they are gone.
I have Giant Russian Daphnia magna that are descended from a bag I received in the eighties from Jim Langhammer's stock. I noticed color variation in these, and so when I started a new culture I would pick out the reddest ones and largest ones. Several years after keeping this variety, I found a screen that would just catch a tiny percent of the daphnia. The rest were too small. Now when I use that same size screen, Most of the daphnia are large enough to get caught in it. I have also noticed a marked increase in size in Moina I bought as "Russian Daphnia". I wanted them small. I didn't do any selecting, so I suspect this is environmental.
The other type of change I have noticed is in productivity and temperature tolerance. My son took some of the Giant Russian and raised it on the hat shelf in his bedroom closet where it was in the nineties. They are not supposed to be able to do that. I seeded some of these into my top row of cultures, and that row, which was warmer than the bottom row, started doing much better than before. I've also noticed an increase in productivity of a variety after I've had it a while. Perhaps it is adaptation to conditions, or perhaps it is the aquarist learning about the variety's needs.
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