SMDVMX: It sounds like an individual planarium cannot keep replacing telomeres; the telomere reset only happens upon reproduction - either by natural fission or by cutting. So the question seems not so much whether the individual planarium is immortal, but whether or not the fission-offspring are the same as the progenitor worm. I wish we could ask the worm if there is continuity of its sense of self!
Gasland: You could test this by training the worms and seeing if they remember the training. That experiment was done in 1955 and appeared to indicate that the memories of the first worm are transferred to the fission offspring. I don't know what happens if you divide the worm.
SMDVMX: From Wikipedia on the 1955 experiment. "In 1955, Robert Thompson and James V. McConnell conditioned planarian flatworms by pairing a bright light with an electric shock. After repeating this several times they took away the electric shock, and only exposed them to the bright light. The flatworms would react to the bright light as if they had been shocked. Thompson and McConnell found that if they cut the worm in two, and allowed both worms to regenerate each half would develop the light-shock reaction. In 1962, McConnell repeated the experiment, but instead of cutting the trained flatworms in two he ground them into small pieces and fed them to other flatworms. He reported that the flatworms learned to associate the bright light with a shock much faster than flatworms who had not been fed trained worms. "This experiment intended to show that memory could be transferred chemically. The experiment was repeated with mice, fish, and rats, but it always failed to produce the same results. The perceived explanation was that rather than memory being transferred to the other animals, it was the hormones in the ingested ground animals that changed the behavior. McConnell believed that this was evidence of a chemical basis for memory, which he identified as memory RNA. McConnell's results are now attributed to observer bias."
OK, chopped up and eaten may be in doubt, but what about the memory survival in natural-fission episodes?
SMDVMX: It sounds like an individual planarium cannot keep replacing telomeres; the telomere reset only happens upon reproduction - either by natural fission or by cutting. So the question seems not so much whether the individual planarium is immortal, but whether or not the fission-offspring are the same as the progenitor worm. I wish we could ask the worm if there is continuity of its sense of self!
ReplyDeleteGasland:
You could test this by training the worms and seeing if they remember the training. That experiment was done in 1955 and appeared to indicate that the memories of the first worm are transferred to the fission offspring. I don't know what happens if you divide the worm.
SMDVMX: From Wikipedia on the 1955 experiment.
ReplyDelete"In 1955, Robert Thompson and James V. McConnell conditioned planarian flatworms by pairing a bright light with an electric shock. After repeating this several times they took away the electric shock, and only exposed them to the bright light. The flatworms would react to the bright light as if they had been shocked. Thompson and McConnell found that if they cut the worm in two, and allowed both worms to regenerate each half would develop the light-shock reaction. In 1962, McConnell repeated the experiment, but instead of cutting the trained flatworms in two he ground them into small pieces and fed them to other flatworms. He reported that the flatworms learned to associate the bright light with a shock much faster than flatworms who had not been fed trained worms.
"This experiment intended to show that memory could be transferred chemically. The experiment was repeated with mice, fish, and rats, but it always failed to produce the same results. The perceived explanation was that rather than memory being transferred to the other animals, it was the hormones in the ingested ground animals that changed the behavior. McConnell believed that this was evidence of a chemical basis for memory, which he identified as memory RNA. McConnell's results are now attributed to observer bias."
OK, chopped up and eaten may be in doubt, but what about the memory survival in natural-fission episodes?