little independent agents
October 19, 2012 10:06 AM   Subscribe

Besides gametes, are there any other animal cells or cell groups that live and function outside of the originating animal?

There's probably something obvious that I'm missing, but I can't think of any. Not counting pathological examples like HeLa cells or tasmanian devil facial tumors.

If not animals, maybe there are examples in other multicellular organisms?
posted by moonmilk to Science & Nature (16 answers total) 1 user marked this as a favorite
Some sea cucumbers expel their intestines as a defense mechanism? The word "live" here makes this tricky, as if it's living, it's a different organism
posted by MangyCarface at 10:14 AM on October 19, 2012

For clarification - would biological offspring qualify, and if not, why not? (I can confirm from first hand experience that my daughter indeed originated from my body but is a very independent agent.)
posted by The Toad at 10:28 AM on October 19, 2012

Response by poster: Yeah, I was thinking other than reproductive cells. Gametes live for a while even without fertilization, so I think they still count as parts of the original organisms before they become a new one, and I'm wondering if there's anything else like that.

Do jellyfish stinger cells die when they sting, or do they live on for a while to keep producing and injecting more nasty torture? Do any creatures produce stinging cells that can float free and sting what they bump into?
posted by moonmilk at 10:32 AM on October 19, 2012

This seems tough to answer on definitional grounds: if you mean that the tissue should "live" as in "independently continue to carry out the totality of processes necessary for ongoing biological function"-- well, cutting off a piece of you that goes on to become a fully-functional organism is just asexual reproduction, isn't it? Plenty of that going on. And conversely, for it not to be a case of reproduction, the detached tissue would have to not be a fully-functioning organism-- i.e., missing some major processes necessary for life-- which means that it's pretty much moribund in any case. The distinction between a human head that blinks for a second or so after decapitation, and a human gamete that swims for a couple of days, is really just time, isn't it?

On a more helpful note: the tails of some lizards thrash for a while after being shed to distract pursuing predators, I believe. Does that count?
posted by Bardolph at 10:54 AM on October 19, 2012

Do jellyfish stinger cells die when they sting?

Nematocysts are basically itty bitty torpedo launchers. The cell shoots out a barb which is tipped with poison. The body of the cell remains where it began.

There are sea slugs that undergo "kleptocnidae". What that means is that they eat critters which have nematocysts, and rather than digesting those cells, they incorporate the nematocysts into their own skins to use them as self defense. So the original organism which had the nematocyst is gone (possibly dead by being completely eaten) but the nematocysts go on, incorporated into the predator.
posted by Chocolate Pickle at 11:06 AM on October 19, 2012 [1 favorite]

There are at least two "transmissible" tumors that I know of: transmissible venereal tumors of dogs and Tasmanian devil facial tumors. These are cancers that grow in/on another animal but have a different chromosome number and genetic profile from that animal. They can be physically transmitted from one animal to another (via a single cell) and grow in and eventually kill the organism, as opposed to regular cancer cells that arise from mutations in cells of our own bodies. Not sure if that counts as being "alive", but it's a cell that makes a mighty fine living being passed along.
posted by SinAesthetic at 11:15 AM on October 19, 2012 [2 favorites]

  • bee stingers, for while.
  • the specific strains of pathogenic organisms in a komodo dragon's mouth.

posted by the Real Dan at 11:53 AM on October 19, 2012

The komodo dragon bacteria don't meet the definition because:
1. Being prokaryotes, they can't be considered animals.
2. They don't share the same DNA as the komodo dragon, so they aren't really a part of the animal.
posted by TungstenChef at 12:39 PM on October 19, 2012

Breastmilk comes to mind. I believe it has white blood cells living in it. I don't know how long they stay alive once the milk is expressed, though.
posted by fancyoats at 12:39 PM on October 19, 2012

Response by poster: Bee stingers and thrashing lizard tails seem like pretty good examples. The fact that they are still alive for a little while (or at least continue to move and metabolize) is part of their function, unlike the sea cucumber intestines, which might as well be dead tissue like porcupine quills.

Breast milk is an interesting example! That reminds me of the continued presence of fetal cells in the mother's body.
posted by moonmilk at 12:43 PM on October 19, 2012

Might as well include organ and tissue transplants. They're artificially moved to another body, but (with suppression of the host immune system) live and operate for potentially many years before giving out.
posted by WasabiFlux at 3:06 PM on October 19, 2012

Starfish? Chop 'em up, you get more starfish. (This is only possible if the pieces each include part of the central disc, but that piece can be as small as 1 cm.)
posted by Specklet at 5:05 PM on October 19, 2012 [1 favorite]

I'm pretty sure that breast milk contains antibodies, but doesn't contain white blood cells. (And even if they were there, they'd be digested by the baby.)

Antibodies are just proteins; they don't really count as "alive".
posted by Chocolate Pickle at 5:42 PM on October 19, 2012

maybe there are examples in other multicellular organisms?

In ferns and other spore-dispersed vascular plants, the products of meiosis are not gametes but spores. The spores, if they land somewhere appropriate, germinate to form a free-living, photosynthestic, multicellular gametophyte. The gametophyte, as its name suggests, is where gametes are produced and fertilization occurs.

More on the fern life cycle here.

A new fern genus named after Lady Gaga for some reason here.
posted by vortex genie 2 at 8:24 PM on October 23, 2012 [1 favorite]

posted by pwb503 at 3:16 PM on April 12, 2013

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