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Plant Sciences, Zoology & Evolution / Re: How do Portugese-man-o-war jellyfish reproduce?

« on: 15/04/2012 17:46:19 »

At the risk of being over simplistic, indulge me an analogy.

Image a person, while building a house, realizes that he will need some nourishment soon. So he decides to invite three people to help him. Well, of course, he is in the middle of the forest, so there isn't anyone around to invite. But his parents taught him an ancient, secret method of cloning himself. So he clones three baby replicas of himself. He then locks them in his house because he would suffer if they weren't there to help him. He raises the first as a hunter, the second as a cook, and the third as a lover. In not much time at all, the hunter is harpooning critters in the yard and reeling them back into the kitchen. The cook is preparing and serving great meals with the catch, and the lover is watching pornos, cuz there ain't no wimmen.

Yet the house owner still isn't getting quite enough nourishment, and since he is so busy taking care of his house, he teaches his helpers how to each clone themselves. By the time the helper's clones have matured and start to help the household, the newest clones are instructed to repeat the cycle. Groups of the newest three clones keep cloning an ever newer group of three. Eventually, the house owner gets pooped, the house is completely full, and he gets tired of the free-loading porno pervs. So, when there are enough houses that have sprung up in the neighborhood, he kicks the lovers out of his house, and tells them not to come back.

The moral of the story? Cloning can help you build your house, but if you want your kids to have a chance to build a better house, ya gotta lay some pipe.

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Plant Sciences, Zoology & Evolution / Re: How do Portugese-man-o-war jellyfish reproduce?

« on: 14/04/2012 22:32:03 »

There is a lot of confusion here, because physalias are very unique, and they are frequently mis-labeled as a colony of individuals. At best, they could be called a colony of zooids. These particular zooids, however, are not individuals in the robust sense of the word. The term colony here is often likened to a coral colony, but that connotes that it is a collection of asexually reproduced clones that can survive on its own if severed from the colony either artificially, or through natural, asexual, reproductive fission. As opposed to corals, physalias grow attached non-viable 'buds' that mature into specialized non-viable zooids.

Scientists have yet to understand the mechanism of zooid differentiation in the physalias, but I imagine that it is likely similar to enzymatic control of vertebrate embryonic differentiation and maturation. Chemical  and spatial influences, controlled by genetic orchestration, may well lead to the specialization of zooids. But that is not to say that physalia ontogeny isn't even more unique, complex, or even more spectacular than the processes that create specialized organs of the vertebrates.

But to answer your actual question as best I can, here is what we do know. Mature physalia are either male or female (not hermaphrodites), and sexually reproduce by releasing gametes into the water, triggered usually by a large gathering of individuals. The fertilized egg becomes a protozooid, or founding polyp, that both becomes the float and initiates the budding process to create the new zooids, each genetically identical to the founder. Physalias never go through a sessile stage and strombilate a juvenile medusa, like the sychozoans, so they must grow, differentiate, and mature entirely while free-swimming.

Unfortunately, at this stage, we know very little about polyp formation in physalias. However, we do know much more about other siphonophore species. Their founding polyp forms a float, while budding a new polyp, and also grows a long, hollow stem that all succeeding polyps stay attached to. New polyps always bud from two separate locations on this stem, the first site generates swimming bells, and the second site produces an alternating succession of groups of dactylzooids, gastrozooids, and gonozooids.

The physalias grow neither a stem nor swimming bells, but we can cautiously hypothesize from their colonial hydroid cousins that many of the same mechanisms apply to physalia zooid differentiation. That is, Kevin, that your gastrozooids are budded from older polyps with the exact same genetic makeup as the 'parent' zooid, and that they are budded in subsequent groups of the three different types of zooids. The only real (meaning viable) reproduction eventually comes when the organism reaches maturity, and sexual reproduction forms a new, genetically varied "individual".