I got thinking about something earlier and I was wondering if any books ever touched on it. How exactly are a Trill's internal organs set up? I'm assuming they probably have all or most of the same organs as other humanoids, but they also have to have room for the symbiont. We've seen a few joined Trill, but most of them have a flat stomach, without any kind of real bulge where the symbiont is. So are the organs in different places, or different sizes to leave room for the symbiont? Or does it just kind of squeeze in there around all of the organs? I would think if everything was the same as humans, and we can assume other humanoids, the symbiont would be noticeable from the outside, even under clothing. And what about if a joined woman gets pregnant, does the baby develop in the same place as other humanoids? Would the pregnancy have any kind of effect on the symbiont?
We don't really know anything about how a Trill's body works or how it's set up. All we do know is, Trills can have symbionts. This is never explained in detail.
We also know that a human can host a Trill symbiont. For a short time, under close medical supervision. And we also know that Trills come in spotted and brow-ridged subspecies. According to Memory Beta, they are marsupials (but that doesn't explain why males would have pouches).
Trill have something - I don't know the proper term - but I guess it is an abdominal pouch. Never heard the term Marsupials regarding Trill, though. Like kanguroos I would think. https://memory-beta.fandom.com/wiki/Trill
Does the pouch really make them marsupials? It serves an entirely different purpose than the ones on kangaroos.
I hope that @Christopher comes up with a logical and scientifically plausible explanation for that.....
In a technical sense, because the word "marsupial" literally just means "having a pouch." But marsupials as a taxonomic order? No, because that would require the pouch to contain the mammaries and be a receptacle in which offspring complete their development. Symbionts ain't offspring, and Trill females' mammaries are clearly not in their bellies. The graphic from Federation: The First 150 Years shows the symbiont nestled between the liver and the stomach, with tendrils connecting to the spinal column. (That seems a logical place for it, since it could draw nourishment from the stomach and use the liver to clean its blood.) That means the "pouch," such as it is, would be more just a sort of "access port" to the innards. Although that raises questions about how the symbiotic relationship began. Did the host humanoids already have pouches for some purpose, allowing the symbionts to co-opt them for their own use? Or did the pouches evolve to facilitate the symbiosis after it became a thing? And in that case, how did the symbionts get into the hosts originally? On second thought, I probably don't want an answer to that one.
Thanks, @Christopher, that's exactly the kind of thing I was looking for. I guess if they're just squeezed in with the other organs, then a pregnancy probably wouldn't have much of an effect on it.
Dax's experiences in Unjoined offer a few clues. Some of the earliest memories from the Annuated include: * a sub-sapient dog-like animal being near death next to a lake, until a symbiont wriggles out of the water, into the dog's pouch, and voluntarily joins itself to the dog, after which the dog recovers and trots away quite happily * cave-Trill ritualising the process, manually inserting a symbiont into one of their own This suggests that perhaps the pouch is a standard feature of many land-based life forms on the Trill planet. The symbionts also appear to have started the whole thing, perhaps deliberately to acquire the mobility and experiences they wouldn't otherwise have. Perhaps they found the lower life forms first, and while they were in there they noticed the higher life forms like Trill humanoids, and manoeuvred some way into joining with them instead for the better advantage. Or perhaps the symbionts started this when there were only lower life forms around, and as humanoids evolved from those lower life forms, the process of joining with symbionts was just part and parcel of the whole thing. It benefits both sides after all – the symbionts get to leave the water and experience more things, and the humanoids get the advantage of experience and the healing, stabilising effect that carrying a symbiont apparently has. Unjoined also tries to explain the difference in appearance between the Dax and Odan symbionts. When Dax goes deep into the pools of Mak'ala, she learns what happens to symbionts after they stop joining to humanoids – they just keep growing, eventually becoming massive whale-sized creatures many thousands of years old. She also sees that as they get older, they grow little stubby appendages which they use for scraping plankton off the cave walls for food. Meanwhile in "First Steps" from The Lives of Dax, we learn that Odan was already on its eighth host (Darzen) when Dax was only on its first (Lela). So the conclusion is clear – Odan as seen in TNG "The Host" looks different to Dax as seen throughout DS9 simply because it is older. Presumably this is also why we saw Odan's abdomen bulging in a way we never saw Jadzia's. This also in turn implies that, the older the symbiont gets, the more uncomfortable it becomes for a humanoid to host it. This might be one of the criteria the Symbiosis Commission uses to match host with symbiont – the former's sheer physical ability to accommodate the latter. Maybe certain body types are just more malleable in shifting their internal organs around to make the symbiont fit. But sooner or later it's just not going to be possible anymore, and that's when the symbiont goes back to the pools. Hiziki Gard says at one point that he has had more hosts than just about any other symbiont you have ever heard of, more than even he himself can remember. This means that the Gard symbiont must be pretty damn big by now, and its hosts just accept the discomfort as the pay-off for getting a more experienced joining partner, and because of the importance of Gard's unique mission of watching out for bad joinings. But surely it can't keep joining much longer. As for pregnancy in joined Trill female hosts, I guess it must happen (Dax alone claims to have given birth five times). The commission probably can't legally forbid joined females from reproducing, that would be against Federation law, but I imagine it must try its best to discourage as many as it can, for the symbiont's safety. Since only a small percentage of Trill humanoids actually get a symbiont, to do so wouldn't have such an effect as to actually damage population numbers, plus one might perceive having a child and having a symbiont as equivalent means of leaving behind a legacy, so maybe they don't feel the need to do both. But for the ones who do, it's gotta be damn uncomfortable, putting a worrying amount of pressure on both the foetus and the symbiont. .
I completely missed the dog having a pouch, and imagined the first symbiont clinging to the back of its neck, riding it around like a tiny jockey (or a giant horse). It probably isn't that hard to accommodate a fetus and a symbiont in the same abdomen. Humans can have multiple births, and an entire second or third fetus is much bigger than any implantable symbiont would ever be. The arrangement of the internal systems are pretty flexible, I'd imagine they'd be even more accommodating in a naturally-pouched creature.
Unless we’re looking at different parts of the text, I think you’ve conflated the contents of these memories a little bit. In the former, a symbiont reflects on “riding” four-legged animals and two-legged ”Walkers,” but I don’t see anything about saving a four-legged animal from death (or about the four-legged animals definitely having pouches). The symbiont uses its psychic powers to draw both animals and Walkers to the pools so it can “ride” them and experience life beyond the pools. The “riding” is explicitly transitory rather than a long-term joining. The latter memory is the one that shows symbiosis as a healing measure; a cave-Trill healer inserts a symbiont into a woman’s pouch (which is described as allowing for post-natal incubation of newborns by both males and females, though it’s also used to insert “cures and medicaments”) in a desperate effort to relieve a fever. The healer has seen the symbionts “attach” themselves to other animals, but it’s not clear whether that’s via a pouch or something else.
Yeah, I realized there would be plenty of room for a symbiont and fetus, I was actually wondering more about nutrition and things like that. Wasn't there also a reference in another book to the Klingon Augment virus infected a Trill colony? Which we can assume was meant to explain why Odan's hosts had ridges instead of spots like the Trills we saw on DS9.
"Divergence" showed Archer briefly growing ridges while the treatment was taking effect. I always preferred to think the "Host"-type hosts were another hominin species, the Trill equivalent of Homo erectus or something, explaining why they seemed less intelligent and didn't contribute any of their own personality to the symbiosis.
Same, difference, I'd think. I understand the human brain takes up a disproportionate amount of calories, so having, essentially, a second one would be a bit of an energy draw, but it still couldn't be as much as a whole reproduced being. Maybe joined Trill are just big eaters. Actually, I'm not any kind of an expert on neurobiology (Car Talk's Andy Letter goes here), but it occurs to me that I don't really know what parts of the human brain consume the most energy. Anecdotally, it'd be concentration, problem-solving, reading, complex high-level social situations like roundtable discussions and business meetings, that sort of thing, but a Trill symbiont is probably nearly entirely long-term memory, physically. Most of the work would be being done by the humanoid, so it actually might not take up as much energy, even proportionally, as the humanoid's brain, which would still be doing most, if not all, of the thinking, never mind all the autonomic and motor stuff.
The symbiont contributes more than just memory, surely, or else first hosts would gain nothing of value. Unfortunately, the show focused so much on what the past hosts contributed to the joining that the question of what the symbiont itself contributed got overlooked.
I feel like the Lela story in The Lives of Dax says they don't contribute much. The first host gains the honor of having their memories last forever.
But that goes for every host. And by definition, symbiosis gives benefits to both members. If only one member benefits, it's parasitism. There had to be an evolutionary advantage for the host species in order for the symbiosis to evolve. Granted, it could be the greater wisdom afforded to later hosts who retain the memories of their forebears, with greater experience to draw on improving their survival skills. But that's kind of indirect, since it takes a generation or more for the benefits to become evident. I think the assumption in "The Host" was that the symbiont was the brains and the host was the brawn, given that the pre-joined host seemed kind of dull-witted. So the hosts gained intelligence while the symbionts gained mobility, senses, and protection. But that was abandoned when DS9 portrayed unjoined Trill as being just ordinary humanoids. I checked "First Steps" (the Lela story), and I didn't notice the passage you mention (though I was skimming). It did say that the symbiont contributed something to the joining, since it gave Lela a curiosity about the stars that she hadn't felt before.
You know, symbionts may be smaller than they look during the joining. There are all kinds of real marine lifeforms on Earth that can pump water into their bodies to swell up to many times their original size. Then, once they expel the water, they smoosh down all small again. Maybe symbionts naturally inflate before being removed from the pouch to facilitate movement and to protect themselves from the air. Then they become much more amorphous once inside the host body.