Facetotecta

[schmiggle]

I would like to pick everyone's brains a bit, if y'all don't mind.

Facetotecta is a clade of crustaceans related to barnacles of which only the larva has ever been observed in the wild (it basically looks like a giant head plate with large eyes and legs). In addition, in a laboratory, when molting hormone was added to a solution with the larvae, they molted into these wormy looking animals with a reduced gut and eyes and no limbs or exoskeleton. For these reasons the group is widely thought to be parasitic; however, no one knows where or in what.

If I'm lucky, I might be able to do research on these guys next year. I would like to find the adults and their hosts, and I had three ideas of a method (one of which credit for goes to Douglass Morse). Here they are:

• Compare frequency of these to frequency of other animals in different areas, and where frequency is correlated, grind up those animals and look for a DNA signature of facetotecta.
• Try to make a nutrient broth of sorts for the larvae and see if I can get them to survive and molt in it. The broth would be made essentially from the juices of common animals in the wild range of facetotecta from as many different major groups (bivalves, gastropods, polychaetes, etc.) as possible
• Immunosupress common animals from the wild range of facetotecta and see if the larvae will infect any of them.

The hope in the latter two cases is to get a broad sense of what the first host is (it might be the only host, or facetotecta might have complex life cycles with multiple hosts). If it likes fish broth and infects fish, it's probably a fish parasite; the same goes for sea cucumbers, snails, and any other group of animals. In addition, it would be nice to see some molts past prematurely molted larval slug thing, so even raising these outside their proper hosts would be pretty cool.

Does anyone have any bright ideas for finding the adults and/or their hosts apart from the three I listed above? None of them are particularly elegant, and I would like something elegant even though I think it's impossible.

 

[Greasylake]

I think the broth idea and the immunosuppression ideas have some merit, especially if you could use them together. If you could figure out what the larvae survived on, then immunosuppress those organisms it would probably give you a better chance of finding the adults in their host.

Would it be possible to mark a large amount of the larvae, and release them into their native range to see if they appear on, or in, any organisms? I'm not sure what kind of marker you could use, but I'm just thinking.

 

[pannaking22]

Those things are freaking weird. Looked them up on Google images and my first thought was War of the Worlds. That's so cool that you're looking into potentially working on them though. It really makes me happy to see someone doing natural history/biology work on organisms in this day and age since that's not the big money-maker.

Something to keep in mind is parasitic conditions for them too. Are they external or internal (I'm guessing internal)? Could they like fish gills or sea cucumber anuses? I know that's impossible to try in a lab setting, but it could also give you something to look for/at when catching organisms for the broth, and to try to replicate those conditions as closely as possible. I assume you're going to do some DNA testing on things before throwing them in the broth? Hopefully the adults stick it out with the original host, but I wouldn't be terribly surprised if they were in something else or were freeliving. That or the females don't wander while the males do.

It doesn't help that these are tiny, so it's not like they're easily monitored or found inside of organisms. I'm guessing the adults wouldn't be more than a few millimeters long.

@The Snark will probably see this thread anyway, but I'm still interested to hear his thoughts on it.

 

[The Snark]

It's topics like this I revel in. Sit back, feet up, utterly dispassionate and objective, leaving it to the applied science crowd to see what they can pull out of the hat. Maybe just a field mouse instead of a rabbit, but now and then, as in the 25.5 GeV at CERN, the occasional elephant or wildebeest comes popping out.
And on that note, it's back to Handbrake and replacing 750 GB of lost videos and the apparent misogyny of Degas. Remember, I'm just a 'lab rat' observing the RNA in the raceway and babysitting a recalcitrant electron microscope. I leave the discoveries to better minds than mine, though I do occasionally take notes.

 

[schmiggle]

Would it be possible to mark a large amount of the larvae, and release them into their native range to see if they appear on, or in, any organisms?

Are they external or internal (I'm guessing internal)?

It's simplest to answer both these questions at once. The adults are widely thought to be internal parasites, which means that marking them in the wild would be impossible.

Could they like fish gills or sea cucumber anuses?

Anything's possible at this point. Given the reduced digestive tract and lack of limbs, my operating guess is that these inhabit the digestive tract of their hosts and absorb nutrients directly through their cuticles. But in that case, I would want to know how they stick (tapeworms and acanthocephala hook themselves into the intestinal wall, flukes attach themselves with suckers, etc., facetotecta seem to be so reduced that they lack any of that). Maybe they cause their host to form some sort of cyst, like a gall wasp? There is a copepod that does more or less that to sea pens. The trick here will, I think, be to read widely and leave weird ideas open.

I assume you're going to do some DNA testing on things before throwing them in the broth?

I wasn't going to, but that is a good idea and I will.

I wouldn't be that surprised if these turned out to have multiple hosts, and it also wouldn't surprise me if there were just one. My hope is that, if I can keep them alive long enough to reproduce, it will be clear if they reproduce sexually or asexually in a given host. Though of course, if these operate like Rhizocephala, we would see sedentary females and wandering cypridiform males (like pannaking suggested).

It doesn't help that these are tiny, so it's not like they're easily monitored or found inside of organisms. I'm guessing the adults wouldn't be more than a few millimeters long.

I haven't a clue how large the adults are, but if they were several feet long or something you would think they would have been found already, so I'm also guessing smallish. My plan was to drop a larva in a very small tank with a potential host, wait a while (24 hours?), and then filter the water for the parasite. If it isn't found then probably the next step is to grind up the potential host and look for parasite DNA using PCR. If it is found then that host can be used in the future to try to rear facetotecta inside. I'm figuring that the raising broth would probably be in a small petri dish (one of the mini ones used for C. elegans), which would make the animal easier to find.

 

[pannaking22]

Anything's possible at this point. Given the reduced digestive tract and lack of limbs, my operating guess is that these inhabit the digestive tract of their hosts and absorb nutrients directly through their cuticles. But in that case, I would want to know how they stick (tapeworms and acanthocephala hook themselves into the intestinal wall, flukes attach themselves with suckers, etc., facetotecta seem to be so reduced that they lack any of that). Maybe they cause their host to form some sort of cyst, like a gall wasp? There is a copepod that does more or less that to sea pens. The trick here will, I think, be to read widely and leave weird ideas open.

Yeah I wasn't really seeing any structures in the pictures that they could use for holding on. I almost wonder if they'd be like angler fish males and fuse themselves somewhere inside the body until they're ready to molt again. But of course anglers have mouths first before they dissolve themselves...hmmmm it's a mystery alright. I can definitely see the gall wasp method being used, but again, it has to hold on somehow to get that process started. That or maybe burrow in a bit. I'd guess that they'd try to set themselves up somewhere that's in an area without much movement so they don't get jostled around as they settle in.

I haven't a clue how large the adults are, but if they were several feet long or something you would think they would have been found already, so I'm also guessing smallish. My plan was to drop a larva in a very small tank with a potential host, wait a while (24 hours?), and then filter the water for the parasite. If it isn't found then probably the next step is to grind up the potential host and look for parasite DNA using PCR. If it is found then that host can be used in the future to try to rear facetotecta inside. I'm figuring that the raising broth would probably be in a small petri dish (one of the mini ones used for C. elegans), which would make the animal easier to find.

From the bits an pieces of info I was finding they were saying the immatures weren't even a millimeter long, though of course with no idea of how many times they molt it's a tossup on size. Who knows, they could end up being something decently sized that's already described, but no one knows about the immature life stage(s). I'd figure 24 hours would be enough time for them to parasitize something, but it may be good to have a second one set up for 48 at least earlier on until you have an idea of how long it takes them to parasitize.

Kind of an odd question, but do most sea animals (non-mammals) operate at about the same temperature? That'll be something to keep in mind with the broth too.

 

[schmiggle]

Yeah I wasn't really seeing any structures in the pictures that they could use for holding on. I almost wonder if they'd be like angler fish males and fuse themselves somewhere inside the body until they're ready to molt again. But of course anglers have mouths first before they dissolve themselves...hmmmm it's a mystery alright. I can definitely see the gall wasp method being used, but again, it has to hold on somehow to get that process started. That or maybe burrow in a bit. I'd guess that they'd try to set themselves up somewhere that's in an area without much movement so they don't get jostled around as they settle in.

I'm betting that, whatever these guys do, they hook in during the cyprid stage and, once they're settled, molt into the slug form. Maybe they dig directly into tissue and wait for it to scab over, who knows. I can think of many possibilities.

From the bits an pieces of info I was finding they were saying the immatures weren't even a millimeter long, though of course with no idea of how many times they molt it's a tossup on size. Who knows, they could end up being something decently sized that's already described, but no one knows about the immature life stage(s). I'd figure 24 hours would be enough time for them to parasitize something, but it may be good to have a second one set up for 48 at least earlier on until you have an idea of how long it takes them to parasitize.

The immatures are a few hundred micrometers long, but that's the size of the immatures of pretty much every barnacle, if I'm not mistaken. It helps to have small larvae to aid with dispersal.

I would probably leave them in the broth indefinitely, but 24 and 48 hours seem reasonable for DNA extraction. If you wait to long you run the risk of death as well, so I wouldn't want to wait much longer than that.

Kind of an odd question, but do most sea animals (non-mammals) operate at about the same temperature? That'll be something to keep in mind with the broth too.

I don't think so, but within an area they ought to, because ocean temperatures don't change as much as dirt or air temperatures. I would likely keep temperatures around the same as where these were collected. I'll also have to be careful about salt contents and osmotic potential (which will hopefully be mostly done by the animals I'm grinding into broth).

Another person I reached out to said he's been researching abundance at the surface vs in the water column, in shallow vs deep water, and day vs night (many plankton go to shallow water at night and descend to deeper water during the day--diel vertical migration--which complicates this whole thing). I'm sure that whatever habits are found in that research inform the temperature--for example, if these are usually found at depth then it's reasonable to think that they'll prefer somewhat cooler temperatures (whatever is found at depth).

 

[boina]

Wonderful thread! I'd never heard of these before!

Well, I like the DNA method best. I can see problems with the other two methods:

That nutrient broth you are planning to make might not bo so easy. These may need specific circumstances, like they are in the gut, or in the gills, or in the tissue... you get my gist. The right family/genus/species alone might not be enough. Still, maybe worth a shot.

That immunosuppressed method: That may actually give you a few false positives. These things may be able to live inside some immunosuppressed animals in the lab that they wouldn't be able to infect in the wild where animals tend to be immunocompetent. Still... might give you an idea what to look at more closely.

 

[schmiggle]

That nutrient broth you are planning to make might not bo so easy. These may need specific circumstances, like they are in the gut, or in the gills, or in the tissue... you get my gist. The right family/genus/species alone might not be enough. Still, maybe worth a shot.

Yeah, not thrilled with this idea, to be honest. However, I bet you don't need to use exactly the right species to keep these guys alive; instead, you make sure to kill the immune cells (maybe a freeze/thaw cycle?) and then it's something like having an immunosupressed animal--you don't need to be as specific. The main reason to do in vitro, IMO, is that you have closer control of the conditions and therefore a potentially better rate of success; it's not to find the actual host.

That immunosuppressed method: That may actually give you a few false positives. These things may be able to live inside some immunosuppressed animals in the lab that they wouldn't be able to infect in the wild where animals tend to be immunocompetent. Still... might give you an idea what to look at more closely.

I agree--I think false positives are more likely than not. However, my hope is to narrow down the potential range of hosts a bit. Right now Facetotecta might live in almost anything, and hopefully in a lab we could get it down to a broad clade. In addition, growing these to adulthood in a lab, or at least to a larger size, is not such a bad thing, even if it's not in the definitive host.

I think the only way this is going to work in the long run, aside from sheer luck, is some combination of these methods. If there's some lab evidence that we should be looking at, say, molluscs, then the analysis of what's common and what's not in these guys' range will prioritize mollusc clades. Otherwise, the DNA problem becomes kind of intractable, with so many different animals to look at. Someone pointed out to me that it's a low probability method. Of course, we might get lucky and have one obvious clade to look from looking at what's common, but given predatory and competitive ecological interactions, I kind of doubt it. But using a broth or an immunosupressed animal is absolutely not good enough evidence for the host in the wild. At the end of the day, looking at animals in habitat will be the only way to settle the issue.

I think the order of operations might look something like this:

1. Collect facetotecta in several different locations, along with counting other animals (plankton and others) in those locations
2. Analyze relative abundance of facetotecta and other groups; simultaneously, attempt to rear facetotecta in immunosupressed animals and maybe also a broth in laboratory
   
3. Based on relative abundances and laboratory work, sample potential hosts at facetotecta heavy sites based on lines of evidence from both field and laboratory work.

Thank you everyone for helping me with this. My ideas have changed as a result of your suggestions, I think for the better. If I find anything, you'll be the first to know after my two friends going into evolutionary biology and paleontology and my advisor lol.

 

[The Snark]

Suggestion. Use the broth to present environmental extremes. Die off - survival extrapolation. Adaptability - mutability will lag behind, at the least helping establish a control.

 

[BenLeeKing]

when you mentioned a larvae with no adults never found, the first thing that popped into my mind is neoteny, though after reading you mention the induced adult exhibiting very derived limbless from I instantly scrapped the idea... Still wanna bring it up here though, cause you'll never know!
Interesting subject by the way, would like to follow along to your progress~