Before the seed. I. Guesswork
Note: I am unsure if I am not forcing people to guess the password. If you find this style okay, the next post will be built similarly.
As we have already seen, it’s a different matter to do anything significant to support a free-living gametophyte than one contained within the sporophyte body (the way seed-bearers do). It is certainly more difficult, but is it impossible?
To start with, let us see exactly what groups of seedless plants, minus mosses, we still have today. Here is a (pruned and decorated) tree of evolution of land plants from Pryer et al.1
The earliest, lowest (‘most basal’) branch is lycopods, who contributed a great lot to the forests of the Carboniferous, but today are quite rare and much smaller.
After lycopods branched off, evolution introduced true leaves—fleshy outgrows of sprouts with many veins in them.
Then, ancestors of ferns in the broadest sense and ancestors of seed plants in the broadest sense parted ways and began diversifying. If you haven’t worked with phylogenies, the picture makes it seem, at first glance, that all groups of ferns just kind of sorted things out more-or-less simultaneously, but it is far from truth. There are some pictures below, to give you a sense of what they look like and try to guess who is older and who is younger—your very first priors for these relationships. Pryer et. al.’s article provides estimates for when these groups did separate.
Don’t Google just yet. Let’s have some fun guessing what properties these plants might have, based on some hints I’ll give you and whatever you remember from other sources.
So.
In general, a life cycle goes like this: sporophyte (diploid, as in two chromosome sets) produces spores (haploid, since they underwent meiosis) that are released (singly or in fours or, in some cases, not released at all but kept where they were formed, in their sporangia). Spores germinate into (haploid) gametophytes that have archegonia (female reproductive organs making eggs) and/or antheridia (male ones, making sperm). Sperm swims to egg and fertilizes it, so that the resulting zygote again has two sets of chromosomes and the embryo develops into a sporophyte. It matures and sheds spores. All done.
What qualifiers can you imagine to make the cycle less general?
Seriously, take five minutes to tweak it. Maybe you can think up some broad restrictions posed by environment. Or a shortcut to success (be radical). Or a stability-oriented strategy. Or the relative advantages of being mobile or sessile (challenge what you are used to think about the issue here). Or being the pioneer of your species in a new locality. Or struggling to keep up with constant disruption of your habitat or even your body. Or not having the resources to produce spores regularly. Or not having to do it at all to maintain your existence for centuries or more. Or being a ruthless user of others (for a given resource). Or putting protective layers around your kids and yourself, lack of seed coat notwithstanding. Or being able to grow only on alkaline substrates. Or irregular meiosis, so that the spores have just as many chromosomes as the parent sporophyte.
Okay? Now look at the adult plants and seek out those who might stand up to what you have thought up. Comment on what fits your ideas and what you think is not presented at all. The first comment is a poll of your estimates:)
Pictures and data from Wiki, unless otherwise specified.
Lycopods.
Lycopodium obscurum (a clubmoss). It has a branching subterranean rhizome. In its roots it has symbiosis with a fungus (mycorrhiza). Its gametophytes are disk-shaped, about 1,5 cm in diameter. First year shoots [of young sporophytes] are unbranched and rarely penetrate soil surface.
What is your probability that
* gametophytes development takes less than a year;
given that,
* it is due to mycorrhiza that young sporophytes can support themselves for another season ununderground;
given that,
* if all shoots are destroyed two years in a row, the population can not recover?
Isoetes lacustris (a quillwort). It does not have traditional rootsa, but instead some of its leaves are modified to act like roots. As Čtvrtlíková et. al. have found2, quillwort germination may also be constrained during the growth season by its relatively high minimum temperature (no less than 12 °C) threshold for macrospore germination.
What is your probability that
* it grows in alpine climate;
given that,
* it is a species of rubbly slopes, adapted to breaking off leaves;
given that,
* the leaves are capable of rooting and establishing new plants;
given that,
* these new plants can shed macrospores that same year, if the weather is mild enough?
Polypodiophyta (leptosporangiate ferns).
Asplenium ceterach. This fern is well known as a resurrection plant due to its ability to withstand desiccation and subsequently recover on rewetting. Can be found growing up to 2700 metres above the sea level.
What is your probability that
* it can also grow on buildings;
given that,
* it is rather common within its range;
given that,
* it is difficult to study its historical spread, because outbreeding and multiple colonizations even out inter-populational differences?
Salvinia natans has two nickel-sized leaves lying flat against the surface of the water, and a third submerged leaf which functions as a root. Flotation is made possible by pouches of air within the leaves. Cuticular papillae on the leaves’ surface keep water from interfering with the leaves’ functioning, and serve to protect them from decay. Spore cases form at the plant’s base for reproduction.
What is your probability that
* it can have many generations during a season;
given that,
* competition between sporophytes of different generations peaks in late summer;
given that,
* older sporophytes depleting the habitat of nutrients restrict the growth of younger sporophytes through negative feedback loop?
Now, what plant was easiest for you to formulate an hypothesis about? The poll is in the first comment.
a—whatever that’s supposed to mean. There are lots of other plants without ‘traditional roots’.
1. American Journal of Botany 91(10): 1582–1598. 2004. Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. K. Pryer, E. Schuettpelz, P. G. Wolf, H. Schneider, A. R. Smith, R. Cranfill.
2. Preslia 86: 279–292, 2014. The effect of temperature on the phenology of germination of Isoëtes lacustris. M. Čtvrlíková, P. Znachor, J. Vrba.
The easiest plant to formulate an hypothesis about was: [pollid:843]
(should we spoiler?)
General:
Expect things long-lived that make ooodles of spores since they have such low chances.
Possibly expect things that are flaky and can recover from near-catastrophic damage so they can skip the whole sporing process altogether—like moss and lichen—but less so than those since this has more of an interior.
Expect roots not to be the highest priority when starting a new plant from a spore since they don’t have a seed with its startup food, and roots don’t directly yield energy, while it’s possible to get water from the air.
If roots aren’t a high priority, expect a skin that can control water flow thoroughly, at least when young
If roots aren’t a high priority, expect it to be fairly tough—can’t recover from lots of surface damage until it’s older.
Or it could avoid the root issue by living on/under water.
1 - Clubmoss − 35%. If it can make spores that fast it could beat the clearing rate; also, the fungus will need time to get paid for the support work it did. If they have kids really quick, the fungus could be getting a bit of a raw deal. But I dunno.
2 - Quillwort − 50%. On the one hand, Alpine tends to be cooler , and also this means of reproduction would tend to send it downhill rather than up, but you said it lives on rubbly slopes, and being on a hill would let anything that breaks off get far enough not to be in the way. And it could advance up in sporing, and the ability to spore the same year would let it live in the summer and spore through the winter. Also, just because it benefits from being on a hill doesn’t mean it needs to be on a mountain.
3 - Asplenium − 75%. You practically threw this one at us with the hints. Still, Building exteriors are fairly inhospitable, so I’m not sure… Mortar cracks could harbor it though. Also, that picture almost looks like it’s on a building.
4 - Salvinia − 60%. If it has until late summer for peak competition, that’s plenty of time. The first few generations won’t saturate the place… or will they? I guess it depends on the starting population and the degree of room to grow. If you’re racing to cover a lake, you want to go early rather than go well. Also, more likely to mature quickly since it has ample water access. So, if given that it STILL takes until late summer for peak competition, that raises the chances that you get a lot of generations in.
Did you multiply your probabilities, or did you estimate only the last claims? That was an interesting and plausible analysis. What alternative hypotheses did you have in mind? (Me? Throw anything? Nonono, wasn’t me...:)
It was so fuzzy—and more importantly, non-independent—I just gave a gut feeling at the end. This gut feeling basically amounted to, “supposing it turns out to be X/not-X, how stupid do I feel?” and taking the balance of those feelings. Basically, minimize regret since being right or wrong either way has the same impact..
Thank you. It is often how I feel IRL, when I need to, for example, compare two species. Maybe there’s a way to formulate it clearer, and maybe subject matter/inferential gaps will always make it fuzzy—dunno, I am mostly trying to unlearn how it was taught to us in uni.
Oh, by the way, I should clarify that the really interesting thing here is not ‘are the answers right?‘, but ‘in what ways the answered questions are different from the asked?’. It took me months to think of seriously reading the post from a totally-not-botanical POV, which is a failure of rationality if there is one, and which is a reason why I am now even more horrified by traditional testing practices.
For me, those two brief Latin words which signify the name of the plant mean the world. I might not know the properties of the species, the genus, the family—heck, there are entire orders which I have never had cause to look up. But for all that, I have an idea of how narrow a category a species is. It means that I will automatically give more precise answers to such questions—wrong, perhaps, but at least more ‘compact’.
A non-biologist will read the same words and completely dismiss the Latin name (which is one reason why I think Feynman’s attitude to biological nomenclature is bad for people who want to understand sufficiently meta problems). He will see overlapping sets and try to guess the more likely intersections from scratch, or worse, since we live in a sea of seed plants and are more used to their combinations of traits.
So my (improved) model of the answered questions is ‘if this thing, unrelated to any other thing, has a habit of doing X, how likely is that once upon a time Y up and happened to it?’ or some such.
Luckily, I can (and do) review the literature to look up the frequency of XY among pteridophytes in general (but not seed plants, because that would take a Singularity) and then correct or not the position taken by (the only volunteer) Luke_A_Somers. Hopefully we’ll see which parts of the species’ descriptions were given more weight in the analysis; I am fascinated by the possibility of actually finding the ‘weakest link’ in the chain.
Just saying it here in case I don’t get to finish the job.
Biology is neat like that, it has to make sense. I think the largest difference between math and the rest of non-humanities we learned in high school was that math doesn’t (have to) make intuitive sense; you solve an equation, it’s like you chop off a Hydra’s head; they can just write another one almost like the first one, but with some other power of x or something, and this new equation has to be solved from the very start. There is no ‘maybe I am a bit wrong here, but if I narrow down or widen this definition in such-and-such way, my answer will be right’, just right or wrong.
I did like pieces of it, like mass point geometry which almost seems ‘humane’ in its ‘here is how we reduce this thing to another thing’ approach. Perhaps other people like me would be fond of it, too.
Something in this post makes Firefox hang on me for several seconds when loading it.
I had some problems with inserting pictures. Maybe I did it wrong (copy past)?.. I know very little about formatting.