Saturday 13 June 2020

'Bitrophy' II (that's animals with photosynthesis)

In the previous post on this subject, I discussed some basic aspects of the feasibility of an animal using photosynthesis as an auxiliary energy source. Mind you, I never said that it would work! It is too early to reach a conclusion yet, and if you expect this post to finally answer that, sorry, no, not yet...

This post will have a look at some other factors that would have influence the efficacy of ‘bitrophy’, and I plan to try to pull it all together in a third post on this subject. So how do you judge whether or not bitrophy is of value for an animal? I thought that the ‘leaf area’ needed to catch light in relation body size might be a suitable measure: a very large leaf would be expensive in terms of material and metabolic costs as well as mechanical unwieldiness.   

So here we go; let’s walk through some factors.

1. Photosynthesis is inefficient
The inefficiency of photosynthesis, as we know it in Earth plants, is well known and was discussed previously in this blog. To summarise: many wavelengths present in visible light are not used in photosynthesis at all and are thus wasted. Photosynthesis has an inbuilt maximum, meaning that above a certain point increasing the level of light will not lead to more carbohydrate production. Finally, the chemical reaction runs almost as easily backwards as it does forwards, and given the fact that there is much less CO2 (0.04%) in the air than O2 (20%), taking out CO2 and adding O2 was an uphill struggle to start with.        

2. Let there be light

How much light falls on a plant on a planet's surface? Well, obvious influences are how bright the star is, and how far away the planet is from that star. If the orbit is circular, the amount of light reaching the planet as a whole will constant during a year, but it will vary considerably if the orbit is highly elliptical. Then there is axial tilt: if the planet's axis is not perpendicular to the plane of that orbit, the planet will have seasons, and the amount of light will fluctuate during a year. The planet will rotate around its axis, and with day and night comes a halving of the amount of light on any point of the surface (except if there is 'tidal locking’: then one half will be perpetually lit and the other dark).
Finally, part of the surface will receive rays of light at a glancing angle, while others receive sunlight perpendicular to the ground, delivering much more energy. You can estimate that the average amount of light is only about one quarter of the maximum (I can expand with some fingures later). And that is at the top of the atmosphere. Below that, you have atmospheric scatter, clouds, and the shade of mountains, other plants, of being under water, etc., etc.

In the previous blog I used the local maximum amount of light to calculate how large a 'leaf' an animal would need to power its 'minimal metabolic rate' (MMR). Well, if you wish to account for the average amount of light, you should make that area four times as large! That means doubling the length of its side, if the leaf is square, or its radius, if it is circular. Of course, you can decide that such large leaves are unworkable, and you can limit the animal to the tropics. Or you can have it shut down and 'hibernate' through the night. 

3. Energy for an active lifestyle
The MMR only powers the energy needs of an animal ding nothing except being alive. More activity requires more energy, and Alexander's book mentions that the average energy need is about three times the MMR. So, if you wish to cater for that, you should increase the leaf area three times; that means increasing the radius by a factor 1.7.

4. More active animals

In the previous post, we learned that the MMR depends on body mass through an exponential function. The exponent was close to 0.75 for all animals, so that doesn’t matter. However, a multiplication factor differed greatly between animal types: mammals (and birds) need much more energy than some other animals.

Click to enlarge; copyright Gert van Dijk
The image above shows three schematic animals: a mammal, a -warm- lizard and a crustacean, all with a mass of 1 kg. I did not bother to refine the shapes, but they should be recognisable.

Click to enlarge; copyright Gert van Dijk

Here they are again, but now with leaves of the right size to cater for an MMR under maximum light. Remember that if you wish to take astronomical and activity problems into consideration, the radius of the leaf should be made 3.4 times as large (1.7 times 2). However, even with the not-adapted leaf, it is obvious that the mammal needs a ridiculously large impractical leaf. The crustacean's leaf looks more acceptable.  

5. Body size
MMR depends on the mass of an animal, and we have set leaf area to follow MMR. But mass is itself a function of size: increasing the size of an animal by a factor x will increase its mass by a factor of x to the third power. For instance, doubling the size will increase the mass eightfold. In reality things are more complicated, as you cannot simply increase all dimensions of an animal by the same amount and expect it to work. For instance, legs need to become thicker. This was explained in earlier posts, here, here and here. If you want more, here and here are posts on the same them devoted to the giants of  Game of Thrones.

Is anyone still there? If you are, we can work out how MMR responds to size as opposed to mass. First, mass is length to the power of three, and second, MMR depends on mass to the power of 0.75, so MMR increases with length to the power of 0.75 x 3 = 2.25.

Does this matter? Yes: say we double all aspects of an animal’s size. The radius of its leaf is doubled, and the area of the leaf becomes four times as large. Its mass increases by a factor 8, but its MMR only by a factor 4.76 (that’s two to the power of 2.25). That particular MMR would require an increase of the radius of the leaf of a factor 2.18 (that’s the square root of 4.75). But doubling the size yielded an increase of the radius of a factor 2.0, slightly too little. So, larger animals need extra large leaves, but the additional increase is not dramatically large. The influence of size on relative leaf area is not all that strong, but still, if you want your bitroph to have a relatively small leaf, the animal itself should be small.

Click to enlarge; copyright Gert van Dijk
The image above shows three sizes of mammal, warm lizard and crustacean, if 0.1 kg, 1 kg and 10 kg. You can see that the leaves are relatively larger for the big animals than their smaller cousins, but the differences between the three sizes are not impressive.            

Well, that concludes this post. It seems that the required 'leaf area' needs to be very large, and I doubt that having such a large structure would be worth it under most circumstances. But what about other circumstances? I will think it over and try to find solutions. No doubt, readers will have suggestions too.


Anonymous said...

At the risk of giving the obvious answer...avoid endothermy.


Luciano N. Ribeiro said...

Just throwing an idea, but, imagine an animal like a pterosaur, its wings double as leaves. Do you think it could work?

Keavan said...

Don't larger animals usually have proportionally lower metabolic needs? Does that offset the increase in proportional surface area needed, or no ?

Perhaps a bitroph could hibernate for months at a time, soaking up nutrients through its skin, before moving to a more nutrient rich patch of soil.

Keenir said...

that sounds like a variation on what the Triffids did, isn't it? They stay in one place, soaking up sunlight, until they move a short distance to more meaty foods.

-anthony docimo

humanoid gerbil said...

Those bitrophs that are just animals with a disc leaf tho lol. reminds me of the pokemon Lotad

Tropes said...

Bringing ballonts back from the dead

You made a possible evolutionary pathway for ballonts to evolve without knowing it, and a way to make it work. Like you've said, it's functionally the same as a bladder. For corals or seaweed wanting to spread their seeds, early ballonts don't need to be lighter then air, only lighter then water, giving their gametes a fast path passed predatory water column, either popping to maximize spread or even reusing the sack as a bladder on the way down, taking it's resistance to pressure differences the other way. This should give the organism thrtthe space to and even play with gas mixes and tissue, before making it's way onto land.
Which brings us to the gas.. remember when you took the example of a ballonts that doesn't have enough hydrogen to fill it's volume but maintains it's shape anyway? Well if it could do that, why have any gas at all? The only purpose of gas in a balloon is to maintain a higher volume relatively relatively to what the weight would maintain otherwise, allowing the air displacement, but if you could maintain that volume without it, the gas is just dead weight, the best gas is a vacuum or a near vacuum... If you can avoid getting crushed into a mashed potato. Perhaps it's not a flying sphere you are after, but a flying hexagon? What kind of material could hold that, I don't know... Nanotubes?

Eepyornis said...

This blog has talked about the plausibility of more "alien" types of legs, such as tentacle like legs or odd numbers of legs. But has it covered another factor most artists manipulate to add "alienness": eyes?

Usually, most sci-fi writers, when designing aliens, try to make them seem more odd by messing around with the eyes: their shape, number and location. So in many Hollywood and literature aliens, you get one big cyclops eye, lots of eyes, eyes on stalks or eyes on places other than the head.

The question is, are these feasible? Would eyes on say, the limbs or torso be of any benefit? Would a single cyclops eye be sensible? (it clearly has its disadvantages, as Polyphemus of Greek myth would know...) What about eyes that dont look like eyes at all, granting the creature vision while externally appearing "eyeless" to the human viewer?

Tropes said...

I also want to know this ∆ can there be an alien evolutionary force or circumstance that would delay cephalization andcand the concentration of senses? Perhaps it made sense for an evolutionary ancesor, or a result of how the body plant was segmented, and as Sigmund likes to say, evolution doesn't go back to the drawing board? Maybe this is how octopuses ended up with 9 brains... Maybe that would also happen to a creature that didn't have all it's eyes in one concentrated area?

gumpa lumpa said...

Is it possible for mammals to become complete r-trategists, forgo parental care entirely, and lose their mammary glands, instead giving birth to entirely independent offspring that recieve no further care from the mother? Or is nursing their young too ingrained in mammal behavior and physiology to lose?

Sigmund Nastrazzurro said...

Anthony: yes, that is certainly one solution, and probably an unavoidable one. In reverse; is the energy turnover in plants low because that is all that photosynthesis allows for?

Luciano N Ribeiro: Absolutely: if an animal needs to have large surface areas for whichever reason, it would certainly help to use those araeas for photosynthesis. A disadvantage could be if the photosynthetic capability would make the wings much heavier, of course.

Keavan: the relation with body size and metabolic need was dealt with in the post, but it remains fairly complex. Hibernation would definitely be a way to decrease mean energy expenditure.

Anthony: the Triffids! I read that a very long time ago. I think I remember them settling down every now and again.

humanoid gerbil: you are probably right, but pokemon came long after I had the age to become interested in them.

Tropes; your comment doesn't really tie i with the post in question, but I'll make an exception. Do I understand it correctly that you wish to use a ballont/swim bladder as an aid with underwater seed dispersal? Whether that is useful probably depends on whether you want to=the seed to float right to the water's surface, or whether you wish to make them float without sinking or rising. It seems that coral seeds and the like manage to have the same specific weight as seawater. so they float with ease, even without bladders. Animals with heavier bodies such as fish and nautiluses do need a bladder, but it is small compared to the body. A bladder that wil take an naiml to the surface can still be quite small but it might form a bridge to a ballont, if there would be a benefit in having a very large bladder before it is large enough to drift into the air.

I agree that a vacuum makes the lightest possible balloon, but how do you keep it in shape? Children's balloons keep their shape because of overpressure in the balloon. so the balloon skin needs no structural elements to keep that shape. A 'vacuum holder' would need to be strong enough to withstand one atmosphere of pressure. I do not know if nanotubes could form such a strong, light and airtight structure. If engineers manage to build such structures, we may yet see 'vacuum zeppelins' in the future. I do not know anything about the strength of such materials, however.

Eepyornis: a comment about something other than the post... Very short: eyes are likely to evolve at the front of an animal. but they can be elsewhere and work. One eye would also work; just no binocular depth vision (actually, there is probably monocular depth vision in mantis shrimps). Eys must admit light, and you can hide that a bit but not abolish it.

Tropes: not about the post... Usually people would say that a concentration of senses plus associated neural tissue at the front of the animal is likely. But I would replace at the front with 'where they do most good'. So where is that for an animal that floats in water without reaching the bottom or the surface? Everywhere? How about animals prone to attack from the rear? Would they evolve a secondary 'sense concentration' at their rear? On Furaha, that is the megarusp story.

gumpa lump: and another comment not related to the post... You realise that there is a whole forum for speculative evolution, don't you? (and this isn't it). Just look at your question from the perspective of an egg-laying reptile; is it conceivable to lose egg-laying as well as the advantage of being able to abandon the eggs after laying them? Yes, if the alternative works as well or better.

Tropes said...

About bitrophy, maybe you could use multiple layers like with leaves, or semi transparent cells that let most of the particles missing chromatophores to go through, or maybe dividing some of the chemical function going in a photosynthetic cells among other tissues or organs to let it specialize further in absorbing light. Maybe a lense - while decreasing total energy intake - can spread the workload internally among more cells. This would also have the affect of releasing oxygen internally, which might also be worth exploring. You could also go the other way around, concentrating light like some power stations which wouldn't decrease the surface area if it's on the animal, but perhaps it doesn't have to be, animals are known to shape their environment, it might shed reflecting scales from it's belly in a weird spiral as it gets ready for it's photosynthetic life stage or season, or maybe it's a photosynthetic queen with reflective worker ants, or a mammalian mother using it's solar surface to produce some sort of milk for her cubs. Or maybe it doesn't constantly have the same surface area, a nactorial animal going to sleep by unfolding it's solar wings like a Mars rover under the sun. And there is always the option of getting closer to the sun, if a low energy way to do that came about...
Maybe this could have been a way for animals to evolve more energetic lifestyles before the oxygen cycle got started, slow moving for us perhaps but they could have been the fastest cowboys of the west in the Ediacarian period, and maybe somewhere else a few of those manage to make it through.

Why that hasn't happened on earth... I don't know. It's my understanding carnivorous plants are relative newcomers, might be a little too soon to discount the prophecy of Audrey 2.

I love your blog and world btw, I've seen a couple of fantastic ones elsewhere, but the level of Dedication and thought you seem to put into every concept and detail is inspiring beyond belief. I am looking forward to see more of it. I am not sure if you'd rather people comment on years old posts or go off topic on newer posts, or maybe neither? I imagine a career in answer comments might be more successful on another planet.

Tropes said...

Thinking about that question overnight i was struck with a stupid idea that probably wouldn't work but... Maybe?
Balloon animal bones: literally a bone held together like a balloon animal, Allowing it to turn tensile strength into compressive strength.
So let's imagine this proto-ballonts, who's cells seem quite obsessed with making everything from spider silk, has a spiders bladder with a spherical network spider silk veins. Sometimes veins become clogged or don't develop properly, and the gas they were supposed to deliver to the bladder accumulates inside until the vein is so stiff it stretches the bladder. This evolves into a network of structural veins, acting as very thin bones arranged in a hexagonal grid around the bladder, taking in more of the gas that was once meant for the bladder itself, and over time allowing it to withstand increasing pressure differences.
While still using pressure to hold the volume, the gas only needs to fill part of the surface area, not the volume itself.

sabershark said...

That lobster with a leaf though. Just imagine this crustacean with a satellite dish on its back. i'd call it the single most hilarious image i've ever seen on this blog...

Sigmund Nastrazzurro said...

Tropes 1: thank you. Many creative ideas there. Usually I do not have the time to answer any question on speculative evolution, and I think the speculative evolution website is well-suited for such requests. That's why I try to limit the replies to questions dealing with the post in question. People sometimes ask questions on old posts, and I do not mind, but not many people will ever see the question or the reply.

Tropes 2: that's a clever idea, to use inflatable structures to form a sphere that can resist atmospheric compression because there is a vacuum inside. I started thinking about how strong such a sphere would need to be, and hoped that someone else would have already done the hard work.

sabershark: thank you. These animals always come out a bit funny-looking, even when I wasn't even consciously aiming for that...

It turns out that a vacuum balloon is not a novel idea. There is even a wikipedia page on the idea:
That page also contains the mathematics. Alas, the wikipedia writers conclude that it will only work in a Venusian atmoshere and that you need fancy materials, such as graphene. If you want more numbers, look here:

The Wikipedia page mentions that a composite structure may be needed for the wall of the balloon, and someone else came up with the idea of making a sort of hollows bricks that fit together in 3D the same way stones in an arch fit in 2D. Pressure from the outside would then squeeze the bricks together.
Here it is:

Actually, many people seem to have had the same idea:

retardedstygimoloch said...

do furahan hexapods reproduce by live birth or egg laying or some other unusual means

Sockmonkey said...

An insect built like a butterfly might be able to get away with biotrophy.
It has the surface area ratio needed and insect wings are naturally translucent.
(butterflies color theirs with tiny scales which could be dispensed with)
The luna moth doesn't actually eat as an adult, so resting and photosynthesizing during the day would extend it's adult lifespan significantly.

One area that I haven't seen touched on very much is waste processing.
As in having the symbiotic plant material take over the functions of the liver and/or kidneys.
Aside from not having to support as many organs, this also means a creature wouldn't have to excrete waste as often, which is an excellent way to conserve water.

There are places like the Atacama Desert that are so barren and dry that an animal using biotrophy to survive there would have virtually no natural predators or competition.
I can imagine a butterfly-like biotroph in a place like that spending months or years in a state of hibernation with all organs except the heart shut down as it builds up it's reserves for the next rain when it would go forth to mate and lay eggs. The heart has to be kept going at a minimum so nutrients can circulate without having to lose water.

Now if the oxygen produced by the plant matter is enough to sustain it in hibernation, then the insect can close off it's spiracles to avoid losing water through respiration and essentially become fully self-contained and solar powered during this time.

Imagine what looks like an odd tree siting in the middle of a dusty, barren land.
Only it's not a tree, but rock formation covered in hibernating, biotrophic butterflies.

Sigmund Nastrazzurro said...

retardedstygimoloch: wrondg post for that question, sorry...

Sockmonkey: it's small, does not have an overdrive metabolism, and has a large area that can be put to double use. So yes, that might serve well. I agree that the metabolism of photosynthesis should be brought in line with that of the organism as a whole, including water use (no evaporation need!) and CO2 delivery (lots!).

Anonymous said...

I feel like bitrophs are much more likely to evolve in a desert world with scarce resources. Bitrophy offers a small advantage at a cost when there are many resources available, but when there isn't the advantage is much larger. Bitrophy is probably pretty unlikely to evolve, and even if it appears early on there's a decent chance of it being lost if the cost is greater than the benefit. If a world has scarce resources then bitrophy is much more beneficial for organisms to develop and is much more likely to be kept.

Carnivorous plants have evolved mostly in places where the soil lacks important nutrients such as nitrogen. If resources were few and far between (and carnivory was often harder then just setting traps) then maybe some rolling seeds (like tumbleweeds) could change shape in response to aerial chemical cues to direct their rolling towards water and dead plants/animals, eventually moving without the help of the wind to a place to take root.

Vespa orientalis, one of the only animals I know of that seems to collect energy from sunlight (it uses pigments that generate electricity from light) seems to use it to reduce the cost of energy-intensive activities like digging.

In nature, strange adaptations often result from strange and/or extreme challenges. From what I've seen of Furaha's current ecosystem, it might not be the best place for large bitrophs to originate, although if bitrophy evolved and increased in efficiency while the climate was quite different, it'd probably become efficient enough to provide an advantage in a time less starved for resources. (perhaps myxomorphs were some of the first organisms on land? )

Sigmund Nastrazzurro said...

Anonymous: my sentiments also move in the direction where bitrophy would be a rare finding in the universe. But whether that is so depends on the cost/gain analysis you alluded to. It is obvious that photosynthesis provides little energy and costs an enormous leaf area. That must change for bitrophy to work.

HAL9891 said...

One very specific case where bitrophy would make sense would be extremely slowly rotating planet which is NOT tidally locked, so it has a day-night cycle which moves so slowly that bitrophs could walk/swim/fly all around the planet (maybe not around the equator, but higher latitudes) to be constantly in sunlight and avoid having to live through extremely long, cold and dark night.

3dmonium said...

What about hairlike leaves instead of flat ones? And assuming ideal chemistry for photosynthesis, can we determine the best efficiency for Amy molecular given a determined value of light inrensity?

3dmonium said...

I'm working in a project like that! Habitats would be determined by the time of day, rather than local climate!

Sigmund Nastrazzurro said...

Hal9891: near permanent light; that would double their energy intake, which would be a goof thing.

3dmonium: I do not think hairs would provide a better ratio of surface to mass than a planar object would. As for which molecule would be best for photosynthesis (if that is what you meant), I do not think anyone knows. There is quite a bit of interest on artificial photosynthesis, and the people in that file might have an idea. I get the feeling they are still largely in the dark about that though... See:

3dmonium: are you 'AirborneTerror'? I love those arthropod models!

3dmonium said...

I was thinking of how pines and trees in general maximize surface area by having lots of tiny flat or thin structures to essentially pack a large 2d área in a "smaller" 3d volume, also this:
Maybe a body covered in tiny leaves could have greater surface area and mobility than one with a flat parasol-like surface?

My design for a photosinthetic animal structure involves large feathery structures with an outer layer of light-absorbing molecule, with a silvery-looking layer beneath so light can be redirected and absorbed by adjacent hairs, but of course to work properly the light-absorbing molecule would need to be much more efficient than chlorophyl and I'm not sure how to make the math to figure it out.

And yeah, AirborneTerror is my DeviantArt account! Glad You like them!

Sigmund Nastrazzurro said...

3dmonium: hairs or needles indeed increase the surface area tremendously. Fir trees have needles and do very well, but as far as i know they have needled not because they provide the largest possible surface per unit of mass, but because they resist cold and dry conditions better.
Mind you, if I were to devise an organism with bitrophy, I would not provide it with just one large photosynthetic area, for the same reason I would not equip a plant with just one very large leaf: wind forces would damage the large leaf, but can be absorbed to a branching structure of small ones. The big leaves in the images in the bitroph posts were just there to show how large the area had to be. I'm sorry if that was misleading.

I like the reflected light solution. I do not think anyone can yet design molecules that would result in a much more efficient photosynthesis than biological evolution came up with. If I knew of one, I would run to the patent office, become filthy rich and hire people to paint and publish several Furaha books.

Sockmonkey said...

Didn't one of your posts a while back have a critter that used transparent spines as a sort of fiber-optic periscope so the sensitive meaty bits of the eye could be safe deep inside the creature's shell?
Why not do that with a plant?
The extruded spines would be solid bits of something metabolically cheap to grow, while the nutritious photosynthesizing bits browsers want to munch stay protected in the trunk.
This raises the question of how to move nutrients around if your "leaves" aren't letting water evaporate from them.
This could be facilitated just by temperature changes throughout the day, if the central trunk was just a hollow chamber filled with water where free-floating chloroplasts could cycle around as the warmer water rises to the top.
That would also make a good home for symbiotic aerobic bacteria.