Why are there no animals that get energy from sunlight?

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gbagcn2
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Why are there no animals that get energy from sunlight?

Postby gbagcn2 » Tue Jul 06, 2010 12:39 am UTC

Plants get there energy directly from the sun so why didn't animals evolve to get this ability? Getting energy this way seems more efficient than hunting to get food like most animals do.

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Re: Why are there no animals that get energy from sunlight?

Postby BlackSails » Tue Jul 06, 2010 12:47 am UTC

The energy you get is way less. Herbivores have to eat large amounts of plants to get the energy they need for movement.

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Re: Why are there no animals that get energy from sunlight?

Postby justaman » Tue Jul 06, 2010 12:54 am UTC

gbagcn2 wrote:Plants get there energy directly from the sun so why didn't animals evolve to get this ability? Getting energy this way seems more efficient than hunting to get food like most animals do.

But there are... see this article from Wired Science.

Most corals assiciate closely with photosynthetic algae, and would not survive without them, while not direct, it would only take a few evolutionary changes to see such symbioses become one organism.
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Re: Why are there no animals that get energy from sunlight?

Postby Sockmonkey » Tue Jul 06, 2010 2:22 am UTC

Going by the way she lounges in sunbeams my friend Catherine is apparently solar powered.

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Re: Why are there no animals that get energy from sunlight?

Postby frezik » Tue Jul 06, 2010 2:28 am UTC

We do in limited ways, like the reaction of your skin with UV rays to produce Vitamin D.
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Re: Why are there no animals that get energy from sunlight?

Postby qetzal » Tue Jul 06, 2010 2:49 am UTC

Check out this post over at Small Things Considered. Certain sea slugs incorporate functional chloroplasts from algae that they eat. Even more amazing, the slugs have managed to transfer a number of plastid genes into the slug nuclear genome, including genes that allow synthesis of chlorophyll a.

So I guess this is indeed an animal that has evolved the ability to get energy directly from the sun, albeit not quite in the way the OP meant. :D

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Re: Why are there no animals that get energy from sunlight?

Postby thoughtfully » Tue Jul 06, 2010 3:39 am UTC

frezik wrote:We do in limited ways, like the reaction of your skin with UV rays to produce Vitamin D.

A better example would be reptiles and other exotherms warming themselves to get their metabolisms going, but neither is a source of energy in the sense the OP intended.
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Re: Why are there no animals that get energy from sunlight?

Postby Mighty Jalapeno » Tue Jul 06, 2010 4:05 am UTC

AFAIK, the energy falling on the the animal's surface area, for nearly any animal of any appreciable multicellular size, even 24 hours a day, isn't enough energy to keep it alive using 'normal' metabolic processes.

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Re: Why are there no animals that get energy from sunlight?

Postby Sockmonkey » Tue Jul 06, 2010 8:45 am UTC

This is why solar is a pipe dream. We need nuclear powered animals!

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Re: Why are there no animals that get energy from sunlight?

Postby tastelikecoke » Tue Jul 06, 2010 9:55 am UTC

qetzal wrote:the slugs have managed to transfer a number of plastid genes into the slug nuclear genome, including genes that allow synthesis of chlorophyll a.

Stings me that the whole sentence sounds like something from Bioshock. plastids sound too close to plasmids.

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Re: Why are there no animals that get energy from sunlight?

Postby Mr_Rose » Tue Jul 06, 2010 10:10 am UTC

tastelikecoke wrote:
qetzal wrote:the slugs have managed to transfer a number of plastid genes into the slug nuclear genome, including genes that allow synthesis of chlorophyll a.

Stings me that the whole sentence sounds like something from Bioshock. plastids sound too close to plasmids.

You're aware that plasmids are a Real Thing too, right? Bacteria have them, mostly, though you can find them all over the place now that we've started mucking about with them.
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Re: Why are there no animals that get energy from sunlight?

Postby Winter Man » Tue Jul 06, 2010 2:06 pm UTC

They wouldn't have any use for limbs, a digestive system, eyes, all the other things that make them animals etc. They'd be plants.
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Re: Why are there no animals that get energy from sunlight?

Postby Neuman » Tue Jul 06, 2010 8:39 pm UTC

They would if they're using photosynthesis to compliment a normal diet instead of replacing one.
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Re: Why are there no animals that get energy from sunlight?

Postby bane2571 » Wed Jul 07, 2010 2:11 am UTC

Winter Man wrote:They wouldn't have any use for limbs, a digestive system, eyes, all the other things that make them animals etc. They'd be plants.


Damn, you got there first with the answer I had. If animals got energy from sunlight, then they'd be plants. Pretty much all of our bodily structures exist either so that we can get energy from non-sunlight sources or to hold in the parts that do.

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Re: Why are there no animals that get energy from sunlight?

Postby qetzal » Wed Jul 07, 2010 3:20 am UTC

So the sea slugs I linked to above are plants?

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Re: Why are there no animals that get energy from sunlight?

Postby tonykng » Thu Jul 08, 2010 8:51 pm UTC

qetzal wrote:So the sea slugs I linked to above are plants?


Biologists do not generally classify life according to physical traits anymore. They classify according to the evolutionary path, so no they are still animals.

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Re: Why are there no animals that get energy from sunlight?

Postby qetzal » Thu Jul 08, 2010 9:46 pm UTC

tonykng wrote:Biologists do not generally classify life according to physical traits anymore. They classify according to the evolutionary path, so no they are still animals.


Yes, I know. I am a biologist. I was just being a bit snide in responding to bane2571 and Winter Man. For which I apologize.

But you knew that, right?

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Re: Why are there no animals that get energy from sunlight?

Postby You, sir, name? » Thu Jul 08, 2010 10:07 pm UTC

Sockmonkey wrote:Going by the way she lounges in sunbeams my friend Catherine is apparently solar powered.


Well, it is, in a sense drawing power from the sunlight. By staying in a warm place, it needs to spend less energy on internal heating.
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Re: Why are there no animals that get energy from sunlight?

Postby Telchar » Thu Jul 08, 2010 10:20 pm UTC

The efficiency is the biggest factor. While relatively simple creatures like the slugs already mentioned can incorporate photosynthesis into it's energy cycle, your more comples organisms require much more energy to maintain homeostasis and gain some alternate benefits (increased control of internal temperature) from being herbi/omni/carnivores.
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Re: Why are there no animals that get energy from sunlight?

Postby Sockmonkey » Fri Jul 09, 2010 1:10 am UTC

You, sir, name? wrote:Well, it is, in a sense drawing power from the sunlight. By staying in a warm place, it needs to spend less energy on internal heating.

Yeah, I know. I was just screwing around.
If one really wanted to be nipicky about it you could say that all animals do this since none could survive if the earth wasn't heated by the sun or ocean vents.

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Re: Why are there no animals that get energy from sunlight?

Postby bane2571 » Fri Jul 09, 2010 1:21 am UTC

qetzal wrote:Yes, I know. I am a biologist. I was just being a bit snide in responding to bane2571 and Winter Man. For which I apologize.

But you knew that, right?


Nothing to apologise for, I admit I ignored that article completely. Just read it now and it is quite interesting. Though it would seem to me that this slug steals the genes of a plant to become plant-like and get it's energy for the rest of it's life. This is one of the reasons I don't like absolute statements, there is usually a counter case.

I am curious as to how biologists define "Animal" though, that slug definitely blurs the line for me.

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Re: Why are there no animals that get energy from sunlight?

Postby Omegaton » Fri Jul 09, 2010 4:07 am UTC

bane2571 wrote:I am curious as to how biologists define "Animal" though, that slug definitely blurs the line for me.

According to Wikipedia, animals are eukaryotes (vs. Bacteria), usually multicellular (vs. protists), and lack rigid cell walls (vs. plants/fungi). In any case, just because the sea slug photosynthesizes doesn't mean it's a plant.

In taxonomy, if lines are blurry, the line is redrawn to accommodate.

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Re: Why are there no animals that get energy from sunlight?

Postby thoughtfully » Fri Jul 09, 2010 4:27 am UTC

As has been stated before, the approach nowadays is genetic, now that the tech exists to study genomes in detail. Animals in this scheme are sponges and anything descended from them. Genetic material acquired from outside sources really doesn't count; the slugs are a glaring example, but pretty much all complex multicellular organisms have DNA from viruses and possibly other sources mixed into their genomes.

Horizontal transfer still occurs, it's just normally benign. Or is it? What would happen if all that "junk DNA" was subtracted from our genomes? I think this is a topic of current interest, but I'm not really up on genetics.

Fancy tech notwithstanding, you can still count on Mother Nature to throw a curve ball at the taxonomists!
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Re: Why are there no animals that get energy from sunlight?

Postby kc7cv9n3o30vov » Fri Jul 09, 2010 5:35 am UTC

To get back to OP's question:
Environmental stresses pushed animals to evolve the way they did. There was a niche for a creature to climb up a tree and eat it's leaves...
There is 'space' in a variety of senses for life to exist and flourish where photosynthetic life cannot. Most of the volume of the sea is denied to photosynthetic life. Same for caves, the earth's crust, other places.
Photosynthetic life is nearly always sedentary, and due to that fact, cannot move to adapt to its environment(e.g. coral reefs are very depth-sensitive, and cannot tolerate long-term changes in sea level or subsidence of the sea floor). Personally, I prefer being an animal.
You may say it's efficient for life to be low-level, sedentary, and photosynthetic, but effective life is really about growing, reproducing, and surviving(as a species).

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Re: Why are there no animals that get energy from sunlight?

Postby SpaceShipRat » Sat Jul 10, 2010 9:01 pm UTC

I think it's a matter of evolutionary pressure. There's not enough pressure for animals to evolve photosynthesis since they already can meet their energy requirements and the advantage they would gain is very little. If you genetically altered an animal to photosynthesise, it might have a very small advantage on it's peers, but I don't see an animal on this current earth evolving such a complex trait.

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Re: Why are there no animals that get energy from sunlight?

Postby You, sir, name? » Sun Jul 11, 2010 7:46 am UTC

Though, when you look at the human energy requirement (~100 W) compared to the solar constant (~1 KW/m^2), it does appear that even with reasonably inefficient energy absorption, it would certainly be both feasible and evolutionary beneficial to have that as a means of secondary energy intake. Especially if you're a species with an uneven access to food (say an ambush predator, big-cat type animal.)
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Re: Why are there no animals that get energy from sunlight?

Postby Sockmonkey » Sun Jul 11, 2010 9:54 am UTC

Unless it's night or winter.

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Re: Why are there no animals that get energy from sunlight?

Postby You, sir, name? » Sun Jul 11, 2010 10:04 am UTC

Sockmonkey wrote:Unless it's night or winter.


How do you figure? We generally don't eat at night either. Why would a supplemental energy intake need to be "on" 24/7?
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Re: Why are there no animals that get energy from sunlight?

Postby Sockmonkey » Sun Jul 11, 2010 10:11 am UTC

Oh, I missed the bit where you said secondary. My bad. I wonder how well the systems would mesh in a higher organism though. Might be complicated.

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Re: Why are there no animals that get energy from sunlight?

Postby SpaceShipRat » Sun Jul 11, 2010 12:51 pm UTC

I still put it down to excessive complexity. Kinda like "why aren't there animals with wheels"

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Re: Why are there no animals that get energy from sunlight?

Postby gmalivuk » Sun Jul 11, 2010 1:41 pm UTC

Considering that photosynthesis is only 3-6% efficient, that reduces it to 50W/m^2 that's actually available to you, assuming a full kW is making it to the ground. And growing high-surface-area leaf-like appendages for a merely supplemental energy source seems really inefficient. Far better to grow specialized organs for your primary energy source, allowing you to get more calories that way than to use something that probably requires more energy to grow and maintain than it would ever provide from sunlight.
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Re: Why are there no animals that get energy from sunlight?

Postby PM 2Ring » Sun Jul 11, 2010 5:57 pm UTC

Why are there no animals that get energy from sunlight?

Because plants own the franchise. :)

Apart from corals, and the aforementioned sea-slug, there is also the sloth. These guys get algae growing in their fur, which give them a few extra nutrients, apparently, but I can't find a good reference for this factoid.
http://www.arthurgrosset.com/mammals/sloth.html
Their diet consists entirely of leaves so they are restricted to areas of evergreen (mainly Cecropia) forest.
Because of this diet, 3-toed Sloths have a compartmentalised stomach and the leaves are broken down by fermentation in both the stomach and the intestines. The stomach and its contents weigh up to a third of the sloth's total weight. As an adaption to the low nutrient content of the leaves, sloths have a low metabolic rate and a low body temperature.

For this reason they favour the crowns of trees that receive the sun so that, when resting, they can regulate their body heat by moving in and out of the sun.

Mind you, they move so slowly that it is difficult to tell when they are resting and when they are not.

Another of the results of their slow movement is that their backs are covered with algae. This is a symbiotic relationship since the algae flourish in the forest humidity while the sloth benefits from the camouflage that the algae provide. The sloth's fur is also home to small moths.


http://www.enchantedlearning.com/subjects/mammals/sloth/index.shtml
Some sloths have colonies of green algae encrusting their fur, both adding to the camouflage effect and providing some nutrients to the sloths, who lick the algae.

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Re: Why are there no animals that get energy from sunlight?

Postby Neuman » Mon Jul 12, 2010 5:00 am UTC

Let's say we're talking about the green anole. It's currently being replaced by the invasive brown anole, and in a fit of patriotic fervor, I decide to give the native greens an advantage. The green anole already spends most of the day sunning itself so it shouldn't have to change it's behavior any. And photosynthesis converts carbon dioxide to oxygen, so that's an additional benefit. Maybe it'll be a little faster or something.
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Re: Why are there no animals that get energy from sunlight?

Postby crayfish » Wed Jul 14, 2010 4:39 pm UTC

Animals evolved the ability to move, that alone negate the possibility of having an animal yield energy from the sun, if you look at the amount of energy needed for actin and myosin to function, and then look at the energy yield from the photosynthetic reaction you realize that ratio of energy created to energy used is very high on the energy used end, I don't know how many chloroplasts the average plant has in any given surface area of a leaf, but to yield the amount of energy from photosynthesis to make a mobile organism would basically require a tree growing out of said organisms back, then you have a walking tree (which already exist but are most definitely plants, and they only "walk" a couple feet in their entire lifetime).

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Re: Why are there no animals that get energy from sunlight?

Postby SpaceShipRat » Wed Jul 14, 2010 9:28 pm UTC

Reversing the whole idea, would a tree be able to grow a moving organism, say, butterfly-like things to carry it's seeds? I suppose it would be a waste of energy that could be used to stock up the seedling, but it might be technicaly possible.

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Re: Why are there no animals that get energy from sunlight?

Postby Levelheaded » Wed Jul 14, 2010 9:40 pm UTC

SpaceShipRat wrote:Reversing the whole idea, would a tree be able to grow a moving organism, say, butterfly-like things to carry it's seeds? I suppose it would be a waste of energy that could be used to stock up the seedling, but it might be technicaly possible.


Seems technically possible under perfect circumstances, but unnecessary and inefficent. The kind of mobility you are talking about took a long time to evolve, and there is no guarantee that the insect-seeds are going to survive and grow.

Why not just recruit the already-present moving organisms and have them spread the seeds? Make your seeds tasty or stick to fur or nesting material.

Or just create many, many, many more seeds that float (cottonwood, willow, maple tree) and let the wind do the moving. Now all of the energy can go to creating more seeds and more trees.

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Re: Why are there no animals that get energy from sunlight?

Postby crayfish » Thu Jul 15, 2010 2:46 am UTC

In terms of evolution nothing is necessarily impossible, over millions of years traits we can't even imagine right now could develop in organisms. However, for these traits to become common they must be beneficial to the organism. Given the amount of energy necessary for mechanical movement in an organism, its unlikely that an organism that relied primarily on photosynthesis for energy production would be in a situation that made mechanical movement a beneficial trait. Perhaps new niches will develop over time where such an organism could thrive. Additionally, keep in mind that most animals have sensory organs that facilitate ordered movement (the only exception is the sea sponge which is incapable of movement), and this requires some type of neural network that interprets sensory information and regulates responses.


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