I was just thinking the other day that it would be pretty badass to have a pet beluga whale. The only thing is, you’d have to have a gigantic tank to keep it in and a colossal supply of fish to feed it - not to mention the difficulty of obtaining the animal in the first place. I thought back to something I’d read by Jerry Seinfeld (admittedly not an expert in biology) about how he wished “they” could genetically engineer a horse to be the size of a quarter. I have no idea what the limits of genetic engineering, either in the present or in the future, are, so maybe someday “they” will be able to genetically engineer a tiny little horse, or a tiny little beluga whale that I can keep in a fish tank.
But the larger question is, why are all whales so huge in the first place? Even the smallest whale (according to Wikipedia, the dwarf sperm whale) is still larger than a man. Gilled fish range from the size of a fingernail to the giant whale shark or ocean sunfish, according to Wikipedia. There is such a huge range in the size of gilled fish, but not in ocean mammals like dolphins and whales.
This doesn’t really make sense to me (though it probably would if I had a better knowledge of the evolutionary biology behind it.) So what’s the deal here? Why aren’t there itty-bitty whales that I could keep as pets in a fish tank?
Sneaking in a WAG to see if I got it right when Colibri or someone shows up:
Since mammals need to keep warm, perhaps they need X amount of thickness to their perimeter to keep the innards sufficiently insulated, which then limits the minimum size of the animal.
That’s my guess too – they need a certain size so that sheer bulk allows them to maintain a minimum temperature without fur. Furred marine mammals like otters can be smaller. Fish, being cold-blooded, can be much smaller. And only the big fish, like Great White sharks, that have semi-warm-bloodedness.
But like Sage Rat, I could be way, way off, so I hope the biologists show up soon.
To sum up what Sage Rat said, “surface to volume ratio”. When the volume of something doubles (depending on the shape, of course, but, let’s use a cube as an example), the surface area only increases by 5/3. Therefore, the bigger the animal, the less energy it has to expend per unit volume to keep itself warm.
Well, whether whales evolved from Mesonychids or from Bunodont Artiodactyls related to them, they originated as moderately large animals – pig to wolf size or somewhat larger.
Also don’t forget that “whale” is a classification from popular-language taonomy – there are dozens of whales smaller than the pygmy sperm whale; we just don’t term them “whale” in everyday parlance, but rather dolphins and porpoises.
Cetaceans adapted to fill niches of large predator and large filter-feeder very effectively, as well as medium-large predator. One assumes that there was no econiche for smaller predator that could be filled by a warm-blooded more-or-less fusiform obligatorily aquatic creature, or which existing adaptations were sufficient to replace existing occupants of those econiches competitively.
Genomes are not infinitely plastic within the limits of a specific morphology. The whale began from a sizable land creature and just got bigger. Their genome would have limit of mutation toward smaller sizes before it really was no longer a whale, or even “whalish” any more.
I think that those who have responded so far have hit on an important part of it - it’s easier for a warm-blooded animal to maintain its body temperature if it is large because of the surface-to-area relationship; the problem of heat loss is particularly severe in aquatic environments.
However, I would note that the term “whale” is somewhat arbitrarily applied to the largest members of the Cetacea, and has no real taxonomic significance. The smallest cetacean, the “vaquita” Phocoena simus of the Gulf of California, is smaller than a man, averaging 80 lb.
As has been pointed out, furred marine mammals like sea otters can be smaller. There are aquatic mice and shrews, but they don’t spend all of their time in the water.
I would say evolution would’ve made all sorts of whales and it still does. But small whales that are that way because of mutations don’t last. They are eaten up and out competed. A small whale’s role is being take by a sea otter or a seal or sea lion. Get rid of those mammals and when by mutations small whales are born they could MAYBE compete and we’d have small whales.
Nature basically says where life can exist it will. Second it says “Where life exists some there’s other life bigger than it to eat it.” Rabbits and rodents survive because they reproduce so fast that way it’s hard for big things to eat all of them.
The second question in the thread title is rather interesting. We know it is possible to enforce dwarfism on biological organisms by denying them resources, such as with bonsai. It is also possible to select for dwarfism. So a more general question is whether it is possible to breed smaller whales that live in controlled temperature environments so the surface area problem doesn’t kill them. And with which species could this be done?
We know miniature trees, dogs and horses (Thumbelina) already exist. It even happens with humans, but the miniaturization ratio isn’t all that pronounced. So I could believe that someone could take one of the smaller whale species, select for dwarfism, and end up with something that fits in a fishtank.
You can start cultivating a Bonsai Whale. First, get a regular whale, then…
If you could be satisfied with a mini-shark, you can get a dogfish. They really are cool looking little guys, and you don’t have to feed then seals or anything.
In a sense, there are such things as small whales - they’re just called seals and otters.
Now of course they’re not all that closely related, so I’m not trying to claim they are actually whales - they’re just occupying a similar niche to that which smaller whales would probably have to exploit - small whales would almost certainly have to come ashore to give birth, so they’d need flippers like a seal or legs like an otter. Filter feeding probably wouldn’t be efficient enough at such a small scale, so they’d have to catch fish like a seal, or fish and shellfish, like an otter.
So we’d have something like a seal or otter, but more closely related to cetaceans. But we don’t, because just being possible doesn’t make things inevitable.
To expound on the genetic-engineering portion of your question:
While in theory, you could just take a huge animal and make it tiny, it isn’t a good idea. Whale instincts are based on being whale-sized. If you take, say, a sperm whale and make it tiny, it will be a huge predator with the ability to predate on… well, nothing really.
All a sperm whale knows how to eat are squid and large fish (and smaller aquatic mammals). If you make one that’s three feet long, you’ll find that its intestinal flora simply aren’t adapted for the stuff you’ll be feeding it.
