No, keeping a goldfish in a bowl does not result in “environmental dwarfism”. The goldfish in a bowl that stays small is no more a dwarf than a poorly fed child locked in a room is a dwarf.
The same people who tell you that fish only reach the size of their tank will also tell you that goldfish only live three years. Hah! They can live for decades, and do need large tanks (15 gallons minimum for the smaller “fancy” varieties), in part because the space they need to move around in, and also because goldfish are dirty and will rapidly foul a small amount of water.
Even if what you say is true, the fish is smaller than it would be in a larger environment. This means it is still environmental dwarfism.
The argument that the domestic goldfish is actually being mistreated in the same sense as a child being locked in a basement is immaterial. Heck, in some cases the human situation is considered dwarfism.
But there are dwarf versions of animals - they are called “runts”, and natural selection usually does its thing on them.
Then consider animals that continue to grow throughout their adult life - say crocodiles. How do you tell the difference between a dwarf crocodile and a crocodile and a young crocodile? Get close enough to count his teeth? “One, two, three - chomp”.
And sometimes humans breed them to get more, like Dwarf Cats. They’ve been bred because people think their stumpy legs are cute, but they can’t jump that high. I suspect most dwarf animals wouldn’t survive in the wild, since they wouldn’t physically be able to adapt and do everything the bigger ones can do. They’d get caught & eaten, or just wouldn’t be able to get to the food.
The runt of a litter of animals won’t necessarily be tiny as an adult, though. They can grow to normal size if they survive infancy, which isn’t uncommon for domestic animals kept as pets.
You are right. One should differentiate between a member of a litter that is small merely because of being on the short end of the dispersal of resources, and one that is small because of a genetic anomaly. aceplace57 said:
It’s a smaller size variation than Chihuahua’s to Great Danes. DrDeth said:
Not heard of this effect called such. Google search on “narnia effect” only turns up links to the movie.
Somebody may clarify this for me, as I’m not a doctor for humans, but… I thought in human dwarfism, there is something more than just being “born a runt”… Either somewhere the genetic machinery is screwed up, or the growth hormones are not working like they should (which goes back to genetics)… Am I wrong?
Because in that case, then I would consider the Chihuahua a poor example for dwarfism in dogs, and I would also consider the “born a runt” thing wrong.
Pituitary dwarfism in dogs is rare, and they usually die young. However, there are a number of dog breeds where chondrodystrophy is incorporated into the breed standard - Dachshunds, Bassetts, Bulldogs and other breeds with similar conformation. Long trunk and short, deformed legs, prone to intervertebral disc disease. Technically, this is a form of dwarfism, which makes dwarfism quite common in dogs.
Chondrodystrophy is genetic and inherited, which is why it has beeen possible to selectively breed for it in dogs. It’s not the same as selective breeding for smaller size. A dwarf is not a miniature version of an animal, it has a genetic disorder of bone/cartilage development.
Gene mutations that affect skeletal development presumably happen in all species, but often result in abnormalities that are incompatible with life, or with long term survival. I’ve seen chondrodystrophic ponies, and there’s not a hope in hell of them outrunning a predator in the wild
Nope. Not quite. The goldfish in a small bowl is actually quite healthy, just small. Fish have all sorts of neat tricks to help them cope with various environments. Small ponds mean staying small in size is a good strategy. There isn’t going to be a lot of food for a big fish. Being small in a large pond merely makes you fish food. However, there’s lots of food all around, so you can grow nice and big and be the one who eats the puny fish.
Fish have been known to change sex to if there’s dearth of one sex or the other, and there are even a few that have been shown to shrink in size when their environment changes. They aren’t under nourished. They’re simply small in size to fit their environment.
On the other hand, a person who grew up with poor nutrition maybe smaller in size, but usually has a lot of other health issues that reflect the poor nutrition.
Some of the mechanisms that result in small stature in humans also result in serious health conditions. Without medical intervention these folks wouldn’t survive. In animals this doesn’t happen, so you only see the much smaller percentage that are healthy miniatures.
Well, the dogs that have pituitary dwarfism do have some other health problems. Although you could say that they do live more than they would in the wild, as they’re cared for by humans.
toodlepip, yea, I forgot about the chondrodystrophic breeds. :smack: Probably because they are not necessarily automatically born with health problems, but are more prone to certain conditions later on. The first thing that popped in my mind was the pituitary dwarfism.
Yes, I know, it’s much more often called those. My Zoo prof and I called it the Narnia effect, due to the fact in Narnia large animals became smaller and small animals larger, see Reechicheep. “island dwarfism” doesn’t cover the fact that small animals often get larger. What really is occurring is that the size changes due to the limited number of species thus the larger number of niches that are open. The various “Darwins” Finches show that perfectly.
The “hobbits” of Flores are believed to be just such a case. Flores was also the home of dwarf elephants and giant rats (which is fitting, since Flores isn’t very far from Sumatra).
Yeah, I’ve already acknowleded that the runt comment was off. But I still stand by the natural selection comment.
You are right, “dwarfism” in humans is due to one of several types of hormonal imbalances or genetic anomalies.
The problem is ambiguity in the word “dwarf”. Dwarf elephants are tiny elephants, but there is no indication they are the result of hormonal imbalances that prevent proper bone formation. Rather, they are tiny all over, the result of selection pressure on limited population groups.
There was a race of “dwarf elephants” on Malta, which only died off a few centuries ago IIRC.
The evolutionary logic is simple. In an area of limited resources (small island) and periodic famines, the smaller animals have an advantage. In a regular-size environment, they just muscle the others out of the way using the advantage of numbers. The reverse is true of small animals; with fewer and less varied (and smaller) big predators, small and able to hide is less of an advantage.
Dwarfism is where certain parts of the body do not grow properly; so a dwarf typically has the odd rib cage, malformed pelvis and legs, and big head - parts of them grow at the normal rate, thers not at all. It’s a genetic (? developmental?) abnormality that obviously would have serious survival disadvantages for a wild animal. OTOH, something like a daschund is similar, IIRC - the growth only kicks in for certain phases; not for the legs.
Midgets are people with a deficiency of growth hormone; so they grow slower or not at all; but shape-wise, they have normal proportions. Nowadays, that can be treated with Human Growth Hormone, same as for shortcomings in professional sports.
Aren’t most of the animals you see now dwarfs, compared to their ancestors?
Like elephants compared to woolly mammoths, or great white sharks compared to megaladon, current crocodiles compared to Sarcosuchus, the monitor lizard compare to T. Rex. etc.
Well, no. Megalodon was almost certainly not a direct ancestor of the GWS. How closely related is another question:
"Taxonomy
Even after decades of research and scrutiny, the controversy on phylogeny of C. megalodon still persists.[1][9] Several shark researchers (e.g. J. E. Randall, A. P. Klimley, D. G. Ainley, M. D. Gottfried, L. J. V. Compagno, S. C. Bowman, and R. W. Purdy) insist that C. megalodon is a close relative of the great white shark. However, several other shark researchers (e.g. D. S. Jordan, H. Hannibal, E. Casier, C. DeMuizon, T. J. DeVries, D. J. Ward, and H. Cappetta) dismiss the proposal that C. megalodon is a close relative of the great white shark, and cite convergent evolution and heterochrony as the reasons for the dental similarity. Many paleontologists, convinced by the arguments, favor Carcharocles genus more over Carcharodon genus for C. megalodon.[19]"
The Mammoth was also not a direct ancestor of the Elephant, and some Elephants are bigger than some Mammoths were. Most species of Mammoth were about the same size as Elephas maximus,which is somewhat smaller than the African Bush Elephant - Loxodonta africana.
Sarcosuchus is only rather distantly related to the modern croc. There were lots of Neosuchia in the past, some very large, some smaller. My WAG is that the average was smaller than a large modern Saltwater Croc.
And o course, Dinosaurs aren’t lizards at all. In any case, the largest Megalania was about dino-sized (perhaps 2 tons, and 26’ long)
In fact today, the whales, especially the Blue whale, are the largest vertebrates ever.
