Microcosmos

You know what’s been on my mind lately? Midgets. Well, dwarfs. Well, actually, pygmies. I’ve been considering a post about pygmy animals for a while, and as luck would have it, a research team in Borneo just found this miniscule marvel:

Yes, that’s an adult frog. (If it weren’t, it’d be a tadpole, silly.) Measuring only 12 mm, the male Microhyla nepenthicola is the smallest frog in Europe, Africa, or Asia — though, amazingly, there are two species in the Americas that are even tinier. M. nepenthicola‘s species name comes from the Nepenthes pitcher plants it inhabits to keep its skin wet. It might never have been found if it weren’t for its loud, rasping call, which conjures for me an image of a puzzled biologist putting his ear to a pitcher plant like a dog to a Victrola gramophone, wondering why it was croaking.

As megafauna ourselves, I think most humans have this idea that species are trying to evolve to be larger, but are somehow limited. But the fact is that being small has its advantages, and many species are more than willing to become miniaturized to seize the opportunities that can only be found once you breach the microcosmos.

I’ve written before about insular gigantism, by which animals on islands can reach unusually large sizes for their genera. But islands have a sort of Wonderland effect on animals that fall down the rabbit hole and find themselves there by accident: one pill makes you larger, and one pill makes you small. (And the ones your mother gives you don’t do anything at all.) While a bird, bug, or reptile might reach an extraordinary size on an island, a mammal or amphibian might actually shrink to fit the reduced resources that ecosystem has to offer, a phenomenon called insular dwarfism. Take, for example, the dwarf elephants that lived on Mediterranean islands such as Sicily, Crete, and Cyprus, or the so-called “Hobbits,” or Homo floresiensis, an extinct teacup humanoid from an island in Indonesia.

Or how about the Dwarf Chameleon, found only on Nosy Be, a small island off the coast of Madagascar. It takes an island off an island to shrink something this small.

Or the Barbados Threadsnake, the world’s smallest snake, only four inches long and as thick around as a strand of spaghetti.

But the limitations of islands aren’t the only reason a species might become, to borrow a term from Halloween candy, “fun-sized.” For one, size usually correlates surface-to-volume ratio, which makes larger animals better at retaining heat and smaller animals better at dissipating it. Take the example of hummingbirds: the Giant Hummingbird, the world’s largest and nearly the size of a sandpiper, lives in the cold Andes, while the bee hummingbird, the world’s smallest bird, lives in the hot tropics of Cuba. (Which, admittedly, is also an island.)

But the biggest advantage to smallness is simply that the smaller you are, the bigger the world becomes. There’s a ceiling to how large most animals can get; if the world were populated by giants, there simply wouldn’t be enough food to feed us all. But if you shrink, the possibilities are endless. The wilderness is full of much smaller wildernesses, micro-wildernesses, under the leaf litter and in the riffling pools of a hot spring. A fallen tree can be a mountain range, and blood can be an ocean of rivers, and with the change in dimension, the world becomes full of feasts and plenty. This is the world on a fractal scale again, ranging from the infinite to the infinitesimal, and with each turn on the microscope, you enter a new niche to exploit and explore. We live on a planet of precise size inside a universe of certain dimensions, but a world can be defined best by subjective experience, and by that measure, there are infinite worlds within our world.

I’ll leave you with one last animal, and a final question: If vertebrate animals are ultimately limited in how large they can evolve to be, what’s to keep them from shrinking into the microscopic? Could there someday be a frog that would be impossible to see with the naked eye? I can guess at a few physiological governors: surface-to-volume ratio, the heart rate needed to sustain something so small, the supernaturally fast metabolism. For example, the Etruscan shrew, one of the world’s smallest mammals, has a life expectancy of 15 months. Its heart beats an astounding 14 times a second. Another danger to small vertebrates is simply that small changes in our macro space can have huge effects in the microcosmos. The world’s smallest mammal, Kitti’s hog-nosed bat (also called the bumblebee bat), lives on the mainland in the limestone caves of Thailand and Burma. Only discovered in 1974, it is already reaching critical endangered status because of habitat disturbance. I wonder how many more species we haven’t discovered yet because they live underfoot and because we are god-like and yet astoundingly near-sighted, species we’ll only find when our giant machines have easily leveled their worlds, species who we’ll only find when they’re clinging to our thumbs for dear life.

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About quantumbiologist

Christian Drake, AKA The Quantum Biologist, is a naturalist and poet formerly of Albuquerque, NM and currently living deep in the backwoods of the Connecticut Berkshires. He has worked in aquariums and planetariums, national parks and urban forests. When not birding or turning over rocks to find weird bugs, he enjoys rockabilly music, gourmet cooking, playing harmonica and writing dirty haiku. View all posts by quantumbiologist

3 responses to “Microcosmos

  • Phyllis Klarmann

    I would think there is a limit to how small a vertebrate can be – I can’t give you a size in particular, but here’s what occurs to me:

    Even the smallest of microorganisms do not fall below a particular size. Let’s just start with bacteria – each individual organism needs a certain subset of structures to keep it intact and functioning properly. Those particular structures are limited by the size of molecules, and the molecules in turn limited by the size of an atom. Assuming atoms are unchanging, molecules can only be so small, and the structures those molecules form can be so small, et cetera.

    That’s just to say for a bacteria. You take a eukaryotic cell, perhaps the cell of a vertebrate, and they’re much more complex. They have organelles – many types – that are necessary for it to run (and seeing as you understand the endosymbiotic theory, the already small former-bacteria-now-organelle would need to be housed within a cell that can also contain other organelles, etc., further limiting the size of the host…). If a microscopic vertebrate were to exist, its smallness would be limited by the size in which its individual cells can shrink to, AND the number of cells necessary to form viable tissues, organs, and ultimately, the organism.

    It is entirely possible, I suppose, that a microscopic frog might be able to possess an arterial/venous system whose cross-section could equal the diameter of a microtubule of a typical cell’s cytoskeleton, but like you said, I don’t think the organism would be very stable.

    Then again, I don’t want to suggest we can fully understand nature’s limits precisely, and the thought of a bat even smaller than the bumblebee bat makes me shudder with happiness. But surely, there’s a limit. What that limit is, however, I can’t really guess.

    I wanna post this comment on your FB link to QB, too, because this topic is not anything I’ve ever considered before, and I would looove to chat it up with other people about this, too, and I think there’d be more viewers there. Lemme know if you’d like to carry it on. Or, you yourself can indulge in my nonsense. I’m kinda craving a biological banter with someone competent enough to keep it going.

  • quantumbiologist

    Sure, I’m not saying there could be a hummingbird the size of a paramecium. If there could be, I bet there would be. Or perhaps vertebrates are still too new?

    There are insects larger than hummingbirds, but hummingbirds can’t even approach the tiny stature of most insects. I’m guessing that an thermoregulation is the first limiter, as a creature of that size couldn’t gain enough calories to support its need to keep its body temperature constant, and such a small creature would be losing a disproportionately large amount of body heat. The only thing that messes up this theory is ectotherms, like that threadsnake. There are enough temperature-stable environments on earth for a creature to remain comfortable. So why no 1-inch snake? I like your theory about the circulatory system, but an animal could get pretty small before it veins reach the microns-across level. Maybe evolution just needs more time.

  • Phyllis Klarmann

    There are many examples most of which (I think) are amphibians and reptiles… we’ve got a few bird species, the hummingbird… and a mammal, the bumblebee bat. I’m sure there’s a statistically significant value to the number of miniscule herps to birds and mammals (the latter are definately “younger”). Over time, that could certainly change, and I hope it does. Like you said, needs more time.

    As for the ectotherms, maybe its a matter of niche availability? Or there may have not been a circumstance where to be smaller would mean you’d have the upper-hand. And that’s where your idea comes in, and it’ll be more advantageous to shrink and shrink until that organism “discovers” a new niche to inhabit.

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