As you might intuitively guess, animals that are brightly colored are probably best avoided in the rainforest. One example that comes to mind are the showy dendrobatid frogs of the New World tropics. Known commonly as the ‘poison dart frogs,’ these amphibians are toxic and advertise that fact with flamboyant colors of bright reds, yellows, greens, and even striking blues. These colors warn would-be predators that ‘I taste bad at best, and at worst, I will kill you!’
Indeed, in nature many animals that are conspicuous in their coloration or behavior do not make a good meal. Most often, such animals are protected by toxins or poisons that they either manufacture de novo or acquire from their food. The famous dart frogs of American rainforests advertise their deadly batrachotoxins with gaudy and obvious colors, toxins which they acquire from the invertebrates—mostly ants and small beetles—that they eat.
Other animals, like an almost endless variety of colorful rainforest butterflies, feed on plants as caterpillars or flowers as adults that provide them with a wide range of noxious chemical compounds that they are able to store. These insects advertise their distastefulness with flashy colors, bold wing patterns, and slow, daring flight. Should a predator attack, it will quickly learn to avoid similar colors and patterns in the future; with these creatures, relatively few individuals bear the cost of educating predators of the toxicity of their species.
Butterflies, nearly without exception, fly during the day when they can use their flashy colors to warn their visually-oriented predators—birds, mostly—of their distastefulness. Moths, on the other hand, generally fly by night, when bright colors serve as a poor warning signal to nocturnal predators that generally hunt without the aid of good vision. In the rainforests of Madre de Dios, however, one group of moths stands as a striking exception to this rule. Here, a large number of species of clearwing moths have evolved a remarkable variety of garish colors, wing patterns, and strange forms; they fly boldly by day, practically daring prospective predators to attack them.
These clearwings belong to a subfamily of moths that entomologists have named the ‘Arctiinae.’ The name comes from the Greek αρκτος, which means ‘a bear’—this refers to the North American common name for their caterpillars: the wooly bears. Some species of wooly bear caterpillars feed on plants that provide them with toxic compounds that they can store in various parts of their bodies as larvae. As a result, the caterpillars are protected from attack by predators that have learned the hard way to avoid them. Other arctiine species acquire their chemicals as adults, often storing them in the integument—the entomological word for the insects’ skin or, more accurately, their exoskeleton.
The clearwing arctiine moths are a brilliant example of one an almost endless variety of incredible ways that rainforest animals protect themselves from the legions of predators that constantly patrol the forest floor, interior, and canopy looking for a meal. Whereas many animals—including most other moths—have opted to hide during the day, coming out cautiously only under the cover of darkness, these colorful moths fly by day, warning would-be attackers: “Eat me if you dare!
This is a species of poison-dart frog from Tambopata, Allobates femoralis.
While not very large or particularly showy–or very poisonous, for that matter–these frogs are very interesting in that they show extreme variation throughout their range. Researchers have discovered that distinct populations that are separated by geologic barriers, such as large Amazonian rivers, have different calling patterns; some populations have a two-note call, whereas other populations have a three- or four-note call. These might seem like unimportant differences, but they may be all that are required to isolate populations and lead to speciation. For instance, if females in one region prefer males that have a four-note call, they might not breed with males that have, say, a two-note call, and over time this can cause a new species to arise from that population. Add in large rivers that form barriers to populations mixing, and you’ve got the potential for a huge amount of genetic diversity and confusion for biologists trying to understand the distribution of frog diversity here. Just another way in which the Amazon continues to reveal its biodiversity to those who pay close attention to it!
Another species of primate from Tambopata, this is the black-capped squirrel monkey (Saimiri boliviensis). Not counting the tiny tamarins, these are the smallest monkeys found in the rainforests of southeastern Peru and, as their common name suggests, are about the size of a squirrel. Squirrel monkeys forage in very large groups of up to one hundred animals or more, searching mostly for fruits and insects, although they will take small vertebrates like tree frogs or baby birds. Interestingly, here in Tambopata they can almost always be found foraging alongside the much larger brown capuchins (Cebus apella). Biologists have been trying to figure this out for decades: brown capuchins can be very aggressive, and animals the size of squirrel monkeys even make up an occasional part of their diet. So the question is this, Why do squirrel monkeys travel with the capuchins? Put another way, why do the capuchins tolerate the squirrel monkeys?
A recent study by Taal Levi et al. (2013) in northeastern South America showed that squirrel monkeys tended to be more abundant where brown capuchins were present, lending support to the long-standing hypothesis that the two species facilitate each others’ foraging. That is, more eyes on the forest might make it easier to find patchily distributed foods, such as fruiting trees or large caches of insects. Alternatively, larger groups might provide better protection from predators, as both species are food for a variety of species ranging from cats to snakes to even birds of prey. Teasing apart the importance of the various benefits associated with mixed-species groups has been difficult, and we still have much to learn.
That human intelligence is superior among the living world is almost a truism. Great intelligence—and a unique ability to reason, to experience emotion, to communicate using complex language and to understand and employ symbolism—are the criteria by which humans are set apart from the rest of the Earth’s creatures. By our own admission, we are the world’s greatest thinkers, and profoundly so.
Yet, for the past several hundred years, scientific discoveries have steadily eroded the uniqueness, the exceptionality, and the centrality of the human species and our place in the world. It all started, of course, with the discovery that the sun does not revolve around the Earth—that our humble little planet is but an insignificant blip in a vast universe replete with countless other worlds, with each one precisely, simultaneously, at its center.
While we do not yet have any direct evidence, astronomers tell us that as many as a million worlds within our own galaxy, the Milky Way, might be inhabited by intelligent life. And with around 400 billion other galaxies sprawled throughout the cosmos, intelligent life is essentially a statistical certainty—a striking and very beautiful proposition indeed.
Most recently, however, it is the cognitive scientists—those who study the acquisition of knowledge and understanding through thought and experience—that are teaching us that we must rethink the notion of our supremacy and our matchless intellect, right here on Earth. They are doing so not only by teaching sign language to gorillas and chimpanzees—an astonishingly impressive feat on the part of researcher and ape alike, to be sure—but by teaching us how the brains of our more distantly-related cousins, the monkeys, work. As it turns out, those monkey brains work a lot like our own.
The brown capuchin monkey, Cebus apella, is one of several species of capuchins found throughout the Amazon basin, including in Tambopata. The brown capuchin is widely considered among the most intelligent of the New World primates, or the monkeys and tamarins of the American tropics.
Recently, a group of researchers working in a laboratory at Yale University have successfully introduced the concept of currency to their captive brown capuchins. After months of introducing the monkeys to the small, metal disks that would serve as coins, the monkeys learned that they could exchange these coins for highly prized food items such as grapes.
Before long, the monkeys learned how to budget their coins, especially after the researchers introduced another highly-prized food item to the menu: Jell-O. When the price of Jell-O was reduced compared to grapes, monkeys reacted in precisely the way that current laws of economics in humans predict: they bought more Jell-O.
Perhaps the researchers’ most stunning find came after a monkey was observed exchanging money for sex with another monkey. The monkey had learned well the value of money, and most importantly, that it could be used to trade for goods and services—even prostitution!
You might ask, Why do monkeys have or need such powerful brains—which appear to have many of the high cognitive functions of our own—if they don’t appear to use them in many of the same ways that we do? Why, if they are able to barter for food and even sex in a laboratory setting using a symbolic currency, do we not see monkey towns and cities dotted throughout the rainforests of tropical America, instead of only human towns and cities?
We can’t yet answer the second question, although it is most likely the result of a combination of factors, including a poorly-developed vocal organ that prevents the use of complex language, limited tool use, a lack of bipedalism, or other factors which we do not yet know. But we can fairly confidently answer the first question, Why do monkeys have such powerful brains?
Although monkeys do not typically do math, or read or write, they do live in cooperative groups with complex social structures. Large groups provide protection in numbers, and with large snakes, jungle cats, and birds of prey standing (or slithering or flying) at the ready day and night to make a meal of a monkey, group life has its benefits.
But living in a group presents other challenges. For instance, a strict social hierarchy, in which dominant animals feed first at an abundant resource such as a fruiting tree, say, allows everyone to access food without a brawl each time food is discovered by the group. But how best to remember one’s place in such a hierarchy? Evidently, a large brain allows monkeys to know and recognize other individual monkeys, as well as their own and others’ social statuses. They also use their powerful brains, just as we do, to analyze the feelings and intentions of others, which is done with the help of a large amount of computing power. As we all know, social life and in-group politics are complex, and powerful brains have given primates the tools they need to survive and reproduce in large social groups.
This explanation makes evolutionary sense for humans, as well. Those individuals with more highly-developed brains—which should, on average, make them more competitive in a group setting—should again, on average, reproduce more. Their offspring, in turn will have bigger, more powerful brains, and so on, until, after many generations, intelligence on the order of that of humans has evolved from our more humbly intelligent ancestors.
There remains so much more to learn about human and non-human primate cognition. But one thing is already certain: monkeys are smart, and they use their brains in many of the same ways that we do, often to achieve similar or identical ends. In reality, this should not come as a surprise—on the grand evolutionary tree of life, we are very close relatives. But monkey prostitution? I don’t think anybody expected that!
Discoveries in the cognition of non-human primates—like the capuchin monkeys of Tambopata—continue to shatter the notions of total human uniqueness and our superiority over the rest of the Earth’s lifeforms. But, instead of viewing this as a demotion, I argue that such amazing discoveries are cause to celebrate. To celebrate the emerging knowledge that we are part of a complex yet beautiful creation in which all creatures share in a history and a future more interconnected and fascinating than we’ve ever before imagined—even if some of our shared characteristics might seem a bit unsavory.
A curl-crested aracari (Pteroglossus beauharnaesii) from the Tambopata Research Center. Why do the aracaris and the rest of the toucans have such big bills? At first glance, it might seem to be the result of sexual selection, the same force that drives many other tropical birds to exuberant coloration and ornamentation. However, in toucans, both males and females are essentially identical–they’re not sexually dimorphic–ruling out this possibility. A recent study in the journal Science suggested that the toucan’s bill performs quite an unexpected function–it acts as a radiator! By controlling blood flow to the bill, the toucan can control its body temperature, much in the same way an elephant uses its big ears to cool off. When the toucan warms up, say, after a long flight that increases metabolic heat by a factor of 10, it can send blood to the bill to dump that excess heat as the bill cools. The bill can also store heat, which explains why toucans sleep with their bills tucked under their feathers. The coolest thing about these findings might be how they were made. The researchers used thermal imaging cameras to measure blood flow to the bill, and changes in temperature, in a variety of rooms adjusted to different temperatures. Now, the biggest question that remains is whether the bill evolved first to regulate heat, or if it evolved for another reason, and the radiator function was a secondary benefit. That question will be much more difficult to answer.
Two more aracaris, part of a flock of 8 observed foraging through the Tambopata rainforest canopy. The bills of the two individuals shown here are different; however, it’s difficult to know if these differences are due to normal variation between individuals or some other factor, such as differences between adult and juvenile coloration. Whatever the case, male and female bills do not differ significantly among toucans, and there is no way to separate males from females apart from examining the sexual organs via endoscope; this provides strong evidence that the toucans’ large and colorful bills evolved that way for reasons unrelated to sex or sexual selection.
I registered this domain months ago with the sincere intention of actually posting to it. Alas, months went by and life kept getting in the way—this comes up and that comes up, and oh yeah, I’m writing my PhD dissertation. But today I turn 31, and I’m again overtaken with that annual sense of urgency that grows with each passing year as I move steadily closer to completion of my life cycle. It’s time to get posting.
When I registered the domain—as you might tell from the name—I also intended for this to be a platform to share my thoughts about and experiences in the tropics, and especially the Neotropics, where I have spent the last several years chasing butterflies, dodging parasites and other hostile wildlife, and just generally learning about and getting beat down by the jungle. I’m going to take a break from all that, before I even get started, to share some thoughts about getting older…
Corals, many people are surprised to learn, are tiny animals, which biologists call invertebrates—animals that have no backbone, like many other creatures in the sea, and also insects and spiders. Unlike most other invertebrates, however, corals have an additive mode of growth, in which growth happens during cycles that occur on a daily, monthly, or yearly basis. These cycles of growth occur because certain times of the day, month, or year, are more conducive to coral growth, and growth thus happens when resources are abundant or conditions are otherwise optimal. Think of a tree adding growth rings during the summer growing season.
Because of this mode of growth, corals have observable growth bands that a meticulous and patient marine biologist can measure, much in the same way a botanist can estimate the age of a tree based on how many annual growth rings are found in the wood.
Scientists generally use the information provided by the growth bands of these organisms to infer the ages of the organisms themselves. However, when biologists compared the daily growth bands with annual bands of fossilized corals many millions of years old, they found something surprising. They did not match—there were more than 365 daily bands for every yearly band in the fossilized coral bodies. Many more, in fact—three hundred million years ago corals appeared to grow during about 450 days per year!
It turns out, this information supports astronomical evidence that the length of a day on Earth is subject to change, and that it has been getting continually longer over geologic time. This explains why corals 300 million years old have 450 growth bands for each year—300 million years ago, there were 450 days in a year.
But how can this be?
The length of a day changes over time for a number of reasons. For one, the force of wind blowing against mountain ranges on the Earth’s surface slows the planet’s rotation and lengthens the day by as much as a millisecond per year. Over time, those milliseconds add up. Changing tidal patterns and other gravitational effect of the moon also alter the day’s length, just as a combination of the dynamics of the Earth’s fluid core, magnetism and chemistry, and its electrical conductivity have done—processes that I won’t even pretend to understand.
Which brings me to my point. If the days have become much longer, and the years much shorter, how old would I be on this day, my 31st birthday, if I were living 300 million years ago?
The simple answer is just over 25 years old—300 million years ago, I’d be 25 years old today!
Of course, that number assumes that I’d lived the same amount of time. And sadly, it’s very likely that, if I were really living 300 million years ago, I might have fewer birthdays but I would also not live to see as many. The reason for that is complex, and despite great advances in modern medicine, our lives will most likely always remain finite, for a variety of reasons. Our bodies are constantly bombarded by cosmic rays and particles that age us; toxic compounds in the air we breath and the food we eat put us at constant risk of getting cancer; the inexorable marching of time generally wears on a body.
There is nothing inherently necessary about our 24 hour cycle, our circadian rhythm on the current Earth. If the planet rotated on its axis once every 12 hours, our ancestors would have evolved in sync with it; today we would rise and go to sleep about every six hours. We might live for more days, but we’d probably live the same number of years.
One day, when our species has broken the shackles of the Earth and colonized the solar system, we may have settlements on the distant Jovian moons, or on the planet Neptune. Extraterrestrial humans living on Neptune, the farthest planet from our sun, will take much longer to revolve about the sun—165 Earth years, in fact. Since Neptune takes only around 16 hours to rotate on its axis, that means that a Neptune year has about 3,764 days. If I were born on Neptune on May 18, 1983, today I would be turning 3.
As you can see, since the length of a day depends on both when and where you are in the universe, this all gets very complicated very fast—and it’s all wishful thinking anyway. Today I turn 31, and I’m getting older, and it looks like there’s no way around it.