I always assumed that the ‘passion’ in ‘passion flower’ somehow referred to the plants’ exotic, almost sensual beauty—a combination of layered stigmas and anthers, colorful radial filaments, and delicate petals and sepals make the passion flower almost too beautiful to be real, especially in a place as non-exotic as the southeastern United States. Here, the passion flower Passiflora incarnata can be found growing as far north as Pennsylvania.
Imagine my surprise when I read that ‘passion’ actually referred to the crucifiction—or passion—of Jesus! That had to be a joke. But, as it turns out, that is where the name came from.
The passion flower—Flos passionis—got its name from seventheenth century descriptions of the flowers by Spanish priests in South America. Back then, the plant was known as ‘La flor de las cinco llagas’ or ‘The flower with the five wounds’. Those five wounds are the five sacred wounds suffered by Jesus during his crucifixion, represented by the five stamen with anthers. Above those, the three stigmas are the nails used during the crucifixion.
The coronal filaments—arguably the most striking feature of most Passiflora—represent the crown of thorns. Under the filaments, the five petals and five sepals are the 10 faithful disciples, minus Judas and Peter of course. This symbology can be seen in a 1610 drawing by Eugenio Petrelli for a book by the Jesuit Antonio Possevino.
And passion flower isn’t the only holy moniker to be used through the ages based on this symbolism: ‘Espina de Cristo’ (‘Christ’s thorn’), ‘Dorn-Krone’ (‘crown of thorns’), ‘Christus-Krone’ (‘Christ’s crown’), ‘Christus-Strauss’ (‘Christ’s bouquet’), ‘Marter’ (‘passion’), ‘Jesus-Lijden’ (‘Jesus’ passion’), and ‘Muttergottes-Stern’ (‘Mother of God’s star’) have all been used.
Personally, I see all this symbolism as a stretch—the passion of Jesus isn’t nearly the thing that comes to mind when I look at Passiflora. But whatever symbolism one ascribes to this flower, I think it’s safe to say that it is inarguably beautiful.
The Kapok tree, known to science by its Latin name Ceiba pentandra, is a true rainforest giant, perhaps the largest of all Amazonian trees, and among the largest trees in the world. Biologists call the Kapok an ‘emergent’ tree—that is, it emerges from the forest canopy and, with individual trees being measured at 150 ft. or more, easily towers over the rest of the forest.
Being very tall presents a number of problems for a tree. First of all, the emergent crown of the Kapok, unshielded by its diminutive neighbors, stands ready to catch any large gust of wind that might come along. And, with a shallow root system common among tropical rainforest trees, the Kapok faces the very real danger of toppling over during storms that occur frequently across the tree’s geographic range.
The Kapok solves the wind problem with buttresses—large, triangular projections that connect the tree’s trunk with the roots in the ground. Indeed, the buttresses of a mature Kapok can be impressively large, and they are very effective. In a study of other buttressed rainforest trees on the tropical island of Borneo, trees that had their buttresses experimentally removed by researchers quickly fell.
But wind isn’t the only factor potentially limiting a tree’s size. Emergent rainforest trees, like all other plants, require water, and extreme height poses a monumental challenge in the uptake and transport of water from the roots—from where water is drawn—to the leaves, where it is needed most, high in the tree’s canopy.
Given its towering height, how does the Kapok get water 150 feet or more off the ground?
The answer is best explained by physics. More specifically, it is largely capillary action that allows the tree to transport water so high.
Two fundamental phenomena underlie the capillary mechanism. The first is cohesion—the weak chemical bonds that allow individual water molecules to attract one another. Cohesion is responsible for the fact that a drop of water resting on the top of your hand, say, retains its rounded shape. This can also be thought of as surface tension—the reason that small insects can glide across the surface of a body of water. The second phenomenon underlying capillary action is adhesion—similar weak bonds that allow water molecules to attract, or adhere, to other substances. The reason, say, that the same drop of water will cling to the top of your hand when turned upside-down.
At the very top of the Kapok, in the tree’s crown, tiny pores known as stomata on the surface of the leaves open directly to the atmosphere. Rays from the sun strike the leaves and provide the energy needed by water molecules there to evaporate. The stomata are the exit points of the woody xylem—essentially long, thin, tube-like vessels that extend from the leaves, unbroken, all the way down through the tree trunk to the roots. As a water molecule breaks the surface of the water column in the leaf’s stoma and evaporates, cohesive forces cause it to tug upwards on the molecule or molecules directly behind it, which in turn pull on other molecules, and so on all the way down each xylem vessel to the roots.
Through capillary action, the tree is able to fight the enormous influence of gravity and transport the water it needs to incredible heights—all without the aid of any active pumps or large amounts of energy input. And the process is incredibly efficient. A single Kapok tree might be able to transport as much as 1,000 liters of water to its crown in a single day!
With the problem of water transport solved, the Kapok is free to invest in other problems that require its attention and energy. And in the rainforest, those problems are numerous—herbivores, diseases, and growth in a nutrient-poor environment are just a few. Thanks to some simple yet extraordinary physical properties of water, the Kapok is able to meet these demands and thrive, towering over the rest of the rainforest and inspiring us with its awesome size and beauty—what little of it we can appreciate from just its giant roots, anyway.
By Geoff Gallice
Bright colors in nature generally indicate danger. A brightly colored animal, for instance, typically uses its flashy hues to warn potential predators of a threat it might pose. Usually that threat is chemical: animals, ranging from insects and other invertebrates to frogs and snakes, have evolved a bewildering array of toxic poisons, venoms, and other chemical surprises that await would-be enemies. Bright colors help predators remember unpleasant experiences—they quickly learn to avoid the colorful meal that made them sick or stung them.
The passion-vine butterflies are a group of brightly colored or aposematic butterflies found throughout the rainforests of Central and South America. The most diverse genus is Heliconius and, as its common name suggests, this group of butterflies feeds on passion vines that are loaded with compounds known as cyanogenic glycosides—you don’t need to be a biochemist to guess that the cyan at the beginning of that name means it isn’t good to eat.
The glycosides are not harmful to Heliconiusbutterflies though. In fact, the butterfly larvae greedily devour vines that are high in these compounds. From them they are able to synthesize derivatives—similar chemical forms—that can be stored in the butterfly’s tissues.
Thanks to its diet of passion vines, a Heliconius butterfly is a mouthful of toxic, foul-tasting poison to a predator, which, in the day at least, is usually a bird. And since Heliconius are brightly colored, birds quickly learn to avoid them. Thus, the butterflies are chemically defended and, once the local birds have been educated, have essentially no diurnal enemies.
But what happens at night, when visual signals are less effective as a warning to nocturnal predators that hunt without good eyesight? Bats, for instance, hunt at night using echolocation or sonar, in which high-frequency sounds are produced and distance and direction to prey are judged largely by the time taken for the sounds to bounce, or echo, back to the bat’s ears. With echolocation, eyesight is unnecessary, and bats that echolocate are able to hunt very effectively even in total darkness. Many have monochromatic or otherwise very poor vision.
One peculiar aspect of Heliconius butterfly biology is their roosting behavior—that is, at night, they sleep collectively in aggregations. Roosts may contain as many as 10-15 individuals, although typically the number is less. The butterflies begin to gather at sunset and take as much as one hour to settle in for the night; they use tiny hooks at the ends of their feet to hang, upside down, from nearby small branches and the tips of dead twigs.
Many biologists believe that animals aggregate in order to dilute the effects of predation. Think of the chances of a buffalo being picked off by a lion alone versus in a large herd. The same should be true for aposematic butterflies in the daytime—considering that their bright colors most likely serve as a warning to birds, daytime Heliconius roosts would make a lot of sense. But the butterflies roost together at night, and it’s not clear why.
As a graduate student interested in tropical butterfly biology at the University of Florida, Christian Salcedo wanted to understand why Heliconius roost at night. Do the butterflies have any predators? Could they be using unseen signals to fend off attack, much in the way they use color in the day?
Salcedo decided to employ technology to study the question of Heliconius roosting at night. He created a camera system—he called it a “stand-alone nocturnal infrared camera system”—that would catch Heliconius predators in the act by activating video when an infrared beam was crossed.
After a number of nights the remote cameras had recorded several disturbance events, during which an animal—there was an agouti, an armadillo, a rabbit, and even a few stick insects—disturbed the butterflies, causing one or more of them to rouse momentarily from their sleep. In a jungle bumping with nocturnal creatures, this wasn’t very surprising. However, the most interesting event occurred when a bat was observed picking a Heliconius butterfly from its roost. Several moments later, the butterfly returned, apparently unharmed, to its roost-mates. Of course, Salcedo captured the event on video.
Watch videos of Heliconius roost disturbances here:
In some ways, these experiments shed light on the mysterious Heliconius night roosts. Based on the footage gathered with the remote camera system, we now know that Heliconius probably do have nocturnal predators. But the fact that the cameras recorded a butterfly returning to the roost after an attack, unharmed, actually raises many more questions.
Did the cameras capture an instance of predator education? That is, the bat clearly tried but did not eat the butterfly—in the video, do we witness the learning event that results in other Heliconius avoiding attack by at least this individual bat? If so, how can the bat recognize future roosting Heliconius and know to stay away?
Some bats are able to see ultraviolet light, which is reflected by parts of the wings of Heliconius. Could that be the key mechanism? Or perhaps predators like bats are able to smell pheromones or other chemical signals produced by the butterflies that act in a similar way as bright colors in the daytime, preventing a repeat bad-taste experience. Do bats typically capture prey and assess their palatability before deciding to devour them or let them go unharmed?
Video footage of a nocturnal attack is tantalizing, but we still have a lot to learn about the roosting behavior of Heliconius butterflies. The rarity of nocturnal attacks on the butterflies—Salcedo’s experimental roosts were attacked only several times in hundreds of hours of filming—make the matter of studying them more difficult. But, as is increasingly the case, technology coupled with a curious, motivated young graduate student willing to brave long, late hours and harsh tropical conditions can make great discoveries regarding the fascinating phenomenon of the roosting passion-vine butterflies.
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.