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Photo Source: Deep Look I jump! I jump! I'm jumping!

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The convenience store near home will sell a magic bean, hold it in your hand, or put it on the sunny ground, and it will keep shaking, rolling, and even jumping up and doing a somersault. Sometimes when you lie in bed, put a few beans in a box, and then put the box under the pillow, you can hear the "happy" jumping sound of a few beans, just like a group of buddies jumping. Or put it on the table and let them jump to play games with us and answer their own question: what are you going to eat tonight?

These magic toys, Mexican jumping bean, which are full of attraction to children, are a kind of plant no matter how you look at them. Did magic make them jump? This is probably the inner confusion of many children in Mexico and nearby areas.

In fact, many plants can move, such as dancing blades of grass dancing up and down, sunflowers turning, and "long legs running away" when wheat ears are ripe, but these are all due to the directional movement of plants stimulated by the external environment. The Mexican jumping bean is a bit special. It can jump because there is really a "little driver" inside-the larva of a kind of moth (Cydia saltitans).

Mexican jumping beans (Photo: Deep Look) the "beans" of Mexican jumping beans were originally the seeds of a Sebastiania pavoniana shrub in the mountains of Mexico, usually brown or brown, with flat sides and curved sides that look like half a hazelnut. But the jump of jumping beans has nothing to do with plants. When shrubs bloom in spring, moths lay their eggs on developing hanging pods. After the eggs hatch, the tiny larvae drill into the immature green pods and begin to eat the seeds. As the pod matures, it falls to the ground and splits into three parts. Among them, beans with moth larvae inside become Mexican jumping beans.

The three-petaled pod (Photo: DeepLook) jumps between life and death. After drilling into the seed, the larvae will keep wriggling on the pod wall to form a soft silk "lining". Air and water seep into the bean through the holes in the pod wall, creating a comfortable and comfortable environment for the sojourner. But life can't always be this easy.

Bean moth larvae (photo: Deep Look) lie comfortably in pods because the shrub lives in a hot, dry area with high sunshine intensity. Whenever the sun comes out, the temperature of the earth's surface rises rapidly. If the sun is allowed to shine directly, the high temperature will cause the rapid loss of water in the larvae, which is fatal to the larvae.

So they must work hard to curl up and stretch out while grasping the silk lining, banging their heads against the pod wall. At this point, the beans will roll or jump. They need to keep beating until they move to a cool, cool place so that they can survive long enough for the pupal stage of metamorphosis.

It doesn't look difficult, but when it's too hot, jump, jump, jump to a cooler place. But for the larvae trapped in the "home" and completely unable to see the external environment, every step is a matter of life and death. If the larvae do not spit out the silk lining on the pod wall in the early stage of growth, the larvae can rotate freely in the beans, but they will not be able to fix themselves at a point through their small claws and they will not be able to really roll. And if they jump around, but still can't find shade, they will die.

But as long as there is enough time, most jumping beans will always find a temporary place to stay away from the sun. Pasha Tabatabai, a physicist at the University of Seattle, and Devon McKee, a computer scientist at the University of California, Santa Cruz, are curious about how these larvae find shade step by step in hot weather. If I were a bean and not in the shadow, "Tabatabai said," I just want to know what the probability of finding the shadow is.

I have a special forward strategy, and they finally found that the trajectory of these jumping beans followed the random walk strategy, a study published in physical Review E (Physical Review E) on February 25 this year.

The random walk strategy dates back to 1827, when scientist Robert Brown (Robert Brown) studied pollen grains floating in the water under a microscope and observed that pollen was wobbling strangely. Brown thinks the pollen is alive. But when he looked at the dust particles that were clearly not "alive" with a microscope, he observed the wobble behavior again. Brown has never been able to determine what makes these inanimate bodies move.

Until 1905, when Einstein tried to confirm the existence of atoms and molecules in a paper, he proposed that fluid molecules such as water move randomly and collide with other small particles suspended in the fluid, such as pollen or dust. this leads to the irregular motion of tiny particles in the fluid observed by Brown about 80 years ago.

Brownian Motion (Photo: Wikipedia) in order to depict Brownian motion more accurately, we can imagine ourselves walking along a straight line. For each step, toss a coin, if it is facing up, go forward; if it is facing up, take a step back. Because the result of each coin toss is independent of other results, the probability of heads or tails of each coin toss is always the same. This also means that our final position is independent of the original starting position, so it is called a random walk.

The insect philosophy of letting nature take its course in order to study the strategy of jumping beans, the researchers designed experiments to try to count the jumping behavior of jumping beans and describe them quantitatively. A previous study has identified a range of 20 ℃ to 30 ℃, which is the ideal temperature range for the most active jumping behavior of jumping bean larvae. Another study found through statistical research that jumping beans basically have three types of sports behavior: flipping, rolling and jumping. Among them, jumping is the most common, accounting for about 87%.

On the basis of these studies, McGee and Tabatabai covered an electric heating pad with aluminum plates to build a temperature-controlled plane. Among them, the aluminum plate can ensure uniform heat dissipation, and the infrared thermometer can be used to track and record the surface temperature of the aluminum plate, which can also ensure that the jumping bean is always in the temperature range with the most active jumping behavior. They also placed a blank piece of paper on the aluminum plate to facilitate comparative imaging.

A total of 37 active Mexican jumping beans were used in the experiment, each of which was allowed to jump freely for more than an hour, while two scientists collected the position data of each of them. based on these data, a computer simulation image is created to describe the trajectory of each bean.

The random walk trajectory of jumping beans (photo source: original paper) shows that almost every jump of beans takes place within 10 seconds, and their trajectory is consistent with the random walk model. Even if the degree of friction between the beans and the flat surface of the platform was adjusted in the experiment, they always adhered to the random walk strategy. This led two scientists to wonder whether random walking is the most effective strategy for jumping beans to avoid direct sunlight.

In general, a random walk that can traverse the entire map seems inefficient. So they combined less random motion patterns with random walks on the computer to simulate the process of looking for shadows. They found that although exercise mixed with non-random processes did make jumping beans find shadows faster, overall, only a small number of beans succeeded. Using the random walk strategy, jumping beans took longer to find shade, but they were much more likely to succeed in finding shade and survive.

In other words, random walking does not optimize efficiency, but it minimizes the probability that jumping beans will never find shade when there is little shade.

Tenacious and fragile survivors from late summer to early winter, pods that fall to the ground need to jump after the sun rises, hoping to find shade to survive. Until winter, it will be ready to cocoon into a pupa. But before cocooning, these larvae with sharp mouthparts also need to prepare themselves for adults-they need to cut open an "escape door" at one end of the cocoon (miraculously, these doors are like electric drills. It is an extraordinarily regular circle). It is convenient for adults without mouthparts to push open the door directly to gain freedom.

But freedom may not be the real goal of this animal, which lives only three to seven days after it is transformed into a bean moth. And if there are no such bushes they are familiar with nearby, they will not lay eggs. In a way, this also makes the economic losses caused by the Mexican bean moth manageable.

The larvae of this moth spend most of their lives in an almost dark environment, surrounded by the same walls and eating the same food every day. It looks safe and idle, but the larvae who have to bump their heads every day to survive say: it's really hard to grow up!

Reference link:

Https://arstechnica.com/science/2023/02/taking-a-walk-on-the-random-side-helps-mexican-jumping-beans-find-shade/

Https://www.sciencenews.org/article/jumping-beans-strategy-shade-moth

Https://www.youtube.com/watch?v=3lkdidU79TY

Https://pubmed.ncbi.nlm.nih.gov/22573786/

Https://en.wikipedia.org/wiki/Mexican_jumping_beanhttp://www.waynesword.net/plaug97.htm

This article comes from the official account of Wechat: global Science (ID:huanqiukexue)

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