Trillions of evolution’s wonders, red-eyed periodical cicadas (蝉) that have pumps in their heads and jet-like muscles in their bodies, are about to emerge in numbers not seen in decades and possibly centuries. Crawling out from underground every 13 or 17 years, with a collective song as loud as jet engines, the periodical cicadas are nature’s kings of the calendar. These black bugs with bulging eyes differ from their greener cousins that come out annually. They stay buried year after year, until they surface and take over a landscape.

This spring, an unusual cicada double population is about to invade a couple of parts of the United States in what University of Connecticut cicada expert John Cooley called “cicada-geddon”. The last time these two broods (a group of creatures) came out together was in 1803. Thomas Jefferson, the then president, wrote about cicadas in his Garden Book but mistakenly called them locusts (蝗虫). Usually mistaken for hungry and unrelated locusts, periodical cicadas are more annoying rather than causing great economic damage. They can hurt young trees and some fruit crops, but it’s not widespread and can be prevented.

The largest geographic brood in the nation—called Brood XIX and coming out every 13 years—is about to march through the Southeast, having already created countless boreholes in the red Georgia clay. It’s a sure sign of the coming cicada occupation. “They emerge when the ground warms to 64 degrees, which is happening earlier than it used to because of climate change,” scientists said. “The bugs are brown at first but darken as they mature.”

Soon after the insects appear in large numbers in Georgia and the rest of the Southeast, cicada cousins that come out every 17 years will inundate Illinois. They are Brood ⅩⅢ. “And when you put those two together… you would have more than anywhere else any other time,” University of Maryland entomologist Paula Shrewsbury said. “These two broods may actually overlap—but probably not interbreed-in a small area near central Illinois.”

A recent study conducted by the Massachusetts Institute of Technology (MIT) has discovered that river erosion (侵蚀) can lead to increased biodiversity in areas with minimal tectonic (地壳构造的) activity. The researchers focused their attention on the Tennessee River Basin and examined how the erosion of various rock types by the river had led to the separation and diversification of a type of fish called the greenfin darter. As time passed, these separate fish populations evolved into distinct families with genetic differences.

Scientist Thomas Near observed that the greenfin darter was exclusively found in the southern half of the Tennessee River Basin. The researchers analyzed the genes of each fish in Near’s data set and constructed an evolutionary tree. This tree helped them comprehend the evolution and differences of the greenfin darter species. They discovered that the fish within the same branch of the river were more closely related to each other than to the fish in other branches.

This study provides evidence that river erosion significantly impacts biodiversity in regions with low tectonic activity. It illustrates how changes in the landscape caused by river erosion can lead to the division and diversification of species over time, even in peaceful environments. These findings enhance our understanding of the mechanisms (机制) that drive biodiversity and evolution, even in areas that are not typically associated with intense tectonic activity.

Subsequently, the team discovered a strong correlation between the habitats of the greenfin darter and the type of rocks present. The southern half of the Tennessee River Basin consists of hard, tightly packed rocks, resulting in turbulent (湍急的) waves in the rivers that flow through it. This characteristic may be favored by the greenfin darter. As a result, the team assumed whether the distribution of greenfin darter habitats had been influenced by the changing rock types, as the rivers eroded the land over time. To test this assumption, the researchers developed a simulation model. Remarkably, the results confirmed their assumption.

Trained goldfish demonstrated a remarkable ability to accurately estimate the distance. Spatial navigation (空间导航) in mammals, birds, and reptiles is well understood, but it was unknown whether similar structures existed in fish. This knowledge would allow us to better understand how spatial navigation systems evolved.

Researchers from the University of Oxford tested whether goldfish could perform a task central to spatial mapping-distance estimation — to see if they have similar spatial navigation systems to land species. The study, led by Dr. Adelaide Sibeaux, trained nine goldfish to travel 70 cm within a narrow tank covered with a repeating pattern of vertical stripes (竖条纹) every 2 cm. When the fish reached the predetermined distance, they were prompted by an external cue to turn around and swim back to the starting point. The researchers then tested whether the fish would swim the same distance if the external cue was removed and the starting position was changed. They also tested whether goldfish would swim the same distance when the background pattern was changed.

According to the researchers, the results indicate that goldfish estimate distances by visually streaming the apparent motion patterns of objects in the environment (called “optic flow”). Many land species are known to use optic flow to estimate distance, but goldfish appear to process the information differently. Land animals, including humans, ants, wolf-spiders, and honey bees, estimate distances by measuring how the angle between their eye and surrounding objects changes as they travel. Goldfish, on the other hand, appear to use the number of contrast changes experienced on the way.

“We present strong evidence that goldfish can accurately estimate distance and show that they use optic flow to do so,” says lead author Dr. Adelaide Sibeaux. “These findings support the use of goldfish as a model system for studying the evolution of the mechanisms in vertebrates (脊椎动物).”