As a popular subject of study among evolutionary ecologists (进化生态学家), three-spined stickleback is known for their different shapes, sizes, and behaviors — they can even live in both seawater and freshwater, and under a wide range of temperatures. But what makes that?

The researchers tracked six populations of the fish before and after seasonal changes to their environment, using genome sequencing (基因组测序). Seasonal changes result in great changes in habitat structure and balance of salt and freshwater, and only those fish able to tolerate these rapid changes survive into the next season.

“These changes probably resemble the habitat shifts experienced by stickleback populations during the past 10,000 years,” says Professor Barrett. “We hope to gain insight into the genetic changes that may have resulted from natural selection long in the past.”

Remarkably, the researchers discovered the evidence of genetic changes driven by the seasonal shifts in habitats, which mirrored the differences found between long-established freshwater and saltwater populations. “These genetic changes occurred in independent populations over a single season, highlighting just how quickly the effects of natural selection can be detected,” says Professor Barrett, “The findings suggest that we may be able to use the genetic differences to predict how populations may adapt to environment.”

The research emphasizes the importance of studying species in dynamic environments to gain a better understanding of how natural selection operates. In further research, they plan to investigate how repeatable the observed genetic changes are, by testing whether they show up year after year. Doing so would demonstrate their ability to reliably forecast the evolutionary future of these populations.

Researchers say the world has lost more than one fourth of its land-based insects over the past 30 years. The finding comes from a major study of insect populations worldwide. The researchers noted the loss of such insects suggests a more complex problem than earlier research has shown.

Ants, bees, butterflies and other land-based insects have been suffering population drops of about nine percent every 10 years or so. The number of insects on average has declined in the air, in the grass and soil, but not in trees or underground, the researchers found. Some estimates show that land-based insects will face a population drop of 24 percent in the next 30 years. The researchers did not find a link to climate change in the loss of insects. But they did note that widespread effects of growing cities and loss of underdeveloped areas to agriculture.

However，freshwater insects，such as dragonflies and mosquitoes，have been a different story. These insects were found to have experienced a population increase of about 1 percent every 10 years. Freshwater covers only 2.5 percent of the Earth’s surface, so the majority of insects live mainly on land. The researchers said clean-water policies established in recent years were responsible for the increase in freshwater insects.

“The decline across insect orders on land is very surprising,’’ said Nick Haddad，an expert on butterflies at Michigan State University. He was not involved in the study. Ongoing decline on land at this rate will be extremely damaging for ecological systems and for humans, Haddad told the Associated Press. He noted that insects are pollinators (传粉昆虫). They move pollen from part of the flower of a plant to another part. This causes the plant to produce fruit or seeds. Insects also help to break down dead plants and animals. Nick Haddad added that insects also serve as food to many animals, making them very important to the earth’s ecosystems.

Other scientists said the findings made sense. They would go on with the study with more accurate data.

Sharks use their good sense of smell to search for prey（猎物）. But a new study shows that the rising levels of carbon dioxide in the ocean could reduce sharks' ability to find food. It's bad news for a healthy ocean. Sharks are top predators（掠食动物）and are like the ocean's weed controllers.

Dixson works at the Woods Hole Oceanographic Institution in Massachusetts. Her earlier work has shown that clown fish in acidifying（酸化的）water act strangely. "We want to expand this research to sharks .because we know how important it is for sharks to find their food through their sense of smell," said Dixson.

Her team started by placing sharks in each of three different pools for five days. Each pool had a different level of carbon dioxide in it. The first had the same amount as today's ocean water. The second had a level of carbon dioxide that scientists expect to reach by 2050. The third pool had the highest level of carbon dioxide that could develop by the year 2100.

Sharks weren't allowed to eat any food while in the pools. This made sure that they would be hungry. Then, Dixson released the sharks one at a time into a pool with two side-by-side streams of flowing water. In one stream, the researchers pumped water, in which a dead squid had been overnight. This water smelled strongly of the squid. The other stream contained ocean water with no scent（气味）. Because each stream flowed at the same rate and in the same direction, the squid smell stayed in its stream. The sharks could choose to swim in either stream.

Sharks that had been swimming for five days in pools of regular ocean water spent more than 60 percent of their time in the squid-scented stream. The same was true for sharks that had been in water with the carbon dioxide level that could develop by the year 2050. But sharks exposed to the highest level of carbon dioxide spent just 15 percent of their time in the squid-scented stream.