March 22, 2018

Last month, in February, scientists published the DNA sequence of an invasive species of crustacean known as the marbled crayfish. The animal’s DNA sequence is unique, and the all-female crayfish species can reproduce without mating. The marbled crayfish, Procambarus virginalis, started as an aquarium species. A few of the animals were released into the wild, however, and the species is now threatening many native animals in the Czech Republic, Japan, Madagascar, the United States, and other nations.

The marbled crayfish threatens to crowd out seven native crayfish species in the east African island of Madagascar. Credit: © Ranja Andriantsoa

The story of the marbled crayfish began in the 1990’s. Its origin is not completely clear, but somehow this species carries three copies of each chromosome. Usually organisms carry two sets of chromosomes, one set from each parent. Procambarus virginalis apparently evolved from a species known as the slough crayfish, Procambarus fallax, which lives only in the tributaries of the Satilla River in the southern U.S. states of Georgia and Florida. Scientists believe that the new species was created after two slough crayfish mated in an aquarium setting, but one of them had a mutation in a sex cell. In crayfish, this can happen in response to sudden changes in temperature. If the cell was then fertilized by another individual in the aquarium, it would have resulted in an embryo with three copies of its genome. And just like that, a drastic mutation in a single crayfish produced the marbled crayfish.

Because the marbled crayfish has an additional set of chromosomes, it does not need a mate to reproduce. It basically clones itself through a type of reproduction called parthenogenesis. All offspring of marbled crayfish are female, and they are all very aggressive.

The marbled crayfish reproduced so quickly and prolifically that the animals were doled out to pet shops, given away to private individuals, or, unfortunately, released into the wild. Other species of crayfish cannot compete with the reproductive abilities and aggressive nature of the marbled crayfish, which quickly dominates any habitat it enters. Release into the wild, then, has been disastrous for other crayfish species, whose numbers have been drastically reduced or completely wiped out when faced with marbled crayfish competition. People have taken marbled crayfish to lands far from Georgia and Florida, and now the crustaceans are wreaking havoc on native crayfish populations in parts of Africa, Asia, and Europe. In the European Union and parts of the United States, bans on marbled crayfish aim to curb the animal’s increasing dominance, but the bans may have come too late.

Some scientists consider the marbled crayfish one of the most remarkable species known to science. Discovering a species with such a recent origin and such remarkable reproductive ability is rare. However, ecologists consider it a pest and a nuisance. Marbled crayfish may have some potential benefits, however. They could possibly become a significant food source, and the marbled crayfish’s unique reproductive talents may help scientists understand how cancer tumors adapt and develop resistance to drug treatments.

August 24, 2016

Monkeys in the Amazon rain forest likely entered their own Stone Age more than 700 years ago, according to scientists investigating a fascinating site at Serra da Capivara National Park in northeastern Brazil. At the site, scientists from the University of Oxford in the United Kingdom and from Brazil’s University of São Paulo observed bearded capuchin monkeys (Sapajus libidinosus) using rocks as hammers to crush hard-shelled nuts atop flat stone anvils. The scientists discovered dozens of discarded stone hammers and anvils once they began shallow excavations at a site regularly visited by the monkeys. The scientists determined that monkeys have been using simple stone tools at that site for more than 700 years. The findings were described in the July 2016 issue of the journal Current Biology.

A capuchin monkey uses stones to crack a cashew nut in Serra da Capivara National Park in northeast Brazil. Credit: © Michael Haslam, Primate Archaeology Project/University of Oxford

Stone Age is a term used to designate the period when prehistoric people used stone, rather than metal, tools. For humans, the Stone Age began about 3.3 million years ago, when small stones were first made into crude chopping tools by prehuman ancestors called Australopithecines. It ended in the Near East about 3000 B.C., when bronze replaced stone as the chief material from which tools were made.

In dry northeastern Brazil, hard-shelled fruits and seeds are more common than the fruit and succulent leaves that capuchins prefer. Centuries ago, a clever capuchin figured out how to pound open a nut using a heavy stone as a hammer on a heavier flat stone anvil, thereby opening up an entirely new and abundant source of food. The scientists observed that the monkeys will carefully select hammer stones and bring them to trees bearing nuts and fruits. The monkeys then stash the stones in hidden spots around the trees for later use. The research site in Brazil is littered with such stones that have accumulated over centuries.

For many years, scientists considered humans to be the only species that made extensive use of tools. In the 1960’s, however, naturalist Jane Goodall discovered that wild chimpanzees in Africa make and use simple tools. Goodall observed them stripping tree twigs and using the twigs as tools for catching termites. She also observed chimpanzees using rocks to break open hard-shelled palm nuts in the forest.

Earlier in 2016, some of the scientists involved in the Brazil research published observations of monkeys called macaques using stones to break open shellfish and nuts in Thailand. Now, with the Brazilian study, there seems little doubt that some species of nonhuman primates have long since entered their own Stone Age. The site in Brazil provides scientists with a unique opportunity to study the ecological, social, and cognitive (mental) factors that likely played a role in the development of technology and culture millions of years ago at the dawn of humankind.

March 15, 2012

The area covered by trees in many United States cities is declining, reports the U.S. Forest Service, and that loss of trees–as many as 4 million annually–translates into an astronomical loss in energy efficiency. According to the Forest Service, urban trees greatly decrease heating and cooling costs, by as much as $2,500 over the lifespan of a mature tree; improve air and water quality; and help control water drainage and erosion. The Forest Service calculates that the financial loss of an urban tree is, thus, three times greater that the cost of maintaining it.

Forest Service researchers David Nowak and Eric Greenfield arrived at their conclusion by comparing aerial photographs of 20 urban areas from the years 2002 to 2010 and evaluating the differences in the canopy coverage. They found that the tree cover in 17 out of the 20 cities had declined. New Orleans, Louisiana, had the largest decrease. (The research suggests that much of the tree loss there was a result of Hurricane Katrina in 2005.) Only one of the 20 cities–Syracuse, New York–showed an increase in the amount of tree cover.

Many urban trees are lost to the artifically made objects in a designed landscape. This is known as “impervious cover,” which includes rooftops and pavement–streets, sidewalks, and parking lots.

Trees across North America are under attack by a number of different diseases and pests. Urban trees are especially threatened by the emerald ash borer, the Japanese beetle, and a number of fungal diseases, including the Dutch elm disease.

Ginkgo trees are popular for city plantings because they are largely resistant to air pollution as well as various tree diseases. (Atoz)

Tree-planting programs in many cities have helped to slow tree loss but have not been able to reverse the larger trend. In an effort to make city planning more tree-conscious, the Forest Service is providing cities with a free software program entitled i-Tree Canopy. The program lets users analyze changes in an area’s tree coverage by pairing aerial photographs from different time periods. U.S. Forest Service Chief Tom Tidwell hopes the tool will help communities plant and maintain trees more effectively.

Additional World Book articles:

• Conservation
• Green building
• Ecology
• Trees Under Threat (a special report)