Wednesday, April 14, 2010

COMMON HOUSE ANTS FORM SUPERCOLONIES, PROSPER IN URBAN SETTINGS

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One of the most common house ant species might have been built for living in some of the smallest spaces in a forest, but the ants have found ways to take advantage of the comforts of city living.

Grzegorz Buczkowski, a Purdue University research assistant professor of entomology, found that odorous house ant colonies become larger and more complex as they move from forest to city and act somewhat like an invasive species. The ants live about 50 to a colony with one queen in forest settings but explode into supercolonies with more than 6 million workers and 50,000 queens in urban areas.

"This is a native species that's doing this," said Buczkowski, whose results are published in the early online version of the journal Biological Invasions. "Native ants are not supposed to become invasive. We don't know of any other native ants that are outcompeting other species of native ants like these."

Odorous house ants live in hollow acorn shells in the forest. They're called odorous because they have a coconut- or rum-like smell when crushed. They're considered one of the most common house ants.

In semi-natural areas that are a cross of forest and urban areas, such as a park, Buczkowski said he observed colonies of about 500 workers with a single queen. He said it's possible that as the ants get closer to urban areas they have easier access to food, shelter and other resources.

"In the forest, they have to compete for food and nesting sites," Buczkowski said. "In the cities, they don't have that competition. People give them a place to nest, a place to eat."

Buczkowski observed the ants in three different settings on and around the Purdue campus. He said it might be expected that if the odorous house ants were able to multiply into complex colonies, other ants would do the same.

But Buczkowski found no evidence that other ants had adapted to new environments and evolved into larger groups as the odorous house ants have. He said it's possible that odorous house ants are better adapted to city environments than other ant species or that they had somehow outcompeted or dominated other species.

"This raises a lot of questions we'd like to answer," he said.

Buczkowski said understanding why the supercolonies form could lead to better control of the pests in homes, as well as ensuring that they don't outcompete beneficial species.

Future studies on odorous house ants will include studying the ant's genetics and trying to understand the effects of urbanization of odorous house ants.

(Photo: Purdue Agricultural Communication/Tom Campbell)

Purdue University

AMOEBA GENOME SHOWS EVOLUTION OF COMPLEX LIFE

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An amoeba with a split personality is giving biologists clues to the ancestry of organisms from fungi to people and insight into how complex organisms evolved.

"We tend to think of protists (single-celled organisms) as 'simple' and humans as 'complex' -- but the Naegleria genome shows us that much of this complexity arose really early in evolution," said Scott Dawson, assistant professor of microbiology at UC Davis.

Dawson is senior author on the paper analyzing the genome of Naegleria gruberi, published in the March issue of the journal Cell. The team also included UC Davis graduate students Michael Cipriano and Jonathan Pham. Dawson had initially proposed N. gruberi as a candidate for genome sequencing back in 2004 while he was a postdoctoral researcher at UC Berkeley.

N. gruberi slurps around in mud as an amoeba but when food runs low it sprouts two whip-like tails, or flagellae, and swims rapidly away. It can also transform into a hard, resistant cyst to wait out bad conditions.

Most previous efforts to sequence the genomes of protozoa have focused on parasitic organisms such as the malaria parasite.

"Because it's free living, it can tell us a lot about early life -- it has genes to do all these different things," Dawson said.

The analysis shows that N. gruberi has 15,727 genes that code for proteins, compared to about 23,000 in humans. With those genes, the organism can eat and reproduce, crawl or swim, live with or without oxygen, and organize itself internally much as a human cell does.

The human body also includes cells that can crawl, such as white blood cells, or that have whiplike tails, such as sperm -- although none that do both. So humans also carry both sets of genes, as did the common ancestor we share with N. gruberi.

The researchers compared N. gruberi's genome to a wide range of other eukaryotes -- organisms that separate their DNA from the rest of the cell -- including green plants, fungi, humans and other single-celled organisms, and found a set of about 4,000 genes that could be traced back to a single ancestor over a billion years ago. Many of those genes have no known function, Dawson said.

"There's a lot of undiscovered biology there," he said.

N. gruberi is harmless to humans, but it does have a relative called Naegleria fowlerii that lives in murky water and can -- rarely -- swim up your nose and eat your brain.

Sequencing was carried out at the U.S. Department of Energy's Joint Genome Institute in Walnut Creek. The joint first authors on the paper published in Cell were Lillian Fritz-Laylin, UC Berkeley and Simon Prochnik, Joint Genome Institute.

UC Davis

UNUSUAL SEX CHROMOSOME CREATES THIRD SEX IN HESSIAN FLIES

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Expectant human parents might wish for a boy or girl, but Hessian flies actually have a third option, and, no matter what, the flies are never surprised by the sex of their offspring.

Jeff Stuart, a Purdue University professor of entomology, and graduate student Thiago Benatti found that a sex chromosome in the mother predetermines the sex of Hessian fly offspring. The chromosome carries a gene called Cm (chromosome maintenance) that can create one of three basic sexes.

"When a mother carries this chromosome, she produces two types of females: female-producing females and male-producing females. Without the chromosome, the mother produces only males," Stuart said. "That means the species is composed of three different sex-related groups."

In humans, an egg contains an X chromosome, and a sperm contains an X or a Y. When sperm and egg unite, offspring with an XX combination become female and offspring with an XY combination become male. In Hessian flies, however, a female with the unusual chromosome, called W-prime (W') produces only females. Half of her offspring will carry the W' and produce only females, whereas the other half lacking the W' will produce only males.

Cm, one or more genes on the chromosome, has caused the evolution of the W' chromosome. It arose because the chromosome combination in Hessian flies isn't created at conception, as is the case with humans, but is established by chromosome elimination during embryonic development.

"I think that the mechanism of embryonic chromosome elimination is an evolutionary remnant of when this insect's ancestors were able to produce offspring without having sex," said Stuart, whose findings were released in the March issue of the journal Genetics.

Understanding the sex-determination process in the Hessian fly could lead to a way to control its populations or eliminate it altogether. The Hessian fly is the major pest of wheat crops, causing millions of dollars of damage annually.

Stuart said it might be possible to genetically modify Hessian flies using the Cm gene to eliminate the fly's ability to produce one of the sexes. Those modified flies could be introduced into fly populations to eliminate it as a pest.

"We're hopefully going to be able to manipulate this to bring the insect to its own demise," he said. "We may be able to use it to drive maladaptive traits into the population."

Stuart said the next step in the research would be to study the evolution of the Cm gene and determine the mechanisms it uses to control sex determination.

Stuart's research was funded by the U.S. Department of Agriculture National Research Initiative.

Purdue University

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