In 1859 an Australian farmer named Thomas Austin released 24 grey rabbits from Europe into the wild because it "could do little harm and might provide a touch of home, in addition to a spot of hunting."
One of the most damaging invasive species in history, kudzu, or Japanese arrowroot, found its way from Japan to the southeastern United States, where it is overtaking much of the landscape. An ecological concept known as the Allee effect governs the spread of invasive species and pathogens, according to a Duke University team that has tested the concept in engineered bacteria.
Credit: Wikipedia Commons
By the end of the century, the rabbits had begun to overrun native ecosystems, reaching nationwide numbers of 600 million by 1950. They were propagating under a principle known as the Allee effect - the observation that larger groups of animals do better at establishing populations in a new environment. Had Austin instead spread the rabbits into many smaller groups across the landscape, things might have turned out differently.
With the help of E. coli and some clever synthetic biology techniques, engineers at Duke University have now tested the limits of the Allee effect. The results have implications for both ecologists dealing with invasive species and medical practitioners fighting infections.
Organisms exhibiting a very strong Allee effect need a certain number of individuals to survive, below which the group will collapse. And while intuition suggests that the more places a species spreads, the more it will thrive, scattering a population too thin by forming too many new colonies could result in the ruin of them all.
The paper appears online in the Proceedings of the National Academy of Sciences the week of Jan. 20."From the perspective of an invasive species, it appears to be a good idea to spread out to many different habitats simultaneously," said Lingchong You, associate professor of biomedical engineering at Duke. "If they all survive, the overall growth is much more efficient. But there's a catch because of the Allee effect; there is also a greater chance each population will fall below the critical threshold and every location will fail."
into, you might inadvertently help them thrive."
In the experiment, researchers engineered E. coli to produce a toxin that, left to its own devices, would soon wipe out the entire colony of bacteria. But they also put in a genetic switch that could turn their fortunes around; if enough bacteria were present and the chemicals they use to signal one another reached a certain concentration, they would begin producing an antidote to the toxin. In this way, the bacteria were engineered to have a high Allee effect.
The researchers then tested how well the bacteria did with different dispersal rates. They plucked the bacteria from their original source wells and colonized new ones. Each trial consisted of a different number of target habitats, which affected the density of the new populations.
Just as theory predicted, the greatest success came when the dispersion rate stayed in a happy middle ground. Too few new colonies and the bacteria barely spread; too many and each floundered, including the original source.
The results also have important medical implications, according to You.
"People need to use caution when using antibiotics," said You. "Our bodies' natural microbes are in some ways the first line of defense against invaders, which can often stop an infection from gaining a foothold. But if we recklessly apply antibiotics, we may destroy these defenses and make it easier for just a few foreign bacteria to spread and grow. We may remove their Allee effect."
Their work was supported in part by the National Science Foundation grant CBET-0953202 and the National Institutes of Health grant 1R01GM098642.
CITATION: "Programmed Allee effect in bacteria causes a tradeoff between population spread and survival," Smith, R.P., Tan, C., Srimani, J.K., Pai, A., Riccione, K.A., Song, H., You, L. PNAS, Jan. 20, 2014. DOI: 10.1073/pnas.1315954111
Ken Kingery | EurekAlert!
Preservation of floodplains is flood protection
27.09.2017 | Technische Universität München
Conservationists are sounding the alarm: parrots much more threatened than assumed
15.09.2017 | Justus-Liebig-Universität Gießen
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
19.10.2017 | Materials Sciences
19.10.2017 | Materials Sciences
19.10.2017 | Physics and Astronomy