Duke Research - July 2011

July 25, 2011

Drawing a Line on Preservation

Conservation programs that perform captive breeding for endangered animals – like the Duke Lemur Center – face a difficult choice when choosing pairs to breed.

DNA analysis suggests that some populations of rare animals which have been isolated from one another by fragmented habitat may in fact be distinct sub-species. If they've been separated long enough without mating opportunities, their genomes have evolved subtle differences.

On the one hand, some conservationists argue that breeding programs ought to preserve those differences by avoiding mixing animals from different areas.

But on the other hand, there may not be enough captive animals in any one of these substrains to maintain that kind of purity without in-breeding the captive animals. And soon, there may not be enough of them in the wild either.

What to do?

Ingrid Porton, curator of primates at the St. Louis Zoo, talked her colleagues through the issue on Monday during the annual meeting of the Madagascar Fauna Group on the Duke campus.

Some of the difficulty comes from the way different branches of biology think about species, Porton said. "Little did I know, there are actually 26 definitions for species!" But this isn't just an academic exercise; the crisis in lemur habitat is real and growing worse every day. "We don't have a lot of time to deal with this. Every animal is drastically important."

The drive for keeping subspecies distinct "comes from a good place," said Duke Lemur Center Director Anne Yoder. But it may not be in the best interest of the bigger picture of species preservation.

Participants in the two-day meeting of the MFG being held at Duke this week agreed that they'll probably need at least a political consensus in the absence of a scientific one.

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Tags: animals, biology, genetics/genomics, Lemurs

July 21, 2011

Flying high on stolen wings

Guest post by Viviane Callier, Duke biology

The wing color patterns on some butterfly species have evolved to copy wings on other butterfly species. In Heliconius butterflies, which are toxic to birds, the convergence of several species on the same wing color pattern gives them all mutual benefit – birds recognize one pattern saying “I’m poisonous; don’t eat me!"

On these butterflies, wing color pattern is primarily driven by differences in red coloring. Now, a team of researchers has discovered that a single gene, known as optix, controls where on the wing this red coloring appears. The results appear in the July 21 Science Express.

The researchers, including a Duke team led by biologist Fred Nijhout, studied species of Heliconius butterflies from five distinct regions in South America. Their color patterns differ depending on the region, but species co-existing in the same region have evolved wing color patterns that mimic each other.

This raised the question of how a single species has the ability to develop different color patterns in different regions, and also how different species have evolved convergent wing patterns in the same region, says Nijhout, who co-authored the new study.

He worked with the study's lead author, Robert Reed, a biologist at UC-Irvine and former postdoctoral researcher in the Nijhout lab, and also Mississippi State biologist Brian Counterman (a former graduate student of Duke evolutionary geneticist Mohamed Noor) to do gene mapping and expression, as well as population studies, to find that this optix gene controls the red color patterns on multiple Heliconius species.

This is the first study to identify a gene that controls mimicry, one of the most spectacular examples of convergent evolution by natural selection. And, according to the research, the observed convergence and divergence in the expression of optix does not come from changes in the protein coded from the gene. Instead, the expression comes from changes in the regulatory regions of optix, which ultimately change the new color patterns on the butterflies' wings.

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Tags: biology, genetics/genomics, research

July 13, 2011

Cooperating E. coli eat better

Guest post by Viviane Callier, Duke biology

In such a competitive world, it's surprising to find examples of animals working together rather than trying to outdo one another. But, under certain conditions, even lowly bacteria like E. coli cooperate to survive and thrive.

Figuring out how they do it could help doctors fight the human infections bacteria cause.

As they eat, bacteria make juices, or enzymes, that break down their environment, the plants and rotting wood they digest. The juices fill a bacterium's surroundings, so the producer not only gets the benefit of its digestive effort, but its neighboring bacteria do too.

Alone, one bacterium can't make enough juice to break down its food, and scientists thought that the cost to bacteria to make their digestive juice independently was too high so they won't get enough benefit back in terms of nutrition and growth.

Working in groups, however, all individuals share both the metabolic cost as well as the benefit of getting nutrition. Bacteria, therefore, have to have a method, called quorum sensing, to detect if they had enough neighbors to make juice and eat, says Duke graduate student Anand Pai.

Although it made sense for bacteria to produce their juice only when there are a lot of them in a small environment, the direct relationship between quorum sensing with bacterial growth success wasn't clear, Pai says.

At least it wasn't, until he worked in the lab of biomedical engineer Lingchong You to change the genetic material of bacteria and test the idea of quorum sensing. To do this, Pai engineered three types of bacteria: one type was unable to sense its neighbors and secreted digestive juice all the time. The second never produced juice. The third produced juice only when it sensed it had a lot of neighbors.

Measuring bacteria's growth rates, Pai saw that the bacteria that couldn't sense their neighbors grew more slowly than the bacteria that never produced juice or those that produced juice only when they had a lot of neighbors.

In other words, bacteria do seem to pay a metabolic cost for producing their digestive juices. Their ability to sense their neighboring bacteria and secrete enzymes together improves their ability to grow. But, keeping bacteria from sensing each other could lead to better defenses against bacterial infections and an alternative to antibiotics.

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Tags: biology, biomedical engineering, research