A vole (photograph by Dr Anna Kołodziejczyk)

"Predatory" voles bred by biologists are not only more eager to hunt crickets, but also more aggressive towards one another and their own offspring. It would take thousands of years of evolution for these traits to develop outside of a laboratory.

The JU Institute of Environmental Sciences houses an artificial colony of voles which is the largest in Poland and one of the largest in the world. Currently it is composed of about 2,000 specimens. When a new generation of young voles is born, and the older ones are still alive, the colony comprises over 4,000 animals.

The researchers have bred three different groups of voles: aggressive "predators," "vegetarians" adapted to low-nutrition diet, and "athletes" with an enhanced oxygen uptake efficiency.

Everything began in 2000, when 320 wild bank voles (Myodes glareolus) were caught in the Niepołomice Forest. First, they were bred for three years. Next, the biologists began their selection.

"Our goal was to ensure the voles would have a large pool of ‘wild genes.' If we conducted a similar experiment on laboratory mice, we would be much less likely to succeed, since mice are more gentle and calm due to years of selective breeding," said Dr Agata Kołodziejczyk.

First, the biologists have conducted a series of behavioural test to determine which voles are the most aggressive. After that, they were crossbred to achieve specimens with a highly developed predatory instinct. The process was repeated for "athletes" and "vegetarians."

A vole's predatory instinct was determined by the time it took before attacking a cricket introduced into its habitat. "At first, they had to go hungry for up to twelve hours before they even looked at the cricket. Satiated voles were not interested in eating insects," said Dr Kołodziejczyk.

After several generations of crossbreeding, the voles became more interested in hunting crickets. Most of them attack the insects after 6 hours of food deprivation, about 30 seconds after they spot it. Previously, this process was significantly longer.

Outside of a laboratory, such evolution would take thousands of years.

The most predatory voles differ from their more peaceful brethren not only in behaviour and physiology, but also anatomy. For instance, the predators have larger brains: 0.55 grams versus 0.50 grams.

The colony is well secured and only accessible for authorised personnel. The specimens are kept in locked cages in environmental chambers, each of them with its own tag and identification number. It is impossible for the animals to leave the colony on their own. "We keep two or three animals in one cage. If we see aggressive behaviour, we separate them," Dr Kołodziejczyk added.

The Kraków laboratory also breeds "athlete" voles, with an enhanced metabolism and oxygen uptake efficiency. "The selection is based on the results of cardiac stress test we conduct when a vole is swimming. It is surprising for many that voles are very frequently avid swimmers. We put them in a container filled with warm water and measure the animal's vitals. The test is 18 minutes long. Voles need not to put excessive effort into swimming, just like humans in salt water. Some of them decide to just float, but others seem to enjoy it. The specimens with best test results are then crossbred. They're more physically active than other voles, they like to move around," said Dr Kołodziejczyk.

One of the central aspects of evolutionary physiology is studying the mechanisms which reshape organs and physiological processes. It is difficult to study such processes in the field by analysing pieces of the genetic puzzle formed over the course of several million years. It is significantly easier to simulate genetic processes by recreating and accelerating them in a laboratory. The experiment's originator is Prof. Paweł Koteja, head of the Evolutionary Physiology Research Team at the JU Institute of Environmental Sciences.

(source: PAP - Science in Poland)