Update: The origins and ends of species, and how inbreeding may hasten the demise of sea lions

Charles Darwin wrote a lengthy tome about the nature of species. Now scientists have managed to artificially transformone species into another by rearranging chromosomes. A team led by Professor Stephen Oliver of Manchester University hasconverted one species of yeast into another as part of an experiment that reveals much about how one species can become genetically isolated from another.

Professor Oliver, working with Isabelle Colson of the University of Wales, Bangor, rearranged the chromosomes of Saccharomyces cerevisiae so they were identical to those of its close cousin S. mikatae. (Saccharomyces is the yeast used by bakers and brewers.) Normally the two microbes cannot interbreed to produce fertile offspring. After the induced mutation they could, although the offspring were not fully fertile.

The study, published in the journal Nature, shows that chromosome rearrangements may be important for driving the evolution of new species. "Our engineered baker's yeast calls into question how we define species," asserts Professor Oliver. "We have shown that chromosome arrangement plays a key role in differentiating between species, so by simply changing the arrangement of the chromosomes are we effectively creating a new species?" he asks.

One central tenet of biology is that close interbreeding within a group of animals eventually produces genetically weakened offspring. This has been supported by a Cambridge University study which analysed the genetic makeup of sick sea lions caught off the coast of California. The team, led by William Amos, found that sea lions born to related parents took longer to recuperate and were affected by more infectious diseases and cancer than thoseborn to more unrelated parents.

"Our findings carry two messages," says Professor Amos. "First, susceptibility to a wide range of diseases, from algal toxins to cancer, appears to be strongly influenced by how related the parents are. Second, since relatively inbred sea lions tend to carry multiple infections, these individuals may provide an easy route by which diseases enter the population. This has strong implications for conservation biology, where the impact of disease may be critical."

The study, published in Nature, looked at the DNA of almost 400 stranded sea lions at the Marine Mammal Centre in Sausalito, near San Francisco. The findings suggest, according to team member Karina Acevedo-Whitehouse, that when conservationists face difficult decisions about saving wildlife it might be more effective to concentrate on individuals affected by non-infectious agents, such as trauma, oil and toxic algal blooms. "This study provides some insight on how we may be able to increase the cost-effectiveness and efficiency of wildlife rehabilitation."