Can we avoid extinction? Evolution behaving badly

The danger that invertebrate and other forms of life in threatened environments, like tropical rainforests, may not survive climate change now appears more acute than previously thought.

This dismal ecological prospect results from research by biologists at La Trobe University's Centre for Environmental Stress and Adaptation Research (CESAR).

The research team, led by CESAR Director, Professor Ary Hoffmann and PhD student Ms Michele Schiffer, and also included Rebecca Hallas and Jenny Dean, found that a minute inhabitant of Queensland rainforests, the Australian vinegar fly, Drosophilia birchii, does not have the ability to evolve and adapt to drier environments.

Despite breeding the fly through 30 generations in a laboratory simulation of a climate drier than that of the rainforest in which it lives, Drosophilia birchii showed no signs of adapting to the changed conditions. This was despite the use of the classic technique of laboratory 'selection' - breeding from only the 15% of each generation that survived in the changed climate - and a previous history of selection for this trait.

"For three years we looked for signs that this intense selection would increase climatic stress resistance - but it simply did not happen," Prof. Hoffmann said. "Such a lack of adaptive response has never been found and it caught us completely by surprise.

"The question now arises: how common is this, not only for other species in rainforests but for other species in threatened environments?"

These results from Drosophilia birchii stand in stark contrast to those obtained for the more common Drosophilia melanogaster. Selection experiments in melanogaster similar to those carried out in birchii led to an increase of more than 300% in their ability to survive hotter and drier conditions.

"When we look at molecular variation at a random subset of genes in birchii, we find that it is highly variable - similar to that found in melanogaster," Ms Schiffer said. "So on the whole birchii has plenty of variation to adapt to changing conditions. But it turns out that this tells us little about how well birchii will adapt to conditions that are critical for its long term survival.

"The conundrum is that if you look at individual flies, you can see that some survive better than others. So if you breed from the survivors you would expect the progeny to inherit these capabilities.

"But parents with some stress resistance did not reproduce offspring that were resistant. Parents passed on other characteristics such as wing size and shape - but not the ability to survive in a drier, warmer climate," she said.

"This low ability to evolve highlights the importance of assessing evolutionary potential in targeted ecological traits and species from other threatened habitats," Prof. Hoffmann added.

Item provided courtesy of La Trobe University