How the fruit fly colonised Europe
Up until 10,000 years ago, if you went looking for the fruit fly Drosophila melanogaster in Europe or Asia, your search would have been pretty unsuccessful, as back then the species was only to be found in sub-Saharan Africa. Today however, the fruit fly is just as common 'out of Africa' as it is within. However, new research from scientists at the University of Veterinary Medicine, Vienna, shows that although the fruit fly's spread north corresponds with the rise of agriculture and the resulting environmental changes, it was in fact genetic factors opposed to environmental ones that triggered the fruit fly's colonisation of Europe and Asia. The study, published in the journal Public Library of Science (PLoS) Genetics, explains how the first fruit flies that moved from sub-Saharan Africa would have found themselves faced with conditions very different from what they were used to, most notably the lower temperatures. As these fruit flies had to adapt to their new surroundings, thousands of years of evolution has resulted in stark differences between the fruit fly populations in Africa and Europe. These differences mainly concern characteristics relating to temperature such as pigmentation, size and resistance to the cold. In a previous study carried out by one of the work's authors, Christian Schlötterer, it was suggested that a single gene protein, known as cramped (crm), could have been involved in helping the fruit flies adapt and survive in the colder climes where they now found themselves. However, there was little proof to support this theory. To build on this work, the team investigated which genes the crm protein, which is a transcription factor, could regulate. They focused on genes known to be key players in wing development, such as the so-called cubitus interruptus (ci) gene, the regulation of which is known to depend on temperature. The results showed that indeed crm protein is required in order for the ci gene to be activated. Following this logic, the scientists thought that if the crm protein is important in the response to temperature it could also be possible to show that variants (or alleles) of the crm protein found in Europe function differently from the variants found in flies who reside in sub-Saharan Africa. To bring to light any of these potential differences in make-up, they removed the effects of other sites in the fly's genome. In the presence of different crm variants they examined how temperature changes affected how the ci gene expresses itself, as well as characteristics like abdominal pigmentation in females and sex combs in males, traits known to be influenced by temperature. And the results showed that the team's conjecture was correct: different crm variants were linked with significant differences in the effects of temperature on these characteristics. As crm protein was found to limit distinct processes at different temperatures, this suggests that changes in crm protein could have been involved in countering the effects of different temperatures on the fly. Christian Schlötterer explains the implications of these findings for our understanding of evolution: 'We normally imagine evolution proceeding by the acquisition of new functions. But the fly's adaptation to a colder environment seems instead to have been accompanied by changes to a master regulator to ensure that previously existing functions were retained despite the changed circumstances.'For more information, please visit:University of Veterinary Medicine, Vienna:http://www.vu-wien.ac.at/en/
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