Evidence for evolution of guppies in a semi-natural environment

In Burgers' Zoo (Arnhem, the Netherlands) a large enclosure was build to mi mic a tropical rain forest. In this so called 'Bush' several ponds exist in which guppies (Poecilia reticulata) can be found. One of these ponds conta ins caymen and is therefore in a secluded area of the Bush were other anima ls can not enter. Among these other animals are snakebirds (Anhinga melanog aster) which in the rest of the Bush predate on guppies devouring up to a 1 000 guppies a day. After several years it became noticeable that the guppie s which were initially from the same stock, differed between the Cayman pon d (without predation) and the Seacow pond (with predation). The two populat ions showed marked differences in length and colouration. Young from both s tock were then raised under identical conditions and were still found to di ffer. This leads to the conclusion that some of the differences are genetic al and therefore the result of evolution within this semi-natural environme nt. The speed of these changes are compatible to what has been published ab out wild guppies. Also differences in behaviour between the two populations were ascertained.