Rapid evolution: New findings on its molecular mechanisms

Rapid evolution of cichlids

The researchers led by Axel Meyer analyze the Midas cichlid fish from Nicaragua's volcanic crater lakes as a model system in their research. Cichlids are known for their ability to adapt to new environments at an exceptionally rapid rate and to form new species. The new fish species originate from a population found in the large lakes of Nicaragua, but after colonizing several very small and young crater lakes, they adapted to new ecological niches, evolved new characteristics (e.g. a more elongated body or a different jaw) and evolved into a variety of new species in less than 22,000 years. A further distinctive feature of these Midas cichlids is that they evolved into different species within the same population, sometimes repeatedly, by adapting to different ecological niches within their small crater lakes. The Midas cichlids of Nicaragua are thus one of the best known examples for sympatric speciation. Within such a short time period new mutations are very unlikely to happen. This made finding a molecular mechanism that can bring about different body shapes, adaptations and thereby distinct ecological niches so difficult and interesting. The evolution of microRNAs and new target sites for them to regulate the expression of genes offers one potential molecular mechanism that can bring about very fast evolutionary change with very little genetic differences between the extremely young species.

microRNA

The biologists from Konstanz carried out genetic analyses of five species of Midas cichlids from the crater lakes Apoyo and Xiloá. Here, they focused in particular on the function of the so-called microRNA -- a non-coding ribonucleic acid that has a regulatory effect on gene expression. The researchers found an increased activity of microRNA in young fish one day after they hatched during a phase in which the fish bodies are formed. They analyzed the interaction between microRNA and gene expression, identifying specific pairs of microRNAs and genes that influence each other. The microRNA suppresses the expression of the target genes and thus has a regulatory effect on them: the more active a particular microRNA is, the more effectively the target gene is suppressed or "switched off." "Our research results provide strong evidence that extremely quickly evolving microRNA regulation contributes to the rapid sympatric speciation of Midas cichlids," says Paolo Franchini.