03.10.2018: The evolutionary consequences of increases in temperature due to climate change are currently a “hot topic” in evolutionary research. A warmer environment results in the complete rewiring of the metabolism in fruit flies – made possible through changes in only a few genes. Researchers at Vetmeduni Vienna, in a study published in Genome Biology, have shown that evolutionary processes result in the adaption to a new, hot environment in just a few generations. Variants of two genes connected to an essential regulator of the metabolic budget system were identified as a key factor for the thermal adaptation. The study shows that fruit flies, contrary to previous assumptions, do not adapt to higher temperatures through many small genetic changes but through changes in a small number of “influential” genes.

The wellbeing and welfare of most animal and plant species depends strongly on the ambient temperature. The ongoing climate change is therefore a major challenge for many organisms, which must adapt to the changing temperatures or face the threat of extinction. It has long been known that this adaption is controlled at the genetic level. What was not known is that this adaptation can happen quite fast, within just a few generations. Evidence of how quickly the genetic composition of populations can change has only been collected in recent years.

Yet the question remained unanswered whether only a few influential genes or many genes with small effect were responsible for this rapid change. Researchers at the Institute of Population Genetics at Vetmeduni Vienna including François Mallard and Christian Schlötterer experimentally tested the adaptation to novel thermal environments in the laboratory. The researchers subjected freshly collected fruit flies to a hot environment and investigated the surviving animals after fewer than 60 generations. The results showed that the entire metabolism was rewired through just a few genetic variants.

Rapid adaptation possible, but only with sufficient genetic diversity

Several Nobel Prize-winning discoveries have helped to establish the fruit fly’s reputation among the general public as the animal of choice for genetic research. Yet its potential for environmental research was recognized only recently. The combination of ecology and genetics holds enormous, previously untapped, potential for understanding adaptation processes in the context of global climate change. The key to a successful adaptation strategy is a sufficiently large gene pool containing a “reserve” of genetic variants for new environmental conditions.

Mallard and his research colleagues were searching for the proverbial needle in a haystack. Using a so-called evolve-and-resequence study, they went about looking for those genetic variants among millions that would give the fruit flies a fitness advantage in a hot environment. The researchers conducted the experiments in the laboratory, “but the comparison of our results with natural populations from hot regions like Florida showed that the same adaptation mechanisms are also used in nature,” the first author explains.

Simple genetic basis triggers complex metabolic rewiring

In their analyses, the research team determined that the genetic adaptation had a direct effect on an essential metabolic regulator, an enzyme complex known as AMPK. However, the resulting metabolic rewiring was not triggered by many changes with small effect, as had been largely assumed, but by just a few influential genes. “Not only among fruit flies does the enzyme complex play a central role in the metabolic process, in this case whether fat is stored or metabolized in a cell. Here AMPK ensures the right amount of ATP, an essential cellular energy source. “We were surprised that two of the strongest adaptation signals affected the genes Sestrin and SNF4Aγ, both of which interact with AMPK,” says Mallard. “But that explains how the flies are able to adapt so quickly to changing climatic conditions. We are currently investigation whether the same principles play a role in the adaptation to summer and autumn temperatures.”

The article "A simple genetic basis of adaptation to a novel thermal environment results in complex metabolic rewiring in Drosophila“ by François Mallard, Viola Nolte, Ray Tobler, Martin Kapun and Christian Schlötterer was published in Genome Biology.