Can Citizen Science Help Save the European Ash Tree?

Fraxinus, the biologically, scientifically, and ecologically relevant version of Candy Crush Saga (Image Credit: Fraxinus) In the November print issue of Discover Magazine, the article “Cooking trees to save citrus” discusses the pathogenic attack of citrus trees by a bacterium spread by Asian psyllids and how heat generation can sterilize trees from these infectious agents. Unfortunately, the ash tree, which is also under attack by a microbial pathogen, doesn’t have the same line of defense. In a race against the spread of the disease across Europe, scientists are trying to uncover the genetic mechanism for fungal resistance by recruiting the help of citizen scientists. With autumn comes a multitude of colors—but the ash tree, faithful to its name, stays a non-conflagrant color while waiting for winter to take its leaves. Or while waiting for its microscopic predator, the Chalara fungus. Chalara causes ash dieback, a disease that has wiped out over 60% of the ash trees in Denmark, and is now sweeping across Europe, with highest incidences in Sweden and the UK. Yet some trees exhibit resilience to infection by Chalara, and it’s this curious display of biological fitness that has incited the interest of geneticists. The Sainsbury Lab (TSL), in collaboration with the John Innes Centre set about exploring this scientific problem by collecting samples from the Chalara fungus and ash trees from all over the UK, infected and resistant alike. But when confronted with the massive amount of genetic information beholden by these samples, they opted to recruit the help of citizen scientists. When Chalara first presented itself in the UK in 2012, Dan MacLean, a professor of bioinformatics at TSL, quickly recognized that uncovering the genetic underpinnings for Chalara resistance would be challenging for current bioinformatics solutions given the complex genome structure of this fungal organism. Computational algorithms can readily sort through DNA sequence data to determine differences between sequences, but only if those sequences are of standard issue. Accordingly, MacLean and colleagues developed Fraxinus, a game named after the scientific name for the ash tree, Fraxinus excelsior, for users to play on real DNA sequence data, leveraging their unique strength over computers—visual pattern matching. Users can log in to Facebook and play against other users to match bases between multiple sequences of Chalara or ash DNA (represented as colorful leaves) in a process called sequence alignment. The player with the best alignment gets to “keep” the sequence, and the player with the most sequences wins. Easier said than done—differing bases can be challenging to resolve optimally, and meandering sequences require intricate problem solving to outcompete other players. However, Fraxinus users have played against high performance software algorithms and matched or beaten their computer opponent in more than 80% of cases.