Nature’s gardeners create a single-species orchard in a forest of biodiversity
Mutualisms occur throughout nature. They may give rise to reciprocal local adaptation, or adaptation of populations of one species to populations of another. This phenomenon suggests the adapted organisms would perform poorly when associated with a different population of the symbiotic species. It has rarely been investigated due to the technical challenges of controlling a field experiment. With support of the Marie Skłodowska-Curie programme for the RELOAD project, fellow Pierre-Jean Malé of the Museum of Comparative Zoology(opens in new window) at Harvard and the Max Planck Institute for Chemical Ecology in Jena(opens in new window) ventured into the Peruvian rainforest to study one of the best-controlled experiments run by Nature.
Better together – but not entirely faithful
Devil’s gardens are created by the mutualism between the plant species Duroia hirsuta and the ants Myrmelachista schumanni. Plants shelter ants inside their hollow stems and ants protect their host plant from plant competitors – by killing off the other plant species with their formic acid(opens in new window). This creates orchards of a single plant species in the middle of the highly diverse rainforest. Malé tested the hypothesis that this mutualism might also be an example of reciprocal local adaptation. He transplanted saplings grown from seeds of Duroia fruit from populations all over Peru into other naturally occurring Devil’s gardens. Observation of Myrmelachista behaviour and genome sequencing of the plants and ants did not reveal evidence supporting his hypothesis. “Myrmelachista ants did not care about the geographic/genetic background of the plants I introduced in their Devil’s gardens. They occupied and used them as if they were their hosts from the start,” he reports.
Luck is what happens when preparation meets opportunity
Despite this unexpected result, Malé first cautions that the absence of evidence is not evidence of absence and, second, notes that the many challenges inherent to the project brought unexpected discoveries. Since the seed germination and seedling growth rates were slower than originally expected, Malé used the waiting time to run parallel experiments. “I discovered two fungi that might play a role in keeping Devil’s gardens devoid of alien plant competitors. I also found another ant species, an apparent mutualistic symbiont but one that does not create Devil’s gardens. It is associated with a much higher nutrient level in the host plants than with Myrmelachista,” he describes. Chemical analyses currently in progress should shed light on this potential example of myrmecotrophy(opens in new window).
Valuing the journey, regardless of the destination
Aside from scientific articles in various stages of publication, Malé maintains Facebook(opens in new window) and Instagram(opens in new window) accounts chronicling the day-to-day life in the field and in the lab. Several short movies(opens in new window) can also be found on YouTube. He concludes: “I believe that communicating the scientific method to the public is at least as important as presenting new results. I would like my project to illustrate the principles of hypothesis testing and the rigour that is required regardless the outcome. As scientists, we are not working to prove that we are right but to better understand the world in which we live.”
