Margarita López-Uribe talks about her newly published research “Crop domestication facilitated rapid geographical expansion of a specialist pollinator, the squash bee Peponapis pruinosa.” Video by Adrian Smith.
The Global Crop Mutualists Alliance
The food you eat is very unlikely to be grown in the same region in which it is native. Our crops have moved, across history. They have been moved by trading among friends, colonization, conquest and accident. But this movement is far from chance. We have depended upon it for the bounty we now consume. When crops are moved they escape their pests and pathogens. Cacao is native to the Amazon, but now grows mostly in West Africa. Rubber is native to the Amazon but grows almost exclusively in tropical Asia. But, eventually, the pests and pathogens seem to catch up and when they do the collapse that follows is often tragic. This much of the story is not fully understood and yet its general arc, the arc of escape, bounty, and fall, we know. What is not known, only understood in the most liminal of ways, is whether, when crops are moved around the world they also escape their mutualists, the partners on which they depend (and, if having lost such partners makes the collapse worse when the parasites and pathogens catch up). We have hints, but they are often more anecdote than science. A bee, it has been suggested, for instance, might pollinate cacao in its native range and might have been lost when cacao was moved. A fungus might have lived in and protected rubber leaves in their native range, but been lost when rubber was moved. Might have been. Possibly. Could be. We really don’t know. The good news is that we now have the tools to know—the tools of modern genetics, microbial culture, and global collaboration. We are now using those tools to study, systematically, the mutualist partners of crop species in their native ranges, and in those other biogeographic ranges into which they have been introduced.
Our approach is simple (albeit not without a fair amount of work). We will study the mutualists of crop plants in the regions in which they are native and in those in which they have been introduced. We will test whether mutualists have been lost with such moves. Of course, such an effort is interestingly basic science. It speaks to the general story of people and plants. But it also sets the stage for application. If we know which mutualists have been left behind, we can also begin to take the next steps necessary to reunite mutualists and hosts.
Crop plants have many kinds of mutualists. Flies, bees, and wasps pollinate many crops and in many cases those relationships are specific. Squash, for instance, are dependent on squash bees, tomatoes on large-bodied bumblebees. Parasitoid wasps attack the pests of crops. Cassava mealybugs, for instance, are kept under control in the native range of cassava by a single species of wasp. But others of the mutualists are smaller, they include the fungi and bacteria that aid plant roots in finding nutrients and also the fungi and bacteria that dwell in and on plant leaves and, in doing so, help to defend them against pathogens and, in some cases, against pests. It is these microscopic partners on which we will initially focus.
In order to study the mutualists of leaves and roots of crops, we have brought together experts on crop plants from around the world. We are asking each of these experts to make collections of crops native to where they work and crops introduced to that same place. We will collect more varieties of crops in their native range than in their introduced ranges so as to understand whether varieties differ in their mutualists even before being moved. Some experts will collect samples of many crop species in one place. Others will, instead, collect samples of their focal crop species from more than one place. Each collaborator then divides the sample into two equal subsamples. One of those subsamples will be used extract DNA which will, in turn, be sent to our core lab in North Carolina. The other sample will be saved and will be used, in the event that we discover interesting mutualists in the DNA sample, to culture and study those mutualists. Importantly, the labs who do the follow up study will be those in the native range of the crop.
So far, the team includes members of CIAT, the International Center for Tropical Agriculture, Langebio, North Carolina State University, and the University of Copenhagen, but our group will grow as we add experts in other regions and for other crop species.
Ultimately, we hope to have as good an understanding of the species that help our crops as those that assail them, but this quest is only just beginning. It is, nonetheless, an important quest, both in as much as our crops needs all of the help they can get and because many of the mutualists of our crops are likely to depend not only on the crop species per se, but also other wild species, wild species we have yet to study, wild species we might or might not, in light have global change and habitat loss, have sufficiently conserved.