Category: Wild relatives

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The plants that statistics forgot

FAO has just put out new guidance on capturing wild foods and neglected and underutilized species (NUS) in dietary surveys. It’s very much worth a look, even if your interest runs more to grain landraces on the farm than to greens gathered from the forest. The methodology is built to overcome a very real problem: standard dietary assessment tools are generally designed with the main staples in mind, so anything outside that narrow frame (think foraged, seasonal, localized, thinly documented) tends to fall straight through the cracks.

FAO’s fix is a set of very sensible, practical steps: engage local knowledge holders to compile inventories under their own names for things, survey markets to see what’s actually being sold and eaten, map harvest calendars against agroecological zones and seasons, and build simple identification tools (photobooks, reference databases) that let enumerators and communities work from a shared understanding of what they’re counting.

None of that machinery is specific to wild foods though. The same toolkit could easily be adapted to survey the diversity hiding in plain sight on farms: crops and landraces known only by a few, grown in a handful of villages, marginalized, on their way to be forgotten. And invisible to national crop statistics that only track the main crops and the most common named improved varieties, if that. A market survey designed to catch wild greens sold at the roadside works just as well for catching a local bean landrace in the same market. A harvest calendar built to track when forest foods peak works just as well for tracking when fonio gets planted or harvested, and why farmers still bother with it. Great for quantifying the opportunity presented by “opportunity crops.”

And there’s a useful downstream application: surveys built this way could help flag where crop diversity is thinning out on the ground, or where it’s abundant but under-represented in genebank holdings. In other words, the kind of gap analysis that ought to be steering germplasm collecting missions.

FAO’s framing kind of gestures at this already: wild, managed and cultivated aren’t three separate boxes but points on a continuum. A methodology built to navigate that blurriness for wild foods is also a methodology that ought to work for navigating the blurriness at the cultivated end. It would be a shame if this toolkit stayed confined to the wild-food side of the spectrum when the conceptual heavy lifting behind it applies just as well to neglected cultivated diversity.

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Crops made, and remade

Two new studies of very different crops – banana and chrysanthemum, of all things – end up telling surprisingly similar, deliciously complicated stories. For these crops, domestication was not once and done, so to speak. They were both repeatedly remade as people moved them through landscapes containing new wild diversity.

In the banana study, the authors suggest that a partly domesticated Musa acuminata lineage from New Guinea was carried westwards through Southeast Asia, encountering and hybridizing again and again with different local wild bananas along the way. Each encounter added new genetic material to an already changing crop, helping produce the genomic mosaics found in mainland Southeast Asian bananas today.

The chrysanthemum study reveals a strikingly parallel history: cultivated plants originating in China were introduced to Japan, where they encountered local wild populations and acquired new genetic diversity, before later movements to Europe and further breeding reshaped the crop again.

The papers also show that an essentially similar process played out somewhat differently in the two crops. In banana, repeated hybridization appears to have been important in the building of the crop itself, as domesticated or partly domesticated plants became the starting material for successive encounters with wild Musa. In chrysanthemum, genomic analysis reveals a more complex network of relationships among multiple wild and cultivated groups, with C. indicum among the important ancestral contributors. In this genetic cauldron, hybridization and introgression repeatedly diversified an established cultivated genepool, contributing to traits such as flower form, colour and plant architecture.

Taken together, these papers challenge the familiar “funnel,” or bottleneck, image of domestication: a one-way downward slide from diverse wild relative to genetically narrow crop. Instead, they point to a more stop-start, two-way, non-linear, geographically contingent process, in which (semi-)cultivated plants continue to encounter, absorb and be reshaped by wild diversity.

In both banana and chrysanthemum — and probably many other cases — wild relatives have been more active, continuous participants in creating the diversity of the crops we know today than we sometimes give them credit for. Or I have given them credit for at any rate.

That argues for treating the wild genepool not simply as a reservoir from which to fish out useful genes one at a time. The historical evidence suggests that crops have benefited in the past from repeatedly absorbing larger chunks of wild genetic diversity, allowing selection to reconstruct useful combinations. Might it be worth trying to make that happen again? Is anyone out there doing pre-breeding explicitly with an eye to the past?

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Brainfood: Biodiversity works through relationships

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Conserving the tangle of grapevines

I think we may have already pointed to Conservation gap analysis for wild grapevines (Vitis L.) of the Americas, the latest in a series of papers by our friend Colin Khoury and a rotating assortment of colleagues on the conservation status of the crop wild relatives of the Americas, genepool by genepool. The authors compiled occurrence records for 38 wild American grapevine taxa, and used fancy GIS to infer the overall distribution and environmental niche of each. They then assessed the degree of representation of each taxon in genebanks and protected areas, and hence any remaining conservation gaps. Here’s the headline finding:

We categorize 25 of 38 of the taxa as urgent priority and 10 as high priority for improving ex situ conservation representation. Three taxa are assessed as urgent and 29 as high priority for enhancing in situ conservation. Further action, with emphasis on conservation gap hotspots, is needed to more comprehensively conserve wild Vitis native to the Americas.

Which is pretty clear.

Or is it?

What if “taxa” are perhaps not always the best units of conservation to use in assessing conservation efforts?

That may in fact be one of the implications of a paper that came out just a few weeks after that of Colin and friends: The dynamics of introgression and parallel adaptation across North American Vitis species.

These authors show that introgression and hybridization are pervasive and evolutionarily important across North American Vitis, based on genomic analysis of 639 accessions representing 48 species. About 14% of the average genome shows evidence of introgression, particularly associated with areas where species come into contact. Some taxa usually regarded as hybrid species are in fact better understood as ever-changing hybrid swarms, rather than distinct evolutionary lineages. Most importantly, the authors find that introgressed genetic variants have repeatedly contributed to adaptation in different species. The paper therefore portrays Vitis diversity as a reticulate network — or tangle — of species, populations and gene flow, rather than a set of discrete species.

This has important implications for conservation: hybrid zones and admixed populations may be really significant reservoirs of adaptive diversity. The framework of the first paper might potentially underestimate the conservation importance of regions where these occur, if they contain substantial genetic variation but aren’t well represented by the taxonomic units used in the gap analysis. For example, it might happen that two neighbouring species are reasonably well represented ex situ, but not from the specific regions where they hybridize and introgression occurs.

This suggests a useful next, synthetic step: take the geographic gaps from the first paper and overlay them with the evidence for introgression and gene flow networks from the second. The resulting map could identify not just under-collected species, but under-collected (or under-conserved in situ) evolutionary processes and genetic mixtures. That could be valuable for designing the next Vitis collecting mission.