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.