Agrobiodiversity is crops, livestock, foodways, microbes, pollinators, wild relatives …
There’s a great exhibit from the Food for the Cities project in FAO’s atrium this week on the occasion of the 22nd Session of the Committee on Agriculture. Here’s a quick look at a couple of the little container gardens (microgardens) they’ve created. Seem to be doing very well too.
The wait is over. Rachel Laudan’s talk at Postopolis is now available in two versions. Rachel herself carries a transcript of her talk, with some photos. And Nicola over at Edible Geography has the same transcript with different photos and a bit more by way of introduction. 1
There is so much content there that I hardly know what to say, except that I am in awe of the research skills and basic understanding of the problem. The basic point is that “without food energy, a city is nothing”. For most people and most of history, that energy came from grains: about a kilo per person per day. And the consequences of that … go read!
A heart-warming story from BBC News: in the village of Dharhara in India, parents plant 10 or more fruit trees when a baby girl is born. The trees mature slightly faster than the girls, and by the time a girl is nubile the profits from the sale of fruit is more than enough to pay the bride price commonly required by the groom’s family. Bihar has the highest death rate among families who cannot pay a bride price. But not in Dharhara.
Although some have emphasized the need to breed crops for future climatic conditions, much of the world’s farming population relies on landrace populations, not formal breeding networks.
Undeniable, of course, and a good reason to not forget landraces (farmers’ local varieties) when thinking about how agriculture will (or will not) adapt to climate change. The new paper by Kristin Mercer and Hugo Perales in Evolutionary Applications from which the above quotation is taken (minus the references for clarity, as with all subsequent quotes) won’t let you forget. 2
The authors look in some detail at each of the possible responses that landraces may have to climate change. They could simply “adjust their phenotype” (plasticity). Or they could adjust their genotype, otherwise known as evolution, and thus “keep up” with the climate. They could also migrate to more hospitable places. And, finally, they could die out (extinction).
What will determine which of these routes any particular landrace follows? Mercer and Perales think two main factors need to be considered: the level and pattern of adaptive genetic variation in the landrace, and the details of how climate, and therefore selection pressures, will actually change. They say they recognize that what farmers do will also determine the outcome, but somewhat disappointingly leave a discussion of that to a later date. They list about a dozen quite specific research questions that would need to be tackled to “understand how landraces in crop centres of diversity may respond to climate change,” which I’ll reproduce in full for those who don’t have access to the paper (they’re in Box 1).
Genetic structure
• Is available genetic variation appropriate for evolutionary response to climate change, especially for selfing or clonal crops?
• At what rate will evolution proceed given heritability of traits and strength of selection?
• Might there be constraints on evolution to multiple environmental changes given the genetic correlations among traits?
• Is there capacity for evolution of plasticity?
• Might populations be plastic in response to climate change, especially for selfing or clonal crops?
• Will different types within a species, or landraces from different regions, respond differently?
• Will adaptive or novel variation be available to populations for evolution based on patterns of gene flow and mutation rates?
• Would gene flow from improved varieties improve or reduce the evolutionary potential or plastic response of landrace populations?Climate change patterns
• What aspects of climate change will impose directional, disruptive, or fluctuating selection?
• Could selection be strong enough to reduce genetic variation within or among populations?
• Could it reduce effective population size or cause major mortality, which should reduce genetic variation?
• Would yearly variability in selection reduce genetic variation or lead to greater plasticity?
That’s a nice research agenda to be getting on with. I was particularly interested in three specific observations made by the authors. The first is that “[f]armer-mediated selection may … contradict natural selection.”
…farmers could select for seed characteristics, such as grain size, which, if negatively correlated with the tolerance to heat during the grain filling stage, could reduce the populations’ productivity in high temperatures.
The second is that
Migration or gene flow could facilitate adaptation and maintenance of productivity with climate change because gene flow can introduce novel variation into landrace populations on which selection can act. (Mutation can also introduce novel and potentially adaptive variation, which could be selected upon as climate shifts.) In contrast, gene flow could constrain adaptation if there is repeated introduction of alleles from maladapted landrace populations.
Where would such non-maladapted material come from? The authors don’t really discuss this question, but we suggested in a recent paper that in many situations the source may well be a different country.
Finally, the authors point out that “since climate change is promised to introduce new extremes in temperature,” the resulting “strong bouts of selection” are quite likely to cause extreme narrowing of genetic diversity in landraces when they don’t cause their extinction.
These points, and indeed others, could only lead to one conclusion as far as I was concerned, and I read on anxiously to see whether the authors would agree. Finally, on the penultimate paragraph, the money quote arrived:
Ex situ conservation could regain primary importance despite the fact that it is an already over-taxed system. Yet climate change promises to complicate the decisions of which locations are most appropriate for grow-outs.
Remember that the paper is written very much from the perspective of in situ conservation. To see the importance of genebanks extolled so clearly in such a context, and the complexity of their operations highlighted to boot, was very welcome, and I must say somewhat unexpected. Are we beginning to move back towards a recognition of the essential complementarity and inter-dependence of ex situ and on farm conservation?
Why are there no perennial grain crops? That’s the provocative question posed by a recent paper in Evolutionary Applications written by three scientists working at The Land Institute. 3 Whose institutional mission, of course, is to breed just this sort of crop, on the assumption that they “could reduce soil erosion while maintaining production of food staples.”
So what’s the answer, and what can be done about it? The authors start by pointing out that if you plot life form against net annual reproductive effort for angiosperms there’s a gap in the graph where herbaceous perennial crops with big, plentiful seeds and fruits should be. You have annual grain crops, of course, and fruit and berry cultivars, but nothing in between. Could it be that this particular “morphospace” is impossible on logical grounds? Or that there has not been enough time for the combination to develop?
After looking at a number of different possibilities, the authors come up with a very stark statement:
We suggest that the simplest explanation for the absence of perennial herbs with high reproductive effort is that, while biophysically possible, this lifeform could not have evolved by natural selection.
Let’s unpack that a bit. The authors point out that wild, out-crossing perennials are great at generating genetic diversity because
…somatic mutation generates heterozygosity in long-lived individuals … and allogamic recombination ‘destroys the associations built by, and favored by, selection’ … yet inefficiently purges deleterious recessive alleles.
This means that high genetic load results (the build-up of lethal recessive mutations), and therefore, the authors argue (with plenty of evidence to back them up), low seed set. Now, couple that with the fact that perennials tend to be ecologically dominant. What do you end up with?
You end up with a bunch of plants which are “poor candidates for rapid natural selection” in the new, open agricultural environments of the Neolithic: slow to colonize, still connected by geneflow to surrounding “wild” populations, and able to spread by vegetative propagation once established. This made “rapid domestication by sexual cycles unlikely.” Rapid domestication by vegetative propagation, yes, but that’s another story.
No wonder that
…domestication of annuals … under natural selection would have been faster than—and probably pre-empted—the domestication of perennials.
So, if you want perennial grain crops, you have to use artificial selection where natural selection has “failed.” The key is to minimize genetic load. You can do that by prioritizing for domestication perennials that are self-pollinating, which tends to be better at getting rid of deleterious mutations. Or by developing inbred lines by selfing and then re-combining the “purged” lines to restore heterozygosity, including in hybrid varieties. Or by selecting forcefully and strictly for high seed set (which has been working, say the authors). Crosses between annual grains and their perennial wild relatives can bring together “domestication traits and the perennial life history,” as has begun to be done for rice, wheat, rye, sorghum and sunflower.
Definitely worth a try. Because, as the authors conclude:
Adding herbaceous grain type crops to the inventory of existing, mostly tree-like, perennial food crops would give farmers additional options for balancing humanity’s demand for both nutritional and ecological services. We predict that artificial selection will open previously inaccessible regions of plant morphospace to agriculture and will reveal that some promising taxa were under-sampled. The grass family, for example, has given us our most valuable grain crops, but 70% of the 8000 grass species are rhizomatous perennials (Crepet and Niklas 2009) and were almost certainly overlooked in the early rounds of domestication which relied on natural selection.