Category: Wild relatives

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A history of viruses

We’re fond of reminding ourselves here that agrobiodiversity isn’t just crops and livestock and their wild relatives — it’s also pests and pathogens and weeds and pollinators and earthworms and brewer’s yeast. It’s one of our leitmotifs. Another is that agricultural and “wild” biodiversity interact. Here’s a paper that kind of brings these two leitmotifs together, into a sort of counterpoint, if I may be allowed to push the metaphor ((C.M. Malmstrom et al. (2007) Barley yellow dwarf viruses (BYDVs) preserved in herbarium specimens illuminate historical disease ecology of invasive and native grasses. Journal of Ecology (OnlineEarly Articles). doi:10.1111/j.1365-2745.2007.01307.x)).

Carolyn Malmstrom and her team at Michigan State University isolated RNA of barley and cereal yellow dwarf viruses from old herbarium specimens of Californian grasses, dating back to 1917. They used such historical samples to trace the history of these agriculturally important viruses back through time, building up a sort of family tree. The analysis suggests that the viruses were present in the Californian native flora in the 18th and 19th centuries, when invasive Eurasian annual grasses (some of them weedy crop relatives) displaced native perennial grasses. In fact, they may have facilitated this invasion by helping the exotic grasses outcompete the natives ((“Non-native invaders amplify spring aphid populations and increase BYDV infection in natives, which in turn suffer substantially reduced survivorship when infected.”)).

The team also found “potential correspondence in the timing of virus diversification events and the beginning of extensive human exchange between the Old and New Worlds.” Humans may have caused the branching of the family tree of some viruses by moving them and their hosts around the world.

Here’s Malmstrom on the significance of her work:

This work points out that the virus world does have an active, long-term role in nature, not just in agriculture… We very much need to understand how viruses can move and influence our crops. If we care about our crops, we need to care about what’s happening in nature.

So: aphids, viruses, native grasses, exotic weedy invaders, crops. Quite a fugue.

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Culling badgers backfires

There’s been a lot of news and discussion recently in the UK on animal diseases such as mad cow, foot and mouth, and bluetongue. Here’s another one to worry about: bovine tuberculosis. A paper just out in the Journal of Applied Biology explores the interaction between agricultural and wild biodiversity in the context of the spread of this disease in the UK ((H.E. Jenkins et al. (2007) Effects of culling on spatial associations of Mycobacterium bovis infections in badgers and cattle. Journal of Applied Ecology 44 (5), 897–908. doi:10.1111/j.1365-2664.2007.01372.x)).

Bovine tuberculosis can be spread by badgers, which have therefore been routinely culled for some years in many areas. But it turns out that badgers are in fact more mobile and adventurous in areas where their numbers have been thinned out. Which means they are most effective in spreading tuberculosis to cattle in exactly those areas where measures have been taken which were supposed to control the disease. The law of unintended consequences in action, I suppose.

Meanwhile, a big cull of feral pigs is on in Australia. ((Our occasional contributor Michael Kubisch wrote an interesting post on feral animals a few months back.)) Is this going to have some unintended consequences too?

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The Cretaceous roots of agriculture

A comment on a long but fascinating post on yeast genetics and evolution at The Loom sent me to a New Scientist article from a couple of years back which is perhaps more immediately relevant to our agricultural biodiversity focus here.

Some time in the distant past Saccharomyces cerevisiae, to give it its full name, developed a chemical trick that would transform human societies. Some anthropologists have argued that the desire for alcohol was what persuaded our ancestors to become farmers and so led to the birth of civilisation.

The article goes on to describe how brewer’s yeast evolved its somewhat surprising abilities. It turns out that its peculiar habit of carrying out anaerobic respiration even in the presence of oxygen — at a steep energetic cost, and resulting in the production of what is usually a poison, alcohol — dates back to an accidental duplication of its genome back in the Cretaceous. Eighty million years ago later, bakers and brewers are daily taking advantage of a genetic mistake that took place in a microscopic fungus when dinosaurs ruled the Earth. Isn’t agrobiodiversity wonderful?

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Can wild relatives survive introgression?

Crops can benefit from the introgression of genes from their wild relatives, but what about the other way around? Is the survival of crop wild relatives jeopardized by the “genetic pollution” caused by hybridization with the cultigen? A paper just out in the Journal of Applied Biology takes an experimental and modeling approach to answering this question ((D. A. P. Hooftman, M. J. De Jong, J. G. B. Oostermejer, H. C. M. Den Nijs. 2007. Modelling the long-term consequences of crop-wild relative hybridization: a case study using four generations of hybrids. Journal of Applied Ecology 44 (5), 1035–1045.)).

The researchers monitored the germination, survival and seed-set of hybrids between wild (Lactuca serriola) and cultivated lettuce (L. sativa). The overall fitness of hybrids was higher than that of the “unpolluted” wild relative in the first couple of generations, but as those hybrids were selfed and backcrossed, their fitness decreased. These data were then entered into a model, to see what would happen over time to a L. serriola population exposed to geneflow from the cultigen. What happens is that the wild relative can indeed be completely displaced by hybrids, but that is not a foregone conclusion, and in any case displacement, if it takes place, will not be as rapid as predicted by previous models which did not take into account the breakdown in heterosis.

So genetic pollution does pose a real threat to crop wild relatives in the field ((The likelihoods of both hybrid occurrence and L. serriola displacement were still at least 60%.)), but perhaps not as great as some have suggested. And in any case we now seem to have a model that can be used to assess the risk of genetic pollution, including by transgenes.