Author: Jeremy Cherfas

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Bee immunity

We’ve spent some time on the big bee die off (although not on the mobile phones) as have many other blogs and newspaper articles. In the US, the problem has reached epidemic proportions and has raised serious concerns about the future of several crops that depend to a large degree on bee pollination. Unfortunately recent evidence seems to suggest that the problem, which has been called Colony Collapse Disorder (CCD) has been spotted in Europe, as well. The cause or causes of CCD are unknown, but the list includes the usual suspects ranging from transgenic crops and pathogens to global warming and newly developed pesticides. Oh yes, and cell phones.

So the e-publication of a paper due to appear in the Journal of Heredity ((Variation and Heritability in Immune Gene Expression by Diseased Honeybees. Laura I. Decanini, Anita M. Collins, and Jay D. Evans Journal of Heredity Advance Access published online on April 2, 2007, doi:10.1093/jhered/esm008)) (behind a paywall) is timely. It describes the heritability and genetic variation of a gene called abaecin which is a key component of the immune system of bees.

Bees, like nearly all eukaryotes, have an innate immunity, but are generally thought to lack the additional adaptive immune response, which we and most other vertebrate species have. That is to say insects can’t get the ‘flu and respond by making specific antibodies to the virus (In fairness, the notion that insects do not have an adaptive immune system has been challenged recently by studies in Drosophila. ((Extensive Diversity of Ig-Superfamily Proteins in the Immune System of Insects Fiona L. Watson, Roland Püttmann-Holgado, Franziska Thomas, David L. Lamar, Michael Hughes, Masahiro Kondo, Vivienne I. Rebel, Dietmar Schmucker. Science Vol. 309, pp. 1874 – 1878 DOI: 10.1126/science.1116887 Abstract here.)) )

To find out whether abacein expression differed between bee populations, scientists at the US Department of Agriculture crossed several unrelated males into a homogeneous maternal background and then challenged the offspring with Paenibacillus larvae. This is the bacterium that causes American foulbrood, a widespread larval disease of bees. Subsequent measurements in affected larvae showed that the level of abaecin was moderately heritable but highly variable, differing by as much as 10,000 times between different lines. Why this is variation exists at all is a matter of speculation, but it might be due to selective pressures: an arms race between hosts and different pathogen strains or species.

At any rate an understanding of the components of the immune response in bees at the molecular level and the realization that there appears to exist considerable genetic variation that could be exploited would seem to offer one of the more promising approaches to selection for pathogen resistance. Whether that will stop CCD is anyone’s guess ((From Michael Kubisch)).

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Smorgasbord: take what you need

Like a perfectly assembled buffet, everyone should be able to find something nourishing in Fidel Castro’s latest essay: Where Have All the Bees Gone? And Other Reflections on the Internationalization of Genocide ((Actually, I don’t know whether that is the title he gave it himself, but it’ll do)). Ranging across more topics than you can shake a stick at, he says a couple of things that I happen to agree need saying. Like criticising the modern mania for biofuels: it’s a sick joke in developed countries. As The Economist said two weeks ago, “It is not often that this newspaper finds itself in agreement with Fidel Castro, Cuba’s tottering Communist dictator. But …” ((In fairness, they were commenting on an earlier essay by Castro, but one that contained the same points))

(Disparities between Cuba’s infant mortality rate and medical services and those of the United States are not the subject of this blog.)

Then there are the bees. Here’s Fidel:

Scientists are entertaining all kinds of hypotheses, including the theory that a pesticide may have caused the bees’ neurological damage and altered their sense of orientation. Others lay the blame on the drought and even mobile phone waves, but, what’s certain is that no one knows exactly what has unleashed this syndrome.

There’s enough trickiness around without going into the mobile phone argument. I’d be happy to be proved wrong on this, but for now I’m not even prepared to link to the many, many outpourings on the subject. Let’s just say that mobile phones are the least of Cuba’s worries, with the lowest penetration of any country in South America.

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Oekologie

The latest edition of a relatively new blog carnival called Oekologie — very groovy — is up at Behavioral Ecology Blog. There’s not an awful lot of direct agricultural interest. A post from GrrrlScientist summarizes a study on the evolution of Soay sheep on the island of Hirta in the Outer Hebrides (not) near Scotland. Cold winters select larger sheep, which selects for fewer sheep. But not all winters are that cold. On the indirect front, there are an awful lot of posts on climate change, including the one from our own Andy Jarvis, which Oekologie compiler Matt admits he found “too depressing … to read”. Shame on you Matt, but thanks for the carnival.

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Lactose tolerance: independent origins and strong selective pressure

Michael Kubisch has submitted another post, based on an article in Nature Genetics. Unfortunately the full article and a News and Views piece about it are behind a paywall. However, I’ve done some sleuthing to find a few links that give more details on the story, which I’ve added at the end. As Michael noted, the article is “not about genetic diversity of agricultural species, but how agriculture has affected human genetic diversity”. That’s good enough for us.

The ability to digest lactose, one of the primary carbohydrates in milk, varies widely among adult human populations. In some European countries nearly 90% of individuals can tolerate lactose, while the incidence in some Asian countries is as low as 1%. The inability to digest lactose is caused by a decline in lactase, the enzyme that breaks down lactose into sugars that can be absorbed into the blood stream. This decline starts shortly after weaning and most likely reflects the fact that until animals were domesticated, milk was simply not a staple of human diets. Lactose tolerance, or lactase persistence as it is sometimes called, in turn is facilitated by a continuous production of lactase throughout adulthood. Not surprisingly, lactase persistence appears to be closely linked to whether a population has traditionally practiced a pastoral or an agricultural lifestyle.

This new study examined the incidence of lactase persistence in several African populations. Based on analysis of genetic markers the authors of the study conclude that the trait appears to have evolved not only independently from Europe, but also more than once in Africa itself. Given that the prevalence of the trait is so high in some populations and domestication of milk-producing animals only goes back 12000 years or so, which is a mere blink of an eye in evolutionary times, milk consumption must have provided a significant benefit for human survival.

Those links:

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