Sex and its unintended consequences
When it comes to plants, there can be no gene flow without two compatible partners. And most plants are quite choosy, preferring a close relative rather than someone outside its family. Pollen travels in gusts of wind, on the pollen basket of bees, as cargo of flies or in the hands of human plant breeders. If the pollen alights upon a compatible mate, there will be fertilization and the resulting seed will carry the genes of the parents. What will happen then if a transgene from a genetically engineered crop plant cross-pollinates with wild relatives?

i-548b9ab9f0d09abf48c9b2d8b5485814-plantstructure pollination 5-1.JPG

A new study in PNAS suggests that we cannot always anticipate the consequences.

In the Central Valley of California where we live, the crops plants are mostly exotic, imported over from afar- tomatoes and corn from Central and South Americas, cotton from Pakistan, safflower and alfalfa from the Near and Middle East, and rice from China. This means that genes from the crops grown in the valley will not transfer to wild relatives in the foothills nearby because the species are not compatible. It is as if California were a large, oval-shaped, flat-bottomed platter with steep, slippery sides holding all the crop plants, and their genes, at the bottom.

In other parts of the world, gene flow between crops and their wild relatives is common. Spontaneous hybridization between transgenic cultivars and wild relatives occurs for 12 of the world's 13 most important crops. Consequently, there are concerns that genes from crop plants could escape and enhance the fitness of wild species, altering native populations.

There is renewed interest in this subject lately because, increasingly, many of crop plants carry "transgenes"- that is they were introduced through genetic engineering.

Most ecologists believe that if pollen carries a gene that confers a "fitness" advantage (e.g., enhancing resistance to a virus for example), and it has wild relatives nearby, hybrid progeny could potentially survive and establish new populations carrying that trait.

It is important to note that the theoretical fitness advantage is not specific to transgenes- it can occur with genes introduced by conventional breeding approaches as well. Virtually all the food that we eat today carries resistance genes introduced by conventional breeding (yes that includes organic produce).

In this 3-year study, Sasu and coworkers examined the consequences of cross-pollination of the Texas gourd,


a native to Texas and states along the lower Mississippi River, with cultivated pumpkins and squashes. They used a crookneck squash


that was engineered with a virus resistant transgene (VRT). The Vrt squashu is resistant to several related viruses including the watermelon mosaic virus shown here.


The researchers found that viral diseases (mostly Zucchini yellow mosaic virus) colonized and spread rapidly through fields during the period of peak gourd reproduction. The VRT plants were highly productive, as measured by fruit, flower and pollen production in comparison to the non-transgenic plants. These data suggest that the VRT trait would confer a fitness advantage when introduced into a population of wild texana gourds.

Surprisingly, the fitness advantage of the VRT plants came with a cost. When the non-VRT plants were infected with the virus, the plants became less attractive to beetles that carried a disease-causing bacteria. That is, even though the VRT plants were resistant to the virus, they were more susceptible to the bacteria transmitted by the beetle. Thus, there is an indirect, ecological cost associated with the VRT when the beetle and the bacteria are also present in the population. Whereas a simple ecological model would have predicted that the VRT would increase in the wild populations, this is not the case when other pathogens are present.

Sasu MA, Ferrari MJ, Du D, Winsor JA, & Stephenson AG (2009). Indirect costs of a nontarget pathogen mitigate the direct benefits of a virus-resistant transgene in wild Cucurbita. Proceedings of the National Academy of Sciences of the United States of America PMID: 19858473

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It'll be interesting to see if this gets used by anti-GM folks to promulgate the idea that release of new varieties has all kinds of potentially scary unintended consequences. When in fact it shows quite the opposite--a gene that you'd expect would have great selective advantage and would make "superweeds" in fact does the opposite. If only the same level of concern, and resulting scrutiny were applied to non-native invasive species, where there really is some environmental hazard! Starlings, house sparrows, kudzu, Japanese stilt grass--pick your favorite--they're in your yard and screwing up the environment. Why not devote time and energy to figuring out some useful measures for controlling import of new alien species, rather than finding still more ways to limit the growth and utility of the most highly regulated agricultural technology ever developed?

Well put. The amount of time, energy, money we devote to GE crops when people are starving and kudzu is taking over is astounding.

i thought PNAS was always open access...

Absolutely thus story will be spun
I think, though, that the locavore story (the link janes provided- thanks) is simply someone that didn't understand the experiments or even the purpose if the expts and reported on it anyway

So what protects the VRT squash from the beetle/bacteria combo on the farm? Is the beetle controlled with pesticide?

By David Hooks (not verified) on 28 Oct 2009 #permalink

Eric - I think you may be over-generalising there. Just because this particular transgene, in this particular species, in this particular ecological context, happens to have a neutral or negative fitness effect because of interactions with other pathogens, that does not necessarily imply that that will be the case with all transgenes in all species in all contexts. It just means that you can't naively assume that they will have a positive fitness effect. What this really shows is that it requires careful study on a case-by-case basis to determine the actual effects of any given transgene in any given population.

And people are already devoting huge amounts of time and energy to controlling invasive species. It's not an either-or choice.

What could be more environmentally pleasing than green sex?!

PNAS is "open access" in the sense that after a period of time (6 months) everything is freely accessible.

I don't have access to the paper, but I don't understand the drama I'm seeing.

1. If the squash isn't susceptible to the "natural" virus, then the plants are healthier. Ok.
2. If the healthier plants are more attractive to beetles, isn't that a good thing for biodiversity--I mean, if you are a fan of the beetles?
3. If some beetles carry another pathogen, why is this a huge surprise? Biology is a giant arms race and there's always another pathogen waiting for an opening in a niche.

I understand the fitness distinction. But that's being lost in the popular press pieces I'm seeing.

OT: @IanW--you should check this series. I think they should be asked to cover ferns and plants: (Irritating that the movie runs on launch, may be NSFW if you aren't a biologist...)

oh that movie is great. Isabella and anchovies.
David, you ask a good question: "So what protects the VRT squash from the beetle/bacteria combo on the farm? Is the beetle controlled with pesticide?"

I dont know the answer to that. I will find out. Apparently the VRT squash is working very well for the farmer all these years with no Erwina infection.


Thanks for the response.

I was commenting on this specific case.

And I agree it isn't either/or--but in a world where we all only have finite time to make an impact, it's amazing to me how much time and effort gets spent criticizing GM technology. My sense is that the most vocal folks doing it are just using it as a proxy for their aversion to big/centralized/industrial etc. That's a shame, and it's dishonest.

My point is there are a bunch of much more significant things they could do to impact their world--combatting invasive species being but one example.

I think the time spent by obsessed folk like locavore is more than balanced by the idiots on the other side with their 'get your retaliation in first' counterspin. Eric is as much a delusional nutter as those he seems to despise.

As for Pam's post, I liked it. Without spinning either way, what it seemed to me to be saying is that the plant in question has had an ongoing historic relationship with a number of diseases and parasites in it's environment and has come to a balance which allows it to survive with all of them. What genetic engineering achieved was taking out one component of that balance with no thought to the consequences for the rest. Species have spent millions of years working stuff like this out and continues to do so. No thought is not a helpful approach.

Also, what's with the knee-jerk anti-kudzu racism?

Seeing that picture of the enormous gourd reminded me that all of our agricultural crops have been highly modified by centuries of conventional breeding, not to survive in a state of nature, but to increase their yield. It's not so surprising that if crossed into wild relatives the genes that makes these plants useful to us would have a negative impact on the weediness of the resulting hybrid. I was given an assignment earlier this year for one of my genetics papers and I came to the same conclusion about the gene I wanted to add to maize - if it crossed into a related species the gene would have a negative impact on survivability.

If agricultural crops had the potential to become invasive species they wouldn't be so hard to grow in the first place.

By David Hooks (not verified) on 29 Oct 2009 #permalink

Regarding Open Access of the paper. The paper was just published and if the authors do not pay an extra Open Access fee, it will not be available for free until 6 months later ... So this is a major limitation to getting people without subscriptions to journals to see new papers and get engaged in scientific discussions. ^ months from now people will likely be discussing other work --- and thus many people will miss out on the chance to fully participate in a discussion of this work. YARFOA - yet another reason for open access.

It isn't knee-jerk, Eddie, it's back-ache. I don't have kudzu at the moment, but if you'd like to understand anti-Japanese-Hops racism, you can come out to my place next spring and help me pull up a few acres of the hellspawn.

Introduced species present an interesting analogy here... The vast majority of them present no problems, either because they aren't well-adapted to the biome they're introduced to, or because they're susceptible to predators / pathogens / competitors already present in that biome. It's only a tiny minority which turn out to be invasive, but that tiny minority can cause major problems.

Arguing "all GMOs are inherently dangerous" is like arguing that all introduced species have the potential to become invasive. Arguing "all GMOs are inherently safe" is like arguing that no introduced species have the potential to become invasive.

I would expect the vast majority of GMOs to turn out to be perfectly safe, but I wouldn't be at all surprised to find a tiny minority which pose problems. The tricky bit is identifying the potential problems before they occur - the history of human modification of ecologies is nothing if not a catalogue of unintended consequences.

"If agricultural crops had the potential to become invasive species they wouldn't be so hard to grow in the first place."

Hammer, meet Nailhead.

There is so much built into this sentence. In a way, it summarizes agricultural history, and thereby, human history.

The big question I have for all the anti-GMO types is this: Has there ever been a time in human history when the genie was stuffed back into the bottle?

My sense is that the most vocal folks doing it are just using it as a proxy for their aversion to big/centralized/industrial etc. That's a shame, and it's dishonest.

Yeah, I think you're right there... From my point of view, the two main problems associated with GMOs are the potential to further cement the grip of a tiny handful of vertically-integrated combines on the global food system, and the potential to further increase our (over-)dependence on a tiny number of commodity crops. I don't have any problem with the fundamental technology itself. (Although there are a lot of people out there with bad cases of the naturalistic fallacy...)

Diversity is good.

From my point of view, the two main problems associated with GMOs are the potential to further cement the grip of a tiny handful of vertically-integrated combines on the global food system, and the potential to further increase our (over-)dependence on a tiny number of commodity crops. I don't have any problem with the fundamental technology itself.

Those are real concerns. From my perspective, the problem is that fear of genetic engineering actually creates them. There's no inherent reason genetic engineering should be confined to a few major crops, produced by only a handful of major corporations. If the regulatory hurdles of bringing a genetically engineered crop to market were more in line with the risks (lower), more companies (including start-ups) could afford to engineer more crops. Would that address your concerns?

Bees spread pollen but cheese doesn't.

Watermelon mosaic virus infects crookneck squash.

Bees pick up pollen on their legs and fly around and accidentally drop it on another flower to make more of its kind.

Bees like Bob know that kids like us and adults like flowers in the chicken coop.

By Cliff, age 10,… (not verified) on 30 Oct 2009 #permalink

James: I'm afraid I do not see any way that deregulation can bring genetic engineering within reach of organisations like co-operative seed banks at present. As far as I understand it, there's simply no getting away from the fact that the sort of research program required to produce new GMOs is a necessarily expensive undertaking.

Dunc, it is fairly easy and cheap to carry out genetic engineering and to carry out field trials. However, it is quite expensive to complete the regulatory requirements. Mostly only large corporations can afford those costs. It benefits the corporations because they have access to the technology but it effectively prevents smaller seed companies from access.

"Knee-jerk anti-kudzu racism"? Are we really comparing concern over the damage caused by invasive species to racism? Really?

Eric is the one overreacting. Sure.

FYI-The EU approved importation of Herculex® RW, Roundup Ready® corn yesterday. It is a Bt and glyphosate resistance transgenic variety.

If you want Dow, DuPont and Monsanto to own the market there is no better guarantee than oversight by three different federal agencies in a state of regulatory capture and the EU 1800 regs acting as tariffs/embargoes in the guise of safety and disclosure.

By Prometheus (not verified) on 03 Nov 2009 #permalink

Pam: just how easy and cheap is "fairly easy and cheap"?

I'm not entirely unsympathetic to the basic argument - for example, here in the EU we have a problem were many seed banks can't actually sell their seed, because they can't afford to register their varieties. But if they can't afford a mere couple of grand to register an existing variety, I doubt they're going to be able to afford GE, unless it's as easy and cheap as conventional breeding (i.e. it can be done by a keen amateur in a potting shed with no specialised equipment).

It costs about $500 to make a GE rice line. The breeding is the expensive part. It can be done in any simple lab anywhere in the world.

OK, that's really a heck of a lot cheaper than I thought. Thanks, you're certainly given me something to think about here. :)

I believe the research in the article shows that modifying a trait in isolation can have a multiplicity of effects. Nature manifests through complex interactions.

This is what many who question the wisdom of GMOs are concerned about. Also, the use of gene guns and microbial vectors to introduce foreign genetic material is not exactly a precision technology. There are also concerns about the use of antibiotic resistant markers.

Obviously, there is also concern about the patenting of living organisms. The saving of seed should be a human right.

In any event, Pamela, I think you and your friends are out of line as characterizing everyone who has concerns about genetic engineering as dimwits who have no critical thinking skills.

And by the way, the gourd shown in picture is not a "Wild Texas gourd" or even a Cucurbita. It belongs to the genus Lagenaria. The hard-shelled Lageneria spp. gourds are the oldest botanical crop known to man. The "wild gourds" that grow in Texas do not look anything like that.

I think, though, that the locavore story (the link janes provided- thanks) is simply someone that didn't understand the experiments or even the purpose if the expts and reported on it anyway