Picturesque, but maybe not practical. Photo by jimw.
Arsenic Life II: The Response-ening. Rosie Redfield responds to responses to her criticism of the “arsenic life” study, and considers how she’d go about testing the original claims; Carl Zimmer discusses how online criticisms like Redfield’s may have changed the way we review scientific results. And the original paper appears in print (alongside critical responses) for the first time this week.
It’s a simple question of weight ratios. A transportation engineer explains why airships will probably never be widely used.
The bright side is you get to write another review, right? The trouble with writing about the ethics of an emerging technology is that the state of the art changes very quickly.
Life’s building blocks aren’t usually re-used to make models of the starship Enterprise. Biological systems’ use of a relatively small set of widely-available building blocks means that life is like LEGO.
Light and dark examples of Holbrookia maculata. Photo courtesy Simone Des Roches.
So, remember my posts back in February about three lizards that evolved lighter coloration after colonizing the white gypsum sand of White Sands, New Mexico, and about Erica Bree Rosenblum, the University of Idaho biologist who has studied them for most of her career? Sure you do. Well, Rosenblum’s grad student (and my former office-mate and continuing friend) Simone Des Roches has started a blog about her work at White Sands this spring and summer. Go check it out for the latest on Holbrookia maculata, and for Simone’s fantastic photography of the beautiful desert landscape and its inhabitants.
Happy Pride Month! There’s just 26 days left to send in your posts for a special Pride edition of the Diversity in Science Blog Carnival to be hosted right here at Denim and Tweed at the end of the month.
Alberto Roca of Minority Postdoc and I are looking for blog posts and other online writing about the science of human sexual diversity, the experiences of sexual minorities in the sciences, and everything in between. Write something brand new, or submit a classic post. Tell us how science, engineering, or technology helped it get better for you—or tell us how they didn’t help at all.
You can submit posts directly to me by e-mailing a link, or use the handy online form Alberto has set up. Please send submissions by Monday, 27 June so I have time to put everything together for the 30th.
Thanks to all the folks who have contributed so far—it’s shaping up to be a great carnival.
Greg Laden hosts this month’s Carnival of Evolution, the monthly compendium of online writing about descent with modification and all its consequences, complications, and controversies. This month, there’s everything from altruistic robots to blind cave fish to bacteria used by hyenas for scent signalling. Check it out!
A large white butterfly caterpillar weaves a cocoon around the wasp larvae infesting its body. Photo by EntomoAgricola.
I’m embarrassed to admit that I’ve only just gotten around to picking up Carl Zimmer’s book Parasite Rex. It’s turned out to be a wonderful compendium of all the peculiar ways parasites evade, confound, and resist the defenses of their hosts. Some of the wildest cases Zimmer examines, though, are parasites that manipulate their hosts’ behavior.
One grotesque and well-studied example is the wasp Cotesia glomerata. Female C. glomerata wasps inject their eggs into butterfly caterpillars, and when the eggs hatch, the wasp larvae eat the caterpillar from the inside, saving critical organs so the poor thing stays alive the whole time. Then, when the wasp larvae are ready to burrow out of the caterpillar and form pupae to complete their devlopment, they induce the half-dead caterpillar to spin a web around them and stand guard against predators. (In technical language, this life history makes the wasp a parasitoid, rather than a parasite.) Christie Wilcox has written up a fuller description of the whole grisly process, if you want more detail.
That sounds like a pretty incredible set of manipulations for one clutch of wormy-looking wasp larvae, but they’re not all that Cotesia glomerata can do. New evidence published in Ecology Letters suggests that C. glomerata can somehow make the plants that its host caterpillar feeds on less hospitable [$a] to the larvae of another caterpillar-infesting wasp. In other words, the wasp larvae may manipulate not just their host, but their host’s host.
First off, here’s video of Cotesia glomerata in action. Don’t watch this on your lunch break.
Now, the wasp’s plant manipulations. Lots of plants have what are called induced defenses against herbivores like the butterfly larvae that host C. glomerata larvae. Induced defenses are usually protective toxins that plants produce in response to herbivore damage [PDF]. Erik Poelman and his collaborators reasoned that, since C. glomerata can manipulate it’s host’s behavior, the parasites might change how plants respond to herbivory by infested caterpillars.
To test this, the team first had to induce plant responses. They grew Brassica oleracea—Brussels sprouts—plants in the greenhouse, then infested them with either un-parasitized caterpillars of the cabbage white butterfly Pieris rapae, cabbage white caterpillars infected with Cotesia glomerata, or cabbage white caterpillars infected with larvae of the related wasp C. rubecula. Once the caterpillars had nibbled on the plants enough to induce defensive responses, Poelman et al. removed the caterpillars in preparation for the experiment proper.
The team then introduced parasitoid-free caterpillars and caterpillars infested with one or the other parasitoid species onto host plants that had been through one of the three induction treatments, or that had never been exposed to herbivores. They then tracked the development of the caterpillars, and whether or not the wasp larvae inside them survived.
A healthy cabbage white butterfly caterpillar feeds on a piece of broccoli stem. Photo by Sam Fraser-Smith.
Larvae of C. rubecula fared more-or-less equally well no matter what kind of plant their host caterpillar fed on. But C. glomerata larvae had substantially higher mortality when their hosts fed on plants induced by caterpillars infested with the competitor species. While about 50 percent of C. glomerata larvae died if their hosts fed on plants induced by uninfested caterpillars or caterpillars infested with C. glomerata, almost 75 percent of C. glomerata larvae died when their hosts fed on plants that had previously been occupied by caterpillars infested with C. rubecula.
This impact isn’t because the host caterpillars fared poorly—in fact, caterpillars developed a little faster on plants induced by rubecula-infested caterpillars. So somehow, Cotesia rubecula seems to have influenced its hosts in a way that makes their host plants less hospitable to C. glomerata.
Poelman et al. are scrupulous to point out that this effect might not be anywhere nearly as strong in nature—host plants and host caterpillars might be plentiful enough that Cotesia glomerata can simply avoid the competitor species. On top of that, any natural selection that C. rubecula could be exerting on C. glomerata via induced responses in their shared hosts’ host plants is occurring at multiple removes. The effect Poelman et al. documented is probably not an adaptation for competition with C. glomerata so much as a side effect of C. rubecula‘s effect on its host.
So although this result shows that one parasitoid wasp can reach out and influence another through three other organisms—its own host, that host’s host plant, and the other wasp’s host—it’s not clear how strong that impact has been over the evolutionary history of these two Cotesia species. That said, this is a pretty nifty proof-of-concept.
Reference
Agrawal, A., Conner, J., Johnson, M., & Wallsgrove, R. (2002). Ecological genetics of an induced plant defense against herbivores: Additive genetic variance and costs of phenotypic plasticity. Evolution, 56 (11), 2206-2213 DOI: 10.1111/j.0014-3820.2002.tb00145.x
Poelman, E., Gols, R., Snoeren, T., Muru, D., Smid, H., & Dicke, M. (2011). Indirect plant-mediated interactions among parasitoid larvae. Ecology Letters DOI: 10.1111/j.1461-0248.2011.01629.x
When Daphnia evolve resistance to pesticides, they become more vulnerable to bacterial parasites. Photo by Chantal Wagner.
If you haven’t read Joseph Heller’s classic Catch-22, cancel your plans for next weekend and spend the time with a copy from the nearest library. It’s a hilarious, bracingly bleak satire of military bureaucracy, as epitomized in the titular clause governing when bomber pilots can be grounded for reason of insanity:
There was only one catch and that was Catch-22, which specified that a concern for one’s safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions.
Heller conceived Catch-22 as a product of malicious middle management, but a similar situation crops up in the natural world when living things are under natural selection from conditions that favor contradictory traits. Biologists most commonly call these tradeoffs.
Over the course of evolution, tradeoffs set up “choices” that natural selection must make—a population can adapt to one alternative set of conditions, or another, or settle on a middle ground. A trivial example is that elephants have long ago “chosen” not to fly (Dumbo notwithstanding) in the course of evolving large, un-aerodynamic bodies suitable for massive-scale herbivory. A more relevant example is a new finding that the evolution of pesticide resistance creates vulnerability to parasites [$a].
The US Environmental Protection Agency estimated [PDF] that in 2006 and 2007 (the latest years for which reports are online) we used upwards of five billion pounds of pesticides to kill unwanted plants, insects, fungi, and other organisms worldwide. Once they’re sprayed, we don’t have much control over where pesticides end up—rain runoff takes them into lakes, ponds, and the ocean. In those bodies of water, critters at the base of the food chain are the first to feel the effects—critters like the tiny, translucent crustacean Daphnia magna.
Of course, those critters may be able to evolve resistance to the pesticides contaminating their environment—but that resistance may come at a cost.
Pesticide application, via the most picturesque method available. Photo by Scott Butner.
Anja Coors and Luc De Meester had already found a hint of this cost [$a] in an experiment using a single clonal line of Daphnia, in which Daphnia exposed to both sublethal concentrations of the widely-used insecticide carbaryl and a parasitic bacterium fared much worse than Daphnia exposed to only carbaryl or bacteria.
In the new study, Coors, De Meester, and three collaborators expand on that initial observation by determining whether Daphnia become more vulnerable to parasites as they evolve resistance to carbaryl, and whether this costly evolution could occur in natural populations. The coauthors took samples of Daphnia from natural populations in four separate lakes and exposed them to carbaryl over several generations—then sampled the resultant evolved populations and tested their vulnerability to the bacterium. Compared to Daphnia left unexposed to carbaryl, the evolved populations were more resistant to the pesticide—and were also more badly hurt by bacterial infection.
It’s hard to say how general this particular result is to the many, many other species that, like Daphnia, must cope with pesticides and other pollutants humans have introduced into the environment. Evolution to resist one pesticide leads to lowered resistance to infection in one aquatic crustacean; in other species, facing different chemicals, maybe such costs are different or lesser or nonexistent. But living things are not infinitely pliable as they evolve in response to the many and rapid changes we’re making in the world. To slow the extinction crisis going on around us, we need to avoid trapping other living things in Catch-22.
References
Coors, A., & De Meester, L. (2008). Synergistic, antagonistic and additive effects of multiple stressors: predation threat, parasitism and pesticide exposure in Daphnia magna.Journal of Applied Ecology, 45 (6), 1820-8 DOI: 10.1111/j.1365-2664.2008.01566.x
Jansen, M., Stoks, R., Coors, A., van Doorslaer, W., & de Meester, L. (2011). Collateral damage: Rapid exposure-induced evolution of pesticide resistance leads to increased susceptibility to parasites. Evolution DOI: 10.1111/j.1558-5646.2011.01331.x
To celebrate Pride Month 2011 (just eight shopping days left!), Denim and Tweed is hosting a relaunched Diversity in Science blog carnival, collecting online writing about lesbian, gay, bisexual, and transgender issues from across the science blogosphere. Alberto Roca of Minority Postdoc is leading the DiS relaunch, and he’s just created a handy online submission form for the carnival.
So now sending in your posts—new for June or years old—is as easy as copying a permanent URL into the form (preferably in the “message” box) and signing it with your e-mail address. What are you waiting for? [Edited to add:] You have until Monday, 27 June to submit, so I can put the carnival online by the 30th!
The rest of my week is going to consist of driving across two time zones, seeing my parents off on a flight further east with many thanks for their assistance in getting me across those aforementioned timezones, and intensive apartment hunting in not one but two new cities. So no new science post this week; we’ll see how next week goes.
Picturesque, but maybe not practical. Photo by jimw.
