Category Archives: science

Is dilution the solution to information pollution?

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ResearchBlogging.orgChris Smith, my good friend and longtime collaborator on all things relating to Joshua trees, pulled into the gas station well after dark. He was on his way back to our field site in the Nevada desert, and this was the last stop before cell phone signals disappeared for good and you had watch the highway ahead for free-range cattle.

It was also the last stop for fresh water, gasoline, and propane. Chris fueled up the van, then went inside for help refilling the spare propane tank. The unshaven, sun-darkened night clerk gave Chris’s flip-flops and tee shirt a sidelong look—they might’ve been perfect back in Vegas around midday, but now it was a freezing high desert night. Clearly unpleased to have to go outside himself, the clerk zipped up his parka and followed Chris out to fill up the tank.

Why do scorpions fluoresce under UV light, anyway? Photo by Furryscaly.

Refilling the propane tank entailed much adjusting of valves and connecting of pipes, which the clerk accomplished with a large wrench. Somewhere a valve misconnected to a pipe, and Chris’s jeans were suddenly soaked in liquid propane. The clerk swore elaborately at the valve, blamed the lazy bastards on the day shift, and took out his frustration on the propane tank with the wrench.

When this miraculously failed to engulf the two of them in fiery death, the clerk straightened out the connection and started filling the spare tank, then turned to Chris and said, “So what’re you doing out here, anyway?”

Evolutionary biologists learn to be vague about their profession in rural areas, so Chris said he was a biologist. No, he wasn’t working for the Air Force base over at Groom Lake. He was studying Joshua trees.

“You must know something about evolution, right?” said the clerk. “I’ve got a question for you.”

Oh, brother, thought Chris. Here we go. How long till this tank fills up?

“You know how scorpions glow under ultraviolet light,” they clerk asked.

Why yes, I do, said Chris.

“How come? I mean, what possible adaptive value does that have?”

Well, you know, said Chris, I don’t have any idea.

“I hear,” said the clerk, “that fossil scorpions millions of years old will glow if you shine a UV light on them. That’s pretty wild, isn’t it?”

You’re right, said Chris. That’s pretty wild.

Chris told this story to everyone else in the field team as soon as he got back to camp, and I think it’s a great illustration of two points that inform the way I think about science blogging. First, that scientists are maybe a bit quick to assume hostility in their audience; and second, that telling cool stories about the natural world is at least as important as confronting the hostility really is out there.

I’ve been thinking about these points ever since ScienceOnline 2011, which I finished with the “Defending Science Online” session, a discussion of strategies for countering all manner of anti-scientific bunk: climate change denialism, opposition to vaccination, creationism, homeopathy. The panelists discussed specific events and general strategies, but they really only discussed confrontation. I left with the nagging feeling that identifying and refuting non-science, however well it’s done, isn’t enough.

Scientific misinformation needs to be contained, but it also needs to be diluted. Photo by kk+.

The trouble with refutation is that once creationists or anti-vaxxers piss in the information pool, it’s nearly impossible to clean up the water. A widely-cited recent study of fact-checking in news articles has shown that corrections often fail to reach people who don’t want to hear them—and the act of correcting a misperception can actually reinforce it [PDF]. Other works shows that even when you convince people that the information they cite in support of political positions is wrong, they hold on to those positions [PDF].

When real-world pollution can’t be extracted from the environment, there’s one final line of attack: dilute it. In the sense that what we call pollution is often a dangerous artificial concentration of some substance that is non-dangerous at much lower, natural levels—carbon dioxide, for instance—the solution to pollution is, indeed, dilution. In the case of information pollution, which we can’t really prevent or contain, we can dilute non-science with, yes, science.

In other words, the best weapon against denialism may not be explicit takedowns of denialism, but good, clear, accessible discussion of science and all the ways it’s awesome. I can speak to this from my own experience growing up in a neutral-on-evolution household in the midst of quite a lot of creationists. I can’t recall that I ever decided evolution was a historical fact because of something I read against creationism. Instead, I came to accept the fact of evolution because I read and watched and listened to a lot of popular science—National Geographic, Ranger Rick, and Nature on PBS—that just took evolution as a given, and showed how it explained the world.

So, while folks like PZ Meyers, NCSE, and Ben Goldacre fight the good fight, I think we shouldn’t forget the value of celebrating science without making it a confrontation. And in the era of Science Online, we’re surrounded by people pointing out things as cool as glow-in-the-dark scorpions. See Scicurious’s Friday Weird science posts, Carl Zimmer’s tale of Vladimir Nabokov’s contributions to entomology, Olivia Judson explaining brood parasitism, or Radiolab’s mind-blowing meditation on stochasticity for just a few great examples selected off the top of my head.

This kind of science communication focuses on the grandeur and fun of the scientific view of life, and it wins supporters to science one story at a time. That’s not necessarily the most exciting part of the struggle against ignorance and denialism. But every time we get someone to say, “That’s pretty wild,” we’re making progress.

References

Bullock, J. (2006). Partisanship and the enduring effects of false political information. Presented at the annual meeting of the Midwest Political Science Association. PDF.

Nyhan, B., & Reifler, J. (2010). When corrections fail: The persistence of political misperceptions. Political Behavior, 32 (2), 303-30 DOI: 10.1007/s11109-010-9112-2

Science online, light fantastic edition

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  • The poetic possibilities alone are staggering. Given a wing with the right optical properties, it’s possible to fly on a beam of light.
  • Which is why I buy in bulk. Serving snacks in smaller packages can help people eat less—but it only works for overweight people.
  • “Digital rectal stimulation.” Really. Science finds a cure for intractable hiccups.
  • Being female ≠ being anemic. Normal blood loss during menstruation does not cause iron deficiency.
  • Two million years of eating bamboo. Although fossils of the giant panda’s ancestors are few and far between, paleontologists are beginning to piece together their evolutionary history.
  • Context! Ed Yong compiles five years of stem cell research into an interactive timeline.
  • Boy, is my face red. How did blushing evolve as an involuntary social signal?

And now, Nature Video explains a new study [$a] that suggests why seahorses are horse-shaped. Via The Hairpin.

Communities within communes: Do bees’ social lives influence their gut bacteria?

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ResearchBlogging.orgAs anyone who’s trying to sell you probiotic yogurt will tell you, what you can eat often depends on what’s living in your gut. For many animals, symbiotic bacterial communities help break down foods that would otherwise be indigestible. Perhaps most famously, termites would be unable to eat wood without specialized microbes in their guts [$a], but many other animals host bacteria that break down cellulose, the tough structural sugar of plant tissue, or to supply nutrients lacking in their diet.

This honeybee is carrying more than pollen. Photo by Danny Perez Photography.

The importance of gut microbes for digesting certain kinds of food has led to the suggestion that acquiring the right microbes can be an evolutionary key innovation—a change that creates access to new resources and spurs adaptive radiation. A 2009 study of gut microbes in ants found that evolutionary transitions to eating plants were associated with acquiring similar gut microbes.

So what about the biggest group of herbivorous hymenoptera, the bees? Bees’ ancestors were most likely predatory wasps, but some time in the Cretaceous Period they began making a living on pollen and nectar instead. A new study of gut microbes in a wide diversity of bees suggests that social organization, not diet, changed what lives inside bees’ bellies [$a].

The study examined the bacteria inside representatives of seven bee families, collecting sequence data from a gene widely used in studies of bacteria. The method employed allowed the authors to identify not just what kinds of bacteria were present, but how abundant each kind was. This microbial profile was specifically compared to the profile for Apis mellifera, the honeybee, whose gut microbes have been studied quite a bit already.

The bees form a monophyletic group—they all share a single common ancestor—and they are overwhelmingly herbivorous. Phylogenetic logic suggests, then, that any changes to the gut microbe community associated with the evolutionary transition to eating pollen and nectar would have occurred once, in the common ancestor. The microbes that facilitated that transition should also be widely shared by herbivorous bees.

In fact, most of the bee families sampled had little in common with the honeybees’ gut bacteria. Close relatives of the bacterial types found in Apis mellifera only turned up in two other Apis species, and bumble bees (genus Bombus). Since herbivory doesn’t explain this pattern of similarity (or lack thereof), the authors suggest that what really matters to bees’ guts is social behavior. Apis and Bombus are eusocial, forming hives of related workers cooperating to support a handful of reproductive individuals; the other bees surveyed in the study live mostly alone.

Life is different in the hive. Photo by stewickie.

As the authors note, eusociality would certainly change the environment offered to symbiotic bacteria. Bees in a hive should transmit bacteria among themselves, especially when feeding larvae. So eusocial bees mostly get their gut bacteria from their sisters. The bacteria in the guts of the solitary bees surveyed were mostly related to strains found in soil and on plants—so solitary bees are probably populating their guts with bacteria from their environment.

The idea that eusociality has shaped bees’ interactions with their symbiotic bacteria is interesting, but the data presented in this study are preliminary at best. The sampling of bee diversity presented here is broad, but not very deep—most of the bee families covered are represented by only one or two species. Understanding the effects of social structure on bees’ gut bacteria will take much finer-grained sampling to focus on evolutionary transitions not from predation to herbivory, but from solitary to eusocial lifestyles.

References

Kaltenpoth, M. (2011). Honeybees and bumblebees share similar bacterial symbionts. Molecular Ecology, 20 (3), 439-40 DOI: 10.1111/j.1365-294X.2010.04960.x

Martinson, V. G., B. N. Danforth, R. L. Minckley, O. Rueppell, S. Tingek, & N. A. Moran. (2011). A simple and distinctive microbiota associated with honey bees and bumble bees Molecular Ecology, 20 (3), 619-28 DOI: 10.1111/j.1365-294X.2010.04959.x

Ikeda-Ohtsubo, W., & A. Brune (2009). Cospeciation of termite gut flagellates and their bacterial endosymbionts: Trichonympha species and ‘Candidatus Endomicrobium trichonymphae’. Molecular Ecology, 18 (2), 332-42 DOI: 10.1111/j.1365-294X.2008.04029.x

Russell, J., Moreau, C., Goldman-Huertas, B., Fujiwara, M., Lohman, D., & Pierce, N. (2009). Bacterial gut symbionts are tightly linked with the evolution of herbivory in ants. Proc. Nat. Acad. Sci. USA, 106 (50), 21236-41 DOI: 10.1073/pnas.0907926106

Carnival of Evolution No. 32

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Correction, 11:25h: I’ve just been informed that the fish in the photograph below are not swordtails, but guppies. Burned again by Flickr taxonomy! The real Darwin would’ve got it right, I’m sure.

The Carnival of Evolution is a monthly collection of online writing about evolutionary biology and its cultural and political implications, hosted by a different blogger every month. Today, Denim and Tweed hosts CoE for the first time. Since Charles Darwin’s birthday is this month (only 12 shopping days left!), I thought it might be appropriate to imagine what Darwin himself might have to say about this month’s posts. Share and enjoy!

Photo via WikiMedia Commons.

Down. Bromley. Kent.
Febr. 1, 2011

My dear Hooker,

I was grateful for your very kind wishes; and for the book about the Anoles of the West Indes, which I expect I shall read with much enjoyment. The merest thought of an approaching 202nd birthday makes me feel the need for another trip to Malvern; but I do find some relief in my reading, of which I must needs do more every day it seems, only to keep abreast of the latest work. My great-grandson presented me last month with an i-Pad, a charming device; I can now consult the “web-logs” in the garden, when it is pleasant.

And there is such a lot of reading to do! It seems I read constantly about work extending the ideas I first proposed more than 150 years ago; it is gratifying, and rather humbling, to see what has grown from my little “abstract.” And dear old Wallace’s, of course. (Have you heard from Wallace recently? The last I knew of him, he was departing on that expedition with Greenpeace; but that was more than a year ago.)

Once I suspected my thoughts upon the origins of species would soon be only of interest to students of history and philosophy, but every-where I look I find someone else building upon my ideas.

For instance, experimentation has recently shown that more diverse communities of microbes use resources with greater efficiency, which extends my own simple trials with grasses on a small plot of ground. I am quite interested in the ongoing study of such interactions between species; there has been much interesting work on the co-evolution of hosts and their beneficial symbiotes, in which it is debated whether hosts may control their symbiotes without the need of punishments. And I recently saw that some species of citrus can attract parasitic worms to drive off weevil larvae.

I was also charmed to discover that butterflies of the species Eurybia lycisca, have evolved elaborately long tongues, long enough to take nectar without pollinizing; an unfortunate development for the flowers they visit! And I have recently seen a delightful study of the leaping of Blenniid fishes, supported by many moving pictures; and the very interesting findings of separated forms of the Clouded Leopard in Borneo and Sumatra.

(Here is a charming moving picture of the Clouded Leopard. What a blessing You-Tube is for the stay-at-home naturalist!)

Which is not to say that I think all developments from my theories are sound; you may have read about the idea that women’s tears are modified to save them from molestation, which seems to me curious indeed. I have also seen some very odd speculations upon the morphology of human beings in the distant future. I do not understand why the form should be arboreal. It may be worth recalling, in this context, that Humankind is only one twig in the evolutionary tree of the Apes.

Still more interesting to me is discovering the ways in which I was mistaken (embarrassing as they often are) and facts I was unable to percieve at the time of first writing. For instance, this extensive essay about Mosaic Evolution, or what I might call the Independent Modification of Parts; which evidently has its roots in Lamarckism. We may have been too harsh on the good Chevalier. Equally as interesting is this disquisition upon conditions in which Natural Selection may not lead to modification of descendants. Of course a lack of adaptation might be just as informative as the process of adaptative modification itself!

Of course the experiments of Gregor Mendel were an important improvement to what little understanding I mustered in The Origin; some suggest that now that Mendel’s thinking is over-simple, but it retains much power I feel. The study of living species is so very complicated! We must keep watch not only upon D.N.A. but the myriad complications of its translation to form the structures of the body, and even the duplication of genic code to originate new structures. The greater understanding we have gained since I first concieved of Natural Selection promises to continue improving the condition of humanity; I read, for example, that we may manipulate adaptations lengthen life at a cost to fecundity in order to breed more productive crops.

I must admit that I badly underestimated the role of chance and mutation in the descent of species; especially the degree to which it could allow imperfection to persist, even costly mis-folding of protein molecules. And yet chance changes may have profound consequences for the future of a species, much as my lucky chance to join the crew of the Beagle started me as a naturalist.


A pair of sword-tails guppies. Photo by Alice Chaos.

I have read recently also of several challenges to my original thoughts on Selection in Relation to Sex; experimentation has found, for example that the sexual ornaments of Xiphophorus sword-tailed fishes, do not hamper the males’ abilities to escape danger, which suggests they carry no great cost.

And of course it seems that there have always been persons who object to the idea that we might share kinship with apes and even sessile cirripedes; but fortuitously they seem not to have come up with any particularly novel arguments since 1859. And we may even use Natural Selection to explain the religions that deny the common descent; I suspect that social influences are greatly to blame.

With learned discussion so abundant and easy to find, it is truly a wonder that ignorance and misinformation persist; if only more people did their researches with proper care!

Yours very sincerely,

Thanks to everyone who contributed to this month’s Carnival! Want to submit posts for next month? Go to the BlogCarnivals form, or check out the list of past and future hosts at the carnival index page. Just as importantly, the Carnival needs hosts starting next month! If you’d like to host the Carnival, CoE overlord Bjørn Østman wants you to e-mail him right now.

Another year, and a new Open Lab

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The hardworking crew behind the Open Lab collection of online science writing haven’t quite finished production of the 2010 edition yet, but they’re already taking submissions for the 2011 collection. Submit your online science articles published after 1 December, 2010 using the handy online form. Self-nomination is not only okay, it’s encouraged. And hey, it worked for me.

Writerly scientist derided scientist-writer?

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ResearchBlogging.orgFollowing up on the recent discovery that novelist and lepidopterist Vladimir Nabokov correctly supposed that Polyommatus blue butterflies colonized the New World in stages, Jessica Palmer points out that none other than Stephen Jay Gould dismissed Nabokov’s scientific work as not up to the same standards of genius exhibited in his novels. She suggests that Nabokov’s work may have been dismissed by his contemporaries because his scientific papers were a little too colorfully written.

Roger Vila, one of Pierce’s co-authors, suggests that Nabokov’s prose style (Wellsian time machine!) did his hypothesis no favors:

The literary quality of his scientific writing, Vila says, may have led to his ideas being overlooked. “The way he explained it, using such poetry — I think this is the reason that it was not taken seriously by scientists,” Vila says. “They thought it was not ‘hard science,’ let’s say. I think this is the reason that this hypothesis has been waiting for such a long time for somebody to vindicate it.”

That’s a little harsh toward scientists, but it seems plausible: creativity in scientific writing is rarely rewarded.

Hyperlink to quoted source sic.

Palmer’s analysis is thoughtful and thorough, and you should read all of it. But she misses what (to me) seems like the best wrinkle in the whole business: Gould, alone of all the scientists, should have been sympathetic to the dangers of writing “too well” in a scientific context.

Stephen Jay Gould, one suspects, never murdered a single darling in a decades-long career of writing for scientific and popular venues. The iconoclastic 1979 paper “The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme” [PDF], coauthored with Richard Lewontin, is a case in point. Gould and Lewontin wanted to make the point that not all traits and behaviors of living species are necessarily adaptive—that is, evolved to perform a function that enhances survival and/or reproductive success. Today it is widely agreed that this point needed making. But Gould’s writing undercut the success of his own argument, or at least gave his detractors a toehold for derision.

The Cathedral of San Marco in Venice, its structurally practical arches encrusted with Baroque decoration. A metaphor for Gould’s metaphors? Photo by MorBCN.

Gould and Lewontin developed their argument with references to architecture and to literature. They compared non-adaptive traits to mosaics decorating the spandrels of the Cathedral of San Marco in Venice. Spandrels being spaces created between arches, anything decorating them is clearly secondary to the architectural decision to build an arch. They also compared “adaptationist” biologists to the character of Dr. Pangloss in Voltaire’s satire Candide, who claims that “all is for the best in this best of all possible worlds.”

Pangloss is a fool, and biologists who felt Gould and Lewontin were critiquing them took the obvious inference. One of the most biting responses to “Spandrels” focused much more on the style than the substance of the paper. The author, David Queller, titled it “The spaniels of St. Marx and the Panglossian paradox: A critique of a rhetorical programme” [PDF], and the parody only continues from there.

Queller built an elaborate and unflattering image of Gould and Lewontin as Marxists focused on their political perspective like the dog in the old RCA ads fixated on a grammophone. He even referenced one of Gould’s favorite cultural touchstones, the works of Gilbert and Sullivan, to tweak Gould as “the very model of a science intellectual.” Queller manages to have his cake and decry it, too—he mocks Gould and Lewontin with overflown metaphors, then backs off to say that such tactics are irresponsible:

So, how did I like my test drive in the supercharged rhetoric-mobile? It’s certainly been fun … but it’s pretty hard to keep the damned thing on the road. … my little parody of Gilbert and Sullivan’s modern Major General, who knows about everything but matters military, might induce an uninformed reader to conclude that Gould knows about everything but matters biological. But this is exactly the complaint that many biologists would level at Spandrels—that colorful language can mislead as well as inform.

So if Gould’s reading of Nabokov’s scientific achievement was predicated on the opinions of Nabokov’s colleagues, who didn’t care for elaborate prose in their scientific journals, well, I think that’s what my English teachers called irony.

References

Gould, S., & Lewontin, R. (1979). The spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. Proc. Royal Soc. B, 205 (1161), 581-98 DOI: 10.1098/rspb.1979.0086

Queller, D. (1995). The spaniels of St. Marx and the Panglossian paradox: A critique of a rhetorical programme. The Quarterly Review of Biology, 70 (4), 485-9 DOI: 10.1086/419174

Vila, R., Bell, C., Macniven, R., Goldman-Huertas, B., Ree, R., Marshall, C., Balint, Z., Johnson, K., Benyamini, D., & Pierce, N. (2011). Phylogeny and palaeoecology of Polyommatus blue butterflies show Beringia was a climate-regulated gateway to the New World. Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2010.2213

Carnival of Evolution—just four days left to submit!

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Photo by zen.

The 32nd edition of the Carnival of Evolution will be hosted right here at Denim and Tweed on the first of February! So send me your evolutionary posts by midnight Monday—use the CoE blog carnival form, or e-mail links to denimandtweed AT gmail DOT com.

(Thanks to everyone who’s submitted so far. Looks like it’ll be a good carnival—so all the more reason to submit if you haven’t yet!)

Science online, caught on tape edition

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Photo by gorditojaramillo.
  • “… dinosaurs using their feathers to fly.” Carl Zimmer digs into the evolutionary origins of feathers.
  • This is your brain wanting to be on drugs. When smokers see movies of other people smoking, their brains light up.
  • Also, raptors are from the Cretaceous. Jeez. Turns out that “Jurassic Park” screwed up dinosaur taxonomy.
  • Biofilm-coated cookware, anyone? Bacterial biofilms are more water-resistant than Teflon.
  • She’s done more than embarrass NASA. A lot more. Dilara Ally interviews Rosie Redfield.
  • My guess: magical rings that made them invisible. Robert Krulwich considers how the “hobbit” people of Flores might have coexisted with six-foot carnivorous storks.
  • Adaptation for a period of extremely short tempers during the Upper Cretaceous. Paleontologists discover a dinosaur with only one finger per forelimb.
  • Hey, nitrogen is nitrogen. A tropical bat species nests exclusively inside giant carnivorous pitcher plants, providing the the plants with an, um, alternative fertilizer.
  • “I want no other fame.” Population genetic data has confirmed a hypothesis about butterflies colonizing the Americas from Asia that was first proposed by Vladimir Nabokov. Yes, that Vladimir Nabokov.
  • When Caenorhabditis elegans catches a cold, scientists celebrate. A species of nematode widely used as an experimental organism has contracted a virus. Let the experiments in coevolution commence!

Video this week: actual, real-time, microscopic video of a malaria parasite invading a human blood cell, via New Scientist TV. The parasite, a smallish blob on the right, attaches to the outside of the big, round, red blood cell and disappears inside it—and then the red blood cell shrivels away.

We need to hear what we’d rather not

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The issues faced by women in the blogosphere—higher expectations, less recognition, and casual sexism—have officially emerged as the most important discussion topic in the wake of ScienceOnline 2011.

Kate Clancy kicked things off with her recap of the conference panel “Perils of blogging as a woman under a real name.” Christie Wilcox followed up by calling out the flagrant sexism of many of her male readers, which made David Dobbs righteously angry—and, seriously, who actually believes that any sentence containing the word “tits” is complimentary in any context? Emily Willingham noted that her voice is unique in ways beyond her gender. And now Clancy is rounding up the rapidly propagating conversation.

The conversation’s ongoing in the comments on all these posts, and (barring a handful of amazingly clueless folks) mostly great reading. My major thought on the subject remains what I said in first tweeting about the post that started it all: the most valuable parts of this conversation are the things that men are probably not all that happy to hear. When I read

  • We are all very, very tired of making a point on a blog, on twitter, or in a meeting, being ignored, having a man make the same point, then having that man get all the credit. Very tired.

my first thought was defensive: I’ve never done that! My second was, Oh, crap. Have I done that?

I’ve long believed that the value of a sermon is proportionate to how uncomfortable it makes its audience. No one needs to be told they’re doing just fine as they are. But if we’re not doing fine, we need to hear about it. So to the women science bloggers leading this conversation, I want to say: keep calling out male thoughtlessness, in specifics as well as in general. If I miss that you said something first because I’m not reading your blog, drop a link in the comments. If I write something stupid, e-mail me and complain. I may not be thrilled to be corrected, but that probably means I needed it.

Finding the middle road: Flowers evolve to work with multiple pollinators

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ResearchBlogging.org

“I’ve had a lot of jobs in my life: boxer, mascot, astronaut, baby proofer, imitation Krusty, truck driver, hippie, plow driver, food critic, conceptual artist, grease salesman, carny, mayor, grifter, body guard for the mayor, country western manager, garbage commissioner, mountain climber, farmer, inventor, Smithers, Poochie, celebrity assistant, power plant worker, fortune cookie writer, beer baron, Kwik-E-Mart clerk, homophobe, and missionary, but protecting people, that gives me the best feeling of all.”
—Homer Simpson

In twenty-two seasons of The Simpsons, the eponymous family’s bumbling father Homer has tried his hand at dozens of different jobs, and failed hilariously at most of them. Homer is a one-man illustration of “Jack of all trades, master of none,” the idea that it’s hard to do many different things well. This principle applies more broadly than the curriculum vitae; in biology, it means that living things face trade-offs between different ways of making a living.


A wild radish (Raphanus raphaistrum) flower. Photo by Valter Jacinto.

For instance, a plant whose pollen is carried from flower to flower by just one pollinating animal only needs to match that one pollinator very well. But most plants’ flowers are visited by many different potential pollinators, and matching all of them probably means finding a middle ground among the best ways to match each individual pollinator. A study of one such “generalist” flower, the wild radish, has found exactly this: working with multiple partners takes evolutionary compromise [$a].

Wild radishes are visited by a wide variety of different insects, including honeybees, bumblebees, syrphid flies, and cabbage butterflies, among others. Each of these pollinators comes to a radish flower with a slightly different agenda. Butterflies are there for nectar, but bees like to eat pollen as well—and bumblebees will sometimes bite into the base of a flower and “steal” nectar without ever coming into contact with pollen. Figuring out how natural selection from each of these different pollinators adds up required some clever experimental design.

The study’s authors arrayed potted radish flowers inside a big mesh flight cage, and then introduced either bumblebees, honeybees, cabbage butterflies, or all three pollinators to visit the plants and circulate pollen from flower to flower. They measured the plants’ flowers before putting them in the flight cage, then let the pollinators do their thing. Afterward, the authors collected seeds resulting from the pollinators’ activity, grew them up, and measured the offspring to see whether their traits differed. The procedure was essentially one generation of experimental evolution.


A cabbage white butterfly (Pieris rapae), one of many pollinator species exerting natural selection on wild radishes. Photo by ComputerHotline.

By taking DNA fingerprints of both the parents and the offspring, the authors could also estimate the relationship between each parental plant’s floral measurements and the number of offspring it produced, either from its own seeds or by pollinating another plant.

The results are complex. Depending on the floral measurement under consideration, different pollinators selected in different directions, or the same direction, or not at all. One particularly interesting result, though, was in the effects each pollinator had on the “dimorphism” of the radish flowers’ stamens—the difference between the length of the shortest, and longest, of the male parts of the flower. Flowers only visited by honeybees evolved less dimorphic stamens, while flowers visited by either bumblebees or cabbage butterflies evolved more dimorphic stamens. Flowers in the treatment visited by all three pollinators, however, evolved to find a happy medium, an evolutionary compromise to work with the different partners.

The way these interactions played out in a flight cage probably don’t reflect exactly how they operate in the wild, but this is a pretty cool result all the same. I’ve written in the past about how incorporating multiple interactions can alter the way coevolution works. Gerbils under attack by fleas are less careful about watching for predators; but for the protists living inside pitcher plants, competitors can help distract predators. Here we have an example of multiple similar interactions pulling a generalized plant in different evolutionary directions.

Reference

Sahli, H., & Conner, J. (2011). Testing for conflicting and non-additive selection: Floral adaptation to multiple pollinators through male and female fitness. Evolution DOI: 10.1111/j.1558-5646.2011.01229.x