Minneapolis, one of my two new hometowns. Photo by jby.
So, now that I’ve defended my dissertation, there’s really not much of grad school left for me. I have to turn in a final, committee-approved version of the dissertation text, and then on May 14 I’ll put on some Hogwarts-worthy getup and accept my diploma from the University of Idaho. I also have some final grading to deal with (Whose bright idea was it to add an independent reading report to the lab curriculum? Oh, right. Mine.) and I’d like very much to get my last Joshua tree paper ready for submission. But, after all that—what’s next?
As it happens, I’ve known that for some time, but there didn’t seem to be a good opportunity to cover it here before now: I’m going to Minnesota.
My new favorite plant, Medicago truncatula. Photo by Minette Layne.
So I’ll be studying a mutualism that might work a bit like yucca pollination—but then again, it might not. The plant-rhizobium interaction is much more widespread than obligate pollination mutualism, and has probably played a big role in the diversification of land plants. Plus, I’ll be working with genome-scale data—it’s all on a totally different scale from anything I’ve done before. There are possibilities for experiments and analyses that we’ll never be able to do with Joshua trees—ye gads, greenhouse experiments!—and it’ll be a learning experience at every step. And, equally importantly, my new collaborators at the Tiffin lab and the other research groups involved in the Medicago genome project are a smart, friendly bunch—I’m looking forward to working with them. All in all, it’s exactly what I want in a postdoc.
Saint Paul and Minneapolis look like a pretty nice place to spend the next couple years, too. It’s not just that they’re cities after six years in small-town Idaho—they’ve got solid mass transit and they’re ranked alongside Portland, Oregon for bicycle-friendliness. One of my new senators will be Al Franken. The Twin Cities are the home turf for Public Radio powerhouse American Public Media. Minneapolis was even named the gayest city in America by the Advocate, and I don’t think that was meant as some sort of elaborate joke.
Of course, as I’ve learned from years of Garrison Keillor exposure, winter in Minnesota does not mess around. Fortunately I’m moving immediately after graduation in mid-May, so I’ll have some time to brace myself. Apartment-hunting priorities include covered parking.
All of this is a long and digressive way of saying, yet again, that I’m making some pretty major changes in the next few weeks. Expect further irregularities in posting, and maybe even a radical reconsideration of how D&T fits in my schedule—I don’t yet know what my life will look like once I’ve settled into postdoc-hood, though I’m excited to find out.
Who needs pollinators? Not monkeyflowers—at least not after a few generations of evolution. Photo by Brewbooks.
The loss of animal pollinators poses a potentially big problem for plants. However, many plant species that rely on animals to move pollen from anther to stigma have the capacity to make due if that service goes undone—and, as a new study released online early by the journal Evolution demonstrates, such plants can rapidly evolve to do without pollinators [$a] if they must.
The paper’s authors, Sarah Bodbyl Roels and John Kelly, demonstrate this using a simple greenhouse experiment with the monkeyflower Mimulus guttatus, a wildflower native to western North America, and a member of a genus rapidly developing into a major model system for studying the evolution of ecological isolation and floral evolution.
Mimulus species vary in their reliance on animal pollinators—some grow minimalistic flowers, with the anther so close to the stigma that pollen transfers without any assistance. In natural populations, M. guttatus is usually pollinated by bees, but individual plants vary in the distance between anther and stigma, and this variation has a genetic basis. So a population of M. guttatus deprived of pollinators would have the raw material to evolve a solution—natural selection would favor plants that are better able to self-pollinate. As the population evolved to be more self-fertilizing, it might also evolve to look more like self-pollinating Mimulus species, losing the bright petals that attract pollinators.
To see whether this could actually happen, Bobdyl Roels and Kelly challenged an experimental population of Mimulus guttatus to do without pollinators, and tracked its response.
The authors raised seeds derived from a natural wild population of Mimulus guttatus in greenhouses under two trial conditions: control populations were provided with hives of bumblebees to pollinate them when their flowers were ready for servicing; and experimental populations were left to produce what seed they could without pollinators. The authors collected the seeds produced by each population, and planted them to form the next generation.
A bumblebee digs for nectar in flowers of Mimulus moschatus. Photo by Mollivan Jon.
Early on in the experiment, the experimental populations deprived of pollinators fared badly. Without pollinators, the average plant produced two seeds or fewer by the end of the generation, compared to eight or ten seeds per plant in the population provided with bees. By the fifth generation, however, this was starting to improve—plants in both populations without pollinators were producing more seeds, and one of the two experimental populations produced nearly as many seeds as the control plants.
Examining the traits of plants produced by this final generation (actually, the grand-offspring of the fifth generation, to control for effects of inbreeding), the authors found that the average distance between the pollen-producing anther and the pollen-receiving stigma had shrunk significantly in plants from the experimental population. Across all the treatments, plants with a shorter distance between stigma and anther produced more self-pollinated seeds. There was no evolved change in other floral measurements, however—plants in the no-pollinators treatment had petals as big and showy as plants evolved with bumble bees.
In a natural population of Mimulus guttatus, the drop-off in seed production created by loss of pollinators should have much the same effect as in this experiment, creating a strong selective advantage for individual plants that can make more seeds on their own. The fact that the experimental plants did not evolve reduced petals could mean that in the cushy conditions of a greenhouse, there wasn’t much need to stop spending resources making showy flowers. Or maybe, when the major source of natural selection is the need to make any seeds at all, selection to save resources on flower production is relatively weak and correspondingly slow-acting.
As the authors point out, one of many changes humans are making to natural communities around the world is to disrupt pollination relationships. In a sense, experiments like theirs are being carried out worldwide, on hundreds of plant species—and each species will adapt, or fail to adapt, in its own way.
Shakespeare, evolution, and Kubrick’s Space Odyssey: brilliant. Brutish, aggressive chimpanzees have long been the assumed model for earlier humans—but more peaceful bonobos might be closer to the truth.
Might as well give up on drug development right now. Masturbation (or, rather, orgasm) has been found to relieve restless leg syndrome.
As already noted in other venues, yesterday I passed my dissertation defense. There has been what I’d call an appropriate amount of celebration (as a result of which I’m taking it slow today) and I’ve been overwhelmed by congratulations in multiple media—thanks, everyone!
So, what with getting my sparrows in a row for my dissertation defense on Friday, I haven’t written any new science post for this week. But! As it happens, I have written about most of the component chapters of my dissertation—so in lieu of something new this week, why not check out those posts?
The first chapter of my dissertation is a literature review about the phenomenon ecologists call ecological opportunity, and how it may or may not explain big, rapid evolutionary changes. I’ve also written about this topic for the Scientific American guest blog.
The fourth chapter is the latest work on my lab’s big study of Joshua trees and their pollinators. The material I’m including in this chapter hasn’t been reviewed and published yet, but you can read the most recent Joshua tree post to learn what we know so far, and what kinds of questions we still want to answer.
Regular posting resumes next week, provided that I pass my defense and the celebrating afterward doesn’t interfere with my blogging capacity.
A week from Friday, I’m finally going to present six years’ worth of doctoral research to my dissertation committee, and they’ll tell me whether or not it’s enough to warrant a Ph.D. I am given to understand that the process will go something like this:
Which is to say, a lot of frantic running around culminating in a highly formalized event at which my fate will depend on answering potentially arbitrary questions. Maybe involving swallows.
I’m still in the running-around bit, which involves tasks like taking my written dissertation to have the College of Graduate studies check the width of the page margins. So, um, wish me luck.
Our culture sets Nature as the highest bar for decorum, while simultaneously giving Nature our lowest standard of respect. Nature is at our disposal, not only for our physical consumption, but also for our social construction. We call geese beautiful and elegant and faithful until they are shitting all over the lawn and terrorizing young children. Then we poison their eggs. Or shoot them.
Having popped the naturalistic fallacy with a few pokes, Johnson proposes queering ecology—a deliberate reference to the term’s usage in human sexuality—to better acknowledge the complications of the natural world and humans’ relationships to it. That summary doesn’t do the work justice, though—go read the whole thing.
(Kate linked to this more-or-less alongside my first volley in the old adaptive homophobia kerfuffle, but Johnson’s essay is another order of thought altogether. Also, how cool is it that I can just go to Flickr and find an illustration for Johnson’s point with a simple keyword search? Pretty cool, I think.)
A Venus flytrap closes on an unfortunate spider. Photo by cheesy42.
Plants that eat animals offend our trophic sensibilities. Those of us who can move independently are supposed to eat those of us who can make sugar from sunlight—that’s just the way the food chain works, right?
Well, not really. From a certain perspective, plants prey on animals all the time, using the sneaky strategy of just waiting us out—when we animals stop moving for good, we’re fertilizer. And there are quite a few plants that aren’t so patient. Venus flytraps, sundews, and pitcher plants have been recognized as carnivores since before Charles Darwin devoted a book to their ecology and anatomy. They all have structures—fly-trapping leaves, or sticky hairs, or deep pitfalls full of water—that are uniquely good at catching wayward insects. All of them also grow in particularly nutrient-poor soils, such as bogs, where the nitrogen from trapped insects makes a big difference.
The vast majority of plants lack either adaptations for trapping, or the same kind of need for nitrogen—they either don’t grow where they can’t get the stuff, or they hire symbiotic bacteria to help fix it. Yet there is a third category of plants, which are not exactly carnivorous, but which might just “eat” the occasional stray fly anyway. Many plants have hairy surfaces that can catch insects, or leaf structures that trap water and create pitfalls—and some of these plants can take advantage of the critters caught in these proto-traps.
Sticky purple geranium can trap insects on its sticky leaves, and seems to get some nutrition out of them. Photo by jby.
One such plant is the sticky purple geranium (Geranium viscosissimum), which grows on dry Palouse hillsides around my current hometown of Moscow, Idaho. As its name implies, sticky purple geranium is sticky—its leaves are velvety with tiny glandular hairs, which leave a gummy residue on your hands if you brush against them. These hairs make it difficult for small insect herbivores to get to the leaves—but they also trap some of those insects.
Back in 1999, a biologist in my department at the University of Idaho, George Spomer (who left the department before my arrival), showed that sticky purple geranium leaves would digest a protein film pressed against them, somewhat like the leaves of a sundew. When Spomer placed protein labeled with carbon-14 on geranium leaves, he found elevated levels of carbon-14 elsewhere in the plant, suggesting that geranium leaves could absorb protein as well as digest it [$a].
Spomer demonstrated that the plants he studied could digest and absorb insects caught on their leaves, but his data can’t tell us whether that ability is of any particular use to a geranium growing in a natural population—whether, that is, geraniums actually need the nutrients they might get from trapped insects. A more recent study of another possibly carnivorous plant gets closer to answering that question.
Water collected in the leaves of a teasel plant forms a death trap for insects, and a source of nitrogen for the plant. Photo by HermannFalkner/sokol.
The plant in this second study is fuller’s teasel, Dipsacus fullonum, a widespread European wildflower that has been introduced into North America. The leaves of many teasel plants form catchments (pictured above) that can collect water and form a makeshift pitfall, which catches and drowns small insects. It has been speculated that, like sticky purple geranium, fuller’s teasel can absorb nutrients from these catchments full of rotting insect corpses. British biologists Peter Shaw and Kyle Shackleton set out to test this hypothesis not by tracking protein from trapped insects, but by determining whether teasel plants benefit from the trapping.
To do this, Shaw and Shackleton experimentally manipulated the number of insects trapped in the catchments formed by teasel plants’ leaves. In one treatment, they watched experimental plants and removed insects as soon as they were trapped; in the other, they “fed” the experimental plants an extra bluebottle maggot at set intervals. They compared both treatments to a group of plants that were left un-manipulated as a control. The “fed” plants didn’t necessarily grow bigger or produce more seeds, but they did produce more seeds as a proportion of their total biomass. That is, fuller’s teasel plants that trap more insects can devote more of their resources to making seeds.
Does this make fuller’s teasel carnivorous? Maybe, but probably not in the same sense that a Venus flytrap is. Teasels tend to grow in better soil than carnivorous plants do in general—they like open fields and stream banks, in my experience. Furthermore, we don’t have any evidence that teasels actively attract insects, as most carnivorous plants do. On balance, it seems far more likely that what Shaw and Shackleton found is not carnivory as we usually know it, but plants making sure that a handy source of nitrogen doesn’t go to waste.
Fuller’s teasel relies on insects for pollination—but does it also rely on them for nutrition? Photo by gynti_46.