*Actually, I’m already well into the re-read — I’d decided to do it following DFW’s tragic death last fall, and hadn’t actually started till a couple weeks ago. But a head start probably won’t hurt.
In the mental_floss morning cup o’ links: The Washington Post has an interesting piece about the cost of poverty. Not “cost of poverty” as in “tax dollars spent on the indigent,” but as in the poor often pay more for basic necessities.
Some of it is familiar if infuriating, like the insane, evil fees for payday loans (an effective annual interest rate of 806 percent!) and check cashing services that are the only option for people without bank accounts. Some of it is not surprising if you’ve lived in a not-quite-yet-gentrified urban neighborhood, like the increased prices at urban supermarkets and smaller shops. And a lot of it just makes sad sense when you think about it — when public transportation is your only option, traveling in search of better prices on milk and bologna isn’t really possible.
If middle-class folks, who are used to getting a response when they complain, had to put up with unreasonable markups on breakfast cereal and effectively useless public transit, something would get done. Maybe more intentionally mixed-income neighborhoods would help.
When humans move from place to place, we almost always bring other organisms with us. Sometimes it’s intentional — domestic animals carried along with Polynesian colonists, for instance. Just as often, it’s accidental, as with mice stowing away on Viking longships. A lot of these introduced species have done so well in their new habitats that they become invasive, outcompeting natives and disrupting local ecosystem processes. But the species that go crazy-invasive — the cane toads and the purple loosestrife — are probably only the very successful subset of the species that hitch rides in cargo holds and ballast tanks. What sets the dangerously successful invasive species apart from others?
A new dataset published in last week’s PNAS suggests that it may be an interaction between available resources in a new habitat and a lack of compatible pathogens [$-a]. This is an amalgam of two hypothesized causes for successful invasion: access to new resources, and escape from antagonistic species. Focusing on European plant species that have successfully invaded North America, the authors, Blumenthal et al., assembled records of viral and fungal infections on each plant species in its native range, and in North America. They classified the plant species based on the habitats each occupies — wet vs. dry, nitrogen-rich vs. -poor — and on whether the plants tended to grow slowly or rapidly. This is because plant species adapted to rich, wet environments are generally thought to evolve fewer defenses against infection and herbivores; they can “afford” to grow new tissue instead of fight to keep it.
If resource availability interacts with freedom from infectious agents to spur a successful invasion, then invasive plants adapted to rich conditions should tend to host more pathogens in their home ranges than they do in their introduced range; and this difference should be less pronounced in invasive plants adapted to dry, resource-poor conditions. This is exactly what the analysis found — plants adapted to richer habitats saw a larger reduction in the number of pathogen species attacking them in their new ranges than plants adapted to less-productive conditions.
This is a valuable result for its basic application — helping to predict which introduced species are likely to become invasive, and target them for eradication efforts before they become well-established. But it also provides us with an insight into how evolution works. Many authors, particularly G.G. Simpson and Dolph Schluter, have described ecological conditions that set the stage for adaptive radiation — the rapid diversification of a lineage into many species — which sound a lot like the “ecological release” that invasive species seem to experience.
Rapid evolutionary diversification may be triggered by the evolution of a key innovation; by colonization of a new, empty habitat; or the removal of antagonistic species (usually by their extinction). These three classes of conditions are closely related, and they can be mimicked, or even replicated, when humans move species to new habitats [$-a]. Blumenthal et al. suggest, for instance, that species invasions entail both colonization of a new habitat and escape from pathogens. This is a broad observation; a good next step would be to directly compare natural selection acting on invasive plants in their native and introduced ranges. Through day-to-day processes like this, the specific ecology of a species can ultimately shape its evolutionary fate.
Blumenthal, D., Mitchell, C., Pysek, P., & Jarosik, V. (2009). Synergy between pathogen release and resource availability in plant invasion. Proc.Nat. Acad. Sci. USA, 106 (19), 7899-904 DOI: 10.1073/pnas.0812607106
Vellend, M., Harmon, L., Lockwood, J., Mayfield, M., Hughes, A., Wares, J., & Sax, D. (2007). Effects of exotic species on evolutionary diversification. Trends Ecol. & Evol., 22 (9), 481-8 DOI: 10.1016/j.tree.2007.02.017
New in the always open-access PLoS One: turns out that a great way to make new species, if you’re a plant, is to have your seeds dispersed by ants. This is because ants aren’t very good at seed dispersal.
Seed dispersal by ants, or myrmecochory, works very much like dispersal by fruit-eating birds and mammals: ant-dispersed seeds typically have a fatty attachment, called an elaiosome, that looks tasty to ants. Ants collect elaiosome-bearing seeds, bring them back to their nest, pry off the tasty bit, and then discard the rest of the seed. This leaves the seed safely underground in an ant-midden, ready to germinate — a great way to dodge seed-eating critters and avoid competition from its parent plant and siblings [$-a].
I didn’t learn about myrmecochory until after I’d finished undergrad — which is surprising, because it was going on under right my nose every time I went out into the Appalachian woods near campus. Lots of wildflowers [$-a] have ant-dispersed seeds, including bloodroot, touch-me-not, and good old trillium. It’s an extremely popular dispersal mechanism, having evolved independently multiple times on every continent except Antarctica. Really, me not knowing about myrmecochory is kind of like not knowing about fruit!
Ant dispersal is also associated with increased species diversity. In the new article, Lengyel et al. use a classic analysis method called sister group comparison to test the hypothesis that ant-dispersed plant groups contain more species than the most closely-related plant group. And they do, by a long way: on average, myrmecochorous groups contain twice as many species as their non-myrmecochorous sister groups. Why is this? As the authors conclude, it’s probably a side consequence of ant dispersal — ants don’t move seeds very far from where they collect them.
Recent evidence from genetic studies shows that limited seed dispersal in myrmecochory can lead to strong genetic structure within populations even at spatial scales as small as a few meters. The failure of myrmecochores to maintain gene flow across barriers may lead to reproductive isolation of sub-populations, which may facilitate speciation. [In-text references omitted.]
So myrmecochorous plants, like Appalachian salamanders [$-a] and tropical white-eyes [$-a], make lots of new species not because their unique characteristics give them some adaptive advantage (although, to be sure, there are advantages to ant dispersal), but because ants do a lousy job moving seeds between populations, leaving them free to follow their own evolutionary trajectories.
Lengyel et al. argue that myrmecochory is a key innovation, a trait that helps a group of organisms spread and diversify in the process evolutionary biologists call adaptive radiation. Based on their results, I have to agree — ant dispersal is strongly associated with evolutionary diversification. But the speciation that myrmecochory promotes is an accident, a side effect. We often think of key innovations promoting speciation by adaptive means, by allowing one group of species to outcompete others. Clearly, however, a key innovation can also be a trait that makes the accident of speciation a little more likely.
Beattie, A.J., & Culver, D.C. (1981). The guild of myrmecochores in the herbaceous flora of West Virginia forests. Ecology, 62, 107-15 DOI: http://www.jstor.org/pss/1936674
Giladi, I. (2006). Choosing benefits or partners: a review of the evidence for the evolution of myrmecochory. Oikos, 112 (3), 481-92 DOI: 10.1111/j.0030-1299.2006.14258.x
Kozak, K., Weisrock, D., & Larson, A. (2006). Rapid lineage accumulation in a non-adaptive radiation: phylogenetic analysis of diversification rates in eastern North American woodland salamanders (Plethodontidae: Plethodon). Proc. R. Soc. B, 273 (1586), 539-46 DOI: 10.1098/rspb.2005.3326
Lengyel, S., Gove, A., Latimer, A., Majer, J., & Dunn, R. (2009). Ants sow the seeds of global diversification in flowering plants. PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005480
Moyle, R., Filardi, C., Smith, C., & Diamond, J. (2009). Explosive Pleistocene diversification and hemispheric expansion of a “great speciator.” Proc. Nat. Acad. Sci. USA, 106 (6), 1863-8 DOI: 10.1073/pnas.0809861105
First real news item for Evolution 2009: The meetings will open Friday night with a public lecture by Eugenie Scott, who is receiving the first Gould Award for Public Outreach from SSE in recognition of her leadership at the National Center for Science Education.
What’s really exciting is that we’re going to open the event to the general public in cyberspace, too — video of the lecture will be streamed online at the meeting website as soon as the UI video production center can put it together (probably the following Monday). If you won’t be at the meetings in person, watch the Evolution2009 twitter feed for notification that the video’s up.
A visiting creationist dared biologists at U.C. Davis to debate him — and even bet $250,000 no one could show “any empirical evidence for macro evolution [sic].” Jonathan Eisen turned him down:
Discussing creationism – fine. Discussing criticism of evolutionary hypotheses – fine. Having a reasonable panel discussion of science and religion – fine. Meeting with creationists to discuss their ideas about evolution – ok too. But engaging in a “debate” and thus even for a second implying that creationism stands on the same ground as evolution – completely ludicrous.
There’s a good discussion emerging below the post; but the consensus seems to be do not feed the trolls. It’s a hard position to take — it certainly goes against my own Aspergers-oid need to refute obvious nonsense when I hear it — but I’ve rarely seen such events work out well.
Picture a local scientist who maybe thinks about creationism a couple times a year “debating” some nut who considers this his life’s work. Advantage: nut.
Consider further that the audience is overwhelmingly on the nut’s side — and, indeed, are there to have their beliefs confirmed — so that the nut has no need to make a coherent argument and can instead focus on scoring rhetorical/ presentational points. Advantage: nut.
Finally, recall that scientific knowledge is necessarily tentative and complex, and a good scientist will have to acknowledge that there are things we don’t know about the history of life on Earth; whereas the nut has an (allegedly) simple and comprehensive story. Advantage: nut.
Of course, ask the two of them do do actual science, develop an answer to an empirical question beyond “because God wanted it to be that way” — then advantage: scientist. But that’s not what a formal debate is.
I’m working through the great New York Times Magazine interview with President Obama, between grading and lit-searching. And something struck me in this section on education. (A question by the interviewer, David Leonhardt, is in italics as in the original.):
My grandmother never got a college degree. … She went to work as a secretary. But she was able to become a vice president at a bank partly because her high-school education was rigorous enough that she could communicate and analyze information in a way that, frankly, a bunch of college kids in many parts of the country can’t. She could write —
Today, you mean?
Today. She could write a better letter than many of my — I won’t say “many,” but a number of my former students at the University of Chicago Law School. So part of the function of a high-school degree or a community-college degree is credentialing, right? It allows employers in a quick way to sort through who’s got the skills and who doesn’t. But part of the problem that we’ve got right now is that what it means to have graduated from high school, what it means to have graduated from a two-year college or a four-year college is not always as clear as it was several years ago.
There’s something awfully comforting about a President who (1) has a personal connection to a world where higher education is a genuine luxury and (2) has first-hand knowledge of the product of modern American education. Quite apart from any objections I had to his policy positions, I can’t imagine the previous President saying anything like this — his family has been assured of college degrees for generations, and he never had the opportunity (or, presumably, the inclination) to critically evaluate law students’ writing. I don’t necessarily mean that as a criticism of the former President; but now that we have Obama, it seems astonishing that this sort of contact with real Americans’ experience isn’t considered more important as a qualification for the Presidency.
Photo from the White House photostream.
The 11th monthly Carnival of Evolution is up at Oh, For the Love of Science. Following Miriam Goldstein’s lead from last month, there’s a cute narrative framing for a long list of interesting posts, ranging from natural history to science education strategies. Lots to read in between undergrad research papers this weekend!