Joshua trees are about to bloom. Which means I’m off to the desert until mid-April first to tour Joshua Tree National Park with my parents for a week, then to spend a month or more at a field site in central Nevada, extending studies of co-divergence in Joshua tree and its pollinator moths.
All of which is to say, posting to D&T is about to drop to near-zero for the foreseeable future. I’ll take lots of photos, and put them online when I get to an Internet connection, but really that’s all I can promise. After all, what good is fieldwork if not as an Internet detox?
Males replaced by an extra round of DNA replication: Female whiptail lizards can lay fertile eggs without the help of a male because they start egg formation with extra copies of their chromosomes. (Not Exactly Rocket Science)
Pathogens. It’s always pathogens: In his inaugural article as a member of the National Academy of Sciences, Robert Rickleffs proposes that coevoluiton with pathogens explains most of the diversity of life on Earth. (Coevolvers)
Evolutionary conservation biology? To conserve the diversity of life, we need to know how it evolved in the first place, and how it might evolve in the future. (The EEB & flow)
Plant vs. plant: The spread of one invasive plant can be checked by creating barriers of native plants. (Conservation Maven)
You mean it’s not just to make winter that much more miserable? Flu cases may peak in winter months because drier air transmits the flu virus more effectively. (Influenza A (H1N1) Blog)
Unintended consequences: Fifty years of selecting foxes at a fur farm for their tameness also changed the shape of their ears and tails. (The Thoughtful Animal)
The virus only has to get lucky once: Even as we find new ways to attack HIV, the virus keeps mutating; which is why the “cocktails” of drugs taken by HIV patients must target many different viral proteins. (The Daily Monthly)
We all made a big mistake in coming down from the trees in the first place: Mammals that live most of their lives up in the trees tend to live longer than similar-sized mammals that live on the dangerous, dangerous ground. (New Scientist, Gene Expression)
For invasive plants, flowering time is a trait that may often be under selection during colonization—when a plant flowers determines its climatic tolerances, its vulnerability to herbivores, and its compatibility with the local pollinator community. In a study just released online at Proceedings of the Royal Society B, Colautti and coauthors examined the evolution of this trait in a plant that has swept across eastern North America since its introduction from Europe: purple loosestrife, and found that it may be reaching the evolutionary limits of its invasive-ness.
Purple loosestrife, Lythrum salicaria, may be running out of evolutionary steam as it invades more northerly climes. Photo by Steve_C.
Loosestrife, like many organisms, faces a trade-off in establishing a time to reproduce, between early flowering and accumulating resources for seed production. Early flowering means producing fewer seeds, or provisioning them less thoroughly—but as loosestrife colonizes more and more northerly climes, it will be under selection to flower earlier in compensation for shorter and shorter growing seasons.
But natural selection can only do so much. In order for natural selection to operate on a population, individuals in the population must vary in some trait that affects how many offspring they produce—if all individuals have the same trait value, or the same number of offspring, they’ll all have equal chances to contribute to the next generation, which will probably look pretty much like the parental generation. Furthermore, species colonizing new territory may actually lose variation, either because new popualtions may be founded by just a few individuals, or because of the action of natural selection itself. Finally, there may be a point at which plants simply cannot flower any earlier, because they must reach a certain developmental point before reproducing.
Add these up for an invasive species moving north, and you might expect that the most recently-arrived (and most northerly) populations would flower earlier, and have less variation in flowering time, than more southerly populations. Using theoretical and experimental approaches, Colautti et al. show that exactly this process is occurring in purple loosestrife. They first built a mathematical model of natural selection acting on flowering time, which behaved as I’ve outlined above. They followed this by raising loosestrife seeds from northern and southern populations together in experimental sites located at different latitudes, and found that, even raised in southern conditions, seeds from northern sites grew into smaller, less productive plants. Raised in greenhouse conditions, seeds from southern populations produced plants with a much wider range of flowering times than seeds from northern populations. Together, these suggest that loosestrife has evolved earlier flowering times at northern sites—and may be running out of variation, the raw material for natural selection, as it moves north.
Invasive species often evolve in response to their new habitats, and force native species to evolve in response to their arrival. As they colonize Australia, for instance, cane toads (soon to be a major motion picture) have evolved longer legs [PDF] so as to win the race for unoccupied breeding ponds; and exerted selection on native black snakes to tolerate the toads’ defensive toxins and to attack the toads less frequently. Better models of how newly introduced species respond to and exert natural selection may help conservation biologists anticipate the results of biological invasions.
Colautti, R., Eckert, C., & Barrett, S. (2010). Evolutionary constraints on adaptive evolution during range expansion in an invasive plant. Proc. R. Soc. B DOI: 10.1098/rspb.2009.2231
Phillips, B., Brown, G., Webb, J., & Shine, R. (2006). Invasion and the evolution of speed in toads. Nature, 439 (7078) DOI: 10.1038/439803a
Phillips, B., & Shine, R. (2006). An invasive species induces rapid adaptive change in a native predator: cane toads and black snakes in Australia Proc. R. Soc. B, 273 (1593), 1545-50 DOI: 10.1098/rspb.2006.3479
Vellend, M., Harmon, L., Lockwood, J., Mayfield, M., Hughes, A., Wares, J., & Sax, D. (2007). Effects of exotic species on evolutionary diversification Trends in Ecology & Evolution, 22 (9), 481-8 DOI: 10.1016/j.tree.2007.02.017
Todd: Daddy, what do taxes pay for? Ned: Oh, why, everything! Policemen, trees, sunshine! And let’s not forget the folks who just don’t feel like working, God bless ’em! — Exchange between Ned Flanders and his son Todd, from The Simpsons episode “The Trouble With Trillions”
I usually send in my tax return as soon as I get all the year-end paperwork, because it’s so insanely easy to do it online these days, and I like to put a refund in the bank. In fact, I’ve already got my refund, and put some of it toward a new camera. The IRS didn’t give me a total refund, though—which leaves me to contemplate what the Feds are doing with the little bit they kept.
In principle, I’m in favor of taxes. There are lots of things that are simply only do-able by lots of people banding together and chipping in, like roads and other infrastructure, the arts, scientific research, or the social safety net. Or national defense. This last gives me pause every tax season for the simple reason that I’m opposed to violence, including the officially-sanctioned kind. Partly this is because I was raised in a pacifist religious tradition, but if my country’s militaristic foreign policy of the previous decade proved anything, it’s that “violence is the last refuge of the incompetent.”
I know I’m in a minority among Americans; but it’s a frustrating minority to be in. As the national debate fixates on government spending, everyone is worried about the Federal budget deficit, but no-one seems to be interested in how the Pentagon is contributing to it. The Obama Administration has proposed the biggest military budget since World War II, and while spending associated with the wars in Iraq and Afghanistan is supposed to end in a couple years (good luck with that), the baseline Pentagon budget will just keep growing, overwhelming savings from the spending freeze the Obama Administration has proposed for select non-military programs. It’s not as though the Pentagon is some paragon of responsible spending—there’s certainly room to cut its budget, if only the Administration would put in the effort.
In short, balancing the budget without cutting military spending will end up cutting non-military Federal programs in support of greater and greater military spending. The Federal spending that’s mostly unproblematic for me threatens to be overwhelmed by the Federal spending that I mostly don’t support.
So what’s a tax-paying pacifist to do?
Some folks who think like me withhold a symbolic portion of their taxes. Many join the campaign for a peace tax fund—the right to request on the tax form that one’s taxes go only toward non-military spending. A very few others make lifestyle choices that let them live on an income below the lowest tax bracket. But each of these options has its own problems.
Withholding taxes implies that the money is used for military spending against my will; but it’s not as though I have any less say in how it’s spent than any other taxpayer. More, in fact, since I vote in off-year elections. I’d object to another American withholding taxes in protest of, say, funding for the National Science Foundation—I can’t very well do the same for military funding.
Similarly with the Peace Tax Fund: I just don’t believe that spending decisions should be made at the level of the individual tax return. Passage of a Peace Tax Fund would imply that there could be an Anti-Medicare Tax Fund, or an Anti-National Endowment for the Arts Tax Fund (under, presumably, less-cumbersome names).
Finally, living below the taxable income threshold is a sacrifice I’ll admit I’m not willing to make. I live pretty simply as a graduate student; I’m frankly not sure how I’d make due with less, even given Northern Idaho costs-of-living.
All of which leaves me to vote for slightly-less-militaristic Democrats, fill out my online 1040EZ, and wait for my refund.
Chad Orzel, over at Uncertain Principles, is giving up blogs (reading, not writing, anyway) for Lent. He has a good point w/r/t the echoic effects of political blogs and political-ish posting on science blogs* – it’s tempting to follow suit, if only for the blood-pressure benefits. Fortunately, there’s also plenty of online writing about new knowledge, and that’s what I aggregate on Fridays:
We have seen the population bomb, and it is us: The solution to unsustainable birthrates in developing countries is to develop them, right? Maybe not: while birthrates decline as development improves, highly developed countries often see their birthrates increase. (Tomorrow’s Table)
Yes, there’s a blog dedicated to spirochetes now: The bacterium that causes Lyme disease takes days to move from the gut of a newly-infected tick to the salivary glands, apparently because it stops moving when it hits the gut. (Spirochetes Unwound)
So far, no saber-toothed dentures found: Analysis of a large sample of broken fossil teeth of Smilodon fatalis suggest that saber-toothed cats frequently resorted to chewing on bones. (Laelaps)
Who doesn’t already do this? Seriously: Scientists should report p-values, rather than just calling results “significant.” (i’m a chordata! urochordata!)
Your (great-to-the-nth-grand) mother was a crab: A new reconstruction of the arthropod evolutionary tree, employing 62 nuclear genes, suggests that the common ancestor of insects was a crustacean. (Palaeoblog)
Malaria and degenerative bone disease: Extensive analysis of Tutankhamen’s mummy (and others) suggests that it was not, in fact, all that good to be the Pharaoh. (NPR, NY Times)
Here be dragons: Teeny-tiny, adorable dragons. (SciencePunk)
OK, this is a little bit political: The Obama stimulus package was pretty good for NSF-funded researchers. (dechronization
*Why, yes, I’m currently re-reading David Foster Wallace’s Consider the Lobster. Why do you ask?
With its mildly lefty contrarian tone and frequent crossovers with NPR – and, I should say, solid but accessible policy analysis and spot-on cultural reviews – Slate has long been a staple in my online reading. It’s also been a staple in my podcast lineup, ever since I got my first iPod and suddenly needed something to put on it for long spinning sessions. Since several of the Slate podcasts are calling for listeners to recruit more listeners this week, I thought I’d note my favorites, and where to get them.
The Political Gabfest is the original Slate podcast, and the template for newer models. Emily Bazelon, John Dickerson, and David Plotz talk about (usually) three topics in the week’s (usually) political news. Plotz is a liberaltarian grump, Bazelon more idealistic, Dickerson focused on the political mechanics behind the issue of the moment; all three bounce off each other in endearing and enlightening ways. Dickerson mediates (or tables) at least one Plotz-Bazelon argument per episode. (Subscribe in iTunes.)
Political Gabfesters Emily Bazelon, John Dickerson, and David Plotz at a live Gabfest event last May. Photo by presta.
The Culture Gabfest applies the Gabfest model to cultural news. Stephen Metcalf moderates in Plotz-y tones, and is usually joined by Julia Turner and Dana Stevens – but the Culture Gabfest often includes fourth or fifth panelists to discuss particular topics. My tastes track Metcalf’s pretty closely, but Stevens’s reviews were informing my movie-going decisions long before the podcast launched. (Subscribe in iTunes.)
Dana Stevens also helms Spoiler Specials, in which she and another film critic or two dissect a current movie, with no regard to hiding plot points. It’s great fun after you’ve seen a movie, or, if you’re into schadenfreude, often just as much fun with reference to a movie you have no intention of seeing (Transformers, for example). (Subscribe in iTunes.)
Hang up and Listen is back to the Gabfest model, but about sports – the conversation between sports journalists Stefan Fatsis, Josh Levin, and Mike Pesca is like sports talk radio, but you don’t call in, hence the name. In fact, it’s not really like sports talk radio, inasmuch as I, a nerd whose sports are unwatchable individual endurance events (running, cycling), find it totally interesting. Part of this may be because both Fatsis and Levin Pesca* are regular NPR contributors, who are used to talking sports with an audience that doesn’t follow them. (Subscribe in iTunes.)
Conveniently, you can subscribe to each of these individually at the links I’ve given above (they’re all on a weekly-ish cycle, with Spoiler Specials somewhat less frequent), or get them as part of Slate’s daily podcast stream. If you go with the daily stream, you’ll get a few less-frequent ‘casts I’ve left out, that are nevertheless good when they show up.
Responding to natural selection often means compromising between different selective forces. A brief paper published online early at Evolution documents one such case – limber pine trees’ compromise between protecting their seeds from squirrels, and making them accessible to the birds that disperse them. Pulled between these conflicting selective sources, some limber pine populations grow cones in a wider variety of shapes [$a].
Seeds of the limber pine are cache-dispersed by Clark’s nutcrackers. That is, the birds collect pine seeds to cache as a winter food source, but they collect many more than they need, and forget lots of them, and forgotten seeds are often able to sprout. However, squirrels also like pine seeds, and they harvest them before the birds start caching seeds. These two seed-harvesters generate conflicting selection on limber pine cones [$a]. Nutcrackers go for cones with lots of seeds protected by thinner scales; but so do squirrels.
However, pine-nut-eating squirrels are not present everywhere limber pines grow. The new study’s authors, Siepielski and Benkman, take advantage of this quirk of distributions to perform a natural experiment, comparing pines that only need to satisfy their seed dispersers with pines that also need to defend against seed predators. Surveying cone shapes in populations of each class, they found that limber pine populations facing conflicting selection were bimodal, with trees mainly growing either squirrel-defended short, thick-scaled cones, or nutcracker-friendly longer, thin-scaled cones. Populations growing in regions without squirrels produced only nutcracker-friendly cones.
This apparently simple pattern conceals more complicated dynamics – in fact, as the authors disclose in the Discussion section, many other limber pine populations are solely composed of trees producing squirrel-defended cones. This is because, when pines establish in areas with large squirrel populations, nutcrackers may never colonize the area, or may visit less frequently and disperse fewer seeds. Without nutcracker dispersal, seeds are mainly dispersed after the cones fall, by rodent species that (unlike squirrels) forage on the ground. This makes squirrel defense the only selective priority. Populations displaying both cone types probably only arise in unique conditions, the authors say, where squirrels are present but not at high density.
Siepielski, A., & Benkman, C. (2007). Convergent patterns in the selection mosaic for two North American bird-dispersed pines. Ecological Monographs, 77 (2), 203-20 DOI: 10.1890/06-0929
Siepielski, A., & Benkman, C. (2009). Conflicting selection from an antagonist and a mutualist enhances phenotypic variation in a plant. Evolution DOI: 10.1111/j.1558-5646.2009.00867.x