- Bayesian methods for reconstructing evolutionary relationships between species may be susceptible to errors created by long branch attraction – one of the problems they were supposed to solve. (dechronization)
- When introduced trout compete for food with gray-crowned rosy-finches, the rosyfinches lose. (Conservation Maven)
- The success of an invasive plant depends on the kind of habitat it’s invading, and how that habitat is managed by humans. (The EEB & flow)
- New fossils are the earliest-known vertebrate footprints on land – 395 million years old. (Not Exactly Rocket Science, Laelaps, Pharyngula, and Palaeoblog)
- Give a meteorologist a green screen, and he’ll tell you tomorrow’s forecast. Give a meteorologist professional certification, and he’ll tell you that climate change is a hoax. (Columbia Journalism Review)
Masquerading caterpillars hide in plain sight
Insects that have evolved elaborate mimicry of inanimate objects – leaves, twigs, even bird droppings – to hide from predators are a staple of nature documentaries. But do these masquerades work because they help insects blend into the background, or because predators actually see the insects and then dismiss them as inedible leaves, twigs, or bird droppings? It’s a tricky question to answer, but a brief paper in this week’s Science presents an experiment that tries to do just that [$a].
The paper’s authors reasoned that if mimicry-based camouflage works through disguise rather than invisibility, a predator’s experience might determine their response to mimic camouflage. They trained three experimental groups of young domestic chicks by introducing them into trial arenas containing either natural hawthorn branches, empty arenas, or hawthorn branches wrapped in purple thread. The wrapped branches were used to test whether the chicks would be more or less likely to attack something twig-like but differently colored (though this is only clear from the supplementary online material).
Larva of the brimstone moth Opisthograptis luteolata, looking distinctly twig-like. Photo by Michael E. Talbot.
The authors then presented chicks from each “training” group with either one of two species of hawthorn-twig-mimicking moth larvae (the brimstone moth, or the early thorn moth), or a hawthorn twig about the size of a caterpillar. Chicks that had previously encountered natural twigs waited longer to attack the caterpillars than chicks that hadn’t previously seen twigs, or that saw the colored hawthorn branches. So, apparently, the chicks were reasoning (inasmuch as chicks reason) that the twig-like object in front of them was the same as the inedible twigs they had tried before.
This is an elegant experimental test of the effect of mimicry as mimicry – what the authors propose to call camouflage by “masquerade.” However, it doesn’t actually show that what the authors term camouflage by crypsis – blending into the background – isn’t also contributing to the benefits that these caterpillars receive from their unique shape and coloration. There’s no reason to think that twig-shaped caterpillars can’t benefit in both ways, by being less visible in the first place, and then easily mistaken for a twig if they are seen.
In conclusion, here’s some video footage of another natural mimic, the leaf insect.
Reference
Skelhorn, J., Rowland, H., Speed, M., & Ruxton, G. (2010). Masquerade: Camouflage without crypsis Science, 327 (5961), 51 DOI: 10.1126/science.1181931
State of the blog, 2009
I really started taking this blogging thing seriously about mid-way through 2008, when I became a member of Research Blogging. But 2009 is the first entire year I’ve spent actually thinking about what I’d like to write about on here, what place blogging occupies in the hierarchy of my to-do list, and what the point of the whole operation might be. So the end of the year (or really, till I finish this post, the beginning of 2010) seems like a good moment to pause and take inventory. Plus, it’ll give me a page to link to for some vital stats I’d like to read into the record.
Weekly visitors to D&T, tabulated by Google Analytics. Blue line: total visitors. Orange line: visitors referred via links from other sites.
- In 2009, I wrote 229 posts (averaging just over 19/month), which drew 14,045 unique visitors (averaging 1,170/month) as tabulated by Google Analytics.
- Most visitors who didn’t come directly to D&T linked here via Research Blogging or its widget on ScienceBlogs.com. I wrote 62 posts on peer-reviewed research for the Research Blogging aggregator, and these received 1,989 visitors via RB or SB. Other major referral sources include the Evolution 2009 blog coverage page (1,081 visitors) and the blogroll over at The EEB & Flow (1,027 visitors).
- I also joined the Nature Blog Network this year. NBN has been less a source of traffic, and more useful for its reminders about upcoming blog carnivals and suggestions for casual bloggers.
- I covered the Darwin 200 festivities leading up to, and throughout, the week of 12 February.
- I also blogged about the Evolution 2009 meetings, which were hosted by my department at the University of Idaho. I ran the conference website, and attempted to coordinate online activities to coincide with the meatspace meeting, with mixed success.
- This was also a year of political furor, in the States if not elsewhere, and I wrote 34 posts tagged “politics”. I did not apply that label to my brief note on Barack Obama’s inauguration as President.
- I’ve continued to write about Christianity on D&T, but only composed 13 posts with that tag, and only 2 posts about Mennonites specifically. This reflects, I think, my present relationship to the tradition in which I was raised. I don’t subscribe to the supernatural elements of orthodox Christian doctrine, and the Mennonite Church as an institution doesn’t seem interested in my company for, um, other reasons (although there are hopeful signs). Time for a change to the masthead? We’ll have to see.
- I made $35.40 in commissions on those nerdy t-shirts of my own design advertised in the sidebar. I will not be quitting my day job any time soon.
- As an extremely pleasant end-of-year surprise, I was also awarded a travel grant for the Science Online 2010 conference, in recognition of a particularly involved post I wrote back in August about the evolution of milk drinking by adult humans. I’m looking forward to the conference and shall, naturally, cover it here.
Which observation brings this post to a tidy narrative end. I remain, I think, a scientist who has a blog rather than a science blogger, though the line between the two is blurry. Like any single-author publication, D&T is a horribly narcissistic enterprise – to me it’s serving a useful function if it provides regular writing practice, structure for my extracurricular science reading, and a place to blow off steam. I’ve been very fortunate this year to garner the occasional comment, some very kind in-person remarks from readers I’ve happened to meet in person, and an opportunity to start 2010 with a conference full of smart people who are way better at this sort of thing than I am ever likely to be. Not too bad, as hobbies go.
Science online, disappearing sea lions edition
Happy New Year! In case it wasn’t previously obvious that I write these posts in advance, here’s the proof.
- In ant-plant relationships, plants seem to be in charge: they cheat! (Thomas’s Plant-Related Blog)
- Bats eat mosquitoes – but do they control mosquito populations? (Cheshire)
- The sea lions of San Francisco’s Pier 39 have abandoned their post, for no readily apparent reason. No word on whether anyone has found a note reading “So long, and thanks for all the fish,” but plans to commemorate the 20th anniversary of the sea lions’ arrival this January are in question (Wired Science and NY Times)
- Good news: a new long-term study confirms that creating marine protected areas allows overfished ecosystems to recover. Bad news: marine protected areas are more likely to be set up in areas that aren’t very economically important. (Conservation Maven)
- After colonizing a region with brilliant white, gypsum sands, three different desert lizard species evolved white skin – but each species evolved a different genetic mechanism to do so. (Not Exactly Rocket Science)
- A bat was found in France carrying the same fungus that seems to be killing bat colonies across eastern North America – but only one bat, and it seems to be healthy. (Effect Measure)
Escaping the “poverty trap” of infectious disease
Even in the twenty-first century, infectious diseases such as malaria, dengue fever, cholera, and AIDS remain widespread in much of the developing world, at tremendous cost to human life and economic productivity. Poorer nations lack the resources for more effective public health measures; but widespread infectious disease may slow or prevent the economic development that can provide those resources. A new paper in Proceedings of the Royal Society tries to sort out this chicken-and-egg problem, and finds that economic development is the fastest route out of the “poverty trap” [$a].
The paper’s authors, Bonds et al. start with a classic model of infectious disease, in which susceptible (healthy) members of a population have a chance of becoming infected whenever they encounter an infected person, and infected people have a chance to recover to susceptible condition if they survive the effects of the disease. The first probability is the rate of transmission from person to person; the second is the rate of recovery from disease caused by the infection.
Bonds et al. insert economics into this basic model by reasoning that the rate of recovery is a function of per-capita income – well-fed people are better able to fight off infection – and that income is a function of the proportion of the population that remains uninfected at any given time. This yields a mathematical version of the poverty trap I outlined above: high-income populations are easily able to fight off infection and remain near 100 percent susceptible, but highly infected societies are unable to increase their per-capita income to reduce their rate of infection. However, there is an internal equilibrium point – a level of income and infection from which a population could easily move in either direction, towards high income and low infection or high infection and low income.
The question then becomes how best to push a developing nation’s population toward that threshold condition – or how best to bring the threshold closer. Bonds et al. compare two options: reducing the rate of disease transmission, and boosting individual economic productivity. The former captures the effect of boosting public health – vaccination, better sewage treatment, food aid. The latter captures the effect of improving infrastructure or financial institutions – making the economy more developed. They found that the threshold condition is more sensitive to economic productivity. Even at low transmission rates, a society can be caught in the poverty trap if its productivity is low enough, but at high enough productivity levels, societies can avoid the trap created by even highly transmissible diseases.
This suggests that, although medical aid can help the acute problem of infectious disease, it’s investment in economic development that can ultimately solve it.
Reference
Bonds, M., Keenan, D., Rohani, P., & Sachs, J. (2009). Poverty trap formed by the ecology of infectious diseases Proc. R. Soc. B DOI: 10.1098/rspb.2009.1778
Bruce Schneier for President
Or at least Secretary of Homeland Security? Of course, this kind of perspective is (by all conventional wisdom) unelectable. But I can dream, right?
Of course 100% security is impossible; it has always been impossible and always will be. We’ll never get the murder, burglary, or terrorism rate down to zero; 42,000 people will die each year in car crashes in the U.S. for the foreseeable future; life itself will always include risk. But that’s okay. Despite fearful rhetoric to the contrary, terrorism is not a transcendent threat. A terrorist attack cannot possibly destroy our country’s way of life; it’s only our reaction to that attack that can do that kind of damage.
Really, any political party that adds the removal of unproductive security theater from TSA procedures – Passenger pat-downs before the flight from Lewiston, Idaho to Moscow, Idaho? Really? – will be a serious competitor for my vote. I’m looking at you, Modern Whig Party.
Science blogging, doubtfully venomous dinosaurs edition
Happy Christmas! I’m with family for the holidays, but still spending too much time online.
- Scientists propose to sequence genomes from 10,000 vertebrate species, sampling almost every vertebrate genus (Dechronization)
- A feathered dinosaur related to Velociraptor has tooth and skull traits that suggest it was venomous – or do they? (Brian Switek at Smithsonian)
- Recalibrating estimates of “background” extinction implicates humans in the disappearance of North America’s ancient mammals (Ecographica)
- The adorable proportions of koala skulls might be the result of selection for both strong jaw muscles and sensitive ears. (Wired Science)
- Male ducks have baroque, convoluted penises, probably because of sexual selection imposed by female ducks’ baroque, convoluted vaginas. (Wired Science, Ecographica, and A DC Bird Blog so far … this is bigger than fruitbat fellatio!)
That last one is probably as good an excuse as any to post the limerick with which I took second place in a department contest for Darwin’s 200th birthday:
A biologist, whom we’ll call Chuck
Said, “Regard, if you will, this poor duck –
“I blame sexual selection
“For his corkscrew erection,
“Since it must make it tricky to …
fly.”
Why aren’t there more sickle-cell anemics in the Mediterranean?
The story of sickle-cell anemia and its malaria-protective effects is a textbook case how environmental context determines the fitness of a given genetic profile. However, the evolution of human blood disorders in response to selection from malaria parasites might be more complicated than that textbook story.
Malaria-causing parasites (dark-stained) among human red blood cells (top), and “sickled” red blood cells (bottom). Photos via WikiMedia Commons.
Malaria is caused by mosquito-spread parasites that attack their hosts’ oxygen-bearing red blood cells. A particular mutation in the gene that codes for part of the hemoglobin molecule – the molecule that actually stores oxygen inside red blood cells – leads to deformed, sickle-shaped, blood cells. People who carry two copies of the sickle cell gene develop sickle-cell disease, in which the sickle-shaped cells reduce oxygen transport efficiency and interfere with blood circulation. People with only one copy of the sickle-cell gene are healthy, and better able to resist malaria infection than those with no copies. The textbook story is that, in regions where malaria is common, such as sub-Saharan Africa, the advantage of malaria resistance is enough to offset the fitness risk of carrying the sickle-cell gene – that one-fourth of children born to parents who each have one copy of the gene will themselves have two copies and develop sickle-cell disease.
However, there are regions like the Mediterranean where malaria has historically been prevalent, but in which the human population hasn’t evolved the higher frequency of sickle-cell genes that you’d expect from the scenario outlined above. A new paper in PNAS demonstrates that this may be because of interactions between the sickle-cell gene and another genetic blood disorder, thalassemia [$a].
Thalassemia is a class of genetic disorders affecting the protein subunits that comprise hemoglobin. Each hemoglobin molecule is formed by binding together two “alpha”-type subunits, and two “beta”-type subunits. If there is a shortage of correctly-formed subunits of either type, then hemoglobin formation is impaired, resulting in anemia or (if the mutation stops subunit production altogether) death. However, like sickle-cell genes, thalassemic mutations can confer resistance to malaria; and if alpha-thalassemia is paired with beta-thalassemia, the reduced production of both subunits can balance out.
As it happens, in combination with alpha-thalassemia, the sickle-cell gene’s malaria protection is neutralized. Using population genetic models, the new study’s authors show that this effect may have actively prevented the sickle-cell gene from establishing in the Mediterranean, where alpha- and beta-thalassemias are more common than in Africa. In the Mediterranean, the presence of beta-thalassemia genes reduces the fitness cost of (mild) alpha-thalassemia genes; and in the presence of alpha-thalassemia genes, the sickle-cell gene confers no protection to people with one copy but still induces sickle-cell disease in people with two copies.
These interactions between genes are called epistasis, and they can have dramatic impacts on evolution. Although I haven’t seen many cases as well-characterized as this one, epistasis is probably widespread in the complex systems of genomes, where thousands of regulatory and protein-coding genes interact to build living things.
References
Penman, B., Pybus, O., Weatherall, D., & Gupta, S. (2009). Epistatic interactions between genetic disorders of hemoglobin can explain why the sickle-cell gene is uncommon in the Mediterranean Proc. Nat. Acad. Sci. USA, 106 (50), 21242-6 DOI: 10.1073/pnas.0910840106
A quantum leap in ethical-eating nonsense
I don’t think this piece in the New York Times is meant to be sarcastic. If it isn’t, it’s the most ridiculous thing I’ve ever read w/r/t the ethics of vegetarianism v. omnivory:
But before we cede the entire moral penthouse to “committed vegetarians” and “strong ethical vegans,” we might consider that plants no more aspire to being stir-fried in a wok than a hog aspires to being peppercorn-studded in my Christmas clay pot. This is not meant as a trite argument or a chuckled aside. Plants are lively and seek to keep it that way. The more that scientists learn about the complexity of plants — their keen sensitivity to the environment, the speed with which they react to changes in the environment, and the extraordinary number of tricks that plants will rally to fight off attackers and solicit help from afar — the more impressed researchers become, and the less easily we can dismiss plants as so much fiberfill backdrop, passive sunlight collectors on which deer, antelope and vegans can conveniently graze. It’s time for a green revolution, a reseeding of our stubborn animal minds. [Emphases mine.]
It’s the pathetic fallacy masquerading as a serious argument.
Unquiet in Lake Wobegon
So this is ancient by internet standards (vintage 2007!), but I just discovered it this morning, via a link-in-passing from Dan Savage. Garrison Keillor is Not Cool with the gays:
And now gay marriage will produce a whole new string of hyphenated relatives. In addition to the ex-stepson and ex-in-laws and your wife’s first husband’s second wife, there now will be Bruce and Kevin’s in-laws and Bruce’s ex, Mark, and Mark’s current partner, and I suppose we’ll get used to it.
The country has come to accept stereotypical gay men — sardonic fellows with fussy hair who live in over-decorated apartments with a striped sofa and a small weird dog and who worship campy performers and go in for flamboyance now and then themselves. If they want to be accepted as couples and daddies, however, the flamboyance may have to be brought under control. Parents are supposed to stand in back and not wear chartreuse pants and black polka-dot shirts. That’s for the kids. It’s their show.
Also back in 2007, Dan Savaged Keillor’s totally unnecessary swipe at gay parents far more effectively than I could.
So why am I writing about this at all? Because, to be frank, it hurts. I’ve been listening to Keillor’s A Prairie Home Companion since I was too young to understand most of the jokes – the storytelling and quirky musical taste and commonsense Midwestern liberalism was one of the predominant flavors of the Public Radio marinade in which I grew up. The “fussy” boy who woke up to Morning Edition on school days and went to bed after PHC on the weekends grew into a closet case who loved This American Life in spite of* the troubling feelings aroused by contributions from David Sedaris, David Rakoff, and, yep, Dan Savage (how’s that for coming full circle?); and finally into an out and moderately well-adjusted gay man who owes his outness and moderate well-adjustedness to Public Radio more than any other cultural institution.
But so my point is that learning that the man whose voice is the bass note of the entire Public Radio mindset is capable of saying things like “… the flamboyance may have to be brought under control,” is like learning that Mr. Rogers made his puppets from the skins of strangled kittens, or that LeVar Burton wrapped up production of every Reading Rainbow episode with a book burning.** It’s like learning that hot cocoa causes cancer. It feels like betrayal.
Maybe I’m being melodramatic, but apparently that’s what Keillor expects of me anyway.
——
* Or because of?
** Yeah, I know – illustrating a point about a Public Radio figure with Public Television figures is pretty weak. But I really don’t hold many institutions in the same esteem I do Public Broadcasting. Not even hot cocoa.