When ecological opportunity knocks, does adaptive radiation answer?

ResearchBlogging.orgOne of the most basic questions in evolutionary ecology is, “why are there more kinds of this kind of critter than that kind of critter?” As in, why are there more than twenty thousand species of orchids, but only one species of ginkgo? Why are there hundreds of thousands of species of beetles, but only four species of horseshoe crab? In a literature review just released online—and my first publication as lead author!—my coauthors and I assess the support for one hypothesis: that species multiply because of ecological opportunity.

Biologists interested in the origins of species diversity frequently focus on the phenomenon of adaptive radiation, the process by which a single species rapidly gives rise to many new species, each with different traits adapted to different lifestyles. Darwin’s finches, with their beaks shaped to suit to different foods [$a], are a classic case; the Anolis lizards of the Caribbean, which have repeatedly evolved into a handful of “ecomorphs” with different body sizes and shapes adapted to different perching locations [PDF], are another.

Why are there so many [insert taxon here]? Photos by Bill & Mark Bell (1 & 2), fturmog (3 & 4).

The two most influential theories of adaptive radiation—by G.G. Simpson and Dolph Schluter—have suggested that it results when a species encounters ecological opportunity. Ecological opportunity might be a newly-evolved trait, or a new habitat, or the extinction of a species’ competitors or predators. For instance, a butterfly might evolve a way to overcome the chemical defenses of an abundant plant species, or a plant introduced by humans to a new habitat might find that local pathogens aren’t as deadly to it as the ones in its native range. Ecological opportunities have the effect of granting access to new resources. We have pretty good evidence that this can allow individual populations to increase in number, and even evolve greater diversity—but is that enough to spur the rapid speciation that forms adaptive radiation?

Ecological opportunity ? adaptive radiation

We’re pretty sure about steps 1 and 3. We’re still trying to figure out step 2.

Readers in certain demographic groups may think this sounds like an underpants gnome problem. But it isn’t, exactly. The gnomes’ business model can’t get to from step 1 (collect underpants) to step 3 (profit) because they don’t have a step 2. Evolutionary ecologists, on the other hand, already have their step 3 in the phenomenon of adaptive radiation. Ecological opportunity looks like a good prospect for step 1 precisely because it suggests some plausible options for step 2.

When a population encounters ecological opportunity, the new habitat, new trait, or extinction of antagonists provides access to new resources, and relaxes natural selection on the population. This leads to three phenomena usually grouped together under the term ecological release

  • The population experiences density compensation—more individuals can live in a particular area, creating stronger competition within the population.
  • Because of this stronger competition within the population, or because there isn’t much competition from other species, members of the population venture into new habitats, or use new food resources.
  • The population becomes more diverse, either because of the relaxed selection, or because of competition-driven selection for using new habitat and new resources.

One or more of these three aspects of ecological release turn up whenever populations find new food resources, or escape predators and/or competitors. Density compensation has been widely observed in populations colonizing new habitats, especially islands; and experiments with sticklebacks and fruit flies [$a] suggest that the stronger competition resulting from density compensation can spur the population to become more diverse in its use of resources. Bacterial populations can even evolve different specialized forms—adaptive radiations in microcosm—when introduced to new food resources.

Anoles show signs of density compensation on Caribbean islands—is that the reason behind their diversification? (Pictured: Anolis oculatus.) Photo via WikiMedia Commons

But where’s the speciation?

However, the evolution of bigger, more diverse populations is not the same thing as the evolution of new species—and that’s what adaptive radiation is really all about. These changes resulting from ecological opportunity might directly promote speciation if stronger competition leads to disruptive natural selection. Similarly, the competition-driven incentive to colonize new habitats or exploit new food sources could expose some parts of the population to different forms of natural selection, eventually causing them to evolve into specialists on the new resources. Finally, even if speciation only happens when natural barriers cut off migration, maybe larger, more variable populations provide more diversity for vicariance events to divvy up.

This is all pretty speculative, though. We still don’t know how often—or how rarely—divergent natural selection contributes to making new species. One way to deal with this is to approach the question from the other direction: look backward at the history of existing species, rather than following what happens to populations immediately after ecological release.

A backward-looking approach might use statistical analyses of the evolutionary relationships between living things to identify points in time when species formed unusually fast, and try to identify the cause. Some of my coauthors from the review paper recently published an analysis of the evolutionary tree connecting all vertebrates, and found that speciation rates increased around the origins of the largest group of birds, a large portion of the lizards and snakes, and non-marsupial mammals, among others.

This is very much a starting point, but maybe by complementing similar studies with research on populations currently evolving in response to ecological opportunity, biologists can work our way closer to understanding the origins of the endless and beautiful forms of life on Earth.

References

Alfaro, M., Santini, F., Brock, C., Alamillo, H., Dornburg, A., Rabosky, D., Carnevale, G., & Harmon, L. (2009). Nine exceptional radiations plus high turnover explain species diversity in jawed vertebrates. Proc. Nat. Acad. Sci. USA, 106 (32), 13410-4 DOI: 10.1073/pnas.0811087106

Bolnick, D. (2001). Intraspecific competition favours niche width expansion in Drosophila melanogaster. Nature, 410 (6827), 463-6 DOI: 10.1038/35068555

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

Grant, B., & Grant, P. (1989). Natural selection in a population of Darwin’s finches. The American Naturalist, 133 (3), 377-93 DOI: 10.1086/284924

Kassen, R. (2009). Toward a general theory of adaptive radiation: Insights from microbial experimental evolution. Annals New York Acad. Sci., 1168 (1), 3-22 DOI: 10.1111/j.1749-6632.2009.04574.x

Losos, J. (1990). Ecomorphology, performance capability, and scaling of West Indian Anolis lizards: An evolutionary analysis. Ecological Monographs, 60 (3), 369-88 DOI: 10.2307/1943062

Schluter, D. 2000. The Ecology of Adaptive Radiation. Oxford University Press. Google Books.

Simpson, G.G. 1949. Tempo and Mode in Evolution. Columbia University Press. Google Books

Svanbäck, R., & Bolnick, D. (2007). Intraspecific competition drives increased resource use diversity within a natural population. Proc. Royal Soc. B, 274 (1611), 839-44 DOI: 10.1098/rspb.2006.0198

Wheat, C., Vogel, H., Wittstock, U., Braby, M., Underwood, D., & Mitchell-Olds, T. (2007). The genetic basis of a plant insect coevolutionary key innovation. Proc. Nat. Acad. Sci. USA, 104 (51), 20427-31 DOI: 10.1073/pnas.0706229104

Yoder, J.B., Des Roches, S., Eastman, J.M., Gentry, L., Godsoe, W.K.W., Hagey, T., Jochimsen, D., Oswald, B.P., Robertson, J., Sarver, B.A.J., Schenk, J.J., Spear, S.F., & Harmon, L.J. (2010). Ecological opportunity and the origin of adaptive radiations. Journal of Evolutionary Biology DOI: 10.1111/j.1420-9101.2010.02029.x

Science online, not so pristine anymore edition

I’ll start with the online science meta-news: The ScienceBlogs PepsiCo saga achieved a preliminary resolution yesterday, when Science Blogs pulled the PepsiCo blog. Many SBers who left in protest, however, are apparently not returning, including Brian Switek (of Laelaps) and Rebecca Skloot. Skullsinthestars has taken on the public service of tracking departing SBers, which include some of the biggest names on the site. Carl Zimmer compiles his own list, and adds some scathing remarks. David Dobbs gave his reasons for not returning, Martin Robbins of the Lay Scientist neatly summed up the issues of reader trust and respect for individual writers underlying the fracas, and Curtis Brainard weighed in at the Columbia Journalism Review. No word yet on coverage by On the Media, but I’m still hoping.

Say it ain’t so, Glacier National Park. Photo by jby.

Meanwhile, in actual science news:

  • Still gushing. As of today (Friday), it’s been 81 days since BP broke the Gulf. Yet another projection of long-term surface dispersal of the oil suggests the U.S. east coast is in trouble. At Deep Sea News, Dr. M rounds up the latest news and Allie Wilkinson flies over the slick with the Coast Guard. Meanwhile ProPublica digs into BP’s horrendous safety record and foot-dragging on compensation and cooperation with scientists.
  • Missed this earlier. BlagHag reports on Portland and Evolution 2010.
  • I’m confused. What about spinach? A new study of bone structure suggests Neanderthals were totally pumped, with “Popeye-like forearms,” possibly because of a highly carnivorous diet. (Discovery News)
  • Well, it doesn’t look its age. New fossils reveal that multicellular life is at least 2.1 billion years old, more than three times as old as previously thought. (ScienceDaily)
  • This just makes me sad. Environmental pollutants, including pesticides, are extensive at national parks—with particularly bad levels at Glacier and Sequoia. (Conservation Maven)
  • It works for cpDNA, anyway. A new method for extraction and amplification of DNA from plant tissue may make life simpler for lab rats like me. (Uncommon Ground)
  • Cichlids do it wherever they can. Since colonizing a volcanic crater lake in Nicaragua—as little as a century ago—a population of Midas cichlid fish has evolved into two distinct forms, with marked dietary differences. (NeuroDojo)
  • Dudes should not wear corsets. Because they may cause you to grow a bone in your penis. Really. (scicurious)

And, as a video-based closing thought, here’s footage of a cuckoo chick evicting the other eggs—and chicks!—in its adoptive nest. The initial, um, cuckholding is captured here

Science Blogs in refreshing, sugary ethics kerfuffle

ScienceBlogs, the mothership of online nerdery, just made a big, bad-publicity splash, launching a nutrition-themed blog sponsored—and written—by PepsiCo.

Photo by Roadsidepictures.

Readers have been irked, and many ScienceBloggers, for whom this apparently came as a surprise, are expressing feelings ranging from barn-burning outrage to nuanced concern to biting dismissal—and also resigning in protest (or exhaustion). It isn’t the first time ScienceBlogs has run a corporate-sponsored column, but those previous ones had writers who were independent of the sponsor. The affiliations of the new blog, Food Frontiers, are indicated in the header bar and the masthead, but not especially loudly—and the blog’s content will apparently be aggregated to Google News alongside the work of non-corporate ScienceBloggers. As Knight Science Journalism points out, ScienceBlogs’ treatment of Food Frontiers pretty clearly violates old media journalistic ethics.

In an e-mail to ScienceBloggers leaked to The Guardian, SEED editor Adam Bly wrote

We think the conversation should include scientists from academia and government; we also think it should include scientists from industry. Because industry is increasingly the interface between science and society. It is our hope that the Xeroxes and Bell Labs of the future will have a real presence on SB – that they will learn from our readers and we will learn from them.

That’s a pretty poor equivalency Bly is making, frankly. As far as I can tell, the academic scientists who write for ScienceBlogs do so without an explicit mandate from their universities or even funding agencies. Pepsico food scientists writing on behalf of Pepsico are not doing the same kind of science communication.

With more visible caveats, and maybe some sort of special treatment in the ScienceBlogs RSS feeds, Food Frontiers doesn’t have to be the end of all credibility for ScienceBlogs. But, boy, it doesn’t look good right now—and, if I’d spent a substantial portion of my blogging career helping to build ScienceBlogs into the hub of respectable online science writing it’s become, I’d be pretty upset. It looks like ScienceBlogs is losing some really strong writers over this, and that seems like a poor trade-off.

The only possible upside? The possibility we’ll get to hear PZ Meyers and Rebecca Skloot interviewed by Bob Garfield.

Losing the scientific lede, continued

So, in spite of having pretty consciously tweaked the science blogging community when I wrote, in Monday’s post

Blog posts are best when they’re less than 700 or 800 words long, and their contents are readily summed up in a headline and only slightly expanded upon by the first paragraph. Think newspaper, not magazine articles. Do people read posts longer than that? Sure they do. But the longer a post is, the more possibility there is that some fraction of the readers will quit reading before the end, and maybe even pass on links or comments based on that incomplete understanding. I realize I’m not in the majority of online science writers in taking this position, but I think this better reflects how the average online reader reads.

I nevertheless managed to miss when Bora Zivkovic gently tweaked back over Twitter:

Do you agree? Losing the scientific lede: http://bit.ly/94zroM by @JBYoder compare: http://bit.ly/cJj3vs Long is fine.

But I did notice a larger-than-usual traffic spike associated with the post, and, being pretty sure of the source, I thought I’d just add to what I said previously, in light of the quite coherent and reasonable defense Bora makes for long-form posts.

In Bora’s older post, the point is not so much that blog posts should be long, but that blogs are a good venue for science communication because posts can be long:

Context – there is no space for context in a short article. Yet it is the context that is the most important part of science coverage, and of science itself – remember the “shoulders of giants”? Placing a new study within a historical, philosophical, theoretical and methodological context is the key to understanding what the paper is about and why it is important, especially for the lay audience. Even scientific papers all provide plenty of context in the Introduction portion (and often in the Discussion as well) which is sprinkled with references to earlier studies.

I strongly agree that context is important, and I also agree that blogs are great at providing context—but because a post can link to context, not necessarily provide it itself.

Much of my feelings about what a good blog post should look like are determined by two things, both of which are more aesthetic than empirically justifiable. Both are also related to my all-but-minoring in English as an undergraduate: I am a devoted follower of Strunk and White, and I wrote for the campus paper and took courses in newspaper writing. So I try to follow the inverted pyramid to some approximation, and when a post starts to spill below what displays in a browser window without scrolling down, much like this one, I start to worry that I’m not omitting needless words.

It’s my own online reading experience that short posts, which communicate a single scientific result, work better than longer posts trying to synthesize lots of different results. Again, that’s mostly an aesthetic judgment, but as I said in Monday’s post, I think that short posts are more likely to be read to the end, and less likely to result in distortions as a post propagates across social media (or, rather, only has the distortions I’ve introduced myself!).

Of course, maybe that’s a moot point. If a reader mischaracterizes my post in a Facebook update, but includes a link to it, everyone who clicks through will see that the post said something different. Right? Well, again, when they do click through, I suppose I’d like them to be able to take in the point of the post quickly, and understand what it actually says without needing to read all the way to the end.

Losing the scientific lede

ResearchBlogging.orgOver at SEED, Dave Munger reflects on how online publishing and dissemination methods can strip the nuance from scientific news:

I thought I was being careful to explain the results of several studies, showing that suicide is a difficult problem with many potential contributing factors and confounding variables, including mental illness, depression, and the seemingly contradictory influences of intelligence. Yet on social-networking sites, many readers latched on to one finding: That countries with higher average IQ tend to have higher suicide rates.

Munger suggests that this problem can be mitigated by careful consideration of both the nut graf sent out via Twitter and RSS and the audience receiving them, and that’s clearly right. But I think it’s also worth considering whether some subjects are less appropriate for blogs.

Consider your medium! Photo by K!T.

Blog posts are best when they’re less than 700 or 800 words long, and their contents are readily summed up in a headline and only slightly expanded upon by the first paragraph. Think newspaper, not magazine articles. Do people read posts longer than that? Sure they do. But the longer a post is, the more possibility there is that some fraction of the readers will quit reading before the end, and maybe even pass on links or comments based on that incomplete understanding. I realize I’m not in the majority of online science writers in taking this position, but I think this better reflects how the average online reader reads.

Posts about individual, straightforward results work well in that context. For example, my colleague Jeanne Robertson recently discovered that desert lizards under divergent selection for camouflage have also become confused about visual mating signals. It’s simple—one lizard population moved to white sand dunes and evolved lighter coloration, so now light males think that dark males from the ancestral population look like females—and it supports a lot of catchy headlines that don’t sacrifice accuracy. The title of the talk at Evolution 2010 in which Robertson presented the discovery was “Dude looks like a lady.” I’d say the Wired Science article I linked to above captures all the interesting details.

Complexity doesn’t work so well. Scientific papers based on broad surveys of the literature, or many interrelated experiments, are inevitably going to lose some potentially important nuance when translated into an RSS-suitable post title, and explaining them accurately may take a lot more than 700 words. I’ve run into exactly this trying to write about complicated papers—either I go on for longer than I think my readers are likely to follow, or I have to omit detail and rely on readers to follow up with the links to the literature.

Mind you, this length-versus-content balance is a universal problem in disseminating scientific results—just look at the short-form journals Science and Nature. Some results are perfectly suited to the three-pages-and-online-supplement format, like an experimental result showing that sexually-reproducing lines of the worm Caenorhabditis elegans maintain more fitness in the face of mutation than asexual lines [PDF]. (I’ve posted about another result in this experimental system.) It’s a simple result easily understood even without getting into the Supplementary Material. Compare that to a recent statistical survey of evolutionary trees that concluded species interactions weren’t important in the history of life [$a]. That, too, fits into three pages of Nature, but the result is deceptively simple—even after delving into the Supplementary Material, the statistical reasoning underlying the core result isn’t clear, as the comments thread on my post about the piece reveals.

Which isn’t to say that online science writers should stick to covering simple experimental results or flashy natural historical notes, any more than scientists should never tackle complicated projects. They do, however, need to consider the limitations of the medium in which they report scientific results. Is a topic too complicated to fit in a single post? Maybe it’s suitable for a series of posts. I like how Slate handles this, building collections of interrelated articles that can stand alone, but link into something like a long-form magazine article—see Will Saletan’s great series on memory manipulation for a recent example.

And now I’ve blown through 700 words in the service of an extended, hopefully nuanced, discussion. Take from that what you will.

References

Morran, L., Parmenter, M., & Phillips, P. (2009). Mutation load and rapid adaptation favour outcrossing over self-fertilization. Nature, 462 (7271), 350-2 DOI: 10.1038/nature08496

Venditti, C., Meade, A., & Pagel, M. (2009). Phylogenies reveal new interpretation of speciation and the Red Queen. Nature, 463 (7279), 349-52 DOI: 10.1038/nature08630

On Independence Day

Ask not … Photo by bacondit.

I’m acutely uncomfortable with the militarism, overt and implied, that accompanies Independence Day. I do, however, have faith—in the sense of being sure of what I hope for—in government by the people, in freedom of speech and of the press, in the separation of Church and State, in not quartering soldiers in any house without the consent of the Owner. In the ugliest moments of U.S. politics, I worry that my fellow Americans don’t care much for our shared history, or even some of the basic principles that underlie our democracy. Yet we’re still muddling through, and I’d rather do what I can to make this a better, more just, more civil society than just throw up my hands and move to Canada.*

In that spirit, here’s a few lines from one of my favorite figures of American history, Abraham Lincoln, on the occasion of his second Inauguration. It seems appropriate for a nation divided, even if not by actual battle lines:

With malice toward none, with charity for all, with firmness in the right as God gives us to see the right, let us strive on to finish the work we are in, to bind up the nation’s wounds, to care for him who shall have borne the battle and for his widow and his orphan, to do all which may achieve and cherish a just and lasting peace among ourselves and with all nations.

The image accompanying this post is part of the winning entry for Studio 360’s Independence Day redesign challenge, and I really like it—it responds to John F. Kennedy’s famous imperative by suggesting things you can do for your country, and it includes teachers and judges alongside the more stereotypical soldier and policeman. It’s not often enough we’re reminded that you needn’t carry a weapon to serve your nation.

——-
*This statement is subject to revision in the event that I get a job offer from a Canadian university.

Science online, #evol2010 hangover edition

Between the all-day conferencing of Evolution 2010 and the fact that car trouble stranded me in Kennewick, Washington, almost exactly halfway between Portland and Moscow, I haven’t done enough online reading to justify my usual end-of the week roundup. I will, however, note a few things:

And, lastly, bluebirds are still frickin’ spectacular photo subjects.

Photo by kevincole.