Carnival of Evolution #26 at The Thoughtful Animal

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I’m late to the party on this one: the 26th Carnival of Evolution is on over at this month’s host, Jason Goldman’s The Thoughtful Animal. This round of submissions is more concentrated on the “endless forms most beautiful” than directly challenging creationism, which is a welcome change if I do say so myself. Don’t get me wrong; creationists need (apparently endless) debunking. But I think the argument is made just as effectively by showing that there’s “grandeur” in the scientific view of life—which these posts do in spades.

Double the mutualists, double the fun?

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ResearchBlogging.orgFor all living things, information is critical to survival. Where’s the best food source? Is there a predator nearby? Will this be a good place to build a nest? It probably shouldn’t be surprising, then, that lots of animals do what humans do when faced with a host of hard-to-answer questions—they take their cues from their neighbors.

Red-backed shrikes place their nesting sites near where other shrike species have set up territories. Many bird species recognize each other’s predator alarm calls, and respond appropriately. And a new natural history discovery published in the latest issue of The American Naturalist shows that treehoppers let one species of butterfly know where to find ants that will tend its larvae [$a].


The ant-tended butterfly (Parrhasius polibetes, above) looks for ant-tended treehoppers (Guayaquila xiphias, below) to know where to lay her eggs. Photos from Kaminski et al. (2010), figure 2.

The treehoppers help out the butterfly inadvertently, because both of them are dependent on a common resource: ants. Like many true bugs, treehoppers make their living sucking the sap of a host plant. This gives them a surplus of simple sugars and water, which they excrete as “honeydew” to attract ants for protection. As it happens, the larvae of the butterfly Parrhasius polibetes do the same thing—so the new study’s authors hypothesized that P. polibetes females might prefer to lay their eggs on plants where treehoppers were already present, since those would likely already have ants ready to protect butterfly larvae.

To test this, the authors set up experimental pairs of host-plant branches, one occupied by ant-tended treehoppers, and one not. They excluded ants from accessing the unoccupied branch with Tanglefoot, a water-resistant glue used in insect traps. After 48 hours, they checked the experimental plants for newly-laid butterfly eggs, and found that P. polibetes was both more likely to lay eggs, and laid more eggs at a time, on branches occupied by treehoppers.

To assess the fitness benefit of laying eggs on treehopper-occupied plants, the authors compared the survival of newly hatched P. polibetes larvae artificially introduced onto branches occupied by treehoppers to the survival of larvae introduced to branches unoccupied by treehoppers (and with ants excluded, again, using Tanglefoot). The larvae placed with treehoppers had substantially better odds of survival—about six times better.

These two experiments confound the effect of treehoppers with the effect of ants, however—so the authors performed one additional experiment. In this one, they set up paired branches with and without treehoppers, but allowed ants to reach both the occupied and unoccupied branches—and the general result from the earlier experiment held. Larvae placed near treehoppers were three times more likely to survive for the duration of the experiment even when larvae placed on a branch without treehoppers were able to attract ants on their own.

So it looks like P. polibetes is able to freeload on the treehoppers’ ant-attracting efforts, and benefits from that freeloading. What effect does that freeloading have on the treehoppers, or the ants, or the host plant? It’s hard to say based on the data presented in the current paper, but I’d guess that the treehoppers don’t lose much—in fact, they might gain from having another ant-attracting insect nearby, just as the butterfly larvae do. Similarly, it’s probably helpful for the ants to have more honeydew-producing species in the same location. It’s almost like that commercial for … what was the product?

(I’ll leave it to you, dear reader, to decide which insects correspond to which gendered pair in that video.)

I’d think, though, that this pile-on isn’t so good for the host plant, if plants already hosting treehoppers are more likely to have to deal with butterfly larvae, too. Untangling all the different ways these four species—ants, treehoppers, butterflies, host plants—exert direct and indirect natural selection on each other should keep the authors busy for a long time to come.

References

Hromada, M., Antczak, M., Valone, T., & Tryjanowski, P. (2008). Settling decisions and heterospecific social information use in shrikes. PLoS ONE, 3 (12) DOI: 10.1371/journal.pone.0003930

Kaminski, L., Freitas, A., & Oliveira, P. (2010). Interaction between mutualisms: Ant‐tended butterflies exploit enemy‐free space provided by ant‐treehopper associations. The American Naturalist DOI: 10.1086/655427

Magrath, R., Pitcher, B., & Gardner, J. (2007). A mutual understanding? Interspecific responses by birds to each other’s aerial alarm calls. Behavioral Ecology, 18 (5), 944-51 DOI: 10.1093/beheco/arm063

Science online, relentlessly negative edition

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Would you be less afraid of the big, bad wolf if we paid you? Photo by Eric Bégin.
  • Can’t say “mission accomplished” just yet. Wednesday was day 100 of the Deepwater Horizon oil spill. The hole has been more-or-less plugged for a while now, and surface oil is disappearing, but we’ll probably be watching the effects of this mess for years to come. Might as well have a Gulf Spill cocktail while you wait.
  • Can’t buy their love. Offering ranchers compensation for livestock lost to wolves doesn’t improve their opinion of wolves. (Conservation Maven)
  • Can’t make them shut up. Disrupting quorum sensing, or “communcation” between bacteria, is a promising new approach to treating infections. Except that—surprise!—bacteria evolve resistance to QS disruption. (Lab Rat)
  • Can’t expect them to be constrained by mere facts. The one little bit of actual science underlying claims that New Zealand was originally settled by Celts —the age of rat bones found on the islands—turns out not to be so accurate. (The Atavism)
  • Can’t afford not to plan ahead. Ecologists should start planning for the end of cheap oil, and its many unpleasant consequences. (Conservation Magazine)
  • Can’t be worse than the status quo … or can it? The “tragedy of the peer-review commons” could be resolved by compensating reviewers, either with credit towards their own submissions, or just plain ol’ money. (Jabberwocky Ecology)
  • Can’t hurt to try. Eliminating soot pollution—which leaves the atmosphere much more quickly than carbon dioxide—could cut the effects of global warming in half within less than two decades. (Wired Science)

Can’t be bothered to care for your larvae? Trick an elaisome-hunting ant, or a sex-crazed bee, into picking it up.

Global warming roundup: There’s bad news, and weird news, but no really good news

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ResearchBlogging.orgRegardless of what James Inhofe thinks, global climate change is going to dramatically reshape the natural systems our civilization depends upon. Unfortunately, even as we embark on the radical experiment of turning our planet’s temperature up to 11, we’re just figuring out what results to expect. A whole series of papers released in the last week exemplify this point, showing that living communities’ response to the changing planet may often be counter-intuitive.

Temperature stress may offset trees’ ability to soak up carbon dioxide. Photo by Wade Franklin.

Let’s start with the bad news:

A study out in last week’s PLoS ONE suggests that, rather than growing more rapidly and absorbing more carbon dioxide as the planet warms, forest trees may actually grow more slowly. More carbon dioxide in the atmosphere should generally increase plants’ growth rates, since carbon dioxide is the raw material for photosynthesis. On the other hand, rising temperatures may put plants under so much stress that it offsets the benefits of more carbon dioxide.

Silva et al. examined core samples from four tree species—black spruce, red pine, red oak, and red maple—growing in Ontario forests, and found that the trees’ growth rings were narrower in more recent years, as atmospheric carbon dioxide increased. Comparison of the growth rings to carbon isotope ratios (which capture a tree’s response to temperature stress) suggested that the growth declines were due to less hospitable temperatures.

A large-scale historical study just out in Nature shows similar results for phytoplankton, microscopic photosynthetic organisms that form the base of ocean food chains. Working from historical records of ocean water transparency—phytoplankton makes water cloudy—going back to 1899, Boyce et al. found widespread declines in phytoplankton density [$a]. That’s bad news on multiple levels, implying that phytoplankton growth isn’t helping to absorb carbon dioxide, and that the oceans’ productivity is declining with its foundational food sources, not just from overfishing. (See also coverage of this result by the BBC and NPR.)

Earlier springs mean bigger marmots. Photo by Blake Matheson.

Now, the weird news:

The rule of thumb for plants’ response to climate change has been that they’ll respond to warmer temperatures by starting the growing season earlier. But a new survey of plant populations in Florida finds that as global warming progressed, most species flowered later. The authors suggest that this is because many Florida plant communities that are already adapted to warm conditions, and because climate change across much of Florida has meant not just warmer temperatures overall, but also greater seasonal variation in temperatures—areas where summer temperatures increased also tended to have decreasing winter temperatures. Faced with the possibility of more late frosts, Floridian plants are waiting till later in the spring to start flowering.

Another weird result of climate change received lots of press last week: a thirty-year study of yellow-bellied marmots in Colorado found that, as their alpine habitats grew warmer, the marmots grew bigger and more numerous [$a]. Warmer overall temperatures mean earlier spring thaws, so the marmots are emerging from hibernation earlier, have more time to grow and pack on fat reserves before hibernation in the fall, and can make more babies the next spring. Is this good or bad? Co-author Dan Blumstein’s answer to that question in an interview with NPR is worth quoting:

I don’t know if I’m worried as much as I’m intrigued by it and I want to continue following the story. … it’s only through these long-term studies that we can gain important insights into what’s happening, what’s happened and ultimately identify mechanisms through which we may be able to predict what might happen in the future.

Climate change is essentially a global gamble, with the function of ecological communities everywhere as the stakes. Even as we humans are unable to muster the will to stop it, we’re finding out daily how many changes are on the way as the planet warms.

References

Boyce, D., Lewis, M., & Worm, B. (2010). Global phytoplankton decline over the past century. Nature, 466 (7306), 591-6 DOI: 10.1038/nature09268

Ozgul, A., Childs, D., Oli, M., Armitage, K., Blumstein, D., Olson, L., Tuljapurkar, S., & Coulson, T. (2010). Coupled dynamics of body mass and population growth in response to environmental change. Nature, 466 (7305), 482-5 DOI: 10.1038/nature09210

Silva, L., Anand, M., & Leithead, M. (2010). Recent widespread tree growth decline despite increasing atmospheric CO2. PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011543

Von Holle, B., Wei, Y., & Nickerson, D. (2010). Climatic variability leads to later seasonal flowering of Floridian plants. PLoS ONE, 5 (7) DOI: 10.1371/journal.pone.0011500

Before they were yucca moths

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This post was chosen as an Editor's Selection for ResearchBlogging.orgYuccas and yucca moths have one of the most peculiar pollination relationships known to science. The moths are the only pollinators of yuccas, carrying pollen from flower to flower in specialized mouthparts and actively tamping it into the tip of the pistil. Before she pollinates, though, each moth lays eggs in the flower—the developing yucca seeds will be the only thing her offspring eat. How does such a specialized, co-adapted interaction evolve in the first place? My coauthors and I attempted to answer this question in a paper just published in the Biological Journal of the Linnean Society, by reconstructing the ecology of yucca moths before they were yucca moths [PDF].

Continue reading →

Science online, confused jumping spiders edition

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Awwww. Photo by coniferconifer.
  • Worth it just for the Journal of Experimental Biology cover image. By selectively covering jumping spiders’ four anterior eyes with (removable) paint, behavioral biologists showed that the spiders orient using only the pair on the side of their heads. (Arthropoda)
  • Not extinct after all. The Horton Plains slender loris, that is. (Wired Science)
  • Only criminals will have serpentine. California seems to be prepared to pass a law removing serpentine‘s status as the State Rock, and, more worryingly, declaring it a carcinogen without any scientific justification. (Summing up by Highly Allochthonous; find out who to call at The Intersection)
  • So did Triceratops use a fake I.D., or what? A new analysis of fossils concludes that the dinosaur formerly known as Torosaurus is actually the adult form of Triceratops. (Dinosaur Tracking)
  • Images Not Suitable for Lunchtime. Culling Tasmanian devils infected with transmissible facial tumors doesn’t seem to reduce the prevalence of the tumors in a managed population. (Wild Muse; see also RadioLab’s discussion of the tumors.)
  • And then Elijah Wood tries to steal your girlfriend. Electrodes implanted in the hippocampus can induce amnesia. (Neuroskeptic)

This week’s video, via Arthropoda, provides scientific proof that jumping spiders are adorable. I love how she wriggles her thorax before she jumps! This video, and the ones on the linked page, are by Thomas Shahan, whose Flickr feed is an entomologist’s dream—and all CC licensed.

Interview at Coyote Crossing

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Nature writer and photographer Chris Clarke is a great fan of yuccas and yucca moths—he’s working on a book about Joshua trees right now—and so he asked me to answer a few questions about the latest research on the evolutionary history of yucca moths, which was just published in the Biological Journal of the Linnean Society. Check out Clarke’s discussion of the mutualism, and our e-mailed interview, on his blog Coyote Crossing. Look for a post about the paper, with some basic explanation of the methods used in it, right here at D&T next Tuesday.

Ladybird beetle on a Joshua tree leaf. Photo by jby.

Where’s Harry Tuttle when you need him?

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I just finished the most emotionally draining telephone exchange I think I’ve ever had. It was with my primary health care provider, concerning the surprisingly thorny question of services received versus services requested versus services covered by my health insurance. I’d been trying to get an answer for more than a week, and it was implied that this was expecting a little too much.

I was exceptionally non-Mennonite. I was sarcastic with a total stranger. I asked to speak to someone’s supervisor. It did not, however, occur to me to ask for the 27B-6. Maybe that would’ve done the trick.

Still more #sbFAIL fallout: Bora bails

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Photo by Roadsidepictures.

It seemed as though the dust had finally settled over the ScienceBlogs/Pepsi fiasco—until yesterday, when another shoe dropped, and it was a big one. In a typically thorough, nuanced post, Bora Zivkovic announced his decision to leave ScienceBlogs, relocating to WordPress.

If you’ll pardon the use of a horrible business buzzword, Bora is a super-connector, spending more effort than anyone else in my blogroll to pass on links, making the ScienceOnline conference a network-y blast, and offering nods to junior members of the online science writing community. In his departure essay, he makes it clear that this kind of connectivity is the point of blogs in general, and the power of ScienceBlogs in particular:

That is huge power. I keep mentioning this power every now and then (see this, this, this and this for good examples) because it is real. Sustained and relentless blogging by many SciBlings (and then many other bloggers who followed our lead) played a large role in the eventual release of ‘Tripoli Six’, the Bulgarian medical team imprisoned in Libya. Sustained blogging by SciBlings (and others who first saw it here) played a large part in educating the U.S.Senate about the importance of passing the NIH open access bill with its language intact. Blogging by SciBlings uncovered a number of different wrongdoings in ways that forced the powers-that-be to rectify them. Blogging by SciBlings brings in a lot of money every October to the DonorsChoose action. Sustained blogging by SciBlings forced SEED to remove the offending Pepsi blog within 36 hours. And if a bunch of SciBlings attack a person who did something very wrong, that person will have to spend years trying to get Google to show something a little bit more positive in top 100 hits when one googles their name (which is why I try to bite my tongue and sleep over it when I feel the temptation to go after a person). The power of the networks of individuals affects many aspects of the society, including the media. [Hyperlinks sic.]

Losing someone who believed so deeply in the social power of the blog network, and who worked so hard to boost that power and channel it to good ends, is a huge blow to ScienceBlogs. It seems to have contributed to PalMD’s decision to quit SB, and decisions by PZ Myers and Greg Laden to go on blog-strike. And now that Bora has joined the ScienceBlogs diaspora, it’ll be interesting to see how his super-connecting shapes the emerging community of independent blogs.

Sex after dawn: Marriage and natural selection

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ResearchBlogging.orgThe book Sex at Dawn, by Christopher Ryan and Cacilda Jethá, has had a lot of press in the last month—it first popped up on my radar with Eric Michael Johnson’s review for SEED, and then it became unavoidable (for me, anyway) when Dan Savage devoted a whole column and podcast to it. The thesis of Sex at Dawn is that early humans were highly promiscuous, and that modern expectations of monogamy are probably not consistent with our biology. I haven’t read the book yet, but the discussion surrounding it has largely missed an important detail—human evolution didn’t stop when we invented agriculture.

In fact, we’ve evolved in response to agriculture. My capacity to digest milk proteins at age 28—most other mammals lose this ability as soon as they’re old enough for solid food—is the result of natural selection acting on my northern European ancestors. Sex at Dawn coauthor Christopher Ryan acknowledges exactly this, citing the same example, in a recent response to a question on his blog. I’m not aware of a study that documents human evolution in response to marriage customs, but conveniently enough, an article in the current issue of The American Naturalist does show that a population’s marital customs can shape its response to natural selection [$a].

Vintage postcard via chicks57.

The intensity and nature of natural selection often varies with age—it’s strongest on traits expressed prior to and during the period of life when most reproduction happens, and weaker on traits having to do with life after reproduction is mostly complete.

The new paper examines the effect of marriage on this relationship between age, reproductive activity, and the strength of natural selection. The authors are able to do this thanks to church records of births (via christenings), marriages, and deaths from four Finnish towns during the nineteenth century—a deep multigenerational dataset. The society described is probably as far away from the Sex at Dawn world of communal relationships within hunter-gatherer tribes as Western society has ever gotten—the births recorded are all in the context of monogamous marriages. How monogamous these marriages actually were is debatable; this was also a world before paternity testing. But the study follows women, who would probably have had less opportunity, and certainly had less social leeway, for affairs outside marriage.

Within that society, women’s reproductive success depended strongly on their husbands’ economic status, as approximated by whether or not they owned land. Women who married landowners married almost three years earlier, on average, than those who married non-landowners (between 24 and 25 years old, compared to 27). Women who married at an earlier age generally had more children survive to age 15, the paper’s benchmark for lifetime fitness—and this effect was stronger for women who married landowners.

Vintage wedding portrait via freeparking.

This meant that the intensity of potential natural selection acting on women in the study group peaked around their 30th birthday, declined slowly for around a decade, and then dropped off sharply. By comparison, an estimate of selection intensity based only the women’s probability of survival to a given age (i.e., without accounting for the need to marry before having children) just shows a steady decline with age. So marriage customs probably shaped the way natural selection could act on this population. (The comparison made, though, is a pretty facile one. I’d love to know what the intensity of selection looks like under other post-agricultural mating systems like, say, polygyny.)

Does that mean that these nineteenth-century Finns were evolving in response to the strictures of monogamy? Not necessarily. This study only estimates how strong selection would be on a trait relative to the age at which it’s expressed. That is, traits that reduced (or improved) a woman’s ability to bear children would be more strongly selected against (or favored), if they were expressed while she was between the ages of 30 and 40.

So the fact that marriage customs shape natural selection doesn’t mean that we’ve evolved to be better adapted to current marriage customs than we are to those of pre-agricultural hunter-gatherers. Marriage customs vary considerably among cultures, and over time—I don’t know of any culture that has maintained strict monogamy since the origin of agriculture. Even if a single culture did prefer monogamy that long, natural selection to adapt to that mating system would be working from a pool of genetic variation evolved from hundreds of generations of our earlier polyamorous lifestyle. It doesn’t matter how strongly natural selection would favor a perfectly monogamous person, if such a person doesn’t exist.

In other words, the key insight of Sex at Dawn—which is also a key insight of evolutionary biology in general—is right: What we can become is shaped by what we used to be. That’s certainly an important thing to keep in mind when considering a commitment that lasts till death do you part.

(For example, you might want to makes sure your significant other is of at least the same genus as you. I mean, talk about biological impediments.)

References

Gillespie, D., Lahdenperä, M., Russell, A., & Lummaa, V. (2010). Pair-bonding modifies the age-specific intensities of natural selection on human female fecundity. The American Naturalist, 176 (2), 159-69 DOI: 10.1086/653668