Monthly Archives: December 2009

I’m going to Research Triangle Park!

Posted on by

Specifically, to attend the National Evolutionary Synthesis Center’s ScienceOnline 2010 conference from 14 to 17 January — I learned today that my post on the evolution of human lactase persistence won one of two awards to cover travel expenses to the conference. The other award went to Christie Lynn at Observations of a Nerd, for a great discussion of how environmental change can turn a useful trait into a dangerous one.

The NESCent site has the details and a complete list of entrants, all of which deserve a read. It’s really an honor to have my work selected, and I’m very excited about the conference. And, yes, I’ll blog about it.

In some strange, alternate universe …

Posted on by

David Lynch directed Return of the Jedi. In our universe, he turned down the job when George Lucas offered it to him.


The mind reels. Would the forest moon of Endor have been covered in Douglas firs? Would Luke have had visions of midgets? Would there be vague references to Eastern mysticism, and gruesome exploitation of women? In short … would it have been all that different? Meanwhile, in this universe, someone is probably working on a Jedi–Blue Velvet mashup at this very moment.

Via Kottke.

This week in science blogging

Posted on by

Photo by MonsieurJC.

Science blog reading from the interstices of Dead Week:

  • The EEB & flow: “Green” product labels break out into categories that parallel competing schools of thought among conservationists.
  • Conservation Maven: Birds provide approximately $310/hectare in pest-removal services on coffee plantations.
  • Conservation Magazine: A hunting ban in Ontario’s Algonquin Provincial Park has allowed the local wolf population to re-establish its former pack structure.
  • Neuroskeptic: Women dosed with testosterone are more likely to treat others fairly than those given a placebo, but less likely to play fair if they think they’ve received testosterone.
  • Cognitive Daily: University students’ “gaydar” is as much as 70% accurate.

Picky eating, not genetics, splits leaf beetles

Posted on by

This post was chosen as an Editor's Selection for ResearchBlogging.orgMany different factors can conspire to create reproductive isolation between populations and, ultimately, separate species. Disentangling them is often tricky, but a study recently published in PNAS takes a crack, and demonstrates that two populations of leaf beetles are divided by food preferences, not genetics [$-a]




Neochlamisus larva, and two possible food plants, red maple and willow. Photos by Scott Justis/BugGuide.net, Mary Keim, and John Tann.

Some populations of the leaf beetle Neochlamisus bebbianae eat red maple, and others eat willow; each type grows better on their native host plant. Hybrids between the two species are possible, and they don’t grow as rapidly when raised on either host. This might mean that ecology — adaptation to the different host plants — is creating reproductive isolation between the two forms of Neochlamisus. But it might also mean that the two forms are genetically incompatible.

Many species are separated by intrinsic genetic incompatibility. In these cases, hybrids have reduced fitness, or die outright, because the two species have evolved separately in such a way that mixed genomes cannot produce important proteins correctly. One example was recently found in two lines of the wildflower Arabidopsis thaliana — both lines had duplicate copies of an important gene, and in each line a different copy mutated into non-functionality, so some hybrids between the two lacked any functional copies [$-a].

To differentiate between this kind of genetic incompatibility and ecological isolation, coauthors Egan and Funk conducted not one but two generations of hybridization between maple and willow Neochlamisus populations. In the first (F1) generation, they bred parents from each host-specialized type; but in the second they performed a “backcross,” breeding the F1 hybrids with mates from one or the other of the parental populations.

This produced a population of backcrossed hybrids with 3/4 of their genes from one parental type, and 1/4 from the other. If intrinsic incompatibility separated the types, then these backcrossed hybrids would grow poorly no matter what their host plant. However, if adaptation to separate host plants isolates the types, then backcrossed hybrids would perform better on the host plant of the type with which they shared more genes. This is what Egan and Funk found — backcrossed hybrid larvae grew faster on maple if they shared more genes with maple-type Neochlamisus, and similarly for willow.

References

Bikard, D., Patel, D., Le Mette, C., Giorgi, V., Camilleri, C., Bennett, M., & Loudet, O. (2009). Divergent evolution of duplicate genes leads to genetic incompatibilities within A. thaliana Science, 323 (5914), 623-6 DOI: 10.1126/science.1165917

Egan, S., & Funk, D. (2009). Ecologically dependent postmating isolation between sympatric host forms of Neochlamisus bebbianae leaf beetles Proc. Nat. Acad. Sci. USA, 106 (46), 19426-31 DOI: 10.1073/pnas.0909424106

On my iPod: Too Beautiful to Live

Posted on by

I’m moving back into a labwork-intensive schedule at the moment, which means that I’m burning through podcasts like nobody’s business. Fortunately, I’ve recently been sucked into the orbit of Too Beautiful to Live, the online incarnation of Luke Burbank’s daily talk/music/newsish show. I only found TBTL after it lived up to its its name by getting dropped from the air by Seattle-area radio station KIRO.


Photo by bonacheladas.

Luke and his co-conspirators Jen “Flash” Andrews and Sean DeTorre put together an amalgam of music, pop-culture sound cues, news commentary, and whatever else happens to drift through Luke’s head at the moment of recording. Topics range from the current status of the Large Hadron Collider to Alec Baldwin’s self-esteem issues; one recent episode revolved around plumbing issues in the Burbank residence.* It’s weird and silly and oddly compelling, and it works great in the background while I’m racking pipette tips.**

Which sounds like damning with faint praise, now that I re-read it, but really isn’t. I mean, Studio 360 doesn’t usually make that particular cut. Anyway, you should totally subscribe.

——–
* The appropriateness of which subject matter was discussed in today’s episode, which was basically a recorded conversation between Luke and his girlfriend on a drive to down to Portland, and which achieved an almost “30 Rock”-grade degree of meta.

** Except for that one occasion when I had to dive across the lab to hit the volume control and kill Jen’s Swedish Chef impression just as my (Swedish) dissertation advisor walked in the door.

This week in science blogging

Posted on by

I’d like to try something new and see if it sticks — a weekly post briefly noting a handful of items from the scientific blogosphere I’ve noticed in the past week. Here goes:


Photo by ehpien.
  • NeuroDojo: Chickadees grow new brain cells while caching food — but they grow more in the wild than they do in captivity.
  • Dechronization: Mitochondrial DNA is not as good for evolutionary and ecological genetics as was once thought. It doesn’t even evolve in a nice, clocklike fashion!
  • The EEB & flow: Plant communities have a lot going on underground.
  • Conservation Maven: Exotic giant tortoises seem to make pretty good replacements for extinct native giant tortoises. (Of course, it’s hard to imagine introduced giant tortoises ever running amok in a new habitat.)
  • EcoTone: Loss of top predatory fish can spur algae blooms.

Evolving antibacterial therapies

Posted on by

On Slate, Brian Palmer says we need better tactics, not better antibiotics, to combat drug-resistant bacteria. But the new “tactics” he describes are, basically, new drugs:

In vitro studies have shown that chemicals like ascorbic acid shut down the movement of antibiotic resistance between cells. (Right now it’s effective only at concentrations that a person couldn’t tolerate, but it’s a start.) Because almost all antibiotic resistance relies on genetic transfer, this technique might be the solution we’ve been seeking since the very first colony of bacteria solved penicillin in 1944.

Drugs that combat gene transfer between bacteria probably would slow the spread of new antibiotic-resistance genes. Until bacteria evolve ways to transfer genes in spite of anti-transfer drugs, that is.

A genuinely new approach to circumvent antibiotic resistance will require actually thinking about the evolutionary consequences of therapy — and creating natural selection that eliminates the damage done by bacteria without also creating a fitness advantage for resistance to the therapy. That’s tricky, to say the least, but it’s not impossible. Such an approach has been outlined to control disease-carrying mosquitoes, for instance.

For yucca moths, does (flower) size matter?

Posted on by

ResearchBlogging.orgIn a paper just released online at Molecuar Ecology ahead of publication, genetic tests on moth larvae provide the latest piece to the puzzle of why there are two kinds of Joshua tree — because the tree’s pollinators need to match its flowers [PDF].

I’ve written extensively about the interaction between Joshua tree and its pollinators. Like all yuccas, Joshua tree is pollinated only by yucca moths. Female yucca moths collect pollen in special mouthparts and deliberately apply it to a yucca flower after laying eggs inside it. When the eggs hatch, the moth larvae eat some of the seeds inside the developing fruit. Yuccas prevent their pollinators from laying too many eggs by selectively killing flowers too badly damaged by egg-laying [$-a].



TOP: The two forms of Joshua tree (western type on left, eastern on right). BOTTOM: Scaled comparison of moth body sizes and tree pistils. To lay eggs in a flower, moths must drill from near the top of the pistil to the positions marked by dotted lines. Photo by jby, Illustration from Smith et al.(2010), figure 1.

This last element of the interaction may have had significant consequences for Joshua trees’ evolutionary history. Joshua trees are pollinated by two different species of moths, which occur in different parts of the tree’s range: the larger Tegeticula synthetica in the west, and the smaller T. antithetica in the east. Joshua trees pollinated by the two different moth species are themselves different, both in their overall shape, and in the shape of their flowers’ pistils — specifically, the length of the route that a moth must drill to lay her eggs [PDF].

How does this difference in flower shape affect Joshua tree pollination? If a larger moth attempts to lay eggs in a smaller flower, it may be do more damage to the flower than the “native” pollinator would, triggering the tree to kill the flower. On the other hand, smaller T. antithetica might be able to lay eggs in a larger western-type flower without this risk. If this is the case, moths probably can’t pollinate western trees with eastern pollen, but they might be able to do the reverse.

Such one-way pollen transfer between the two Joshua tree types could produce a population genetic pattern called “chloroplast capture.” Joshua tree pollen doesn’t contain the full genetic code of the tree that produces it — it lacks the genes contained in the chloroplast, the cellular structure that conducts photosynthesis, because pollen grains typically don’t have chloroplasts. The DNA in the cellular nuclei of newly-formed seeds is a mixture of nuclear DNA (nucDNA) from a pollen grain and from one of their “maternal” parent’s ovules, but they get all their chloroplasts, and chloroplast DNA (cpDNA), from the ovule. If moths carry pollen from eastern trees to western trees, then the seeds produced would contain western cpDNA, but also some eastern nucDNA.


Asymmetric pollen transfer can lead to eastern-type trees with western-type chloroplasts. Figure 2 from Smith et al.(2010).

This is what we’ve found in Joshua tree populations near the region where the two tree types and their pollinators come into contact. At these sites, trees look like the eastern type (meaning they likely have eastern nucDNA, though we haven’t tested that yet) but have cpDNA that matches nearby populations of western-type trees [PDF].

The genetic pattern is only suggestive of one-way pollen transfer between the two Joshua tree types, though. We haven’t yet tracked the movement of moths directly, or estimated whether they actually are less successful when laying eggs on the wrong tree type. The newly-published study provides exactly these data. My colleague Chris Smith placed glue traps on Joshua tree flowers at the contact zone to estimate how often adult moths of each pollinator species visited each type of tree in the mixed population. Adult moths were more likely to be trapped on their “native” trees, though they did show up on the other type sometimes.


A yucca moth larva emerges from a Joshua tree fruit in the lab. Photo by jby.

Chris and I then collected fresh fruit from trees in the contact zone, and caught yucca moth larvae as they chewed their way out. Chris and another coauthor, Chris Drummond, then identified the species of each larva based on their genetics (the two pollinators look very similar at that stage) — and in our sample, the pattern of specificity was even stronger than that in the adults. The larger moth species, T. synthetica, never emerged from fruits of the small-flowered eastern trees. The vast majority of larvae of the smaller T. antithetica were also found inside their “native” tree’s fruit — but a handful did emerge from large-flowered western trees.

This mechanism could create the genetic pattern we see in Joshua tree populations. Larger T. synthetica doesn’t seem to lay eggs in (or pollinate) small-flowered eastern trees, but smaller T. antithetica can occasionally lay eggs in (and pollinate) large-flowered western trees. This should create asymmetric gene flow, with pollen moving from eastern trees to western trees, but not the reverse. The two Joshua tree types may not yet be reproductively isolated, separate species — but we won’t know for sure without looking at the plants’ nuclear DNA. As it happens, I’m working on that right now.

References

Godsoe, W.K.W., Yoder, J.B., Smith, C.I., & Pellmyr, O. (2008). Coevolution and divergence in the Joshua tree/yucca moth mutualism The American Naturalist, 171 (6), 816-823 DOI: 10.1086/587757

Marr, D., & Pellmyr, O. (2003). Effect of pollinator-inflicted ovule damage on floral abscission in the yucca-yucca moth mutualism: the role of mechanical and chemical factors Oecologia, 136 (2), 236-243 DOI: 10.1007/s00442-003-1279-3

Smith, C.I., Godsoe, W.K.W., Tank, S., Yoder, J.B., & Pellmyr, O. (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: Asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x

Smith, C.I., Drummond, C., Godsoe, W.K.W., Yoder, J.B., & Pellmyr, O. (2010). Host specificity and reproductive success of yucca moths (Tegeticula spp. Lepidoptera: Prodoxidae) mirror patterns of gene flow between host plant varieties of the Joshua tree (Yucca brevifolia: Agavaceae). Molecular Ecology DOI: 10.1111/j.1365-294X.2009.04428.x