Fence lizards versus fire ants: Evolutionary fail?

As many know, this is the 150^th anniversary of the publication of On the Origin of Species. If I may be so bold, one of the things that might distinguish our thinking about evolution in the last 50 years from the first hundred years might be the speed at which natural selection can operate. For a long time, we thought of evolution taking long times: millions of years would be needed to see the gradual accumulation of changes. We learned in the past few decades that we can see the effects of selection over the course of a few decades.

There are a few fast changing situations that should press the fast forward button on natural selection. Invasions are one. That’s why they’re invasions, not slow expansions. Boronow and Langkilde look at how the invasion of red fire ants are affecting fence lizards.

The ants (Solenopsis invicta) are nasty little buggers. A dozen will kill a fence lizard in less than a minute. You’d think that would apply some pretty strong selection on the lizards if they have any traits in the population that provide even a little defense against the ants.

To test whether natural selection has started acting on the fence lizards (Sceloporus undulatus), they collected lizards from two locations: one was invaded by the ants 70 years ago, and the other has not been invaded yet. Then, they allowed some angry ants to bite restrained lizards, and measured the animals’ performance on several behavioural tasks, like biting, running, and so on. A control group of lizards where handled, but not bitten. They also looked at the effect of dilute venom on the lizards’ blood directly.

The bottom line?

There’s no effect.

The lizards from the region that had been putting up with ants for seven decades had the same behavioural responses to the ants as lizards from the region with no ants. No differences in the blood responses to venom, either, though the blood was affected by venom.

The authors suggest that the ant venom might have a “tipping point.” Less than a certain dose, and the lizard is fine. More than that dose, and you’ve got a scaly corpse. The range in between “fine” and “dead” could be minuscule, in which case, there may not be a lot of variation for natural selection to work on. Thus, if the lizards can keep the bites under the critical value, they suffer no fitness consequences.

Another issue is that the fence lizards do live with other fire ants, like Solenopsis xyloni. These have weaker venom, and they’re not as numerous as the red fire ants, but it might be that the fence lizards have already been pushed to have defenses against fire ants.

A third possibility is simply that there is no existing variation that gives some members of the population greater resistance than others. Seventy years, which is about 35 generations of lizards, is quite a while, but may not be long enough. Who knows when just the right mutation will give some lucky lizard – and its offspring – a selective advantage.

Reference

Boronow, K., & Langkilde, T. (2009). Sublethal effects of invasive fire ant venom on a native lizard Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 9999A DOI: 10.1002/jez.570

Lizard picture by J.N. Stewart on Flickr, used under a Creative Commons license.

Ant picture by AJC1 on Flickr, used under a Creative Commons license.

Born funky

I recently discovered that my name is an anagram for “sleaze funk.”

Little did I know that this was an actual musical genre.


If you can’t read, the tag at the bottom, it says, “A Collection Of Greasy Soul, Sleaze Funk, Psychedelic Cumbia, Fuzzy Jazz, & More.”

Lab invader! And... it’s kind of cute!

Does this look like something deserving a message in all capitals and a triple exclamation point?


This little guy found his way into my lab today. It’s a recently hatched Mediterranean gecko (Hemidactylus turcicus), which are quite common here. Herbert (for that is what I named him – or her, makes no nevermind) was duly released back into the local habitat.

Mousy blondes: Ready for evolution textbooks?

This paper on mice evolving a new coat colour has been making a big splash in science news. It’s being touted as a new textbook example of evolution. Actually, not just an example, but an “icon.” I’m not sure what to think about that, given that Icons of Evolution is a notorious creationist book. Plus, the last time someone was touting “it’ll be in all the textbooks” were the promoters of the breathlessly over-hyped Darwinius / Ida fossil.

Reading the technical paper is very frustrating. I hate to say, but I don’t think the story is as complete or as impressive – yet – as the press releases indicate.

The press release version of this story is that in Sandy Hills, Nebraska, a region that has very light coloured soil, local deer mice have evolved a light coloured fur coat in a relatively short geological period of time. (In the picture, light deer mice are shown on dark soil, not their matching soil; same for the dark mice: they are shown on light soil.) In fact, the light coat was not present in the original population, and only evolved after the region emerged.

That is an interesting story. On what basis do Linnen and collegues make these claims?

First, they measured and compared the coats of five mice from two locations. Based on these measurements, they show the Sandy Hills mice are more reflective across the light spectrum, and this appear to be due to a pigment called pheomelanin.

In lab mice, a well known gene called Agouti affects coat colour. By breeding laboratory deer mice with mutations related to this gene, they showed these differing coat colours are classic Mendelian genes, where light is dominant over dark. Two dark mice will breed true; two light coloured mice will either breed true, but could have a mix of light and dark offspring (about three light offspring for every one dark offspring).

They also measured the expression of the Agouti gene during development, by tracking mRNA levels for the gene. As expected, they found Agouti more heavily expressed in light deer mice than dark.

They then captured deer mice in the wild, near the edge of the Sand Hills, to see if an Agouti mutation was associated with coat colour. As predicted, it was. In doing so, they found no relationship between where they collected the deer mice and their coat colour. From this, they argue, mice of both colours are interbreeding. I would like to see actual behavioural mate choice tests to support this.

The argument that selection has occurred revolves around the variation of the genome sequence. It’s fairly technical and I am not going to pretend that I fully understand the logic here. But I’ll spot that it’s all correct, and I would still argue that this is the weakest part of the paper. The molecular data are an indirect inference suggesting selection for colour. The field experiments I’d like to see demonstrating colour advantage seem to have been done, but they’re in a fairly obscure journal from the 1940s. Anyone have copies of Contributions from the Laboratory of Vertebrate Biology of the University of Michigan handy?

Similarly, there are no archaeological pelts that they base their arguments for a recent evolution of light coat colour on. It’s all mathematical models that assume population size, relate strength of selection and variability. To be clear, I’m not coming down on using models, just pointing out what kind of evidence is being used to make the case. To give an example, they note Sand Hills is about 8,000-10,000 years old, but they don’t give an approximate age for the origin of the Agouti mutation in years. 8,000-10,00 years is ~0.4 to 0.5 4N generations of deer mice, and they estimate the Agouti mutation arose 0.05 to 0.18 4N generations ago. And I am not going to pretend I understand what those figures mean or how they calculated them.

I could be badly biased here, because I am an organismal biologist, and this is mostly a molecular biology paper. But if I’m having problems understanding the details, I wouldn’t unleash this as a case study in evolution on students who weren’t graduate level or very close to it. The level of complexity a student would have to master to get a firm grasp on the evidence is high enough that to a lot of undergraduate students, this would be a plausible “just so” story. This research would fail as a textbook example right now, fine work though it is. For this to become a textbook example of evolution in action, I do think that there would have to be better explanations of the existing field experiments, and probably a whole lot of new ones, too.

Reference

Linnen, C., Kingsley, E., Jensen, J., & Hoekstra, H. (2009). On the Origin and Spread of an Adaptive Allele in Deer Mice Science, 325 (5944), 1095-1098 DOI: 10.1126/science.1175826

If creationists ran the DMV

I was reading a new column in the Dallas Examiner attacking evolution that contains an oh-so-familiar refrain: “What does Darwinian evolution have to fear from free scientific inquiry?”

The answer, of course, is nothing. I’ve written about this before here, but I came up with a new analogy to express why researchers are bored and frustrated by creationists.

I imagine most people reading this have a driver’s license. To get it, you had to prove you were capable of driving. You occasionally have to get it renewed.

Imagine that to keep your driver’s license, you had to go through that whole lengthy driving exam – written and in the car – once a week. Every week.

Is that a valuable, productive use of your time? No. It’s a waste.

What would be your emotional response? Boredom, frustration and maybe just a pinch of royally pissed off.

And if people said to you, “If you can drive, why are you so afraid of the driving exam?”, might you have a intemperate moment where you consider making them eat their lower molars?

You have proved that you are road ready. While it’s no guarantee that you’ll ever get in an accident, things normally don’t change so much that what held true one week won’t hold true the next. Why go through all the hassle of proving it again... and again... and again?

While I’ve used “creationist” in the title, but it could be replaced with “anti-vaccer,” “climate change denier,” “birther,” or any of the other denialist lines of though out there. They all use the same argument to impugn and create questions about motives rather than evidence.

Editor’s choice

I just discovered that (A) ResearchBlogging.org has an “Editor’s selection,” and that; (B) a couple of my recent posts have been selected! I am pleased.

The two picked posts concern ankylosaurs and crabs. If you haven’t seen them, please check them out.

Incentives, economy, and science

During an interview on the radio show This Week In Science, astronomer Neil deGrasse Tyson said something to the effect of:

Before it’s anything else, America is a capitalist country.

His point was that American interest in science, science education, and so on, would be driven by its effect on people’s wallets. But it got me thinking about Dan Pink’s recent TED talk on how financial incentives work only for a very limited set of tasks: very rote, defined, mechanical tasks. And I thought, “Is it any accident that this most capitalist of countries did so well throughout the first half of the 20^th century, when so much of the economy was based on rote, defined, mechanical tasks, like manufacturing?”

This is turn got me thinking about Richard Florida’s arguments that the “creative class” is becoming the significant driver of the economy. This fits with Pink’s thesis that we are increasingly being asked to solve “candle problems” in work. And science is about those hard, not easily defined, creative problems most of the time.

If you put those three things together, that America is the pre-eminent capitalist society of the world could, paradoxically, hurt its ability to retain its economic competitiveness.

Holding steady

My review article in Brain, Behavior and Evolution continues to hold its grip on the #2 slot. I am pleased.

Tuesday Crustie: Mud bug

Not only is there a large commercial harvest of Louisiana red swamp crayfish (Procambarus clarkii), and not only is it a terribly invasive pest species in many parts of the world, they are the “white lab rat” of crustacean research. But this picture shows why many people in the southern U.S. call them, “mud bugs.”

From user birdgal5 on Flickr, used under a Creative Commons license.

A bitter taste in your lungs

Smell is the oldest and most basic sense. Smell is the detection of external chemicals, which bacteria, without even having neurons (because they are one-celled), are able to do with ease. Taste is a mere spin-off of smell, as it is also about detection of chemicals, just those in a little higher concentrations a little closer to the body.

A new paper by Shah and colleagues blurs the already fuzzy line between small, taste, and even nociception (detection of tissue damaging stimuli). They examined skin cells in the interior of the throats and lungs of humans. These cells are not neurons. There are many examples of skin (epithelial) cells generating electrical activity (“skin pulses”) that resembles the action potentials of neurons, however.

The skin cells on inside of the airway have lots of little hairlike cilia (pictured), beating away to keep nasty bits out. Traditionally, it’s been thought these just beat, but some cilia have sensory jobs, and the authors decided to see if these might do both.

This project should the advantage of high-throughout molecular techniques. They were able to look for a whack of genes for bitter taste receptors in one go, using microarrays: little chips with dots that “light up” if the right molecule is present. They found four bitter receptors being expressed in these ciliated skin cells.

It’s not fair to the authors to say it was all downhill from there, as there was clearly a lot of hard work, but I think the authors had a pretty easy time conceptually from here on out.

You’ve got receptors in the cells: where are they, specifically? With antibodies, you can show they’re found in the cilia.

You got receptors: are they physiologically active? By put on a bitter chemical on these cells, you can see all kinds of calcium, which is important in cell signaling, running into these skin cells (using fluorescent molecules that detect influxes of calcium ions).

You’ve got a physiological change inside the cell: does that change the beating of the cilia? Yes, you can increase the beating about 25%. I’m guessing this was just detected with regular old optical microscopes.

The last logical question is the one that the paper doesn’t have data to answer directly. If you get one of those bitter chemicals in your lungs, how does the beating cilia get rid of it? This is one question that can’t be answered with the cultured cells that were used for all the experiments above.

Reference

Shah, A., Ben-Shahar, Y., Moninger, T., Kline, J., & Welsh, M. (2009). Motile Cilia of Human Airway Epithelia Are Chemosensory Science, 325 (5944), 1131-1134 DOI: 10.1126/science.1173869

Picture from here.

Comments for second half of August 2009

More than PowerPoint talks about the difficulty of answering the question, “Who are you?” I point to an artistic exploration of the matter.

At Flowing Data, I get pendantic about an interesting graph and the word “data.”

As author of the Better Posters blog, I had to stick my nose in a couple of times on SciCurious’s suggestions for posters at Neurotopia.

Did they say that? Is evolution optional in Texas textbooks?

An editorial in the Corpus Christi Caller takes some shots at the Texas State Board of Education:

(T)he State Board of Education has rarely failed in its efforts to look ridiculous, as when it voted, some time back, not to require biology textbooks to include the theory of evolution.

I think that’s incorrect. It’s hard to tell, since the science standards (which were earlier this year, and which I wrote about at length) are rather different from textbook adoption (which hasn’t happened yet).

If you look at the high school science standards that go into effect next year, section §112.34.(c).7 says:

The student knows evolutionary theory is a scientific explanation for the unity and diversity of life.

There it is, plain as day. It’s a required standard. Textbooks will have to have it in there.

Evolution is not optional in Texas public high schools.

True, Texans should not be proud of their science standards. But at least Texas isn’t the butt of a joke in Futurama. If you missed it last night, the latest movie, Into the Wild Green Yonder, features a gag in the first bit about evolution.

Thank you, Kansas.

First day of class speculation

If I went into class today on the first day of the Fall semester, and said to students, “Anyone who wants a passing grade can give me their name and student number, and I’ll give them a D for the class on the spot,” I wonder...

• How many would take me up on it? (My suspicion is that nobody would.)


• How many would not take me up on it because they think they can do better?


• How many would not take it because they think it’s a trap? (Sadly, I think more students would fall into this category than the former.)


• How many would regret not taking it by the end of the semester?


• How much trouble I’d get in for trying it?

Product of Canada

One of the down sides to having lived in different parts of the world is that you find certain foods that you love. And then you move, and you can’t get them any more. Or only with great difficulty.

Red Rose Tea turned this problem into a virtue in their commercials, with a tag line that many Canadians know:



“Only in Canada, you say? Pity...”

This morning I was shocked when I realized there was something on the shelf I hadn’t seen in eight to ten years...


Dare cookies! In south Texas? What?!

Time slice

Today is the last weekday before our Fall semester starts. I’ve worked hard this summer to get some research projects going. Between my students and myself, there are about four papers nearing completion, which is good.

What is not so good is that I am not feeling the love for teaching this coming semester. This is normally not the sort of thing an instructor should admit, let alone blog about. Let me try to explain why.

Recently, I read something pointing out that administrative and managerial types slice the day into one hour blocks. Those faced with some sort of problem-solving task, be it writing, coding, engineering, or what have you, don’t break up their time into convenient one hour blocks. (I’ve been looking for the original source and can’t find it; sorry. Can anyone help me give due credit?)

We teach classes in one hour clocks. We hold meetings in one hour blocks. And they’re scattered throughout the day and week. And there are zillions of little bits of paperwork that start coming in droves. Authorizations, reconciliations, questions...

I want to finish those research papers so badly. But even though classes haven’t started yet, my days are already getting carved into one hour blocks with meetings and students wanting appointments. I can feel my ability to sit down and do the hard reading, thinking, writing, and figure creation, needed to grind away at those research projects for long, uninterrupted periods being sliced up into small, unproductive slivers of time.

How the internet sees me

From the MIT project Personas. This is meant to be an artistic installation, from the looks of things, but I do wish that there was some more explanation of the proportions and colours the project generates.

And there doesn’t seem to be a “science” tag. Pity.

Hat tip to Nerdy Christie.

Additional: New Scientist has a good story on this piece of art.

Were glyptodonts’ clubbed tails weapons?

Yesterday, I wrote about ankylosaurs’ clubbed tails. Today, I get another new paper on another group of vertebrates to have clubbed tails, the massive armored mammals called glyptodonts. To the best of my knowledge, these two groups may be the only vertebrates to have massive bony clubs on their tails. This paper is also concerned with whether glypotodonts could use their tails as weapons, but takes a decidedly different approach.

Blanco and company are trying to characterize a feature in the glypotodonts’ clubbed tail that we are familiar with in our own clubs: the center of percussion. Annoyingly, the authors don’t define this, or explain why it is interesting, in their introduction.

The center of percussion is a “butter zone” or “sweet spot.” If you wield a club – say, a baseball bat (which the authors use in their figures) or cricket bat – the center of percussion is the point where hitting something has the least effect on the closer joints. Hit away from that point, and the force is transmitted through rest of the structure. If you hit a ball too close to your hands, you’ll feel it more, and the flow of your movement is interrupted.

How this relates to the “club as weapon” hypothesis is that glyptodonts’ clubs may have had thick spikes or pads on the club itself. If they were there, they were not bony, so didn’t preserve, but the structure of the clubs is suggestive. If the tails were being used as clubs, you would predict that the center of percussion would be right in the center of the club.

Blanco and company worked with the fossils of five different glyptodont species, whose clubs ranged in mass from an estimated 2 kg to a whopping (pun intended) 50 kg or so. While some glyptodonts had tails that were flexible,in these five, some of the bits at the end of the tail are completely fused, making it more like a true, rigid club.

They measured the sizes of the tail bones, estimated their mass and density, and ran the numbers to estimate the location of the center of percussion. They varied their estimates of the bone density, but this didn’t move the predicted center of percussion much at all. The authors found that the center of percussion was pretty much square in the center of the clubbed end of the tail, as predicted, nicely sitting in among where those spikes or pads are thought to be.

This paper has an hypothesis in common with the ankylosaur paper in that it suggests the club was being used, not as a defense against predators, but as a weapon in fights with other glyptodonts. I am skeptical, because when you look at animals that fight within other members of their species, the weapons are at the front end: crayfish claws, mountain sheep horns, elephant tusks... The list goes on and on.

Despite my skepticism, there seems to be fossil evidence of the sort I was talking about yesterday that support it: broken bones and wounds in glyptodont fossils that could have been caused by another glyptodont. But why glyptodonts and ankylosaurs alone should have stuck their nasty bits at the rear end is a strange evolutionary puzzle.

Reference

R. Ernesto Blanco, Washington W. Jones, & Andrés Rinderknecht (2009). The sweet spot of a biological hammer: the centre of percussion of glyptodont (Mammalia: Xenarthra) tail clubs Proceedings of the Royal Society B : 10.1098/rspb.2009.1144

Glyptodont picture from here.

I’m grotesque

From the What font are you? quiz.

Were ankylosaurs’ clubbed tails weapons?

I’m going to dare to step way outside my research expertise on this post, and look at a paper just because I love me some dinosaurs. I particularly love ankylosaurs; there’s one within arm's reach in my office. Ankylosaurs are often depicted in art locked in combat with a savage meat eater like Tyrannasaurus rex, mainly relying on its armor, but wielding one massive weapon: a huge bony club at the end of its tail.

I was disappointed to learn that the ankylosaurs I had as a kid (and that I still have on my desk) didn’t really exist, but were composites of many different species. Now, will Victoria Arbour destroy another childhood memory with her analysis of whether ankylosaurs could really use their clubbed tails as weapons?

The first couple of paragraphs made me quaver in my decision to try understanding this paper. I have no idea what “postzygapophyses” are, except that they’re some part of skeletal anatomy. But I march on to the descriptions of the X-rays slices they did of some skeletons.

Arbour estimated of the placement of tail muscles by looking at tendons that fossilized, and using crocodiles as a model. She suggests that the tail could be bent sideways, but says nothing about swinging it up, as is often depicted in art.

To figure out the forces the animal might have been able to generate by swinging the tail, Arbour crunches some numbers using estimates of muscle mass, inertia, and so on. Unfortunately for a casual reader like me, the number presented are not linked to anything that I might reasonably be able to relate to. That comes in the discussion, fortunately, where the $64,000 question starts to take shape: Could these clubbed tails do damage?

For some of the ankylosaurs with small clubs, Arbour argues, probably not. But some of the animals with larger clubs probably could break bones. Since the shear forces needed vary from bone to bone, Arbour suggests future studies might try to quantify the strength of leg bones of meat eating dinosaurs as well as ribs of ankylosaurs.

Arbour is more interested in the latter possibility, in fact: she suggests that the size of the clubs is such that juveniles probably did not have very large clubs, which she argues means they are unlikely to be defensive weapons. Instead, she thinks the clubs may have been used in ankylosaur on ankylosaur competition. This may be testable. Recent research on ceratopsian dinosaurs (like Triceratops) showed injuries consistent with the horns being used for competition. If ankylosaurs were clubbing each other, the breaks in the bones should be preserved.

So the notion of ankylosaurs using their tails as weapons may not be completely wrong, although the hypothesis has taken a bit of a beating here. (Pun fully intended!)

Reference

Arbour, V. (2009). Estimating Impact Forces of Tail Club Strikes by Ankylosaurid Dinosaurs PLoS ONE, 4 (8) DOI: 10.1371/journal.pone.0006738

Tuesday Crustie: Dappled

Periclimenes brevicarpalis.

From budak on Flickr, used under a Creative Commons license.