Wednesday, February 18, 2009

And it's not just the gammas...

(Sorry for all the insectoid posts; Science just seems to have the most interesting articles on our six-legged friends lately!)

It's not just gamma male beetles that benefit from fake-outs. According to an article by Barbero et al., some species of butterfly also benefit from mimicry--of ants, of all things.

Ant society is very complex; most species include a number of different "genders" and societal roles, all of which are rigidly defined. (Emancipation has not yet come to the ant world.) Certain castes of ants are more valuable, and therefore more highly protected, than others. The extreme of this is, of course, the queen, who receives the most care and attention.

Although most of the communication necessary to keeping such a complex society running is chemical (e.g., pheromones) and physical (i.e., physical contact), apparently some of it is acoustic. Adults in certain ant subfamilies can produce "stridulations" (which I assume sound something like scraping noises, although I could be wrong) to communicate. Within these subfamilies, different castes produce different sounds (and larvae and pupae produce no sounds at all).

A number of ant species are also parasitized by the larvae and pupae of other insects. Barbero et al focused specifically on the butterfly species Maculinea rebeli, which parasitizes the ant species Myrmica schencki. M. rebeli larvae and pupae can infiltrate M. schencki nests and fool the ant workers into taking care of them. A significant characteristic enabling the butterfly caterpillars to survive in the ant nest is their ability to produce chemicals that mimic the chemicals produced by the ant larvae.

However, M. rebeli larvae and pupae apparently show higher "social status" than would be expected simply from the chemical mimicry. For example, M. schencki workers will rescue M. rebeli larvae and pupae instead of "dummies" that have been painted with the same chemical mimics. In addition, M. schencki queens will sometimes treat the butterfly larvae and pupae as rivals; at the same time, the ant workers treat the butterfly larvae like queens. This discrepancy led Barbero et al to guess that perhaps the butterfly larvae and pupae are able to produce acoustic signals that increase their status in the ants' social heirarchy.

As it turns out, they may be right. M. schencki workers and queens do produce distinct stridulations (i.e., they sound different to the other ants), and M. rebeli larvae and pupae produce sounds that are more similar to the queen ant sounds than to the worker ant sounds.

To test their hypothesis, Barbero et al carried out a number of tests. First, they recorded the sounds produced by the ant workers and queens. They played those sounds to "naive" worker ants. (They also exposed control groups to white noise and to silent speakers.) The worker ants showed more interest in the ant noises than the white noise or the silent speakers. In addition, the noises from the queens caused the workers to become more alert and to assume postures that are associated with "serving" the queens. This test confirmed that worker ants do respond to acoustic signals from other ants.

Next, the researchers recorded sounds from butterfly larvae and pupae. They played those sounds to similarly "naive" worker ants. The ants responded to both larval and pupal calls in the same way they responded to the queen ant calls.

Based on their observations, Barbero et al conclude that M. rebeli larvae and pupae are first able to enter an M. schencki nest through chemical mimicry. Once they are inside, however, acoustic mimicry may also play an important role in preventing the ants from rejecting them.

Barbero, Francesca, Jeremy A. Thomas, Simona Bonelli, Emilio Balletto, and Karsten Schönrogge, 2009. "Queen ants make distinctive sounds that are mimicked by a butterfly social parasite." Science 323: 782-785. doi: 10.1126/science.1163583

More insect phenotypic funkiness

Like the male members of many species, male beetles fight over female beetles. And, like male deer and antelope, many male beetles sport formidable (for a beetle, anyway) horns, spines, and mandibles, which they use to intimidate (if not outright harm) other males. In the February 6 issue of Science, Rowland and Emlen report that some male beetles take a different tack: instead of fighting over the ladies, they pull an Achilles and "dress" like them.

Rowland and Emlen conducted statistical analyses of body size and horn, mandible, or spine length for several different species of beetles. Most previous analyses had assumed only two main male phenotypes for each species (e.g., big horns and small horns, with hornless males being classified in the "small horns" phenotype). Rowland and Emlen, however, found that several species of beetles actually show facultative male trimorphism--that is, the males actually demonstrate three distinct phenotypes (alpha, beta, and gamma). Alpha males have large bodies and large horns (or mandibles, or spines). Beta males have smaller bodies and smaller horns (mandibles/spines). Gamma males have the smallest bodies and no horns (you get the idea).

The differences in phenotype are facultative because they don't seem to be related specifically to genotype. Instead, the main factor determining whether a male is alpha, beta, or gamma seems to be his body size at maturity--beetles that get lots of food and good living conditions end up as alpha males (big bodies = big horns), while beetles that get less food and are smaller at maturity end up as betas or gammas.

Alpha, beta, and gamma males also seem to employ somewhat different mating strategies. Alpha males have the typical pissing contests for access to mates--for example, some alpha males will guard the burrows where the ladies are living, and fight off all comers. Beta or gamma males, though, are sneakier: they might dig side tunnels into the burrows and cuckold the alphas without ever having to fight them. In some other species (e.g., cuttlefish), "gamma"-type males actually get in with the ladies by "cross-dressing"--for example, some male cuttlefish can change color to mimic female cuttlefish, thus allowing them to get in close enough to mate with the females while the other males are busy showing off.

According to Rowland and Emlen, previous studies (and phenotypic analysis methods) have assumed that the majority of beetles display male dimorphism, rather than trimorphism. They suggest that alternative analyses may be necessary to detect trimorphisms--apparently, some of the traditional analyses did not detect all three male morphs in the beetles they studied.

I suppose the moral of the story is, if you're an alpha male, you might want to check the skirts of the ladies in your harem!

Rowland, J. Mark, and Douglas J. Emlen, 2009. "Two thresholds, three male forms result in facultative male trimorphism in beetles." Science 323: 773-776. doi 10.1126/science.1167345

Thursday, February 12, 2009

Darwin in Context

I've been trying to figure out what to write about for my Blog for Darwin entry. I've been reading Origin, but I haven't finished it yet (the last few chapters are not nearly as interesting as the first few). Even so, as I've been reading, I haven't really been struck with any brilliant insights or profound thoughts. One thing that has occurred to me a lot, however, is just how much we've learned since Darwin's time. So, I thought that for my BfD contribution, I would outline what was going on in science while Darwin was doing his thing. I'm hoping it might give some insight into what Darwin did and didn't know, and how his ideas may have been influenced by what was going on around him.

Disclaimer: I am not a historian; the summary below is not intended to be exhaustive. I'm mainly going to focus on the big ideas and events; if you're interested in the gory details, there are a plethora of excellent books out there to satisfy you, I'm sure. Also, please note that I've done my best to verify all of the information below, but I'm not an expert in this stuff. Any errors are solely my responsibility. If you find any, please let me know!

By the 1800s, the study of chemistry was becoming modernized. In the 1600s and 1700s, naturalists began to discover general laws that govern natural processes. Both Boyle's law and Charles's law (on the properties of gases) had been discovered by the early 1800s; a number of gaseous elements and compounds (including oxygen, nitrogen, and nitrous oxide) had been isolated and described.

John Dalton proposed his atomic theory in the early 1800s; although his concept of the atom (i.e., hard, solid, indivisible sphere) has since been replaced, his work on the conservation of mass and the law of definite proportions still underlies much of modern chemistry. His law describing the partial pressures of gases in a mixture is still used today.

The early 1800s also saw the publication of Avogadro's hypothesis (i.e., that equal volumes of gases at the same temperature and pressure contain the same number of molecules).

In the mid 1800s, Lord Kelvin proposed the idea of absolute zero and an absolute temperature scale.

What Darwin didn't know: Most elements were not identified or isolated until after the 1860s. Electrons were not discovered until the late 1800s; the concept of the atom as we know it today (i.e., nucleus of protons and neutrons surrounded by electrons) was not developed until the twentieth century. The nature of chemical bonding was also unknown in Darwin's time, as was the periodic table and the notion of periodic properties.

Electricity and magnetism were the order of the day in eighteenth and early nineteenth century physics. Franklin "discovered" electricity in the late 1700s; Ohm's law was proposed in the 1820s; Oersted discovered evidence of a magnetic field around a current-carrying wire in 1820; Faraday discovered electromagnetic induction in the 1830s; Joule and Helmholtz proposed the law of conservation of energy in the 1840s.

Newtonian mechanics were well established by the 1800s.

What Darwin didn't know: Radioactivity, quantum physics, relativity, and nuclear physics were decades to centuries away in Darwin's time.

As Origin does a pretty decent job of summarizing what was going on in evolutionary biology (such as it was) at the time it was written, I won't spend space on that here. In the mid-1800s, the idea that all living things are made of cells was just beginning to take hold; spontaneous generation was beginning to be discredited. Taxonomy was becoming more rigorous. Paleontology was starting to become a well-established field; most naturalists accepted that the majority of the fossils being unearthed around the world represented organisms that no longer exist.

What Darwin didn't know: Genetics and the theories of inheritance had not been discovered when Darwin did his work; a story I've heard (which I have not verified) is that Darwin had Mendel's papers on his desk when he died. Molecular biology, most of microbiology, and, of course, genomics were completely unknown. The germ theory was still a few years off, as was the discovery of many disease-causing microorganisms.

Earth Science
Naturalists were just beginning to come to grips with Earth's immense age during the late 1700s and early 1800s. The best consensus was that Earth was a few hundred million years old at most; these estimates were based on rates of physical processes (such as sedimentation and cooling). Radioactivity was unknown, so both a method for accurate dating and a mechanism for keeping Earth "warm" for long periods of time were lacking.

However, the principle of uniformitarianism was pretty well accepted, having been proposed in the late 1700s. As I mentioned above, paleontology was becoming more rigorous and "scientific," although some of the interpretations of fossils--especially dinosaurs--were rather interesting.

The idea of a global geologic column or time scale was becoming increasingly popular. Indeed, Darwin makes many references to the accepted contemporary time scale (although the time scale of the mid-nineteenth century bears little resemblance to our modern one).

What Darwin didn't know: The theory of plate tectonics was still about a century away. Radiometric dating (and an understanding of how radioactive decay has heated the planet) wouldn't be developed for quite a while, so Earth's true age was unknown to Darwin. In addition, research into the fossils and strata of the planet was generally restricted to Europe and North America, so Darwin's (and everyone else's) ideas about geologic history (and paleontology) were accordingly limited.

Well, there you have it: the two-bit tour of the state of science in the 1860s. I hope this is helpful to someone. If I had time, I'd go into more detail...yet another item to add to my "things to do when I win the lottery" list!

Tuesday, February 10, 2009

If the Egyptians had only known...

According to legend, one of the way the Egyptians were punished in the time of Moses was with a swarm of locusts.

Locusts are insects that look a bit like big grasshoppers. They're a classic example of what's called phenotypic plasticity. An organism's phenotype is basically its observable characteristics--behavior, color, size, etc. (Phenotype is the outward expression of genotype; genotype is the specific group of alleles that an organism has. Most--all? I'm not sure--genes have at least two alleles, or "flavors." The classic example is, of course, Mendel's peas; the gene that controls flower color in pea plants has two alleles, purple and white. A pea plant's flower-color genotype is the particular combination of alleles that it has; its flower-color phenotype is the particular color of flower it produces.)

Organisms such as locusts that demonstrate phenotypic plasticity can undergo significant changes in behavior, appearance, etc due to changes in their surrounding environment. Locusts are a classic case because the change is so dramatic. If you take two locusts and put them in a box, they will pretty much avoid each other--that is, assuming they're demonstrating the "solitarious" phenotype. This is pretty much the default position for locusts; most of the time, they hang out by themselves (not a lot of singles bars in their neighborhoods, I guess).

Now if you had put, say, 20 or 30 solitarious locusts in that box and shut them in for a couple of hours, they would be quite changed when you opened the box. They would be swarming together, and they would have changed in appearance (from kind of boring and green to a rather striking, Steelers-like combination of yellow/tan and black...sorry, couldn't help it). They would be demonstrating the "gregarious" phenotype.

Solitarious (top) and gregarious (bottom) desert locusts. Image from Dr. Tim Matheson, University of Leicester

Locusts in the gregarious phase are the stuff of legend. These are the critters that mow crops down to the roots and blacken the skies. (Presumably, the Egyptians crowded their locusts.)

The cause of the transition from solitarious to gregarious has been known for a while, at least in broad strokes: being in the presence of lots of other locusts makes a locust more gregarious. In a recent article in Science, Anstey et al identify the mechanism that triggers the transformation.

There are two different sets of stimuli that can make a locust more friendly: mechanical and "cephalic." Mechanical stimulation involves being jostled by other locusts; in contrast to most humans, most locusts become more friendly when strangers stroke their legs. Cephalic stimulation involves the sight and smell of other locusts; locusts apparently have really great makeup and cologne. Both types of stimuli cause the locust's central nervous system (CNS) to produce (what else?) serotonin. (Yes, that serotonin.)

Previous researchers established that serotonin levels are higher in locusts undergoing the solitarious-to-gregarious transition. Anstey et al set out to determine the limits of this relationship. They did four main experiments: first, they figured out whether artificial stimulation of the individual sensory pathways could stimulate serotonin production and gregariousness. Then, they tested whether serotonin antagonists (i.e., chemicals that block the action of serotonin) could prevent the onset of gregarious behavior. Third, they determined whether artificially increasing serotonin levels was enough to induce gregariousness. Finally, they determined whether giving the locusts a serotonin precursor (i.e., a chemical that is easily converted to serotonin) increased their sensitivity to environmental stimuli.

In the first experiment, the researchers either stroked the hind legs of solitarious locusts, stimulated the nerve connecting the legs to the CNS directly, or put the locusts in a cage that allowed them to see and smell (but not touch) other locusts. In all cases, the locusts switched from solitarious to gregarious, and serotonin levels increased, suggesting that either type of stimulation is sufficient to induce gregariousness.

Next, they injected some of the locusts with serotonin antagonists (they also, of course, injected others with just saline--this was the control group). After the injections, the treated locusts (the ones that received the antagonist) were significantly less responsive to stimuli than the control locusts; treated locusts did not become gregarious, even when exposed to stimuli that caused the control locusts to boogie down. This relationship showed that inhibiting the action of serotonin prevents the "phase change."

In the third experiment, Anstey et al applied serotonin directly to the locusts' nerves (again, they also used a control group that received just saline). They also injected a third group of locusts with a serotonin agonist (i.e., a chemical that increases the activity of serotonin--the opposite of an antagonist). The treated locusts became much more friendly, but the control locusts remained aloof. In other words, just increasing serotonin levels (without actual stimuli) can make solitarious locusts more gregarious.

In their final experiment, the researchers determined whether increasing the ability of the locusts to produce serotonin would cause them to become more gregarious after only a small amount of stimulation. Typically, a solitarious locust has to hang out with other locusts for a couple of hours before putting on its party shoes. However, when solitarious locusts were injected with a serotonin precursor, 30 minutes of exposure was enough to get them dancing.

There's some hope that these results might lead to new possibilities for locust control. Individually (i.e., in the solitarious phase), locusts aren't too much of a problem--no more so than, say, grasshoppers, really. It's only when they start to swarm that they become economically disastrous. If a way could be found to prevent locusts from become gregarious, even when crowded, then locust swarms could be controlled. (Too late for Rameses, of course.) Such possibilities are still in the future--currently, there is no locust-specific serotonin antagonist that can be applied appropriately--but it does give some hope.

Until then, there is one thing we can definitely conclude: keep the locusts away from the Prozac!

Anstey, Michael L., Stephen M. Rogers, Swidbert R. Ott, Malcolm Burrows, and Stephen J. Simpson, 2009. "Serotonin mediates behavioral gregarization underlying swarm formation in desert locusts." Science 323: 627-630. doi 10.1126/science.1165939

Stevenson, P.A., 2009. "The key to Pandora's box." Science 323: 594-595. doi 10.1126/science.1169280

(Yes, I know this isn't quite 1,000 words. But it's pretty darned close!)

Blogging for Darwin

I joined the Blog for Darwin blog swarm (which means I have to actually finish Origin soon, so I have something to write about). Check it out--it's pretty cool.

I haven't decided yet what to write about; I'm having a hard time coming up with anything super profound. I'll wait and see if any inspiration strikes as I keep reading.

Thanks to Newton's Ocean for the link.

Thursday, February 5, 2009

From opposite ends of the spectrum

Apparently, the downturn in the economy is causing some of us to become a bit too obsessed with language.

On the other hand, some are just giving up in disgust (or despair?).

And some are robbing stores with bat'leths.

(Thanks to Lou for the first link, erv for the second, and Gwynne for the third.)