It’s An Evolutionary Trap!!!

“A Cuban Tree Frog tries to eat a Christmas light. Photo by James Snyder. National Geographic My Shot”

You might be wondering why a frog would eat a Christmas light, but it may have simply confused the glowing bulb for a luminescent insect it normally feasts on. This is just one example of how even the mundane ways we’ve changed the environment can trip up other creatures–and sometimes with evolutionary consequences. As Carl Zimmer explains in a blog post over at The Loom,

We have altered the environment in a vast number of ways, both small and large. And when animals try to read the cues from our human environment, they can get tricked. They can end up doing something that kills them, loses them the opportunity to reproduce, or simply wastes their time. Scientists call these situations evolutionary traps.

Hydropsyche pellucidula
Caddisfly species Hydropsyche pellucidula
While the Cuban tree frog ultimately spit out its mistaken meal and survived its run-in with holiday lighting, other organisms are not as fortunate.

When caddis flies become adults and are ready to mate, they need to get to a body of water. Without Google Maps to help them, they do what their ancestors have done for countless generations: they take advantage of the fact that ponds and streams change the reflection of moonlight, altering its polarization. Unfortunately, large plate glass windows can polarize light in the same way, with the result that caddis flies will sometimes blanket the glass, mate, and lay their eggs there.

Carl Zimmer goes on to mention several other examples of evolutionary traps, like the Australian beetles that vigorously try to mate with empty beer bottles, and also discusses ways that we might disarm them. Head over there and have a read.

It's an evolutionary trap

I couldn’t resist.


Battle of the Sperms

Inside every Drosophila melanogaster (fruit fly) female is a battleground where sperm from two different males jockey with each other for the honor of fertilizing her eggs. By sequentially mating females with males genetically-engineered to produce sperm that glow either green or red (see video below), scientists have been able to directly observe sperm competing in what looks like the fruit fly version of Tron. Color coding the sperm in this way allows researchers to distinguish one male’s sperm from another’s and determine who the winners are.

“Sperm from two different males genetically-engineered to express either green or red fluorescent proteins compete within the female reproductive tract of the fruit fly Drosophila melanogaster.”

Surprisingly, it’s not always the fastest sperm that wins.

Continue reading

Emasculated by the Asian Glow

Like for many young adults, college was an opportunity to “find” myself and, in particular, connect with my Asian Americanness. In fact, one of the first college courses I enrolled in was Asian American Literature in which one of the prevailing themes in the class was how history and media depicted Asian men as passive, subservient, effeminate or asexual individuals. These emasculated stereotypes would set the stage for my own experience in college, where I learned that masculinity is often measured by how much alcohol you can drink.

It was in this light that I found my own “manhood” challenged because, like many Asians, when I drink my face betrays me. I flush and turn red, often after having just one drink. But while the spectacle of an Asian flushing  is not uncommon, in my experience it almost always solicited comments that were variations on one stereotype: Asians can’t drink.

“Cut that Asian kid off.” 

“What? You’re already drunk? After one drink? Oh right he’s Asian.”

“He can’t handle drinking. He’s Asian. Look, he’s already red.”

Dismissive and disparaging comments like these accomplished two things: they labelled me as “other” and marked me as less than by some arbitary and artificial measure of masculinity. Worse, though, was that inevitably someone would add insult to injury by trying to explain the biology underlying my deficits…incorrectly.

“It’s because you don’t have the alcohol dehydrogenase gene.”

“Your alcohol dehydrogenase doesn’t work.”

To set the record straight, the “Asian Glow” results from buildup of acetaldehyde, an intermediate of alcohol metabolism. The first step in metabolizing ethanol is its conversion into acetaldehyde by the alcohol dehydrogenase enzyme (ADH1B).  Acetaldehyde is, in turn, converted into acetic acid, a reaction catalyzed by the aldehyde dehydrogenase enzyme (ALDH2). Sufferers of alcohol flush syndrome have either a mutation in ADH1B that supercharges the enzyme and dramatically increases the rate that it churns out acetaldehyde from ethanol or a mutation that renders ALDH2 defective in converting acetaldehyde into acetic acid. The consequence of either mutation is the same: a traffic jam of acetaldehyde. The accumulation of acetaldehyde in the system leads to the dilation of capillaries in the face, causing the stereotypical flush. This is followed by early symptoms of hangover such as lightheadedness, nausea, and palpitations– signs indicating that you should probably stop drinking. Carriers of either mutation often feel the effects sooner and more severely.

These undesireable effects might explain the lower incidence of alcoholism amongst East Asian men. After all, why would you keep subjecting yourself to such torture? In fact, these effects mimic to a lesser extent reactions to disulfiram, an inhibitor of ALDH2 activity that is used to treat alcoholism. These mutations in ADH1B and ALDH2 could, therefore, serve as built-in anti-alcoholism mechanisms. Humiliating effects of flushing aside, acetaldehyde also carries with it a significant health risk as it is a known carcinogen. Consistent with this, these mutations in ADH1B and ALDH2 correlate with a higher incidence of esophageal cancer. Furthermore, the mutation in ALDH2 in particular may reduce both the effectiveness of nitroglycerin in treating angina and survival after a heart attack, while increasing the risk for neurodegenerative diseases such as Alzheimer’s. 

With these health risks in mind, why would these mutations be so prevalent Asians? From an evolutionary standpoint, the high frequency of these mutations in people of East Asian descent (>59% carry the ADH1B∗47His variant, while approximately 40% carry the ALDH2∗487Lys variant) suggests that these mutations in ADH1B and ALDH2 were positively selected for in recent human history. Why would evolution select for mutations that increase levels of the toxin acetaldehyde? Under what conditions would these mutations provide an evolutionary advantage? And, more importantly, is there an evolutionary basis for drinking wussiness in Asians? While these questions remain unanswered, scientists have proposed several hypotheses. One explanation proposes that the higher concentrations of acetaldehyde resulting from these mutations may act as a defense against infections by parasites that are unable to metabolize acetaldehyde. Alternatively, the adverse reactions to alcohol in individuals with these mutations may have provided greater protection against alcoholism or risks associated with alcohol consumption. For instance, given that alcohol consumption and  Hepatitis B virus (HBV) infection can synergistically increase the risk for liver cancer and considering that the geographic distribution of the mutation in ALDH2 overlaps with areas endemic for HBV, the mutation in ALDH2 may have mitigated the effects of HBV infection. Similarly, it has been proposed that sensitivity to alcohol could be a defense mechanism that limits consumption of alcoholic or fermented foods containing toxic or disease-related compounds. All of these hypotheses, however, remain speculative.

While this version of the emasculated Asian male stereotype bothers me on a visceral and instinctual level, I don’t subscribe to this view of masculinity defined by alcohol consumption. There are countless things I’d rather do than trying to prove myself by drinking to oblivion and end up hugging cold, hard porcelain at the end of the night. But I can’t say the same is true for all Asian Americans (women included). Regardless of whether we come to a concrete evolutionary explanation for the prevalence of these mutations, the biology indicates that for a significant number of Asians drinking poses potentially more severe health problems than just alcohol flush, low tolerance, or hangovers alone. These are health concerns that we must keep in mind as Asian Americans conform to a culture that places significant emphasis on drinking, especially in cases where they are pressured into trying to break the stereotype that “Asians can’t drink” because for many of them, they’ll be fighting biology also. 

Related Reading:

Check out these posters celebrating “Asian American masculinity, with minimalist depictions of five different Asian American icons: George Takei, Richard Aoki, Bruce Lee, DJ QBert and Jeremy Lin.” (h/t @angryasianmanasian american “manhood” poster series for sale

How Asian Americans Are Portrayed in U.S. Media. Who Should Be the Next Asian Old Spice Guy? (Answer: Me, obviously)

The Biology of Star Wars: Are exogorths just really big caecilians?

     ResearchBlogging.orgDon’t be fooled, what you’re looking at is a recently discovered species of a limbless amphibian called a caecilian. They prefer tropical climates and can be found in South and Southeast Asia, East and West Africa, and parts of South America. These creatures are burrowers and have adapations that make them well-suited for life underground. Their heads are reinforced through the fusion of bones in the skull and they are capable of using their bodies like a piston to drive through earth. Caecilians also have “primitive” eyes that allow them to see light and dark. Some species are known to secret toxins from their skin like other amphibians do.

     As hinted by the picture, caecilian mothers tend to their offspring by building a nest and staying with her eggs until they hatch. Unlike other amphibians that have a larval stage (think tadpoles), caecilians emerge from their eggs as miniature adults. Some species of caecilians continue to care for their newly-hatched young through an interesting exfoliating behavior: (see video).

“What’s the secret to my youthful, radiant glow? I make my kids eat my skin.”

Evolution of Caecilians     The story of caecilian evolution is rather murky given their incomplete fossil record. In fact, the evolutionary history of the living amphibians (frogs, salamanders, & caecilians) remains  a hotly contested debate in the field of batrachology(study of amphibians). Who knew! While its accepted that frogs, salamanders, & caecilians all belong to the subclass Lissamphibia (a subclass of Amphibia), there is disagreement about the evolutionary relationship of these amphibians with now extinct subclasses of amphibians. Currently, there are three competing hypotheses:

  • current day amphibians are monophyletic, meaning they all share a common ancestor with either 1) Lepospondyli (a subclass of “newt-like, eel- or snake-like, and lizard-like” tetrapods) or 2) Temnospondyli (a subclass of primitive, amphibian tetrapods)
  • current day amphibians are polyphyletic, meaning that they were derived from different ancestors 3) with frogs and salamanders being more closely related to Temnospondyli and caecilians more closely related to Lepospondyli
     Now depending on which strategy is used to build the phylogenetic tree–it’s like a family tree that shows the degree of evolutionary relatedness–different conclusions are reached. Using morphology and the fossil record, Anderson et. al (1) place the caecilians among the Lepospondyli and frogs and salamanders with the Temnospondyli, which supports hypothesis 3:

     However, taking a molecular clock approach Diego San Mauro (2) estimates that caecilians split from the other amphibians around 315 million years ago which is a timeframe more in line with hypothesis 1 or 2:
     The molecular clock is a technique that is used to estimate when in geologic time two species diverged. When species diverge from each other, scientists noted that the DNA sequence between the two species will change over time at a fairly constant rate. Scientists thus can use the number of DNA sequence changes (percent difference) in combination with this rate to back calculate the time at which the divergence occurred. The problem is determining the rates at which these changes occur. Here is a great example/analogy from The Molecular Clock and Estimating Species Divergence:

“Assume, for example, that researchers have two DNA sequences that have a content difference of 5%. From this information alone, it is not possible to tell whether these sequences have diverged from each other at a rate of 1% per 1 million years over a period of 5 million years, or whether they have diverged at a fivefold higher rate over a period of just 1 million years…This is equivalent to trying to determine the average speed of a car merely by looking at its odometer. To deduce the average speed, one would also need to know the length of time for which the car has been travelling.”

     To circumvent this, molecular clocks need to be “calibrated” against the fossil record which can tell us when an evolutionary event occurred, such as the split between bird and lizards lineages. Armed with that date and DNA sequence data of modern day birds and lizards it is possible to calculate the rate at which DNA sequences change between birds and lizards. For amphibians, however, this is problematic because the fossil record is pockmarked with gaps, so San Mauro calibrated the molecular clock against the 3 evolutionary events: the split between reptiles and mammals, the split between the Archosauramorpha and Lepidosauromorpha reptiles, and the split between birds and reptiles. The molecular data he compared was the DNA sequence of 23 different genes from 18 representative species of current day amphibians. As more of a molecular biologist, I am biased toward San Mauro’s approach. However, both strategies could benefit from a more complete amphibian fossil record, which could not only move some of the branches of the morphologically-based phylogenetic tree but also provide for a better calibration of the molecular clock. Alas, the controversy lives on.

But I thought this post was about the biology of Star Wars…
     Sorry for the bait and switch. Now after all this talk about evolution and after watching the caecilian video (especially the yawning juvenile), let me come back to my original premise: Are exogorths just gigantic caecilians? You know, the giant space slug that tries to eat the Millennium Falcon:

According to Wookieepedia, exogorths are a silicon-based, “gigantic species of toothed gastropod” that generally reaches 10m in length. Thesespace slugs inhabit the caves and craters of asteroids where they feed on minerals, stellar energy fields, and mynocks. They also reproduce “asexually by fission. Once an adult slug reached a certain size, a chemical trigger would cause it to split apart into two identical slugs. The two new space slugs would immediately become self-reliant. Space slugs also molted as a result of their growth.”

Ok, so maybe I was wrong about that one, but you can’t tell me they don’t look a lot alike.

Next up in the Biology of Star Wars series, I’ll cover the ever divisive midichlorians.
Correction: In the original post I misspelled exogorth as exogarth.
Picture credit for amphibian taxonomy.tif  (edited by me)

1. Anderson, J., Reisz, R., Scott, D., Fröbisch, N., & Sumida, S. (2008). A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders Nature, 453 (7194), 515-518 DOI: 10.1038/nature06865

2. San Mauro, D. (2010). A multilocus timescale for the origin of extant amphibians Molecular Phylogenetics and Evolution, 56 (2), 554-561 DOI: 10.1016/j.ympev.2010.04.019

Happy Birthday Charles Darwin!

Evolution can’t catch a break.     

     Today marks Charles Darwin’s 203 birthday. It’s been 153 years, since On The Origin of Species was published and yet according to a 2009 Gallup poll only 40% Americans “believe” in evolution (more on this poll in a moment). Of particular concern, four states are considering legislation that would impact or limit teaching evolution in highschool. Kimberly Winston reports

“One of the bills, New Hampshire’s House Bill 1148, not only singles out evolution, but would require teachers to discuss its proponents’ ”political and ideological viewpoints and their position on the concept of atheism.” 

— In the Indiana Senate, a bill would allow school districts to

‘’require the teaching of various theories concerning the origin of

life within the school corporation.” That bill has already passed a statehouse

committee and was scheduled for a vote on Jan 31.

— The “Missouri Standard Science Act” would require the equal treatment of evolution and “intelligent design,” an idea that the universe was created by an unnamed “designer.” A second bill would require teachers to encourage students “to explore scientific questions, learn about scientific evidence, develop critical thinking skills, and respond appropriately and respectfully to differences of opinion about controversial issues, including biological and chemical evolution.”

— A bill in the Oklahoma Senate would require the state’s board of education to help teachers promote “critical thinking, logical analysis, open and objective discussion of scientific theories including, but not limited to, evolution, the origin of life, global warming, and human cloning” if a local school district makes that request.

— A second bill in the New Hampshire House would require science teachers to instruct students that “proper scientific inquir(y) results from not committing to any one theory or hypothesis, no matter how firmly it appears to be established.”

— A bill in Virginia would make it illegal for state colleges to require a class that conflicts with a student’s religious views. Critics say that would enable a student to receive a biology degree, for example, without studying evolution if he or she objected to it.

     As Brown University Professor Ken Miller points out, “Our Darwin problem is really a science problem. The easier it becomes to depict the scientific enterprise as a special interest immersed in the culture wars, the easier it becomes to reject scientific findings. We see this everywhere in American culture and politics today, from the anti-vaccine movement to the repeated assertion that global warming is a deliberate “hoax” rather than a straightforward conclusion driven by reams of scientific data.” 

What’s in a Question?

The problem with polls is that it’s all in the way the question is phrased. The 2009 Gallup poll posed the question as such:


By framing the question in the context of belief, it places evolution in the realm of faith and by extension equates the theory with religion. This makes it easier for the religious community to reject evolution. However, the currency of science is not belief. Science deals in knowledge ascertained by testing proposed explanations (hypotheses) of phenomena. Where faith is essential for religion, proof and evidence is required for science. Furthermore, the poll assumes that the respondent knows or understands what the theory of evolution is. Without properly defining it, it doesn’t take into account misconceptions or preconceived notions that the public often has in regard to the theory. Practically speaking, it would be impossible to properly define the theory in the context of a poll, but a more honest attempt could be made.

The question should be posed this way:

I don’t know that rephrasing the question would necessarily change the outcome of the poll, but I do…believe think we should be mindful of the language we use when discussing science.