Fighting "the glaze".
I love protein structure, but my students don't find it quite as fascinating as I do--to say the least. However, one thing many of us do agree on is that we like coffee. I know this because I often meet students in the coffee line at one of the cafes that have sprung up around campus. They are ordering elaborate, caffeine-laced concoctions while I'm getting a medium decaf. The beauty of biology is that I'm able to use this coffee mania to elicit a little interest in protein structure, while throwing in some immunology and zoology to boot. The link here is a new caffeine test being developed to monitor whether or not decaf drinks really are decaffeinated. The test is based on llama antibodies against caffeine. Yes, llama antibodies--isn't biology wonderful! Some llama antibodies are composed of heat-resistant chains of amino acids. Antibodies to caffeine from other animals are presently used in tests, but these proteins denature at the high temperatures of hot coffee (Webb, 2006). Antibodies from llamas and their fellow camelids, camels, retain their activity at temperatures up to 90[degrees]C, which makes for pretty hot coffee. Researchers are now working on a dipstick assay for random testing of decaf right in a cafe.
In the Gut
This item on llamas is the sort of rather useless but interesting information that can make my day. I may use it in my class because of its relationship to protein folding and how heat causes protein denaturation. It is also a good example of employing biological material in chemical tests, something that is becoming more and more common. The reason why I'm not positive that I'll mention this in class is that there are so many wonderful ideas like this afloat in the literature that it's easy to inundate, and even drown, students in information. But such items are great to keep in mind for those days when "the glaze" is particularly rife. This phenomenon is on my mind because I've had several conversations with faculty recently about what to do to counter those glaze-eyed stares that are the bane of every teacher. There are many remedies, most of them involving active learning--getting students to sit up, think, do, and learn. However, it's often good to start the ball rolling with a tasty bit of information. In this column, I'll share a few I've come across, that I, at least, find interesting, and some have even been student-tested. For example, they sat up and took notice on one particularly bleak and cold winter morning when I mentioned that more than 2000 bacterial species live on and in the average human--definitely a factoid with "yuck" value, and one that's a great lead-in to a discussion of the digestive system, since so many of these bugs live happily there.
Discussing gut bacteria can also lead to immunology since Margaret McFall-Ngai (2007) contends that the rich bacterial diversity in the vertebrate gut, much greater than in invertebrates, could explain the development of immunological memory. Invertebrates, which harbor a relatively sparse number of gut bacterial species, only possess innate immunity that is not adaptive like that in vertebrates. McFall-Ngai argues that adaptive immunity, involving antibodies and immunological memory, is an adaptation to the development of complex bacterial communities of coevolved species that are beneficial to their host. These microbes produce needed substances like vitamins and also aid in digestion. In humans, such communities are composed no only of bacteria but of archaea and protists as well; all work together to break down complex carbohydrates (Hooper, 2006). In order to accommodate such diverse organisms in the body, the immune system had to become flexible, that is, adaptive.
Another attention grabber is new research indicating a link between gut flora and obesity (Bajzer & Seeley, 2006). Firmicutes and Bacteroidetes are the two predominant microbiota in both mice and humans, and in both species the Firmicutes are more abundant in the guts of obese individuals. In addition, when put on low-calorie diets, the portion of Firmicutes decreases and becomes similar to that in non-obese mice and humans. This is new work, and it has to be confirmed with larger experimental groups. Also, it's not clear whether the changing gut flora plays a role in weight loss or is simply the result of a different chemical climate in the digestive system. However, it is significant that mice given bacterial material from obese mice extracted more calories from their food and had a gain in fat. With weight-conscious students, this information is an interesting way to get them to appreciate some of what those 2,000 bacterial species may be doing in the body.
Students might also be interested to learn that fat droplets in cells are more than just storage sites, or this might be information only a biologist could love (Beckman, 2006). It makes sense that something as vital as lipid would be dealt with carefully in the cell. I find it intriguing that lipid globules might really be functioning as cellular organelles because as a cell-lover, I like the idea that cells are even more complex than we had thought. Researchers have discovered that lipid globules are involved in lipid transport within the cell, store energy, and help to maintain cell membranes. The new respect for these droplets began to develop when proteins called perilipins were discovered on the surface of droplets and were found to be involved in the synthesis and degradation of fats. Mice without perilipin broke down fats more rapidly, so naturally this protein became a focus of interest. More recently, cholesterol-synthesizing enzymes have also been found in globules as have dozens of other proteins. Some biologists want to rename these structures "adiposomes" and thus consider them full-fledged organelles. This item may not thrill students who might see adiposome as just another term to memorize. That's why I mention it here; this column gives me an opportunity to share something with an audience that might, I hope, appreciate this information. In addition, you might also be interested to know that lipid droplets are implicated in disease. Hepatitis C virus associates with globules in liver cells, and when Chlamydia reproduce in cells they coat themselves in droplets. So from obesity to infection, lipid globules or adiposomes are indeed worthy of interest.
Another fat-related item may be one you hesitate to share with students. This is the fact that resveratrol, a substance in red wine, seems to prevent some of the effects of overeating. This is the type of idea that sticks in the minds of young and old in our weight-conscious culture, but do we really want to encourage ways around healthy eating and even worse, wine-drinking, among the young? However, this is also the kind of thing students get wind of outside of class, and then want more information about, so it's good to be so armed. Yes, mice given resveratrol along with a high-fat diet had lifespans longer than mice fed such diets but without resveratrol and similar in length than those of control animals (Kaeberlein & Rabinovitch, 2006). This increased longevity was due to less obesity-related illnesses like diabetes and liver damage.
However, the compound did not prevent obesity, and perhaps more importantly, it is an ingredient of red grapes as well as of red wine, so fermentation isn't necessary. In fact, some researchers are moving to eliminate the grape connection completely by testing resveratrol as a dietary supplement (Check, 2006). This may be taking things too far too fast, since only one mouse study has been completed. No one knows if the same effect will be found in other mice strains, let alone other animals, including humans. Also, the mice in the study were given quite high doses of resveratrol. Would such doses even be safe in humans, assuming that resveratrol would probably have to be taken long term? Another troubling issue is that researchers aren't sure how resveratrol produces its effects. Studies in yeast, and subsequently in other species, indicate that it increases levels of the sirtuin family of proteins, that have been implicated in at least small lifespan increases in yeast and fruit flies. But researchers have had difficulty finding a direct link between resveratrol and sirtuin levels. Also, it's important to remember in all this hype, that one glass of wine only contains 0.3% of the resveratrol dose given to mice, taking relative weights into account. This is the kind of information students need to know. While you might or might not want to use this particular item in class, this type of example is useful to examine in depth when news reports fail to give really important information, such as the dosages used.
I want to mention one more digestion-related item that is relatively trivial, but then again, is any biological information really trivial? It's been noted that mountain gorillas like to eat wood though animal behaviorists weren't sure why. Now research on gorillas in Uganda indicates that they get more than 95% of their sodium from rotting wood, even though this delicacy makes up only 4% of their diet (Bhattacharjee, 2006). And they are picky eaters: They avoid wood that has a low sodium content. It remains to be seen if wood plays a similar role in other primates' diets, but this is a nice example of exploiting resources to provide essential nutrients.
Nutrition may also play a role in another odd item, this time from the avian world. Many bird species produce blue-green eggs, but the adaptive advantage, if any, of this coloration was always a question. The color source, the pigment biliverdin, is expensive for birds to produce, which suggests that blue eggs have a selective advantage. A recent study of pied flycatchers by a biologist at the National Museum of Natural Sciences in Madrid found that the bluer the egg, the more antibody proteins in the egg and the better the survival chances of the chick (Holden, 2006). So the blue pigment is a sign of the mother's nutrition levels and general health, and of the amount of energy she can expend to produce protective antibodies for her chicks. The next step is to see if males invest more care in bluer eggs, thus indicating that the blue color is used to convey information.
Speaking of eggs, it turns out that the offspring in some Komodo dragon eggs are products of parthenogenesis (Watts et al., 2006). One female produced viable offspring two and a half years after her last contact with a male. This might be explained by long-term sperm storage, but DNA fingerprinting indicates that the offspring are homozygous. In another case, a female produced eight eggs that developed normally, and she had never been kept with a male. This parthenogenesis came as a surprise because it's rare in reptiles, especially ones as large as the Komodo dragon. The phenomenon is of concern to conservation biologists because of the low genetic diversity in the homozygous offspring.
It has been common for extra Komodo dragon females to be kept isolated from males in order to maintain the sex-ratio in the breeding population and because of the risk of aggression. But this practice can mean that if females can't find partners, they are likely to produce parthenogenic offspring. It may be that some of the animals bred in zoos and presumed to be the products of sexual intercourse may, in fact, be homozygous. Also, female Komodos have dissimilar chromosomes, Z and W, while the males are ZZ. Parthenogenesis produces only males since the WW embryos are not viable, thus limiting the number of offspring that hatch. This study may change the way captive Komodo dragon populations are managed and will spur research to see if other endangered reptiles are also parthenogenic.
This research on the Komodo is a reminder of the great diversity of approaches to reproduction among living things. There has been recent work on reproduction in a number of sea creatures that bears this out. To grossly understate the situation, an ocean is a very large place, which can make it difficult to find a mate. Also, as with species anywhere, competition for a mate can be fierce. One solution is to mature fast to beat out rivals, and some species have taken this approach to the extreme. The female blanket octopus, Tremoctopus violaceus, weighs 40,000 times more than the male. Because the male is so small it can develop rapidly. Constance Holden (2002) notes: "If a sparrow tried to mate with a fighter jet, that would fairly describe the kamikaze sex lives of the males" of this species (p. 1687). Australian zoologists had the first recorded encounter with such males in deep water off the Great Barrier Reef. The adult male blanket octopus, weighing about a quarter of a gram, is the size of a jellybean and comparable to the size of the pupil of his mate's eye. The male has a specialized reproductive arm filled with sperm and during encounter with a female the arm breaks off and crawls into the female's gill cavity. This usually spells the death of the male. Biologists have found females with several arms still living in them, thus indicating male competition.
The size dimorphism of the blanket octopus is not unique; there are even more extreme cases. But usually the diminutive male lives on the female, which is another approach to dealing with the ocean's size: stick close to your mate. This is what male tubeworms of the genus Osedax do. They've become the focus of study since a rich harvest of them was found in a decomposing whale carcass discovered at a depth of nearly 3000 meters off the coast of California. The Osedax worms were embedded in the whale's bones. All the visible worms were females, each of which had up to 100 microscopic males in her gelatinous tube.
Like the blanket octopus males, the male tubeworms have streamlined their development, in this case, almost eliminating it. They remain immature in all ways except the production of sperm, carrying the idea of sexual maturity to an extreme. They look like nothing more than tubeworm larvae: they have no mouth, gut or anus, and no circulatory system. The females store large numbers of bacteria on which they feed; males store none. The latter are simply filled with sperm and have a unique sperm duct that opens at the top of its head--definitely a novel approach. In an article on this research, Elizabeth Pennisi (2007) quotes the marine biologist Kenneth Halanych of Auburn University as saying: "It reminds us that there are still many interesting discoveries that await us in the oceans' depths" (p. 457). The work on Osedax alone bears this out. After the first carcass find, oceanographers have examined several others decomposing at various depths, and at each location they've discovered new Osedax species. There is also evidence suggesting that whether Osedax larvae develop as males or females depends on where they land. If they settle on whale bone, they grow and become females, but if they land on already burrowing females, they remain small and become males.
Among the interesting discoveries being made in oceanography is one concerning the mixing power of its inhabitants (Kerr, 2006). A krill such as Euphausia pacifica that's only two centimeters long wouldn't seem like a major player in stirring up the Pacific Ocean, but when thousands of its kind get together, they have a significant effect on turbulence. In Saanich Inlet on the British Columbia coast, the water is stratified and turbulence is usually as low as in the deep ocean, except when krill are on the move. They spend days in deep water and at night move toward the surface to feed. Sensors indicate that turbulence levels increase by three or four orders of magnitude as the krill pass by. Based on what's known about animal movements, researchers calculate that schools of fish even the size of anchovies can create turbulent mixing on the order of a sustained local storm, to say nothing of the effect of a pod of whales on the move. In fact the numbers are so significant that some oceanographers think that the decimation of fish and sea mammal populations may be having a serious effect an sea water mixing, and in turn on climate, at least in some locales.
This is to say nothing of what phytoplankton may be doing. Florida State oceanographers estimate that phytoplankton store 63 terawatts of energy in new organic material each year, and that about 1% of that, or almost one terawatt may go into swimming motions. Since a terawatt is 1012 watts, this is quite a large turbulence contribution from organisms that make krill look huge. Information like this is admittedly speculative, but it is also fascinating because it forces the land-bound like myself to think differently about the sea. Waves are obvious phenomena but to know that a great deal of movement is going on beneath the surface just adds to the fascination of the deep. It's also disturbing to think that an occurrence we weren't even aware of, could be yet another part of nature being skewed by human activity. This is a great example for students of how little we know about what we are doing to the Earth.
I don't want to leave the water yet; its comparative inaccessibility relative to the land makes it a particular source for the exotic. Some of these wonders are described in an article called "Plant Wannabes" (Pennisi, 2006). It's about sea slugs, mollusks without shells, that carry algae or chloroplasts in the cells of their digestive systems. Just as the examples I've noted above deal with extremes of reproductive adaptation, these cases involve extremes of symbiosis and coevolution. For example, sea slugs of the genus Phyllodesmium acquire algae from the soft corals they eat. The microscopic algae, zooanthellae, live in the slug's gut. With them, the animal can survive for months without food. The key to this relationship seems to be that a richly branched midgut region that harbors the algae. With the ingestion of algae, the slug takes on the color of the coral, and this camouflage protects it from predation. Biologists hypothesize that this protection was what drove the evolution of the relationship between the two species. Only later did the gut evolve to better accommodate the algae, thus leading to a nutritional advantage for the slug.
In another case, the symbiosis seems to have gone even farther. Larvae of the sea slug, Elysia chlorotica, not only ingest the seaweed, Vaucheria litorea, they then suck out its chloroplasts. If the larvae don't encounter this species and acquire the chloroplasts, they don't survive. The chloroplasts live in the slug for months, usually for its entire 10-month life span. The secret here is that the slug has genes to produce two proteins that the chloroplast needs and are similar to plant nuclear proteins. This item might not instantly make a student sit up and take notice, but it's nonetheless wonderful. Since it might stir your biologist's heart, your enthusiasm may then help to deglaze students. There are endless such examples of co-evolution and of complex symbiotic relationships. We can't share them all with students but a case such as this can illustrate a number of important concepts and also spark a sense of wonder.
I want to end with one of my favorite items of recent vintage. Of course, there are some old standbys that I use regularly. It doesn't hurt to know that Frank Lutz (1941) identified 1,400 insect species in his New Jersey backyard or that within a few days after birth, a baby has acquired a bacterial population greater than the number of its own cells (Jones, 2000). Of course, insects and bacteria are two particularly good sources for anti-glazing info, which brings me to my last item. Princeton University ecologists tracked the migration of green darner dragonflies, Anax junius (Wikelski et al., 2006). Using a plane and a car, they found that the insects' travel patterns during the fall migration are similar to those of migrating songbirds. Both fatten up before leaving; both fly during the day and when there isn't much wind. They take days off to replenish their fat, but will fly on a day when the night before was colder than the previous night; this pattern indicates northerly winds useful to their flight. Though many migrating birds will make the return trip while most of the short-lived dragonflies will not, it seems that the same behavioral adaptations are useful for very different winged travelers. There is something satisfying about this idea, a little bit of unity in the diversity of life, like krill and whales both stirring up ocean waters.
This column comes with no guarantees. I can't insure that any of the ideas I mentioned are full-proof awakeners. I'm certain that many of you have had the experience which is all too common for me, of using a favorite idea to spur interest and having it fall silently into a sea of glazed faces. Such are the trials of teaching, but they are offset by those times when things go right, when students are indeed fascinated by the fact that a black bear eats up to 20,000 calories a day in preparation for hibernation (http://www.jaxzoo.org/things/biofacts/ AmericanBlackBear.asp), and that elephants in German zoos are treated to five Christmas trees each, as a post holiday delicacy--and a novel form of recycling (http://news.nationalgeographic. com/news/2007/01/070104-christmas.html).
Bajzer, M. & Seeley, R. (2006). Obesity and gut flora. Nature, 444, 10091010.
Beckman, M. (2006). Great balls of fat. Science, 311, 1232-1234.
Bhattacharjee, Y. (2006). Sodium source. Science, 312, 667.
Check, E. (2006). A Votre Sante now in pill form. Nature, 444, 11.
Holden, C. (2002). Octopus as extremist. Science, 298, 531.
Holden, C. (2006). Bluer is better. Science, 311, 1687.
Hooper, L. (2006). Journal club. Nature, 442, 851.
Jones, S. (2000). Darwin's Ghost. New York: Random House.
Kaeberlein, M. & Rabinovitch, P. (2006). Grapes versus gluttony. Nature, 444, 280-281.
Kerr, R. (2006). Creatures great and small are stirring the ocean. Science, 313, 1717.
Lutz, F. (1941). A Lot of Insects: Entomology in a Suburban Garden. New York: Putnam's.
McFall-Ngai, M. (2007). Care for the Community. Nature, 445, 153.
Pennisi, E. (2006). Plant wannabes. Science, 313, 1229.
Pennisi, E. (2007). Whale worm sperm factories. Science, 315, 457.
Watts, P., Buley, K., Sanderson, S., Boardman, W., Ciofi, C. & Gibson, R. (2006). Parthenogenesis in komodo dragons. Nature, 444, 10211022.
Webb, R. (2006). Cause for a Llama. Nature, 441, 169.
Wikelski, M., Moskowitz, D., Adelman, J., Cochran, J., Wilcove, D. & May, M. (2006). Simple rules guide dragonfly migration. Biology Letters; Royal Society, London, 2(3), 325-329.
Maura C. Flannery, DEPARTMENT EDITOR
Maura C. Flannery is Professor of Biology and Director of the Center for Teaching and Learning at St. John's University, Jamaica, NY 11439; e-mail: firstname.lastname@example.org. She earned a B.S. in biology from Marymount Manhattan College; an M.S., also in biology, from Boston College; and a Ph.D. in science education from New York University. Her major interests are in communicating science to the nonscientist and in the relationship between biology and art.
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|Title Annotation:||BIOLOGY TODAY|
|Author:||Flannery, Maura C.|
|Publication:||The American Biology Teacher|
|Date:||Apr 1, 2007|
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