Ask a Naturalist.com

The Short Answer: Geoff Peach, Coastal Resources Manager at The Lake Huron Centre for Coastal Conservation, in Ontario, Canada,
looked at your pictures. His response:

“This is a common wetland phenomenon. You generally see it in shallow pooled water amongst the vegetation. The oil is produced by microbes and we tend to see it when it becomes concentrated, as it does in these isolated pockets.”

More Information: We often think of the natural world as separated into animals and plants. Or maybe multi-cellular life and single-celled life. Or if you are a biologist, maybe eukaryotes (animals, plants, fungi) and prokaryotes (bacteria, archea). But another interesting way to divide the natural world is into those organisms that live in habitats with free oxygen (aerobes) and those that live in habitats without free oxygen (anaerobes). In habitats with oxygen, aerobic bacteria release carbon dioxide. In habitats without oxygen, anaerobic bacteria release methane. The surface of a marsh is aerobic – it has enough free oxygen for plants, animals, and aerobic bacteria. But because there is so much biological activity by all the oxygen-loving organisms above ground, most of the oxygen in the water gets quickly used up, and the resulting low oxygen water seals off the underlying mud from atmospheric oxygen.

Just a couple of inches down, there is no free oxygen and the anaerobic bacteria rule a world of drowned muck.

Because methane is a small, easily evaporated molecule, most of the methane produced by the anaerobes in their mud world escapes into the atmosphere. But some small percentage of it gets converted into larger hydrocarbons that are less likely to evaporate. They still are lighter than water, however, so they float on the surface. There is little difference between these naturally produced compounds and hydrocarbons like gasoline or oil, so the sheen on the water looks the same as if someone had spilled gas or oil.

Another possible source for oil on the water of a marsh is oil released directly by plants, or oil released when plants and animals die. Because there is so much living and dying of plants and animals in a marsh, there is a fair amount of oil produced.

Having said all that, of course, it is always possible that a gasoline or oil spill nearby caused this sheen. Lakes with heavy boat traffic are always subject to spilled gas and oil. Or it could be oil washed off from the oiling of the road, as you suggest. It’s hard to know for sure, and impossible to tell from pictures alone, of course. You’ll just have to use your judgment as to whether what you are seeing could be the natural marsh production of hydrocarbons, or something too thick and heavy and localized to be natural.

Tom | Environmental, Questions and Answers, Uncategorized | 09 3rd, 2010 | Click to Leave a Comment »

The Not So Short Answer: This sounds like the Asian tiger mosquito (Aedes albopictus), an invasive species that arrived in Texas in the mid 1980s and has spread rapidly across much of the United States since then. It is currently considered to be the most invasive mosquito in the world and is now found on every continent except Antarctica.

You mention black and white on the wings. The black and white of the Asian tiger mosquito is actually on the body and the legs, but the wings are fairly transparent, so that the pattern can be seen through them. They are also relatively small mosquitoes, so unless you get out a magnifying glass and observe one before you smash it, it may be hard to see exactly where the black and white pattern is. Look for a diagnostic white line that runs down the middle of the thorax behind the head.

Part of the reason I feel fairly comfortable in suggesting the Asian tiger mosquito is your pest is that Aedes albopictus is famously annoying to people for two reasons – exactly the ones that are driving you nuts. First, they are active and biting during the daytime hours, unlike most mosquitoes that are active at night. So they bite people a lot. And second, in association with people, they are able to thrive during droughts that drastically reduce the populations of other mosquitoes. They can reportedly lay their eggs successfully in as little as an ounce of water, so even in a drought, the Asian tigers seem to keep right on multiplying … and biting.

As for what you can do about them, scientific studies (anyone want to volunteer to be bitten by mosquitoes?) have shown that DEET, picaridin, and PMD all have similar repellent effectiveness, with one or the other being slightly more effective against a particular species of mosquito or in a particular type of application. DEET (N,N-diethyl-m-toluamide), of course, has been in use for decades and can be found in many insect repellents. Picaridin (2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester) has been in use in other countries (under brand names such as Bayrepel and icaridin) for many years and was originally created to imitate an extract of the Japanese Prickly Ash (Zanthoxylum piperitum). PMD (p-menthane 3,8-diol) is the synthesized version of oil of lemon Eucalyptus (some produces may list the oil itself). There are also products that are essentially oils of one type or another. A simple application of soybean oil to your skin is at least somewhat effective in repelling mosquitoes.

By checking the active ingredients on commercial repellents, you can choose which repellent you want to use. DEET is the most widely used and has the longest track record. However, some people are sensitive to it, it can dissolve some plastic-based fabrics, and there are concerns about its safety in high concentrations (click here for the American Association of Pediatrics recommendations for repellents for children). Picaridin’s main selling point is that it is a non-oily alternative to DEET. Some people assume PMD, the oil of lemon Eucalyptus product, to be safest because it is the closest to being a natural product. But all three are generally considered to be safe when used according to the directions, and in many places, the risk of mosquito-borne disease is probably greater than the risk of toxicity from these repellents. The Asian tiger mosquito has been show to successfully transmit 30 or more disease-causing viruses under laboratory conditions, including West Nile virus and Dengue fever in areas where these diseases are prevalent. Whether it is a serious vector for disease in the United States is an open question.

Here is a link to the U.S. Centers for Disease Control page on repelling mosquitoes: http://www.cdc.gov/ncidod/dvbid/westnile/RepellentUpdates.htm

Other than repellents, I’m not sure there is much you can do. The Asian tiger mosquito is fairly resistant to malathion and other commonly used insecticides. Empty any standing water on your property, even water at the base of flower pots. But unless you’re willing to go door to door dumping all the water in your neighbors’ yards, you probably won’t cut down on the population of mosquitoes much. Citronella candles work but probably not much better than any other smoky candle. If you really want to hang out in your backyard, you might try getting a screen tent.

The other thing to try is not breathing. Mosquitoes are attracted to carbon dioxide and will hone in from some distance to the carbon dioxide in your breath. (Black flies do the same thing. Click here to see my article on that subject at CuriousNature.net, a companion website.)

More Information: For those of you who are opposed to globalization, you could add the Asian tiger mosquito to your list of reasons. It’s fairly well established that this little blood sucker was shipped around the world in old tires being sent from one country to another for retreading. Water collected in old tires is well-known to make great nurseries for mosquito larvae of many mosquitoes.

There is a very nice 3-minute video on youtube.com that shows the entire 4-stage life cycle of a typical mosquito from egg to larvae to pupae to adult. http://www.youtube.com/watch?v=wFfO7f8Vr9c&feature=related At the end of the video, the male and female adults also very nicely show that typically male mosquitoes, which don’t bite, have bushy or feathery antennae, while females (the biters) have thin antennae.

The life cycle of our Asian tiger mosquito friends is very similar to the mosquitoes (genus Culex) in this video. The one difference is that the Culex mosquitoes lay their eggs on the water, as do most mosquitoes. The Asian tiger mosquito is odd in that it lays its eggs just out of the water. The eggs then hatch and the larvae drop into the water. After a week to two weeks, they metamorphose into adults and begin looking for you.

Tom | Animals, Questions and Answers, Uncategorized | 08 23rd, 2010 | 1 Comment »

The Question: I live in Kolkata (Calcutta), India. We have a few natural ponds here and I found this eel-like species. I’ve seen people here keep it in aquariums. But the people here don’t know it’s scientific name or English name. The reason I think it’s not an eel is because it has no fins in the front or on its tail. I’d like to know what it is. Submitted by: Debashis, India

The Short Answer: Two Indian fish experts identified your pictures as Monopterus cuchia, which goes by the common name Swamp eel, Rice eel or Mud eel. These common names are also used throughout Asia for several closely related species in the genus Monopterus. M. cuchia is found in freshwater in Pakistan, India, Nepal, Bangladesh and Myanmar.

More Information: As you correctly suspected, the Asian Swamp eels are not true eels from the family Anguillidae, they are members of another family, the Synbranchidae. In fact, despite the similarity in appearance, Swamp Eels and the true eels are found in different orders (Synbranchiformes versus Anguilliformes), and are therefore not closely related at all.

The Swamp eels are notable for several things. As adults, they have only vestigial fins. They are also without scales. But the most unusual thing about these fish is that they breathe air. M. cuchia, for example, has small gills, but can’t get enough oxygen from water to survive. So the fish swallows air, increases its heart rate to rush as much blood as possible through the many small blood vessels of the throat, and then expels the air again. The throat acts as a rudimentary lung allowing the fish to absorb oxygen directly from air. M. cuchia goes one step further in that it has pouches in its throat lined with blood vessels. This increases the surface area for absorption of oxygen.

Swamp eels are a food source and cash crop in many parts of Asia. They have the advantage of being able to thrive in water with little oxygen. They often dig burrows in mud where they hide. Swamp eels eat insects, other fish, and small vertebrates such as tadpoles. They grow to a length of about 60 cm (two feet).

Trivia: Swamp eels are protogynous hermaphrodites, which means they begin life as females and become males as they get older.

Sources: My sincere thanks to Dr. K. Rema Devi of the Zoological Survey of India for passing on this question to Indian fish experts Marcus Knight and Beta Mahatvaraj, who generously identified the fish from the photos.

The transition to air breathing in fishes v. comparative aspects of cardiorespiratory regulation in Synbranchus marmoratus and Monopterus albus (Synbranchidae). Graham J.B, Lai N.C., Chiller D, and Roberts J.L. The Journal of Experimental Biology 198, 1455–1467 (1995).

Structure of the air breathing organs of a swamp mud eel, Monopterus cuchia. Munshi J.S.D., Hughes G.M., Gehr P., Weibel Ewald R. Japanese Journal of Ichthyology, vol. 35, no. 4, 1989.

Investigation on health condition of a freshwater eel, Monopterus cuchia from Ailee beel, Mymensingh, Bangladesh. G. U. Ahmed, M. N. Akter1, S. A. Nipa and M. M. Hossain. J. Bangladesh Agril. Univ. 7(2): 421–426, 2009 ISSN 1810-3030.

Tom | Animals, Questions and Answers, Uncategorized | 08 17th, 2010 | Click to Leave a Comment »

The Short Answer: Kelly, the bird in your picture looks like a Sharp-shinned Hawk (Accipiter striatus) to me.

More Information: Your question is a very common one for birders. Cooper’s Hawks (Accipiter cooperii) and Sharp-shinned are closely related and very similar small hawks. They both prey on birds. Their ranges overlap over most of North America.

The Cooper’s Hawk is considerably larger, about the size of a crow, while a Sharp-shinned hawk is closer to the size of a Blue Jay. But as with most raptors, females are considerably larger than males, and a large female Sharp-shinned Hawk is about the same size as a male Cooper’s Hawk, so unless you have the two species side by side, or the bird is definitely crow-sized, it’s difficult to use size to separate the two. In Kelly’s photograph, there are few size cues, so size isn’t much help here.

One of the most easily noticed differences between the two birds is that the Sharp-shinned Hawk’s tail is squared off when resting, with the outer feathers slightly longer and a small cleft in the middle, and a thin white tip. A Cooper’s Hawk’s tail at rest is rounded, with a larger white tip. It’s on that basis that I feel pretty confident in saying that Kelly has taken an excellent picture of a Sharp-shinned Hawk.

Another tip is that the dark grey coloration on the top of the head of the bird in the photo seems to continue down the back of the neck and connects with the dark coloration of the back. It’s a little hard to tell in the photo, since the bird’s neck is turned away from us, but I’m pretty sure I can see the extension of the color down the back of the neck. This is also indicative of a Sharp-shinned Hawk. A Cooper’s Hawk has more of a “cap.” The dark grey coloration on the top of the head is interrupted by lighter feathers on the back of the neck, so that the bird looks like it has a cap of grey. One way to remember this is that “a
Coop has a cap.”

For more detailed descriptions of the two, the Cornell Lab of Ornithology has excellent pages on each species, where you can also hear their different songs:

Sharp-shinned Hawk

Cooper’s Hawk

Tom | Animals, Questions and Answers, Uncategorized | 08 10th, 2010 | Click to Leave a Comment »

The Short Answer: Recent research has confirmed that different tissues in the body replace cells at different rates, and some tissues never replace cells. So the statement that we replace every cell in the body every seven years or every ten years is wrong. Using a revolutionary new technique (described below), researchers have shown that:

1. Neurons in the cerebral cortex are never replaced. There are no neurons added to your cerebral cortex after birth. Any neurons that die are not replaced.
2. Fat cells are replaced at the rate of about 10% per year in adults. So you could say that on average, human beings replace all their fat cells about every ten years.
3. Cardiomyocyte heart cells are replaced at a reducing rate as we age. At age 25, about 1% of cells are replaced every year. Replacement slows gradually to about 0.5% at age 70. Even in people who have lived a very long life, less than half of the cardiomyocyte cells have been replaced. Those that aren’t replaced have been there since birth.

Scientists are now studying other tissues to determine the turnover rate.

More Information: What’s a little confusing about the data given above is that obviously, our brains grow bigger after birth, and so do our hearts. So where is all the extra bulk coming from? In the brain, no neurons are added, but lots of other cells are added. Glial cells, for example, may actually make up 90% of the cells in the brain. It used to be thought that glial cells were simply the scaffolding of the brain, with no real role in the processing of the brain. In recent years, however, it has become clear that glial cells play key roles in processing.

Cardiomyocytes are the true muscle cells of the heart, but the heart is also made up of connective tissue and other cell types that may turn out to have different growth and replacement rates. And while cardiomyocytes replace very slowly, and some are never replaced, the individual cells do grow in size.

The Interesting Science: The technique used to investigate the replacement of cells in humans ingeniously utilizes the unfortunate fact that during the Cold War the nuclear states conducted above ground nuclear tests that spread radioactive Carbon-14 all over the globe. Carbon-14 combines with oxygen in the atmosphere to form CO₂. This results in a mixture in the atmosphere of CO₂ formed with normal, non-radioactive Carbon-12 or Carbon-13, and CO₂ formed with Carbon-14. This CO₂ is then used by plants such as wheat and eaten by animals such as cattle. When we eat crops or livestock, the mixture of Carbon-12, Carbon-13 and Carbon-14 becomes part of our cells, and most importantly, part of the DNA formed when a new cell is born. Since the DNA is not replaced over the life of a cell, the Carbon-14 in a cell’s DNA when the cell is born is pretty much the Carbon-14 it will always have. Since we know how much Carbon-14 was in the atmosphere before nuclear testing, we know how much was in the air during the testing years, and we know how it was eliminated from the atmosphere after the Nuclear Test Ban Treaty outlawed above ground testing in 1963, it’s possible to estimate the turnover of cells.

For example, if a person born just before nuclear testing shows no Carbon-14 from the fallout years in his cerebral cortex neurons, that suggests that no cerebral cortex neuron cells were added after birth. If any new cells had been formed, they would have incorporated Carbon-14 into their DNA. If, on the other hand, a person born right at the peak of the fallout years shows little or no fallout Carbon-14 in his cerebral cortex cells, that would suggest that all the cerebral cortex neuron cells had been replaced. They would have incorporated non-radioactive carbon into their new DNA relatively recently, after most of the Carbon-14 had been washed out of the atmosphere. Otherwise most of them would have some Carbon-14 still in the DNA from when the person was born during the height of the Cold War.

This is a very much simplified version of what a team lead by Dr. Jonas Frisén at the Department of Cell and Molecular Biology at Karolinska Institute in Sweden has been doing. It is their studies that produced the estimates for turnover of cerebral cortex neurons, fat cells, and cardiomyocytes given above.

By the way, Dr. Frisén is very interested in tracking down the origin of the “We replace every cell every 7 or years” myth. If any readers have information on where they heard or read this idea, leave a comment on this page by clicking below and I’ll forward your information to Dr. Frisén.

Sources:

Evidence for Cardiomyocyte Renewal in Humans. Olaf Bergmann, Ratan D. Bhardwaj, Samuel Bernard, Sofia Zdunek, Fanie Barnabé-Heider, Stuart Walsh, Joel Zupicich, Kanar Alkass, Bruce A. Buchholz, Henrik Druid, Stefan Jovinge, and Jonas Frisén. (3 April 2009) Science 324 (5923), 98.

Dynamics of fat cell turnover in humans. Spalding KL, Arner E, Westermark PO, Bernard S, Buchholz BA, Bergmann O, Blomqvist L, Hoffstedt J, Näslund E, Britton T, Concha H, Hassan M, Rydén M, Frisén J, Arner P. Nature. 2008 Jun 5;453(7196):783-7.

Tom | Animals, Questions and Answers, Uncategorized | 08 10th, 2010 | Click to Leave a Comment »