Tag Archives: ecology

Malaria, Climate Change, and the Next Top Model

by Joseph DeSisto

Both malaria and climate change are complex global problems that scientists are working hard to understand. Malaria, a mosquito-borne disease, kills roughly 600,000 people every year, mostly in Africa. Attempts to control malaria have been massive and relatively well-funded, but the disease continues to pose a serious threat to human life in the tropics. Climate change has no body count (yet), but will dramatically change our planet, altering weather patterns, sea levels, and human life.

These two problem have another thing in common: scientists use mathematical models to try and predict how they will change in the future. For example, climate scientists use past and current data on temperature, carbon emissions, and many other factors, to predict how the earth’s climate will change. Most models anticipate a global temperature increase of 2̊ to 6̊  by the year 2100 (e.g., Paaijmans et al. 2014). Those predictions may not be perfectly accurate, but that is the nature of predictions, and in the absence of time travel, it’s the best we can do.

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Anopheles minimus, a malaria-transmitting mosquito. Photo by James Gathany, in public domain.

Malaria, the microbes that cause it, and the mosquitos that carry it, are all affected by temperature. Scientists have tried developing models to predict how malaria infection rates will change as the world gets hotter. In general those predictions have been bleak: models tend to show an increase in the amount of people affected by malaria (e.g. Pascual et al. 2006, Paaijmans et al. 2014), on the basis that warmer temperatures are most hospitable to malaria-carrying mosquitos. They also show malaria spreading to areas that used to be too cool, like South Africa and the southeastern United States. Yet other models show a decrease in malaria on a global scale (Gething et al. 2010), and some suggest an increase in some areas but a decrease in others (Rogers and Randolph 2000).

Before looking forward, it’s important to look back – how has malaria changed in the last few years? The maps below show malaria infection rates (the percentage of people infected) across Africa, in 2000 (left) and 2010 (right). Darker colors mean more malaria.

 

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Photo by Noor et al. (2014), licensed under CC BY 3.0.

The two maps may not look all that different, but look closely. The red arrow points to West Africa, where the darkest area has grown smaller. Malaria is still common there, but has declined. In Kenya and Tanzania (purple arrow), malaria has declined even more. Even though efforts to completely eradicate malaria have failed, improved mosquito control programs have been successful in reducing the threat of malaria in these regions of Africa.

A model is basically an equation, and in the case of malaria it serves to calculate R0: the basic reproduction number. The basic reproduction number is the answer to the question, for each person already afflicted with malaria, to how many other people will their infection spread? This gives us an idea of how many people are likely to contract malaria in a given year.

For example, if R0 is 15, that means every person with malaria is likely to pass it on to fifteen other people – that’s about the R0 value for measles. If R0 is 0.5, then on average, half of all malaria patients will pass their infection on to another. For all diseases, when R0 is less than 1.0, the disease will decline, and if R0 is greater, the disease will increase in the population. Very high values of R0 can lead to pandemic.

Malaria is a complicated disease, affected by all three players: humans, microbes (more on them later), and mosquitos. In turn, each of these players are affected by temperature, moisture, population density, and other local conditions. As a result, malaria’s basic reproductive number varies depending on where you are. In 2007, a group of scientists attempted to calculate R0 for 121 different human populations in Africa (Smith et al. 2007). The study had two important results.

First, R0 varied wildly across Africa. Although the average value was near 115, many populations had values below 10 and many more had values over 1,000. Second, some R0 were extremely high, approaching 10,000. Remember what this means – on average, each person with malaria has the potential to transmit their malaria to 10,000 other people!

In some cases the R0 value was greater than the human population, suggesting that everyone in the population had malaria when of course this was not the case. Is there a problem with the model? The scientists in question didn’t think so. Instead they pointed out that although malaria’s R0 is much higher than for most other diseases, malaria also takes much more time to spread (on average, 200 days per generation) because of its complex life cycle.

The parasites that cause malaria are single-celled, apparently simple, but with strange and complicated lives. I say parasites, plural, because there are at least five species that cause malaria, but all are protozoans in the genus Plasmodium. The cycle, of course, has no “beginning,” but we will start with the oocyst, a kind of “egg sac” containing multiple Plasmodium cells and surrounded by a protective membrane.

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A Plasmodium sporozoite (purple). Image by Ute Frevert; false color by Margaret Shear, licensed under CC BY 2.5.

The oocyst lives in the body of a female Anopheles mosquito, and by the time the mosquito lands for a blood meal, the membrane bursts. Single-celled Plasmodium parasites surge forth, down the mosquito’s mouthparts, and into the blood-stream of an unsuspecting human. The freed cells are called sporozoites; they are worm-like and active, and waste no time snaking their way through the host’s body until they reach the liver.

Here the parasites eat, grow, and change shape. They divide and transform into masses of globular cells, similar to oocysts, once again enveloped in a bag-like protective layer. As time goes on, liver becomes tiresome, and the parasites crave blood. The bag of cells bursts, and the Plasmodium cells return to the blood stream. Now they have a new mission: find a red blood cell.

Red blood cells are hollow and doughnut-shaped, like inflatable inner tubes. You use them to transport oxygen and carbon dioxide into and out of your body, with every breath. The blood cell’s membrane is thin, almost fluid, and easy for a Plasmodium cell to invade. Once inside, the parasite has two options. It can grow and divide, forming a new mass of cells (like the oocyst). If it does so, these cells will ultimately break out of their shelter to find new red blood cells of their own. More ambitious parasites, however, refrain from dividing. Instead they metamorphose, transforming into either male or female cells.

For the Plasmodium life cycle to complete, a second mosquito is required. The new mosquito lands on a malarial host, sucking up blood and with it, lots of red blood cells. Some of these are empty, but others, if Plasmodium is lucky, contain either male or female hitchhikers. In the mosquito’s digestive system, red blood cells burst open to release their passengers. The freed Plasmodium cells, male and female, meet and unite. Once they do, they are able to multiply and grow into a multi-celled oocyte, full of wriggling sporozoites ready to enter a new human host at the mosquito’s next meal.

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A mosquito in the genus Anopheles, capable of transmitting malaria. Photo by Jim Gathany, in public domain.

For this system to work, mosquitos not only have to be infected with Plasmodium, but sporozoites have to be fully developed and ready to pounce when opportunity (i.e., a bite) comes along. Lots of mosquitos need to be biting people, so that at least some will slurp up the male and female cells when they are ready. Mosquitos need to have reasonable lifespans – those that meet their end in a frog’s belly or a spider’s web are of no use to Plasmodium. The mosquitos, in turn, have requirements of their own: they need optimal growing temperatures, pools of water in which to lay their eggs, and plenty of warm-bodied hosts from which to drink.

All of these factors (and many more) are variables that might appear in an equation to calculate R0. Smith and colleagues (2007) used them to calculate the R0 for all those 121 African populations. More recently, a group of scientists and mathematicians got together to predict how R0 will change with the earth’s climate (Ryan et al. 2015).

In general, both mosquitos and Plasmodium can only develop at temperatures between 63̊ and 93̊ F. That’s good, useful information, but not enough — each of Smith’s variables (mosquito life span, number of bites per person, etc.) is affected by temperature, but each in a slightly different way. Only by combining all of these factors, and considering how each will change under future climate conditions, can we accurately predict how the threat of malaria will change over time. That’s what Ryan and colleagues did, and published this month in Vector-Borne and Zoonotic Diseases.

It turns out that if you combine all those variables, you get a much more complex picture of how climate change and malaria interact. Although some areas will get warmer and more suitable for malaria, others will actually get too hot, so malaria will decline.

This particular study shows a decrease in malaria in West Africa, but an increase in East Africa. In other words, the hot-spot for malaria will shift east over the next six decades.

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From Ryan et al. (2015), licensed under CC BY 4.0.

In the maps above, purple indicates the greatest increase in malaria transmission rates, while the palest tone indicates a decline in malaria.

Caution is important. When different models produce vastly different results, it usually means that some of those models are better than others. This model happens to consider more factors than many others, which suggest it may be more accurate, but as I have tried to show, malaria is a complex disease that will be affected by temperature in complex, hard-to-predict ways.

Having an idea of what the future might hold can inform us – where should we concentrate efforts to control malaria? Where will malaria pose the greatest threat to human health? This latest model suggests our focus will have to shift as Plasmodium, mosquitos, and malaria follow their optimal temperatures in an eastward march across Africa.

Cited:

Gething P.W., D.L. Smith, A.P. Patil, A.J. Tatem, R.W. Snow, and S.I. Hay 2010. Climate change and the global malaria recession. Nature 465(7296): 342–346.

Noor A.M., D.K. Kinyoki, C.W. Mundia, C.W. Kabaria, J.W. Mutua, V.A. Alegana, I.S. Fall, and R.W. Snow. 2014. The changing risk of Plasmodium falciparum malaria infection in Africa: 2000-10: a spatial and temporal analysis of transmission intensity. The Lancet 383(9930): 1739-1747.

Paaijmans K.P., J.I. Blanford, R.G. Crane, M.E. Mann, L. Ning, K.V. Schreiber, and M.B. Thomas. 2014. Downscaling reveals diverse effects of anthropogenic climate warming on the potential for local environments to support malaria transmission. Climate Change 125: 479-488.

Pascual M., J.A. Ahumada, L.F. Chaves, X. Rodó, and M. Bouma. 2006. Malaria resurgence in the East African highlands: temperature trends revisited. Proceedings of the National Academy of Sciences U.S.A. 103(15): 5829–5834.

Rogers D.J. and S.E. Randolph. 2000. The global spread of malaria in a future, warmer world. Science 289: 1763–1766.

Ryan S.J., A. McNally, L.R. Johnson, E.A. Mordecai, T. Ben-Horin, K. Paaijmans, and K.D. Lafferty. 2015. Mapping physiological suitability limits for malaria in Africa under climate change. Vector-Borne and Zoonotic Diseases 15(12): ahead of print.

Smith D.L., F.E. McKenzie, R.W. Snow, and S.I. Hay. 2007. Revisiting the basic reproductive number for malaria and its implications for malaria control. PLOS Biology 5(3): e42. doi: 10.1371/journal.pbio.0050042

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Why Scorpion Venom is So Complex

by Joseph DeSisto

Scorpion venom, like many animal venoms, is incredible complex. It is made up of hundreds of different toxins and other proteins, each with a specific function, all mixed together in a lethal cocktail. Why do scorpions need so many different toxins? Last week, scientists at the Chinese Academy of Sciences published the results of their attempt to answer this question (Zhang et al. 2015).

They began by studying a particular class of proteins found in scorpion venom, which work by attacking the sodium ion-channel proteins in their victims.

The stripe-tailed scorpion, Vaejovis spinigerus, ready for action.. Photo by Joseph DeSisto.

The stripe-tailed scorpion, Vaejovis spinigerus, ready for action. Photo by Joseph DeSisto.

Sodium ion-channels help regulate the amount of sodium inside animal cells, which is vital for cells to function properly. In nerve cells, they are even more important: the change in sodium concentration inside and outside the cell is what transmits electric signals.

Toxins that inhibit sodium channels prevent the nervous system from working, which leads to death if the victim is small (like an insect). Scorpions have toxins called sodium-channel toxins to do exactly that. The puzzle is, scorpions have many different genes that produce sodium-channel toxins, each of which has a slightly different structure.

All proteins are essentially strings that are wound, twisted, and tied into a specific structure. The structure of a protein is critical to its function, since proteins need to have certain shapes in order to interact with each other like a lock and key. All sodium-channel toxins have a portion designated as the “interactive region” — the key — which attaches to a series of loops on the prey’s sodium ion-channel (the lock). If the key fits and the connection is successful, the prey’s ion-channel can no longer function.

A mother stripe-tailed scorpion, carrying young. Photo by Joseph DeSisto.

A mother stripe-tailed scorpion, carrying young. Photo by Joseph DeSisto.

Zhang and his colleagues studied the genome of their scorpion, a desert-dwelling East Asian species known as the Chinese golden scorpion (Mesobuthus martensii). They found no less than 29 different genes coding for sodium channel toxins.

There was a time, perhaps hundreds of millions of years ago, when scorpions only had one gene for sodium-channel toxins. Eventually that gene was duplicated, and thereafter the scorpion genome had multiple copies of the same toxin-producing gene. Since then, each copy of the gene has continued to mutate and evolve in its own direction. Now each toxin, despite having the same basic structure, is just a little bit different from the rest.

As it happens, the genes for sodium ion-channels in a scorpion’s prey also exist in multiple copies, each with minor variations. Zhang and colleagues hypothesized that scorpions need so many varieties of toxins because each toxin can only interact with a specific variety of ion-channel. In other words, scorpion venom needs lots of different keys because the prey have so many different locks.

To test this, the scientists examined the different toxin-gene copies to better understand how they had evolved. Sure enough, the “interactive region,” the key, of each toxin had mutated and evolved much more quickly than the “body” of the toxin. This provided strong evidence that natural selection has caused scorpion venom to evolve different types of toxins to keep up with the ever-evolving ion-channels in their prey.

Scorpions are incredible animals for so many reasons. They have been around for more than 400 million years — as long as there have been insects to hunt on land, scorpions have been there to hunt them. They are amazing and diverse in form, lifestyle, and hunting strategy. How fitting that they should be just as amazing on the molecular level.

Cited:

Zhang S., B. Gao, and S. Zhu. Target-driven evolution of scorpion toxins. Nature Scientific Reports 5:14973 doi: 10.1038/srep14973

The Alligator’s Nest

by Joseph DeSisto

If you are careless in wandering along the swamps of the southeastern United States, you may hear this sound emanating from the brush:

[Recording by Adam Britton, used with permission.]

That is the hiss of an angry American alligator — if you hear it on land, you may have stumbled upon an alligator nest. If so, do not delay in your retreat. A mother alligator’s warning is no bluff.

An American alligator (Alligator mississippiensis) from South Carolina. Photo by Gareth Rasberry, licensed under CC BY-SA 3.0.

An American alligator (Alligator mississippiensis) from South Carolina. Photo by Gareth Rasberry, licensed under CC BY-SA 3.0.

If you could stay, however, you might be surprised at the tenderness with which alligators treat their offspring. When a female is ready to lay, she hauls herself on shore and finds a shaded, protected area not too far from the water. She lays her eggs in a pile of mud and leaf litter, then heaps more litter on top of them, so that the end result is a leaf-and-mud pile 2-3 feet tall and 5-7 feet wide (McIlhenny 1935).

A thick layer of insulating leaves also keeps the eggs at a more-or-less constant temperature. On a daily basis, even though the environment might go through wild changes in temperature, the inside of the nest stays within 3° F (Chabreck 1973). Alligator eggs usually take around 2 months to develop, and stable temperatures are critical.

Baby American alligators from the Okefenokee Swamp in Georgia. Photo by William Stamps Howard, licensed under CC BY-SA 3.0.

Baby American alligators from the Okefenokee Swamp in Georgia. Photo by William Stamps Howard, licensed under CC BY-SA 3.0.

In human beings, the presence or absence of a Y chromosome decides whether one develops into a male or female. In other words, human sex determination is chromosome-dependent. Alligators instead, like many reptiles, show temperature-dependent sex determination. Between days 20 and 35 of incubation, if eggs are kept between 86° and 93°F, a roughly even mixture of females and males will be the result (Ferguson and Joanen 1983). If, however, the batch stays above 93°, only males will emerge, and if below 86°, only females.

Alligator babies aren’t the only things that grow in alligator nests. The heap of dead leaves, twigs, and mud provides a haven for bacteria and other microorganisms. As bacteria digest the rotting vegetation, they produce heat — enough to keep the eggs 3-4° warmer than the habitat outside the nest (Chabreck 1973). In fact, bacteria keep alligator nests so consistently warm that the nests are also home to unique, heat-loving fungi (Tansey 1973).

More baby alligators! Photo by Ianaré Sévi, licensed under CC BY-SA 3.0.

More baby alligators! Photo by Ianaré Sévi, licensed under CC BY-SA 3.0.

Eggs, alligator or otherwise, look simple but are surprisingly complex. The “solid” shell is mostly made of calcium, but it’s far from a perfect seal — the whole surface is peppered with thousands of tiny holes, allowing the egg to take in oxygen and water, while “exhaling” carbon dioxide (Kern and Ferguson 1997). The thickness of the shell must be precise — too thin and the egg is easily crushed or infected by disease, but too thick and breathing, drinking, and hatching become difficult.

On alligator farms, where alligators are bred and raised for their skins, roughly 30-60% of eggs hatch successfully. Meanwhile more than 90% of alligator eggs hatch successfully in the wild (Kern and Ferguson 1997), as long as the nest isn’t flooded or raided by predators first. Experiments have shown that captive alligator eggs are less porous than their wild counterparts, and of the captive eggs, the least porous are doomed to die before hatching (Wink et al. 1990). Captive alligator eggs also have much thicker shells than wild eggs. So where is the difference coming from?

A baby American alligator. Photo by Ianaré Sévi, licensed under CC BY-SA 3.0.

A baby American alligator. Photo by Ianaré Sévi, licensed under CC BY-SA 3.0.

The bacteria in wild alligator nests, aside from producing heat, also produce acids. These acids aren’t strong or abundant enough to harm the developing reptiles, but over the 2 months it takes for them to develop, acids gradually erode the hard, calcium shell around each egg (Ferguson 1981). By the time the alligator is ready to hatch, its shell is significantly thinner than when the egg was first laid — just thin enough for the hatchling to easily break through.

[Recording by Adam Britton, used with permission.]

As they leave their eggs, baby alligators sound an alarm to their mother, who industriously digs them out of the nest where they spent the first two months of their lives. Although these months might seem uneventful, they are in fact full of challenges, which alligator eggs, however simple and unassuming, have ways to overcome.  Those hatchlings that survive face yet another gauntlet of obstacles, including predators and ruthless competition from their siblings. It’s tough being a baby alligator, and maybe even tougher being an egg, but the toughest few have a chance to become some of the most awe-inspiring top predators in North America.

Dr. Adam Britton, a crocodile researcher at the Charles Darwin University in Northern Territory, Australia, has graciously allowed me to use the audio files in this article. More files, along with a wealth of information about crocodilian biology and conservation, can be found at his website, crocodilian.com.

Cited:

Chabreck R.H. 1973. Temperature variation in nests of the American alligator. Herpetologica 29(1): 48-51.

Ferguson M.W.J. 1981. Increased porosity of the incubating alligator eggshell caused by extrinsic microbial degradation. Experientia 37(3): 252-255.

Ferguson M.W.J. and T. Joanen. 1983. Temperature-dependent sex determination in Alligator mississippiensis. Journal of Zoology 200(2): 143-177.

Kern M.D. and M.W.J. Ferguson. 1997. Gas permeability of American alligator eggs and its anatomical basis. Physiological Zoology 70(5): 530-546.

McIlhenny E.A. 1935. The Alligator’s Life History. Christopher Publishing House, Boston. 117 pp.

Tansey M.R. 1973. Isolation of thermophilic fungi from alligator nesting material. Mycologia 65(3): 594-601.

Wink C.S., R.M. Elsey, and M. Bouvier. 1990. Porosity of eggshells from wild and captive, pen-reared alligators (Alligator mississippiensis). Journal of Morphology 203(1): 35-39.

Life in Blackwater

by Joseph DeSisto

Just a few years before Darwin published his work on evolution by natural selection, his contemporary, Alfred Russel Wallace, finished a four-year-long tour of the Amazon Basin. During these travels he explored the Amazon River and its tributaries, met with indigenous tribes, and collected a shipload of biological specimens, which he planned to return to England to sell. Sadly the ship and all its contents, save a few notes and sketches, were lost in a fire at sea. From those notes was forged a book documenting Wallace’s travels and his observations on natural history in the Amazon (Wallace 1853).

When Wallace began to explore the Rio Negro or “Black River,” the Amazon’s largest tributary, he noticed that the water seemed darkly stained, like tea or coffee. Similar, smaller rivers could be found across the Amazon — such rivers were usually deep, slow-moving, and wound through forests or swamps. “Blackwater” (aside from being an episode of Game of Thrones) is the name Wallace (1853) used to describe these stained waterways. Where the blackwater of the Rio Negro meets the silt-laden, “whitewater” of the Amazon, the transition is sharp and visible from space.

The junction of the whitewater Amazon (left) and the blackwater Rio Negro (right) near Manaus, Brazil. Photo by Lecomte, licensed under CC BY-SA 3.0.

The junction of the whitewater Amazon (left) and the blackwater Rio Negro (right) near Manaus, Brazil. Photo by Lecomte, licensed under CC BY-SA 3.0.

Not only do blackwater rivers look like tea, they effectively are tea — the color comes from tannins, organic molecules that seep into the water as certain types of tannin-bearing plants die and decompose (Janzen 1974). Whether a river has blackwater or not depends entirely on the plant life growing at its banks. In life, certain plants use tannins as a protection against insects. In death, the tannins play a new role, altering the aquatic environment and the life therein.

Blackwater rivers have a very different chemistry than other water bodies. They are more acidic but lower in oxygen, nutrients, and the dissolved elements many animals need (Ribeiro and Darwich 1993). There are, therefore, fewer animals in blackwater than in clearwater or whitewater. Snails and some other invertebrates, for example, need calcium to build their shells, and these do not fare well in low-calcium blackwater rivers. With fewer invertebrates to eat, fish and other predators are relatively scarce. Yet there is life in blackwater, and although it is a bit harder to find, it is unique and, in its own way, amazing.

A bdelloid rotifer. Photo by Donald Hobern, licensed under CC BY 2.0.

A bdelloid rotifer, found in a wet clump of moss. Photo by Donald Hobern, licensed under CC BY 2.0.

The deformed-zucchini-shaped thing above is in fact an animal, smaller than a grain of sand, called a rotifer. Rotifers can be found almost anywhere with moisture, though you’d need a microscope to spot them. They feed on tiny particles of all kinds, from bits of detritus and algae to bacteria and other single-celled organisms. Despite being tiny, rotifers are relatively complex creatures with minute brains, feelers, and a large mouth surrounded by hair-like appendages called cilia. Some species even have simple eyes.

When a rotifer wishes to swim, it simply vibrates the cilia to pull its body forward. The cilia are also important in feeding — if the rotifer is anchored by its “tail” end, the vibrating cilia create a water current that draw particles towards the mouth. Rotifers eat pretty much the same way street-sweepers sweep. Below is a video of what this looks like:

[Video credit is to “NotFromUtrecht,” licensed under CC BY-SA 3.0.]

In the Amazon Basin, blackwater is dominated by rotifers which, unlike many planktonic invertebrates, do not need calcium or other dissolved minerals to construct cells. At the junction of the Rio Negro and the Amazon River, rotifer populations can be up to ten times higher in the blackwater than in whitewater (Ribeiro and Darwich 1993), even though the two extremes are separated by only a few feet of transition. The same pattern exists in Argentina, where a different “Rio Negro” (also blackwater) meets the whitewater Rio Salado (Frutas 1998).

As long as there are rotifers and other blackwater-tolerant plankton around, fish can also live in blackwater, but low nutrient and oxygen levels make it difficult for them to do so. Still, some very special fish have evolved to tolerate blackwater, and perhaps the most recognizable of these is the neon tetra, a fish made famous by its popularity in home aquariums.

The neon tetra (Paracheirodon innesi), a popular aquarium fish. Photo by Holger Krisp, licensed under CC BY 3.0.

The neon tetra (Paracheirodon innesi), a popular aquarium fish. Photo by Holger Krisp, licensed under CC BY 3.0.

In Rio Negro (Brazil, not Argentina), fish are not especially abundant, but many of the species that live there are endemic. Of the 700 or so fish known from the river, around 100 are found nowhere else on earth. Among these fish is the cardinal tetra, a close relative of the neon tetra with similarly vivid red and blue streaks. Another is the cururu, a freshwater stingray.

Freshwater stingrays are common in the Amazon Basin, where they are considered to be more dangerous even than piranhas. The greatest abundance and diversity of stingrays is found in the whitewater, but surveys have revealed there are several species that prefer blackwater, and at least two in the genus Pomatotrygon are found exclusively in the blackwater of the Rio Negro (Duncan and Fernandes 2010). One of these is the cururu ray, a unique species that has only been discovered in the last decade.

One of the cururu ray's closest relatives, the porcupine river stingray (Potamotrygon histrix). Photo by Jim Capaldi, licensed under CC BY 2.0.

One of the cururu ray’s closest relatives, the porcupine river stingray (Potamotrygon histrix). Photo by Jim Capaldi, licensed under CC BY 2.0.

Studying the cururu ray has helped us understand what is required for a fish to thrive in blackwater. First, the extremely low levels of sodium, chlorine, and other salts in blackwater presents a problem, since fish and all other animals require salts to keep their bodies running. The cururu, like many fish in Rio Negro, can survive with far less sodium and chlorine than most other fish, but it is also more efficient at extracting salts from the water, however scarce they may be (Wood et al. 2002).These rays also have gills with finger-like projections, adapted to be as efficient as possible in gathering both salts and oxygen from blackwater (Duncan et al. 2010).

Although scientists have known for some time that the cururu ray represents an undescribed species, it has yet to be given a Latin name. Many more new species may yet be discovered in the tannin-soaked waters of Rio Negro and other blackwater rivers. Unique places yield unique creatures, often with amazing stories.

Cited:

Duncan W.P. and M.N. Fernandes. 2010. Physicochemical characterization of the white, black, and clearwater rivers of the Amazon Basin and its implications on the distribution of freshwater stingrays (Chondrichthyes, Potamotrygonidae). Pan-American Journal of Aquatic Sciences 5(3): 454-464.

Duncan W. P., O.T.F. Costa, M.M. Sakuragui, and M.N. Fernandes. 2010. Functional morphology of the gill in Amazonian freshwater stingrays (Chondrichthyes: Potamotrygonidae): implications for adaptation to freshwater. Physiological and Biochemical Zoology 83: 19-32.

Frutos S.M. 1998. Densidad y diversidad del zooplancton en los Rios Salado y Negro — planicie del Rio Parana — Argentina. Revista Brasileira de Biologia 58(3): 431-444.

Janzen D.H. 1974. Tropical blackwater riversm animals, and mast fruiting by the Dipterocarpaceae. Biotropica 6(2): 69-103.

Ribeiro J.S.B. and A.J. Darwich. 1993. Phytoplanktonic primary productivity of a fluvial island lake in the Central Amazon (Lago do Rei, Ilha do Careiro). Amazoniana 12(3-4): 365-383.

Wallace A.R. 1853. Narrative of travels on the Amazon and Rio Negro. Reeve, London.

Wood C.M., A.Y.O. Matsuo, R.J. Gonzalez, R.W. Wilson, M.L. Patrick, and A.L. Val. 2002. Mechanisms of ion transport in Potamotrygon, a stenohaline freshwater elasmobranch native to the ion‐poor blackwater of the Rio Negro. Journal of Experimental Biology 205: 3039–3054.

The Milk Adder

by Joseph DeSisto

Many times I was told, growing up in Maine, that if I looked hard enough I could find adders. People alleged to find them in parks, along rock walls, even in their homes. The word “adder” confused me, because this is the “true” adder:

The European adder, Vipera berus. Photo by Zdeněk Fric, licensed under GFDL.

The European adder, Vipera berus. Photo by Zdeněk Fric, licensed under GFDL.

That’s the European adder, a viper found in Europe and northern Asia. It is venomous, like all vipers, although not especially prone to biting. In New England, we only have two vipers, the copperhead and the timber rattlesnake. Neither are known to occur in Maine. Presumably copperheads never occurred here, prohibited by the cold winters.

The timber rattlesnake, meanwhile, is absent from Maine not because of the climate, but because the species was systematically exterminated through rattlesnake hunts. In Maine as in much of the United States, the timber rattlesnake has been stoned, burnt, and bulldozed out of our lives. Now it has become something of a legend, a name whispered when a rustle in the leaves is heard, or when a large snake slithers out of sight, just quickly enough to evade scrutiny.

A timber rattlesnake from Iowa. Photo by Psychotic Nature, licensed under CC BY-SA 3.0.

A timber rattlesnake (Crotalus horridus) from Iowa. Photo by Psychotic Nature, licensed under CC BY-SA 3.0.

Yet the adder of Maine is neither copperhead nor rattlesnake, but the harmless eastern milk snake. Why they should be called adders, I haven’t a clue. Despite looking nothing like a viper, milk snakes are sometimes confused with rattlesnakes and copperheads because they

a) shake their tails in dead leaves to mimic the sound made by a rattle,

b) aren’t afraid to hold their ground and defend themselves, and

c) are snakes.

That they should be killed is shameful, because milk snakes happen to be some of the most beautiful snakes in New England. As hatchlings they are creamy-white, with brick-red spots running down the back, each outlined in black as if traced with a fountain pen. With each year the snake loses a bit of its color — by adulthood most milk snakes are a pale gray, with red spots faded to a duller, but still handsome, chestnut brown.

A young milk snake or "milk adder" from Iowa. Photo by Psychotic Nature, licensed under CC BY-SA 3.0.

A young milk snake (Lampropeltis triangulum) or “milk adder” from Iowa. Photo by Psychotic Nature, licensed under CC BY-SA 3.0.

For most of my childhood, the eastern milk snake was my herpetological holy grail. I spent hours wandering through fields, digging in wood piles, and painstakingly tracing the edges of rock walls. Finally I tried my luck at a car junkyard, where I was told that snakes liked to hide under the heat-soaked, mouse-infested hoods and spare parts. When I asked the manager if he had seen any snakes with red spots, he told me that yes, many of the snakes had red spots, but only after he killed them and nailed them to trees like the Old Testament bronze serpent.

Milk snakes are not uncommon, but they are very secretive. Unlike the sun-loving garter snakes and racers, milk snakes are mostly nocturnal and subterranean, emerging from hiding only when necessary to track their rodent prey. When they are uncovered, milk snakes often defend themselves violently, shaking their tail, rearing up, and striking. The six-inch-long hatchlings are just as tenacious, although their bite amounts to little more than a soft pinch.

An adult eastern milk snake -- less striking than a hatchling, but still a handsome snake. Photo by Trisha Shears, licensed under CC BY-SA 3.0.

An adult eastern milk snake — less striking than a hatchling, but still a handsome snake. Photo by Trisha Shears, licensed under CC BY-SA 3.0.

I never did find my milk snake, but I like to think those years taught me something about nature. Milk snakes, like so many wonders of the natural world, are not found – they appear, like angels or shooting stars or gusts of wind. I don’t look for milk snakes any more, but I still go for long walks, flip logs, and scrutinize rock walls. Without fail, something amazing is there, and with luck one day that amazing thing might be a milk snake. Until then I look forward to a few moments reveling in its beauty before, with a flick of its muscular body, it vanishes.

This blog is mostly focused on invertebrates, but you can expect me to write more about reptiles as well, because I love them. My last article on snakes focused on vipers, and the chemicals they use to track their prey.

Happy World Snake Day!

Death by Disintegrin

by Joseph DeSisto

Disintegrins. Definitely the coolest-sounding proteins, manufactured by some of the coolest animals, the vipers.

Snake venom contains thousands of different proteins, making it one of the most complex substances in the natural world. Not all of these proteins are toxic, but those that are belong to four major categories, depending on their effects.

Neurotoxins act on your nervous system, which can make for a bad time. Your nerve cells are needed to control muscle movement, and since muscle movement allows you to breath, neurotoxic venom can cause death by paralyzing your ability to do so. Neurotoxins are found in cobras, sea snakes, and their relatives, but seldom in vipers.

Cytotoxins are the good old-fashioned cell-killers, found in many snake venoms. If you get bitten by a venomous snake, these are the proteins that start killing the tissue around the bite. If enough tissue dies on a limb, amputation might be necessary. More often, cytotoxins just make venomous snake bites really, really painful.

A Russell's viper (Daboia russelli) from Bangalore, one of the deadliest vipers in the world. Photo by Sandilya Theuerkauf, licensed under CC BY-SA 2.5.

A Russell’s viper (Daboia russelli) from Bangalore, one of the deadliest vipers in the world. Photo by Sandilya Theuerkauf, licensed under CC BY-SA 2.5.

Hemotoxins are more a viper’s purview, and act on the cardiovascular system. They can destroy red blood cells, prevent the blood from clotting, or just destroy cardiovascular tissue. While neurotoxins are relatively fast-acting, death by hemotoxin is slow. When a mouse or other prey animal is bitten by a viper, it typically runs away for some distance before it succumbs to shock. This presents vipers with a problem — how to track down prey after it has gone off to die? But before we answer that question …

The fourth category, proteases, are proteins that specialize in breaking down other proteins, and viper venom is positively loaded with them. Disintegrins are just one class of proteases, but have many functions. Their primary purpose is to break apart integrin, the stuff animals use to keep their cells stuck together. Disintegrins can also prevent blood from clotting, and have been used in medical research (McLane et al. 2004). Finally, two special disintegrins have a third purpose: they serve as tracking signals that can help the predator find its poisoned prey.

The western diamondback rattlesnake (Crotalus atrox). Photo by Holger Krisp, licensed under CC BY 3.0.

The western diamondback rattlesnake (Crotalus atrox). Photo by Holger Krisp, licensed under CC BY 3.0.

It was only a decade ago that Parker and Kardong (2005) first demonstrated, through a set of experiments, that rattlesnakes (a subfamily of vipers) use airborne scents to relocate their prey after injecting venom. Prior to that, it was thought that rattlesnakes followed a scent trail on the ground. Although experiments had since suggested that rattlesnakes are attracted to prey containing venom, it was unclear just how venom was being used to track prey.

Modern chemistry was the key. Saviola and colleagues (2013) extracted venom from diamondback rattlesnakes, then separated it into some of its major chemical components. With the venom divided, the authors injected each mouse with a different component, then offered these mice to the snakes, as well as mice that had been injected with un-divided venom. Snakes were by far the most responsive to mice that had either been injected with whole venom or with two proteins: crotatroxins 1 and 2, both of which are disintegrins.

So, rattlesnakes don’t merely “smell their own venom” — they smell to a particular pair of compounds, without which they would be unable to find prey after it had been bitten. Vipers very well might not have evolved the bodies, venoms, and life strategies we see today if it had not been for this tiny but crucial adaptation.

The western diamondback rattlesnake (Crotalus atrox) Photo by Clinton & Charles Robertson, licensed under CC BY 2.0.

The western diamondback rattlesnake (Crotalus atrox). Photo by Clinton & Charles Robertson, licensed under CC BY 2.0.

Cited:

McLane M.A., E.E. Sanchez, A. Wong, C. Paquette-Straub, J.C. Perez. 2004. Disintegrins. Current Drug Targets: Cardiovascular and Haematological Disorders 4(4): 327-355.

Parker M.R. and K.V. Kardong. 2005. Rattlesnakes can use airborne cues during post-strike prey relocation. In Mason R.T. et al. (Eds.), Chemical Signals in Vertebrates 10 (397-402). Springer.

Saviola A.J., D. Chiszar, C. Busch, and S.P. Mackessy. 2013. Molecular basis for prey relocation in viperid snakes. BMC Biology 11(20) doi: 10.1186/1741-7007-11-20

Basketballs, Shark Teeth, and Millipedes: Meet the Haplodesmids

by Joseph DeSisto

I feel like I’m on a roll with the whole common-name-inventing thing, so I’m going to have a go at another millipede family: the Haplodesmidae. These millipedes are poorly known, largely because they are often tiny and cave-dwelling. Beneath the microscope, however, they become utterly captivating. The haplodesmids have intricately shaped and textured exoskeletons, appearing almost as if they were crafted by an artist with very tiny instruments. For the purposes of this blog they will be called the “sculptured millipedes.”

For example:

The star-shaped haplodesmid Eutrichodesmus asteroides. Photo from Golovatch (2009b), licensed under CC BY 3.0.

The star-shaped haplodesmid Eutrichodesmus asteroides. Photo from Golovatch et al. (2009b), licensed under CC BY 3.0.

The millipede above has curled into a protective spiral, with its head at the center. The species name asteroides means “star-like” and refers to the shape formed when it spirals.

Here’s another, Eutrichodesmus incisus, newly described in Golovatch et al. (2009a) from remote Chinese caverns:

A preserved specimen of Eutrichodesmus incisus, shown under a scanning electron microscope. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

A preserved specimen of Eutrichodesmus incisus, shown under a scanning electron microscope. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

Notice the way the back plates, or tergites, have bumps and sutures like the surface of a basketball. They even look a little fuzzy, but it isn’t fuzz — each one of those tergites is covered in microscopic spines. Here’s a close look at the junction between a tergite and a prozonite (the part of a segment that goes before/under the tergite).

Tergite and pretergite of E. incisus. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

Tergite and prozonite of E. incisus. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

The tergite and prozonite have very different textures! Not only is the tergite bumpy, each bump is covered in tiny, finger-like projections or microvilli:

A single bump on a tergite of E. incisus. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

A single bump on a tergite of E. incisus. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

The prozonite, meanwhile, is covered in tiny spines. If we look even closer we can see that these spines even come in two different shapes, neatly arranged in rows like a shark’s teeth:

The surface of a pretergite of E. incisus. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

The surface of a prozonite of E. incisus. Photo from Golovatch et al. (2009a), licensed under CC BY 3.0.

Pretty cool, right? At this point you’re probably wondering why sculptured millipedes look so weird, but I haven’t even shown you the weirdest one. The most bizarre-looking haplodesmid is star-shaped like E. asteroides, but even more so. Also like asteroides, it was only just described in 2009, from a series of Vietnamese caves (Gorovatch et al. 2009b).

The even-more star-shaped Eutrichodesmus aster. Photo from Golovatch et al. (2009b), licensed under CC BY 3.0.

The even-more star-shaped Eutrichodesmus aster. Photo from Golovatch et al. (2009b), licensed under CC BY 3.0.

Back to the obvious question: why are sculptured millipedes so sculptured? It’s an interesting question, but unfortunately not too much attention has been paid to the minute details of these already minute millipedes. In addition to being tiny, sculptured millipedes are also almost always found in caves, which are often remote and difficult to explore.

So, no one really knows why aster is star-shaped, or why incisus has tiny shark-teeth on its body. If I had to guess I would say that aster‘s projections make the millipedes more difficult to swallow, which is one of the reasons millipedes form spirals in the first place.

As for the teeth on the prozonites — I really haven’t got a clue.

The sculptured millipedes, like many invertebrate families, were barely known until a few intrepid taxonomists got to work on documenting the species. Now that this is starting to happen, perhaps we will find out what their strange projections/ridges/teeth/villi are for. I’m betting we will, and I certainly hope so — whatever reason there is, I’m sure it’s amazing.

Cited:

Golovatch S.I., J. Geoffroy, J. Mauries, and D. VandenSpiegel. 2009a. Review of the millipede family Haplodesmidae Cook, 1895, with descriptions of some new or poorly-known species (Diplopoda, Polydesmida). ZooKeys 7: 1-53

Golovatch S.I., J. Geoffroy, J. Mauries, and D. VandenSpiegel. 2009b. Review of the millipede genus Eutrichodesmus Silvestri, 1910 (Diplopoda, Polydesmida, Haplodesmidae) with descriptions of new species. ZooKeys 12: 1-46.

Mossy Millipedes: Meet the Platyrhacids

by Joseph DeSisto

I’ve been wanting to write an article about bryophytes — mosses and related plants — for some time now, ever since I was able to take a course on bryology here at UConn. Conveniently, bryophytes and invertebrates have formed some amazing relationships, giving me the perfect excuse to write about them! Today’s story comes from one such relationship, between several different bryophytes and an unusual millipede in the family Platyrhacidae.

A platyrhacid millipede, Nyssodesmus python, from Costa Rica. Photo by D. Gordon E. Robertson, licensed under CC BY-SA 3.0.

A platyrhacid millipede, Nyssodesmus python, from Costa Rica. Photo by D. Gordon E. Robertson, licensed under CC BY-SA 3.0.

The platyrhacids are just one of many “flat-backed” millipede families in the order Polydesmida, which itself accounts for roughly a third of the known millipede diversity. What makes the platyrhacids a bit odd-looking among other flat-backs is that their back plates (tergites) often have backwards-pointing triangular projections, like the enlarged scales on crocodile backs.

While other millipedes have such projections, and some platyrhacids do not, I’ll still take this opportunity to give platyrhacids a common name: the crocodile millipedes. The name works on a second level: just as crocodiles often have algae growing on their bodies, so does one crocodile millipede have mosses and liveworts growing on its tergites.

First, a primer on mosses and other bryophytes. Just as millipedes are one of the oldest terrestrial invertebrate lineages, so bryophytes are the oldest living land plants. Because of this, they are often regarded as primitive, but in fact bryophytes are both complex and incredibly diverse.

The resilience and diversity of mosses have allowed them to colonize an immense variety of habitats. Photo by Thomas Bresson, licensed under CC BY 3.0.

The resilience and diversity of mosses have allowed them to colonize an immense variety of habitats. Photo by Thomas Bresson, licensed under CC BY 3.0.

Mosses and liverworts grow all over the place, from streams and on the surfaces of tree leaves to bare rock and the sides of houses. Their ability to colonize new habitats is aided by their modes of reproduction: in addition to producing microscopic spores, bryophytes can develop from broken-off fragments. A study by Lewis et al. (2014) suggests that some moss populations owe their existence to tiny moss fragments spread by birds migrating from Alaska to sub-Antarctic Chile!

Now let’s get back to crocodile millipedes. The species in question is Psammodesmus bryophorus, which I’m going to call the mossy crocodile millipede. The mossy crocodile millipede was discovered in a mountain rainforest, high in the Andes of Colombia (Hoffman et al. 2011 — incidentally this was one of the last new millipedes described by Hoffman, one of the greatest millipede taxonomists of all time).

The mossy crocodile millipede, , complete with its bryophyte camouflage. Photo from Martinez-Torres et al. (2011), licensed under CC BY 4.0.

The mossy crocodile millipede, Psammodesmus bryophorus, complete with its bryophyte camouflage. Photo from Martínez-Torres et al. (2011), licensed under CC BY 4.0.

These millipedes are not common — only 22 specimens could be found in the site where they were discovered, the Río Nambi Natural Reserve. Of those, 15 specimens carried at least one, and typically many, moss or liverwort species on their backs (Martínez-Torres et al. 2011). Although moss spores are often spread by insects, for bryophytes to actually be growing on an animal is unusual. Among arthropods, only a few kinds of weevil and one harvestman have been reported carrying just a few moss species.

And yet, Martínez-Torres et al. (2011) report on their specimens “complex mosaics of bryophyte species.” Not only were the millipedes carrying bryophytes, they were carrying ten different species, in five different families! Many of these had never been reported as living on arthropod exoskeletons before, making this a big discovery both for diplopodologists (millipede scientists) and bryologists.

A liverwort growing on one of the tergites of the mossy crocodile millipede. Photo from Martinez-Torres et al. (2011), licensed under CC BY 4.0.

A liverwort growing on one of the tergites of the mossy crocodile millipede. Photo from Martínez-Torres et al. (2011), licensed under CC BY 4.0.

This may not be a totally symbiotic relationship — it’s entirely possible that the mosses and liverworts benefit only by having a growing site, while the millipedes get a nice suit of camouflage. All ten of the bryophytes here are also found either on soil or on the surfaces of other plants. Even so, it’s tempting to think there might be a more complex relationship.

Perhaps the millipedes help the bryophytes disperse their offspring. Or maybe the millipedes deter tiny animals that might eat the mosses, since millipedes are essentially walking cyanide bombs. We can only hope more mossy crocodile millipedes will be found — perhaps then we can get a better idea of what’s really going on in the mountain forests of Colombia.

I know I said only Tuesday and Thursday, but I’m on a bit of a writing binge right now. If you’re someone who gets an e-mail notification every time I post a new article … sorry about that (only a little). When I come down from whatever this is, things will normalize, I promise.

For an excellent blog devoted to bryophytes, be sure to check out Moss Plants and More by Jessica Budke.

Cited:

Hoffman R., D. Martínez, and A.E.F. Daza 2011. A new Colombian species in the millipede genus Psammodesmus, symbiotic host for bryophytes (Polydesmida: Platyrhacidae). Zootaxa 3015: 52-60.

Lewis L.R., E. Behling, H. Gousse, E. Qian, C.S. Elphick, J.F. Lamarre, J. Bêty, J. Liebezeit, R. Rozzi, and B. Goffinet. 2014. First evidence of bryophyte diaspores in the plumage of transequatorial migrant birds. PeerJ 2:e424 doi: 10.7717/peerj.424

Martínez-Torres S.D., A.E.F. Daza, and E.L. Linares-Castillo. 2011. Meeting between kingdoms: Discovery of a close association between Diplopoda and Bryophyta in a transitional Andean-Pacific forest in Colombia. International Journal of Myriapodology 6: 29-36.

Potato Wars: Meet the Gelechiids

by Joseph DeSisto

Today’s story comes from the tiny but remarkable twirler moths, the Gelechiidae. The moths themselves are small and typically brown, attracting little attention, while the caterpillars go by names like splitworm, bollworm, pinworm, tuberworm, and so on, usually referring to the plant tissues they consume.

Human interest in twirler moths, then, is largely focused on their relationships with the plants that both humans and twirlers relish — potatoes, tomatoes, grains, almonds, and many others.

The gelechiid caterpillar Chionodes pseudofondella, freshly coaxed from its silken shelter. Photo by M.J. Hatfield, licensed under CC BY-ND-NC 1.0.

The gelechiid caterpillar Chionodes pseudofondella, freshly coaxed from its silken shelter. Photo by M.J. Hatfield, licensed under CC BY-ND-NC 1.0.

Twirler caterpillars live sheltered lives — they typically either live inside twigs, fruit, leaves, or other plant tissues, or else use silk to roll leaves into shelters. This way the caterpillars can dine in relative peace, with fewer predators able to find and attack them.

The opening to a shelter in mountain mint, made by the caterpillar above.

The opening to a shelter in mountain mint, made by the caterpillar above. Photo by M.J. Hatfield, licensed under CC BY-ND-NC 1.0.

Shelters can be effective against spiders and wasps, but they haven’t stopped humans from using all kinds of strategies, from pesticides to natural predator, to keep twirler caterpillars out of their crops. With good reason — many of these caterpillars cost farmers a huge portion of their annual yield.

Today we are going to focus on one of these moths, the Guatemalan potato moth, Tecia solanivoria (GPM). GPM caterpillars feed underground by boring into a potato and hollowing out a set of tunnels, in which they live until ready to emerge as adult moths. By eating out the inside of the potato, the caterpillars not only damage the crop themselves, they also allow fungi to enter the potato and begin the decomposition process, resulting in a rotten vegetable.

The Guatemalan potato moth's caterpillar, in all its glory. Photo from Hayden et al. (2013).

The Guatemalan potato moth’s caterpillar, in all its glory. Photo from Hayden et al. (2013).

The caterpillars can feed on potatoes both before and long after harvest. As a result, they are easily spread when infested potatoes are shipped across long distances. Although GPM is native to Guatemala, it was first discovered in Costa Rica where it had been introduced in imported potatoes. Entomologists estimate that the introduction occurred in 1970, but the species was not formally described until three years later (Povolny 1973).

Why so long between introduction and description? Here I must editorialize — if Central America had had an active expert in gelechiid taxonomy, the species that was causing so much damage would surely have been discovered much earlier, perhaps even before the species ever left Guatemala! Instead the species was described by a Czech taxonomist, by which time Central American farmers were reporting 20-40% crop losses to the unnamed pest (Povolny 1973). The “outsourcing” of tropical biodiversity research to scientists in first-world countries can have dire consequences.

For reference, here's a map showing Central America and northwestern South America. GPM is native to Guatemala in the northwest, then quickly spread through Central America, Venezuela, Colombia, and Ecuador. Map data: Google, Landsat.

For reference, here’s a map showing Central America and northwestern South America. GPM originated in Guatemala (upper left) and has quickly spread southeast as far as Ecuador and Colombia. Click to enlarge. Map data: Google, Landsat.

Before 1970, the most significant potato-eating caterpillar in Latin America was the potato tuberworm (Phthorimaea operculella — try saying that out loud). Unlike GPM, the tuberworm is a leaf-miner, munching its way through the 2-dimensional world inside leaves. After its introduction to Costa Rica, however, GPM saw a meteoric rise, and quickly stole the show as the most economically injurious caterpillar for Latin American potato growers (Carrillo and Torrado-Leon 2013). In 1983 GPM was accidentally imported (via infested potatoes) into Venezuela from Costa Rica, and South America became the new front in the moth’s conquest. By 1996 the caterpillars had reached Ecuador, and in 1999 a population was even introduced to the Canary Islands off the coast of Northwest Africa.

Managing GPM is an economic necessity. Unfortunately, this can be difficult since once the caterpillar hatches and starts making its tunnels inside a potato, you’ve pretty much lost the potato. Pesticides are generally targeted toward the more vulnerable eggs and adult moths, but these stages are short-lived. Timing is crucial, and only pesticides applied at the right stage will reduce crop losses. Despite this, potato growers frequently err on the side of caution, applying pesticides intensively throughout the growing season (Carrillo and Torrado-Leon 2013). This is not only a waste of money, it can also lead to the moths becoming resistant to the pesticides, not to mention the environmental and human safety consequences of pesticide overuse.

A pinned specimen of the Guatemalan potato moth. Photo from Hayden et al. (2013).

A pinned specimen of the Guatemalan potato moth. Photo from Hayden et al. (2013).

The most effective methods of reducing GPM infestation are not chemical but cultural (Gallegos et al. 2002). Growers can help protect their plants by tilling the soil to break up clumps (havens for moths and eggs), planting their potatoes deeper in the soil, and removing “leftover” potatoes from the soil.

Here’s the twist: under certain conditions, it can actually benefit the farmer to let the caterpillars feed.

In 2010, Poveda and colleagues experimented with GPM abundance in potato fields in Colombia. Surprisingly, fields in which caterpillars were allowed to feed in moderation actually showed higher total yield than when caterpillars were completely excluded. It turns out that when caterpillars feed, the chemicals in their saliva are strewn about the potato, and the plant is able to recognize and react to these chemicals.

Flowers from a potato plant. Photo by Keith Weller, in public domain.

Flowers from a potato plant. Photo by Keith Weller, in public domain.

Each potato plant contains many tubers, the things we call potatoes. If less than 10% of these are infested with caterpillars, the plant compensates by diverting resources to the remaining tubers. The result: a greater number of extra-large potatoes, and an increase in overall yield. Plants with limited caterpillar infestations yielded 2.5 times as much useable potato mass as plants in which there were no caterpillars at all.

The lesson? Plant-insect relationships are complicated, and understanding the subtle details can matter. So can the taxonomy of small, “boring” moths. There are a lot of important things we wouldn’t know about GPM if it weren’t for the hard work and dedication of entomologists from Colombia to the Czech Republic. With invasive pests an increasing problem, we need to make sure to invest in both applied and basic research, and study even the insects that most people would rather ignore.

This post marks the start of a kind of experiment for me. Starting here, I will be posting a new article every Tuesday and Thursday. Here’s the catch: each post will focus on a different family of invertebrates, and I can’t cover the same family twice! The goal is to try and write about as many families as possible, starting with Gelechiidae.

Cited:

Carrillo D. and E. Torrado-Leon. 2013. Tecia solanivora Povolny (Lepidoptera: Gelechiidae), an Invasive Pest of Potatoes Solanum tuberosum L. in the Northern Andes. In: J.E. Pena (Ed.), Potential Invasive Pests of Agricultural Crops (126-136). Boston, Massachusetts: CABI.

Gallegos P., J. Suquillo, F. Chamorro, P. Oyarzun, H. Andrade, F. Lopez, C. Sevillano, et al. 2002. Determinar la eficiencia del control quimico para la polilla de la papa Tecia solanivora, en condiciones del campo. In: Memorias del II Taller Internacional de Pollila Guatemalteca Tecia solanivora, Avances en Investigacion y Manejo Integrado de la Plaga, 4-5 June 2002, Quito, Ecuador pp. 7.

Hayden, J.E., S. Lee, S.C. Passoa, J. Young, J.F. Landry, V. Nazari, R. Mally, L.A. Somma, and K.M. Ahlmark. 2013. Digital Identification of Microlepidoptera on Solanaceae. USDA-APHIS-PPQ Identification Technology Program (ITP). Fort Collins, CO. 7 July 2015 <http://idtools.org/id/leps/micro/&gt;

Povolny D. 1973. Scrobipalpopsis solanivora sp. n. — a new pest of potato (Solanum tuberosum) from Central America. Acta Universitatis Agriculturas, Facultas Agronomica 21(1): 133-146.

The Fork-tailed Dragons

by Joseph DeSisto

Meet Furcula borealis, the caterpillar of the white furcula moth:

Furcula cinerea, the caterpillar of a medium-sized, gray moth. Photo by Joseph DeSisto.

Furcula borealis, the white furcula caterpillar. Photo by Joseph DeSisto.

It’s a weird-looking caterpillar already, but even weirder when viewed head-on:

The fork-tailed dragon caterpillar, Furcula borealis. Photo by Joseph DeSisto.

The fork-tailed dragon caterpillar, Furcula borealis. Photo by Joseph DeSisto.

Like all insects, caterpillars have only six legs, and these are located near the front of the body, just behind the head. The sticky, climbing appendages along the rest of the trunk are not true legs but “prolegs,” which are lost during metamorphosis. In Furcula caterpillars (and the related Cerura, shown below), the last pair of prolegs are modified into long, rigid “tails.”

Cerura scitiscripta, showing six true legs near the head (upper left), four typical prolegs on the trunk, and the special modified pair of prolegs at the rear of the body -- the forked

Cerura scitiscripta, showing six true legs near the head (upper left), four typical prolegs on the trunk, and the special modified pair of prolegs at the rear of the body — the forked “tail.” Photo by Joseph DeSisto.

The furcula moths belong to the strange and beautiful family Notodontidae. These are sometimes called prominent moths, despite mostly being brown, gray, or some combination thereof. Recall, however, that in my last post about caterpillars I referred to notodontid caterpillars as the dragon caterpillars. Furcula, then, are unofficially dubbed the fork-tailed dragon caterpillars.

In case you’re wondering what F. borealis looks like as a moth, here’s an example specimen:

The white furcula moth, Furcula borealis. Photo by Tom Murray, used with permission.

The white furcula moth, Furcula borealis. Photo by Tom Murray, used with permission.

So what is the forked tail for? To find out, we simply tap our little dragon on the head. This is what happens:

Furcula borealis. Photo by Joseph DeSisto.

Furcula borealis, beginning its display. Photo by Joseph DeSisto.

Bright red tentacles begin to emerge from the  modified prolegs. In less than a second they are fully everted:

Don't mess with the fork-tailed dragon! Photo by Joseph DeSisto.

Furcula borealis, tentacles emerging from modified prolegs. Photo by Joseph DeSisto.

The fork-tailed dragon then waves these tentacles about, and even attempts to rub them onto the offending party (i.e., my finger). The “strike” reminds me of a scorpion trying to sting, if scorpions dressed up as clowns and went to birthday parties. After tapping me, the tentacles disappear as quickly as they emerged, while the caterpillar tucks its head and braces itself for another attack.

Furcula borealis. Photo by Joseph DeSisto.

Furcula borealis. Photo by Joseph DeSisto.

In a less dramatic fashion, many insects use eversible organs to rub toxins on their predators. Rove beetles are an example — this explains the way many of them run, with abdomens held high in the air like scorpions. If you grab one, it will use its flexible abdomen to rub a cocktail of nasty chemicals on you, some of which can cause blistering. But in Furcula and Cerura caterpillars, the tentacle-rubbing is actually a harmless show designed to scare off predators. I must admit, were I a foraging bird, I would think twice about attacking a caterpillar with such a bizarre and intimidating display.

And yet, in an ironic twist, these caterpillars are not harmless. If sufficiently disturbed, they can fire off a burst of formic acid — the stuff fire ants sting you with — from glands behind the head. In F. borealis, these are stored in spiky, poisonous-looking projections:

If you're mean enough, this caterpillar might just spray formic acid at you. Photo by Joseph DeSisto.

If you’re mean enough, this caterpillar might just spray formic acid at you. Photo by Joseph DeSisto.

Don’t mess with the fork-tailed dragons!