Biodiversity Counts!

Biology concepts – biodiversity, kingdoms of life, animalia, plantae, fungi, protist, archaea, bacteria, extant, extinct

It seems that contests counting things in jars

always involve food. M&Ms, jellybeans, candies,

and gumballs are common things to estimate. I like

another estimate game – how many grains of sand

can be held in one human hand?

Amazingly, only about 10,000.

At some point in our lives, we have all tried to win the prize by guessing how many jellybeans are in the jar. Number estimation is a skill few people possess, just try ordering mulch by the square yard – you end up with either half as much as you need or buried in pine bark!

There is a large group of scientists playing the jellybean game for a living, but their jar is the entire earth. The jellybeans are species of organisms. The prize? Well, you don’t get to keep the jellybeans; and just how will we know who wins?

The Question of the Day – How many species of life are there on Earth?

It seems like a straight forward question, but let’s look at it in a bit more detail before we try to answer it.  What is it we're counting, animals? Animals and plants? Let’s include everything – everything that is considered alive. So what is considered alive? You can have a great discussion as to what should be considered alive, but for these purposes, let’s stick to the kingdoms of life as taught in every biology class – Archaea, Bacteria, Protists, Fungi, Plants, and Animals.

So now that we know the biodiversity we are assessing, we need to define our unit. We said above that we would count species, but it isn’t that simple. We have discussed before what constitutes a species in general – those animals that can breed and produce fertile offspring. So we don’t count ligers and tigons (crosses between tigers and lions), but should we count all the hybridizations of orchids? More than 24,000 species are named already, with about 800 added each year. For our purposes, and for most people estimating species, we will stick with those found in nature, unaided by man.

In 2012, Japanese botanists crossed two orchids and

created a new orchid. No big deal right, orchids are

crossed all the time. But this was the first time that a

photosynthesizing orchid was crossed with a purely

parasitic orchid that doesn’t perform photosynthesis.

They think the plants are doing some photosynthesis –

they’re pretty anyway. Is this a species we should

count in our estimate?

We are counting species, but is it live (extant) species or all species including those that are extinct? The World Wildlife Federation estimates that between 0.01% and 0.1% of all species go extinct each year. However many species we end up with as an estimate for all life on Earth, this is a huge number of species to lose EVERY YEAR. It is scary to think how many undiscovered species will go extinct this year. There must be thousands and thousands of species that we will never get to describe using a live specimen or discover how they might add to the diversity of the planet.

Scientists refer to “catalogued” species, but does that refer to those alive at the time the were described, or any species that has ever been described and named? Scientists estimate that extant species account for only 3% of everything that has lived on Earth, so including all species would greatly increased the overall number. However, in most estimates of species on Earth, the species being talked about are alive now, except for the one went extinct just this second, and the one that will go extinct two minutes from now, and the one….

The opposite action is also occurring; we discover new species every year. Most people think that perhaps a few new species are found each year, but it’s really in the thousands. The International Institute for Species Exploration (IISE) at Arizona State University publishes a list each year of the newly discovered species. For 2011 the list was more than 18,000 species long! You can see from the picture (below, right) that many discoveries were made in every kingdom of life in the decade of the 2000’s, more than 170,000 discoveries in all.

This graph shows the relative number of new species in many groups of

organisms. The scales are variable for each group and can’t be compared

amongst the groups. The trends show that in some groups, more and

more species are being discovered each year, while in others, fewer and

fewer are being found. In still others, some years a bunch are found and

some years provide few or no new species.

If 170,000 were discovered in ten years, the total number of species on Earth must be huge. Let’s break down the numbers of catalogued species and the estimates by kingdom.

Animalia – These are what most people think of when asked to name a species. Most animals are relatively big and can be seen in everyday life. The number of catalogued species includes the dinosaurs and humans, birds and sponges.  The numbers in each group vary greatly.

People love to study birds – so we have probably found a greater percentage of the total number of birds than we have worms. We have named about 10,000 species of birds, and more than 22,000 species of annelids (segmented worms). But there are probably many more annelids that we have not found as compared to birds. Therefore the estimate for annelids will be harder to make and perhaps less accurate.

For all animals, the total number of catalogued species by 2010 was 1.2 million. A recent paper (2011, Mora et al.) has predicted the number of species in most kingdoms based on several mathematical models. The authors predict that there are more than 9.9 million animal species on the Earth and in the oceans. According to this estimate, we have found only 12% of all the animals on Earth!

Meet the Giant Gippsland Earthworm 

(Megascolides australis). It can reach 3meters 

(10 feet) in length. First described in 1878, this 

worm lives in the deep clay soil in a small 

area in Australia. Similar worms live in North

America, but they are rarely observed.

Plantae – Plants include the non-vascular mosses, the vascular, spore-forming ferns and horsetails, the seed bearing gymnosperms (conifers and such) and the fruiting and flowering angiosperms. So many of these organisms are crucial for human life (medicine, food, oxygen!) we have done a good job of cataloguing them. The 2011 Mora paper surmises that we have already described nearly 50% of the total number of species.

Their methodology uses a lot of math to relate the number of higher taxa (phylums, orders, families) that are known in well-described kingdoms to the possible number in lesser studied groups. They found that there was a consistent pattern in which the more families there are now can be used to predict how many total genera there might be, and each level then can be used to predict the number in kingdoms for which the number of higher taxa are known. They also use methods to predict unknown higher taxa, so they can be included in the species estimate.

For plants, the Mora group predicts that there are 314,000 species extant on Earth. Other estimates also come out at about 300,000 species, but they include algae, which are actually protists, not plants.

Fungi – These organisms range from the invisible to the visible. In fact, in the paleoworld, fungi represented the largest organisms on Earth. Even today, the largest single organism is a fungus in the Malheur National Forest in Oregon, where a single 8,000 year old honey mushroom covers 2,200 acres (8,900 square meters) of land.

On the top is a fossilized prototaxite fungus in Saudi Arabia 

that once reached 20 ft (6 m) in height and was the tallest 

organism on the early Earth (this one is on its side). On the 

bottom is the national forest where a single honey mushroom mat 

has killed 2200 acres of trees. Each mushroom is a clone,

connected by a rhizoid mat just under the ground.

If you compare plant diversity to fungi, fungi win hands down. Described species of fungus lag behind; only 43,000 species have been named, but there is much more room to add new species. Estimates are that by the time we are done, whenever that is, we will have nearly 700,000 different mushrooms and other fungi.

Protista – Protists are a bit of a catch-all kingdom. Some have aspects that make them look like plants; they perform photosynthesis or they have central vacuoles. Others are much more animal-like. Overall, they are free-living organisms that are usually single celled or made up of many cells not forming tissues. Two examples show you the diversity in this group. Giant sea kelp (Macrocystis pyrifera) is a type of brown algae that can grow at a rate of 2 ft/day and can reach a length of 300 ft (91.5 m), while picoplankton are 0.2 microns (0.00000002 m) in diameter, are single celled, and may or may not perform photosynthesis.

The estimates for the number of protists vary greatly. A 1998 study indicated that they had no reason to believe the total number of protist species would be greater than 3000. However, a 2005 report puts the estimate number anywhere from 140,000 to 1.6 million. The Mora group’s paper estimates that about 73,000 will be found; that’s 57,000 more than have been described as of 2010.

Archaea and Bacteria – These are the prokaryotes. They live in tar pits and arm pits; they own the planet and probably outer space as well. There are more bacteria in a scoop full of dirt then people who have ever lived on Earth. But for the purposes of our discussion today, the important part is that same scoop of dirt has thousands of undiscovered bacteria.

The J. Craig Venter Institute is leading the Global Ocean Sampling Expeditions to discover new marine microorganisms. A pilot expedition in 2003 identifed 1800 new species in just a couple of months. This was followed by global expeditions in 2005-2009 and an expedition to the European waterways in 2009-2010. They will analyzing the data and naming species for decades to come.

This map represents the expeditions of the Global Ocean Sampling Projects

of the Venter Institute. As they traveled, they would acquire 200-400 gallon

samples of water from different depths every 200 miles and put them

through a series of filters to catch smaller and smaller organisms. The filters

would be dried and used for DNA analysis. In just a couple of months, 1.2

million genes were identified using this methodology.

Most bacteria and archaea can’t be grown in the lab because we don’t know what they require to live. This makes them hard to describe and classify.  Therefore, the Venter Institute uses DNA techniques from dried whole organisms to identify new “species.”

But perhaps classification is not the proper term for these organisms. I talked to Dr. Mora about why prokaryotes were not analyzed to the same degree as other kingdoms in their paper.  He rightfully pointed out that species definitions don’t really apply to prokaryotes as neatly as they do other types of organisms.

Certainly they don’t conform to the mating and fertile offspring definition of species since they don’t mate. Also, since they swap DNA as usual business (lateral gene transfer), who is to say where one species stops and another begins.

Other sources are little more daring in projecting possible numbers of prokaryotes. It is possible that there are a billion distinct bacteria and archaea, but it more likely that the number is in the 10-20 million range.

What are our final numbers when add up all the estimates? Predicted species numbers for life on Earth range from 11.3 million in the Mora paper, to perhaps more than 1 billion if you include prokaryotes. If we leave the bacteria out of the equation, there could still be as many as 30,000,000 forms of life on the planet. We have described about 2 million (according to IISE), so only 28,000,000 left to find!

Mora, C., Tittensor, D., Adl, S., Simpson, A., & Worm, B. (2011). How Many Species Are There on Earth and in the Ocean? PLoS Biology, 9 (8) DOI: 10.1371/journal.pbio.1001127
 

ADL, S., SIMPSON, A., FARMER, M., ANDERSEN, R., ANDERSON, O., BARTA, J., BOWSER, S., BRUGEROLLE, G., FENSOME, R., FREDERICQ, S., JAMES, T., KARPOV, S., KUGRENS, P., KRUG, J., LANE, C., LEWIS, L., LODGE, J., LYNN, D., MANN, D., MCCOURT, R., MENDOZA, L., MOESTRUP, O., MOZLEY-STANDRIDGE, S., NERAD, T., SHEARER, C., SMIRNOV, A., SPIEGEL, F., & TAYLOR, M. (2005). The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists The Journal of Eukaryotic Microbiology, 52 (5), 399-451 DOI: 10.1111/j.1550-7408.2005.00053.x

It’s An Airtight Case

Biology concepts – respiration, aerobe, anaerobe, CAM plants, plastron respiration, cutaneous respiration

Question of the Day – what living thing can hold its breath the longest?

It may seem like an exaggeration, but people whose
tissues are low on oxygen (hypoxic) can have a bluish

hue (cyanosis). Blood that is oxygenated is redder

than blood that is deoxygenated. In animals with more

hemoglobin than humans, like whales, the blood can

actually turn almost purple. Blue Man Group will turn

you blue - from laughter, not disease.

The world’s record for holding one’s breath (voluntarily) was set in May, 2012 by Denmark’s Stig Severinsen. Even though it wasn’t technically cheating, he did hyperventilate with almost pure oxygen for 19 minutes before he then held his breath for an amazing 22 minutes and 0 seconds!

Hyperventilation works by reducing the CO₂:O₂ ratio in your blood. CO₂ concentration is measured by sensors in your large blood vessels. Signals are sent to the brain to increase the breathing rate if there is too much CO₂ in the blood or to reduce the breathing rate if the pCO₂ is too low. By breathing fast and breathing pure O₂, there will be less CO₂ in the blood and your brain will tell you to stop breathing until the pCO₂ increases to normal levels.

Stig said he used two mental tricks to increase the time he can hold his breath. One is scientifically valid; biofeedback allows Stig to slow his own body activity. By concentrating on his heartbeat, Stig has learned to stimulate neural pathways to reduce his cardiac output and his overall metabolism rate -lower metabolism and heart rate - less need for oxygen. His second technique? He thinks about dolphins.

Twenty-two minutes seems like a long time; indeed, this feat required arduous training by Stig. In truth, 22 minutes isn’t very long at all. In fact, humans are weenies when it comes to going without oxygen. Lots of animals can hold their breath longer than we can.

Sperm whales and elephant seals are the banner carriers for the marine mammals in our contest. Sperm whales can submerge for more than two hours, while elephant seals may stay under water for an hour or more. Being mammals, they have physiology very similar to humans in some respects, but they do have modifications that allow for the long submersions.

Elephant seals have a large proboscis; hence the

elephant name. There are two species, Northern and

Southern, with the Southern species being slightly

larger. Males can weigh over 5 tons and they fight for

females. The females are more like 1500-2000 pounds,

making this the largest relative difference in weights

of two sexes for any mammal.

Whales and seals have more blood than humans do – duh! Even compared pound for pound, they have 3x as much blood. More blood means more oxygen carrying capability. They also have increased oxygen carrying proteins in their blood and tissues. In addition, they can reduce their metabolism in all but the most necessary organs, and they can divert their blood to just these organs.

New research shows that marine mammals also have oxygen carrying proteins in their brains, called neuroglobin and cytoglobin. So, while blood levels of oxygen may plummet when diving, the brain remains oxygenated.

Sea turtles and crocodilians are examples of reptiles that can hold their breath for amazing lengths of time. Aligators and crocodiles can stay submerged for a couple of hours, while a Galapagos sea turtle can easily stay underwater for 4-7 hours, depending on its level of activity. Maybe they think about Stig in order to stay submerged longer.

Sea turtle hibernation is controversial, but some freshwater turtles do just that. They can stay submerged for weeks or perhaps months at a time! But many turtles cheat at our contest, they have a bimodal respiratory system, through their lungs and through their skin. Cutaneous gas exchange is apparent in all freshwater turtles to some degree, but it is much more efficient in some soft shell turtles, according to a 2001 study.

Let’s look at a different type of reptile. The Belcher’s sea snake (Hydrophis belcheri) is the most venomous snake on the face of the Earth, or under it, as the case may be. It is a sea snake that can remain submerged for 7-8 hours. Sea snakes like H. belcheri have a single lung that runs almost the entire length of their body, and their trachea can also transfer oxygen to the blood. This reduces the “dead space” in their respiratory system and allows them to absorb more of the oxygen they inhale.

This diagram gives you an idea of how little respiratory

space humans use for gas exchange. The only places

that move oxygen in to the blood are the pinkish

alveoli at the ends of each airway. Sea snakes use

their available respiratory space to exchange gasses.

Humans, as a comparison, only absorb about 15% of the oxygen in each breath, partly because the gas exchange takes place only in the alveoli (terminal air sacs). Oxygen in the nose, pharynx, trachea, bronchi, and bronchioles is just exhaled without any chance to be used by the body.

However, sea snakes are cheaters as well. Their bodies have been streamlined to help them move through the water. One adaptation in this direction is the complete loss of scales. As a result, these snakes have evolved the ability to exchange some oxygen and carbon dioxide with the water through their skin. So they aren’t really holding their breath when submerged.

Almost all amphibians are cutaneous (skin surface) breathers as well. In air, most amphibians can survive exclusively by exchanging gasses through their skin, and in water, adult gills or rudimentary lungs are supplemented by exchange of gas from the water. Cold water and turbulent water contains more oxygen, so in these environments amphibians can survive indefinitely by garnering oxygen from water.

Indeed, the largest family of salamanders (the plethodontidae), don’t have any lungs at all. They exchange gasses only through their skin and the mucosa surfaces of their mouths. And many of these salamanders are primarily aquatic, they don’t take a breath in their entire lives – but they aren’t holding their breath either.

But none of these animals are the champion breath holders. There are organisms that laugh at holding their breath for a couple of hours. But let’s limit our discussion to those organisms that require oxygen. It’s no fun watching an anaerobic bacterium hold its breath; it doesn’t need oxygen! In many cases, air kills them!

Cockroaches, ticks, and ants do last a long time underwater, just try flushing one. But they can’t win our contest either. They seem to trap a bubble of air as they submerge. They have long hairs on their abdomens that trap air via the surface the surface tension and cohesion of water.

A plastron is the bottom portion of the turtle or tortoise shell,

made up of flat pieces. On the right is the plastron of a tick.

In some ticks there can be gas exchange from water to bug

through the plastron. This is called plastron respiration.

Surrounded by the bubble, they can oygenate their tissues via the breathing holes on the sides of their bodies (spiracles). This allows them to be underwater for nearly an hour and still be breathing. New research in ticks shows that the plastron (flat portion under the abdomen) is capable of some gas exchange itself via the air trapped by the hydrophobic hairs on the abdomen.

We make a big deal about how plants take in carbon dioxide and give off oxygen, and they do during photosynthesis in their chloroplasts. But that’s only half the story. They also have mitochondria that produce ATP from photosynthesis products via oxidative phosphorylation, just like we do.

For plants that grow in hot, dry environments, loss of water is a serious threat. To minimize water loss, some can close the pores in their leaves (stomata), but this also prevents gas exchange, including taking up carbon dioxide and oxygen. The stomata will open only at night, when the temperatures are cooler and water loss would be lost. This is the only time they exchange CO₂ and O₂ with the environment as well.

CAM (crassulacean acid metabolism) plants can store the carbon dioxide they take in at night in the form of malate. They then can perform photosynthesis even though their stomata are closed. CAM physiology also reduces the amount of O₂ bound by RuBisCo enzyme instead of CO₂. RuBisCo + O₂ leads to inefficient carbon fixation, so waiting until night time when CO₂ is relatively more abundant and more soluble will increase photosynthesis productivity. As a result, CAM plants hold their breath for 8-15 hours every day!

CAM plants close their stomata during the hot day, but

exchange gasses during the cooler night. They convert

carbon dioxide to malate as a temporary fixation, which

they store in the central vacuole. During the day, they

convert the malate to carbon dioxide and then to

carbohydrate in the chloroplast using normal

photosynthesis pathways. CAM plants include the

prickly pear, as shown on the extreme right and left.

But the winners of our lack of oxygen survival contest – bacteria, of course! Bacteria come in many flavors, including those that don’t need oxygen for respiration (chemosynthesizers and anaerobes), those that can take or leave oxygen (facultative bacteria), and those that must have oxygen in order to make ATP (obligate aerobes).

Mycobacterium tuberculosis is an example of an obligate aerobe. I talked to Martin Gengenbacher at the Max Planck Institute in Berlin about M. tuberculosis and its survival time without oxygen. He has recently published a great review of M.tuberculosis biology. In a series of experiments that resulted in the development of something called the Wayne model, M. tuberculosis was sealed in a vessel in which they consumed all the available oxygen over time.

However, even after the oxygen was gone, the organisms remained viable for 25 days! They do seem to go dormant, but this dormancy is not the same as ceasing activity completely. It seems that some metabolism and respiration is maintained in the complete absence of oxygen – even though we know that M. tuberculosis absolutely requires oxygen to survive.

These 25 days make M. tuberculosis better than any of our other example organisms at living without gas exchange, though there may be other obligate aerobes that can perform similar feats. But there’s more to the skills of the tuberculin bacterium. In tuberculosis, the body has a difficult time killing off the organism, so it does the next best thing – it walls off the bacteria and traps them in a prison cell of immune cells. These whirls of cells are called granulomas and are very complex structures.

On the left shows a tuberculin granuloma forming and breaking

down. You can see in the middle a formed granuloma, with

macrophages surrounded by a fibrous cuff and lymphocytes.

When immunosuppression sets in, the granuloma breaks down

and the organisms is released to cause disease. On the right is a

photomicrograph of granulomas. In the right corner is a

tuberculosis bacterium before granuloma formation.

Granulomas are extremely hypoxic (oxygen poor), and M. tuberculosis does undergo dormancy in these structures. But again, Dr. Gengenbacher states that this is a metabolically active dormancy, which would by definition require ATP, and therefore require cellular respiration.

The patient still has TB, but no symptomology. This remains the case until the patient undergoes some form of immunosuppression, some disease or condition that prevents the immune cells from keeping the organism in prison. There have been cases where TB has reactivated some 50 years after the original infection. So – M. tuberculosis can hold its breath for half a century! We have a winner.

Next week, another question to ponder. Just how many species call Earth home? 



Gengenbacher, M., & Kaufmann, S. (2012). Mycobacterium tuberculosis: success through dormancy FEMS Microbiology Reviews, 36 (3), 514-532 DOI: 10.1111/j.1574-6976.2012.00331.x  

Fielden, L., Knolhoff, L., Villarreal, S., & Ryan, P. (2011). Underwater survival in the dog tick Dermacentor variabilis (Acari:Ixodidae) Journal of Insect Physiology, 57 (1), 21-26 DOI: 10.1016/j.jinsphys.2010.08.009  

Williams, T., Zavanelli, M., Miller, M., Goldbeck, R., Morledge, M., Casper, D., Pabst, D., McLellan, W., Cantin, L., & Kliger, D. (2008). Running, swimming and diving modifies neuroprotecting globins in the mammalian brain Proceedings of the Royal Society B: Biological Sciences, 275 (1636), 751-758 DOI: 10.1098/rspb.2007.1484

 

Venomous Plants – A Hairy Situation

Biology concepts – venom, toxin, poison, nettle, urticating hairs, trichomes, defense behavior

The cobalt blue tarantula is a beautiful old world

tarantula, but not very cleverly named. They are

popular as pets, even though they are fast,

aggressive and have a potent venom. Fortunately,

they don’t have urticating hairs.

A tarantula, a jellyfish, and an ongaonga tree walk into a bar – O.K., maybe not the best start. But these three organisms do have something in common, something that has been recognized since the time of their classification and naming. Follow along.

Tarantula spiders are a popular example of venomous arthropods, arachnids to be exact. “Tarantula” is a vague term as it is used in the general population. The name comes from Taranto, Italy and came to mean any unknown, hairy, long-legged spider. In scientific taxonomy, tarantulas belong to the family Theraphodsidae, a group containing at least a dozen subfamilies and more than 900 species.

Many tarantulas have impressive fangs that deliver potent toxins to their victims. The fringed ornamental tarantula (Poecilotheria ornate) has produced a coma in a human; however, no known tarantula possesses venom that is acutely lethal to people.

But biting isn’t the only way tarantulas can defend themselves. Besides giving you the heebie-jeebies, two subfamilies of tarantula spiders have defenses called urticating hairs. These hairs are easily lost from their hairy backs or legs when the spider is touched by a predator. These small hairs can lodge in the eyes or skin of predators and cause significant physical irritation, enough to ward off a predator.

There are at least four types of urticating hairs, each differing in size and in the type of predator against which they are most effective. The old world tarantulas have type II urticating hairs that are dislodged by touch, but some tarantulas from the Americas can go one step further. They can fire their urticating hairs from a distance (types I, III or IV).

Urticating hairs often cause urticaria (hives), but

sometimes the red bumps will coelesce and form a

rash. And if you allergic, as seen here, the rash will

become big, ugly, and painful. You can see blister

development at the bottom. Explain to me why he is

affected on his belly?!

Species like the chilean rose and the mexican red-knee tarantulas have urticating hairs that can be fired by kicking their back legs against the back of their abdomen. When threatened, the tarantulas turn and rise up on their legs – ready! They point their abdomen at the threat – aim! And then they rub their legs against their abdomen and release a cloud of hairs toward the target – fire! This leaves a bald patch on their back and a very annoyed predator.

Most urticating hairs are mildly irritating to humans, unless you hold the spider up to your face. This is what happened in 2013 to a three year old boy at his birthday party. He held a rose tarantula up to his face to get a good look, and got two eyes worth of uritcating hairs! He cried for days, as they are so small as to become completely buried in the cornea and cannot be removed. He has made several subsequent trips to the hospital for care.

Other tarantulas have more damaging urticating hairs.  The Goliath Birdeater has larger hairs that can cause very bad rashes, and feel like fiberglass shards embedded in the skin. Some people will become allergic to the hairs, and the rash and reaction will be even worse (see the picture above).

So what has tarantula hair got to do with jellyfish or the ongaonga tree? Urtica is the Latin word for “nettle,” and the ongaonga tree is also known as the tree nettle or Urtica ferox. And the Greek word for nettle is “cnida,” as in cnidarians – like the jellyfish and coral we talked about two weeks ago. All three of these types of organisms use stinging cells for defense or offense.

Cnidarians use nematocysts to envenomate their prey, shooting toxin filled harpoons at the target. Tarantulas (and some caterpillars) use urticating hairs, not to poison but to irritate their predators. And there are some plants, the nettles, which use urticating hairs as venom delivery systems – the best of both worlds.

The nettles (genus Urtica, approximately 80 species) have hollow uricating hairs that can deliver toxins when they are broken off and embedded in an unfortunate victim. The hairs are actually modified trichomes, epithelial structures found in many plants that are merely raised areas on the plant surface.

Trichomes evolved many variations, those termed “hairs” can be thick or thin, long or short, fuzzy or smooth. Some may be used for water absorption or evaporation, while others will physically impede the movement of insects along the plant, or act as sensors. Venus flytraps (Dionaea muscipula) have three different kinds of trichomes; two secrete digestive juices and one is the sensitive trip wire for closing the trap.

These are the trichomes (stingers) of the ongaonga

nettle. Most nettles have smaller hairs, but this makes

for a more ominous picture. Remember that it isn’t

just their sharp points, they contain venom too.

Typical toxins included in nettle tricomes are formic acid, like in many ant species, and neurotransmitters like serotonin, and histamine. The pain or itch goes away in a few hours. They raise red welts that itch, called hives. In scientific terms, all hive-producing reactions are called urticaria. Get the connection? Most nettle trichome envenomations, like those from Urtica dioica (common nettle) are irritating, but little else.

However, the ongaonga tree (Uritca ferox) is the exception. There has been at least one death associated with just brushing against it. The ongaonga has unusually large spines; the lightest touch brings pain for more than five days.  Its neurotoxins also include an acetylcholine (Ach)-like chemical, yet another neurotransmitter.

The late symptoms can include breathing problems, blindness and paralysis. A 21 year old student developed a paralysis after a brush with the ongaonga. The neurotoxin caused her motor nerves to malfunction, firing too slowly and without pattern. It took weeks for her to recover.

But the news isn’t all bad. Nettle toxins may be used to in medicine, including diabetes, infection and even liver damage. A 2013 study in India treated rats with common nettle oil before performing a partial liver removal. The oils helped promote liver regeneration and decreased cell death after surgery. They also reduced the amount of oxidative damage in the surviving cells. So if you plan on destroying your liver, go run through a nettle patch first. However, I couldn’t find any studies using ongaonga oils – it is just too toxic. So be sure of your nettle patch species prior to your liver-protecting frolic.

A strange picture to see here, but follow along. You can

have part of your liver removed if it is damaged and live

just fine. A partial removal is called a hepatectomy. Some

parts can even regenerate after you have them removed.

Hepatectomy is important, as it makes it possible to have

living liver donors – you give someone part of your liver,

and you grow it back. This is where the nettle medicine

could be useful.

Our king of venomous plants comes from a different genus of the same family of plants as the nettles. You would think a plant that could kill you by touch would have a tough name, but it turns out to be just another insult added to the injury. You have tell your best buddies that you are laid up for weeks by a plant; and when asked, you have to tell them it was the “gympie gympie!” I can hear the laughter now.

The gympie gympie (Dendrocnidae moroides) lives in Australia, the land of painful deaths. The Australian Geographic website says that being envenomated by the gympie gympie is like, “being burnt with hot acid and electrocuted at the same time.” It has killed people, horses, and dogs.

Minor stings can last for hours to days with increased heart rate and sweating. The gympie’s trichomes seem to be silica based, like glass. You can heat them with a flame until they glow red, but they will still hold their shape. Add being stabbed with glass shards to the description of the gympie's sting.

Severe encounters can bring pain for months, with symptoms waning and then brought back by hot or cold air, water, or rubbing. Some people have shot themselves to relieve the pain, while others have had to be strapped to the bed.

There isn’t much you can do to treat the pain, but you might be able to shorten the length of your torture. The best first aid is to immediately apply hair removal wax and yank out the trichomes. You go for a hike and end up with silky, smooth skin and a pain that won’t stop – oh, wait, that could be just be describing the waxing.

The gympie gympie has huge leaves, like it is trying to ruin

your day. You can’t even see the hairs here, they are too

small. But you know it if you touch it. Did this guy lose a bet? 

Just being this close is a very bad idea.

Usually the pain comes from rubbing against the leaves, stem, or twigs. But the gympie wants to reach out and touch you, even if you don’t reach out and touch it. It sheds its urticating hairs all the time, so if you hang around a tree long enough, you will get a nosebleed and start to sneeze painfully. And you can’t wax the inside of your nose ….. I hope.

Fortunately, few deaths have been associated with the gympie gympie. It grows in the rainforests of northeast Australia where the population is very low, about 5-10 people per 2.5 sq. mile. The aborigines live here, and they actually eat the berries of the gympie gympie. Since all its trichomes point one direction, the natives know how to move along the stems and leaves in the right direction to harvest dinner. Apparently the berries aren’t poisonous.

D. moroides toxins include those said to act as neurotransmitters Ach, serotonin,  and histamine, but their chemical structures are different. They also include moroidin, a short peptide toxin that was first isolated from the leaves and stalks of the gympie.

No, this isn’t a picture of some electrical spark experiment

gone wrong. The green spines are the mitotic spindle and

the red blobs are the chromatids being pulled apart during

mitosis. More mitoses, more cell divisions. More divisions,

more cells. Too many more cells = cancer. It would be nice

to stop the spindles in that case.

Moroidin is a mitotic inhibitor; it interrupts the polymerization of tubulin during the formation of the mitotic spindle. If no spindle forms, then there is no alignment or segregation of chromatids during mitosis, so no cell division. Moroidin is supposed to be the factor that makes the sting pain last a long time, but not enough research has been done in this area. No one can even tell me specific chemicals the gympie possesses or how it causes pain! How can we make use of it in medicine if we don’t know how it works? I would think that a mitosis inhibitor might work well against cancer – let’s get to work people!

School is winding down, so why don't we start our summer posts. Each week will be a separate question in biology, from misconceptions to things that make you wonder, to weirdness galore. Next week - how good are different species at going without oxygen, and who can hold their breath the longest?

Oguz, S., Kanter, M., Erboga, M., Toydemir, T., Sayhan, M., & Onur, H. (2013). Effects of Urtica dioica on oxidative stress, proliferation and apoptosis after partial hepatectomy in rats Toxicology and Industrial Health DOI: 10.1177/0748233713480211

Hammond-Tooke, G., Taylor, P., Punchihewa, S., & Beasley, M. (2007). Urtica ferox neuropathy Muscle & Nerve, 35 (6), 804-807 DOI: 10.1002/mus.20730

For more information, see:

Tarantula urticating hairs –

http://arachnophiliac.info/burrow/urticating.htm

http://regalpet.com/content.php?1052-Tarantulas-Urticating-Hairs

http://www.animalcorner.co.uk/venanimals/ven_spidtarnw.html

http://www.arachnoboards.com/ab/showthread.php?240029-Best-way-to-treat-tarantula-urticating-hair

http://www.youtube.com/watch?v=vDkSIrbw5gA

http://arthropoda.wordpress.com/2010/01/30/tarantulas-attack-with-their-back-hair/

https://sites.google.com/site/tarantuladb/resources/urticating-hairs

http://tarantula-care.com/urticating-hairs/

http://ezinearticles.com/?The-Tarantula-Defense-Mechanism---Urticating-Hairs&id=1960205

Nettles –

http://www.richsoil.com/nettles.jsp

http://www.herbwisdom.com/herb-nettle.html

http://www.webmd.com/vitamins-supplements/ingredientmono-664-Urtica%20%28STINGING%20NETTLE%29.aspx?activeIngredientId=664&activeIngredientName=Urtica%20%28STINGING%20NETTLE%29

http://www.blueplanetbiomes.org/stinging_nettle.htm

http://www.kew.org/plants-fungi/Urtica-dioica.htm

http://www.nzpcn.org.nz/flora_details.aspx?ID=1354

http://www.youtube.com/watch?v=yGZBlhJpcT8

http://www.trimblefoundation.org.nz/urtica-ferox-onga-onga-at-rewanui/

http://www.nhm.ac.uk/nature-online/species-of-the-day/scientific-advances/disease/urtica-dioica/

http://depts.washington.edu/propplnt/Plants/Urtica%20dioica.htm

Gympie gympie –

http://www.australiangeographic.com.au/journal/gympie-gympie-once-stung-never-forgotten.htm

http://www.youtube.com/watch?v=nkTlaF1sP_A

http://therovingapothecary.blogspot.com/2012/11/a-curious-australian-plant-gympie-gympie.html

http://www.ebaumsworld.com/video/watch/81008069/

http://blog.cairnswildlife.com.au/gympie-gympie-%E2%80%93-better-known-to-us-as-the-stinging-tree/

http://wildflowerfinder.org.uk/Flowers/N/Nettle%28Stinging%29/Nettle%28Stinging%29.htm

A Death Apple A Day Keeps…..

Biology concepts – toxin, poison, urushiol, oleander, hapten, allergic contact dermatitis

A cloudburst threatens to ruin your summer hike. You dart under a tree for protection from the rain and break out a granola bar. You decide to wait it out, but after a few minutes, your skin starts to itch and your eyes sting. After a few more minutes, you notice a rash on your arms and your throat feels like it's closing. Is it bad granola? Is it acid rain? Are you going to die?

The manchineel tree is toxic enough that just touching it can

do you serious harm. The sign should say, “Don’t even get

near me!” because dripping sap can be just as bad. On the

right you see the apples of the manchineel. They look good,

they are sweet, and the price is right – and then you die.

No, no, and maybe. You just picked the wrong tree to use as an umbrella. This is the manchineel tree (Hippomane manciella), native to several countries in the around the Americas and the Caribbean.

The latex that oozes from this tree contains the toxins hippomanin A and B. Both toxins are present in the latex, leaves, bark, wood, roots, fruit, flowers, and nectar of the manchineel. Eat it or rub against it, and you get sick. Cut it up and the sawdust makes you sick; get it in your eyes (even the smoke from burning it) and you can go blind!

Most deaths have occurred from eating the apple of the manchineel; hence the common name for the tree – the Death Apple. Your mucosal surfaces blister, your larynx swells shut, your GI system rebels loudly and explosively. Massive hemorrhage can follow the closing of your throat, so you drown in your own blood.

In the 1500’s, South American Indians threw death apples down their own wells to poison the invading Spanish conquistadors. It worked because this toxic plant is an exception; it is sweet. Most often, plant toxins taste bitter and that's how we know to avoid them. The death apple’s taste prevents us from making a judgment that could save our life. Definitely, this is a plant to be respected and feared.

Now that I have your attention, let’s talk about a seemingly more common plant toxin. Urushiol is the name for the offending group of molecules in poison ivy, poison oak, poison sumac, even more exotic plants like mango, lacquer trees and cashew nuts.

Mangoes (left) and cashews (right) are in the same family

of plants as poison ivy and poison oak. They contain

urushiol and can cause significant damage to those who have

a heightened allergic response. Urushiol is present in the

skin of the mango fruit and in the shell of the cashew nut.

This is why you can’t buy cashews in the shell, the shell

must be removed to make them safe. Cutting a mango will

give you a small exposure, but most people tolerate this well.

The urushiol (Japanese for lacquer) is exuded from the leaves and stems of the offending plants, and is found in the cashew nut shell. Skin contact leads to blisters and a rash; these are seen earlier in patches that get a larger dose. Urushiol is only partly water soluble, so it can stay on the skin or other surfaces and be spread for quite a while. It can stay on clothes until they are washed; even if that may be years, as in the case with my teenagers.

Urushiol toxicity comes from the immune reaction it generates in about 60-80% of the population. However, urushiol doesn’t spark an immune response on its own. It turns your body against itself. Immune responses are aimed at antigens (not born of, so not self), but urushiol breakdown products are haptens (to fasten to); think of them as half antigens. Haptens must combine with something else to become full antigens. In the case of urushiol, they combine with proteins from our own cell membranes.

When portion of the urushiol combines with the integral protein, now the protein is seen as foreign and your immune system might start to attack, in a process called type IV delayed hypersensitivity. This produces inflammation and tissue damage in a reaction termed allergic contact dermatitis.

Allergic contact dermatitis is different from irritant contact

dermatitis in that irritants damage the skin directly, while

allergens invoke an immune response that causes the

damage. The hapten, in the case of urushiol, penetrates and

is modified by Langerhan cells. The lymphocytes are

exposed to the modified urushiol + membrane protein and

initiate a response. The activated T cells then circulate and

react the next time the urushiol is touched.

As with other allergy reactions, contact dermatitis requires a sensitizing dose, in which your body is exposed to the allergen and ramps up a small reaction. Subsequent episodes are worse because part of the allergic reaction in the immune system sticks around (immune memory).

Not everyone’s immune system recognizes or overreacts to the hapten + membrane protein, so not everyone gets a rash from poison ivy – lucky devils! Other permutations are possible as well. You can be resistant and then develop an allergy late in life, or you can have contact dermatitis when young and later on become resistant. We know a lot about allergic hypersensitivity, but there's also a lot we don’t know. Much research is underway on plant toxins and allergens.

And herein lies the rub - pun intended - with many toxic plants. They cause pain, damage and irritation, yet Paracelsus said, “only the dose makes the poison.” Does that mean that a lower dose has no effect? Well, most of our medicines – antibiotics, anti-cancer, anti-depressive - come from fungi and plants. It isn’t just that less may not be harmful; less might actually be helpful!

Take urushiol for instance. A 2011 study shows that urushiol can kill H. pylori, the bacterium that causes many stomach ulcers. Within 10 minutes, urushiol can strip the membrane off of the bacterium and cause it to lyse. Traditional treatments were found to eradicate the disease in 75% of cases, but adding urushiol brought a 100% cure rate. It even worked in a mouse model, but no one asked the mice if their stomachs itched. Even hippomanin A is an inhibitor of herpes simplex virus 2 replication. It seems that every toxic plant we talk about here has some medicinal use – nothing and nobody are completely evil.

There are several plants that could wrestle for the title of most toxic, but anyone’s top five contenders would have to include oleander (Nerium oleander). You can die just from eating honey collected from bees that landed on the plant and partook of the pollen or nectar.

Nerium oleander is a bush like plant that can have red or

white flowers. It is deadly, but is repairing its reputation

by being used as a medicine. Oleander is the official flower

of Hiroshima, Japan, as it was the first flower that grew

after the atomic bomb was dropped. In Texas, oleander is

used as a decorative plant in road medians – don’t mess

with Texas medians!

The principal toxin is oleandrin, a cardiac glycoside. This type of toxin messes with the electrical impulse generation in heart muscle cells. As a result of the toxin, cardiac activity is dysfunctional, often to the point of arrythmia and heart attack. In other cells, it interferes with calcium levels and can induce cell death. Despite these evil tendencies, oleandrin is proving to be a very useful medicine.

A 2012 study has shown that oleander distillate is therapeutic in diabetes. Rats with induced diabetes were treated with oleander extracts for 12 weeks. Those treated rats had better blood sugar levels, reduced insulin resistance and cholesterol, and improved insulin levels. Not only was the diabetes positively affected, but fat levels were also positively affected – all through treatment with a lethal poison.

But wait - there’s more! Oleandrin has been show to be effective in inhibiting cancer. In at least five different kinds of cancer, oleandrin can stop cancer cells from increasing in number (proliferating), and can even induce the cancer cells to kill themselves (apoptosis). That’s a good start, but it gets better.

A 2005 review discusses the idea of resistance to treatment that develops in many cancers over time. Wouldn’t it be great if we had something that could make the cancer cells sensitive to the drug treatments again? Well, this review discusses studies that show oleandrin can do just that. Oleandrin acts not only as a chemosensitizer, but makes cancer cells more sensitive to radiation therapy. Therefore, oleander is synergistic with other cancer therapies and makes them work better.

Can you stand any more wondrous uses for this poison? A more recent study indicates that oleandrin reduces infectivity of HIV. AZT, a traditional HIV drug, reduces replication but not infectivity, while oleandrin reduces infectivity but not replication, so they could work together.  Oleander can save you from infectious diseases, cancers, and metabolic diseases – but eat the berries on your next hike and you’ll die a horrible death.

Both the cinnabar caterpillar (left) and the moth (right) are

brightly colored. This is called aposematism, warning predators

that they are toxic. It usually works, but the common cuckoo is

apparently opposed to aposematism; it has learned to avoid the

most toxic portions of the larvae and adult.

So humans are animals that can’t just willy-nilly start munching on toxic plants. But other animals can. We have talked about animals that use the toxins they eat (2˚ toxin sequestering), usually from either insects or plants. But is there an exception – does any animal sequester a toxin that its prey sequestered from a plant? I looked for one.

There is a cuckoo that eats the cinnabar moth caterpillar that eats toxic ragwort. The plant has alkaloids. In the stomachs of most animals, they are quickly converted to toxins. But a 2012 study shows that the cinnabar moth caterpillar’s enzymes can convert the metabolic products back to their non-toxic alkaloid forms. Then they are ready to poison the unwitting animal that eats the caterpillar and hasn’t had the forethought to evolve a detoxification process!

However, the common cuckoo (Cuculus canorus) avoids the toxins in the cinnabar caterpillar by biting off the head of the larvae and discarding it, then shaking the carcass to expel the liquid toxin. This is like how some birds can eat monarch butterflies. Monarchs are toxic, having sequestered milkweed toxins they ate as caterpillars. Shining cuckoos in New Zealand and some North American birds know to get rid of the most toxic portions and just eat the rest. Therefore, these birds are not 3˚ toxin sequesterers. I couldn’t find an example – can you?

The monarch caterpillar eats only milkweed – ONLY milkweed.

This is where is picks up its toxins. The adult will drink nectar

of many flowers, but the toxin is maintained as the larvae

metamorphed to the adult.

Most birds just stay away from monarchs most of the time, but even this has weirdness associated with it. Monarchs lose toxicity as they age, and males usually have less toxin than females, yet somehow the birds can sense it. Research has shown that monarchs with higher levels of toxin are less likely to be attacked by a predator. How do the birds know?

We have just touched the surface of toxic plants; there are more than we can mention. In Australia alone there are said to be over 1000 toxic plants! Let’s next look to our exceptions; plants that aren’t just toxic, they’re venomous.

Bas, A., Demirci, S., Yazihan, N., Uney, K., & Ermis Kaya, E. (2012). Nerium oleander Distillate Improves Fat and Glucose Metabolism in High-Fat Diet-Fed Streptozotocin-Induced Diabetic Rats International Journal of Endocrinology, 2012, 1-10 DOI: 10.1155/2012/947187

Suk, K., Baik, S., Kim, H., Park, S., Paeng, K., Uh, Y., Jang, I., Cho, M., Choi, E., Kim, M., & Ham, Y. (2011). Antibacterial Effects of the Urushiol Component in the Sap of the Lacquer Tree (Rhus verniciflua Stokes) on Helicobacter pylori Helicobacter, 16 (6), 434-443 DOI: 10.1111/j.1523-5378.2011.00864.x

Garg, A., Buchholz, T., & Aggarwal, B. (2005). Chemosensitization and Radiosensitization of Tumors by Plant Polyphenols Antioxidants & Redox Signaling, 7 (11-12), 1630-1647 DOI: 10.1089/ars.2005.7.1630

For more information, see:

Plant toxins –

http://www.wilderness-survival.net/chp10.php

http://onnaturemagazine.com/field-trip-poisonous-plants.html

www.researchgate.net/...Plant_toxins.../d912f4febf07dd4572.pdf

http://www.sciencedaily.com/releases/2012/02/120221090240.htm

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CGcQFjAF&url=http%3A%2F%2Fddr.nal.usda.gov%2Fbitstream%2F10113%2F13290%2F1%2Find44006837.pdf&ei=43htUe_1HdKp4AOW24C4Bg&usg=AFQjCNGY0vEzK-waYT4YGnt0S0K7N3aR_w&sig2=9J-AyxT1YW7i2FV8heujKA&bvm=bv.45175338,d.dmg

http://www.accessdata.fda.gov/scripts/plantox/detail.cfm?id=21479

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CD4QFjAC&url=http%3A%2F%2Fjournals.cec.sped.org%2Fcgi%2Fviewcontent.cgi%3Farticle%3D1421%26context%3Dtecplus&ei=OHltUYz_OpfJ4AP0kYDYBQ&usg=AFQjCNE-PTQtnOBB4l8so_fCVMcanNJ2dA&sig2=IjyArHrd_xA6hSskaJkGXw&bvm=bv.45175338,d.dmg

http://aggie-horticulture.tamu.edu/earthkind/landscape/poisonous-plants-resources/common-poisonous-plants-and-plant-parts/

http://www.cdc.gov/niosh/topics/plants/

http://www.cancer.org/treatment/treatmentsandsideeffects/complementaryandalternativemedicine/herbsvitaminsandminerals/oleander-leaf

http://ip.aaas.org/tekindex.nsf/0/99b535e7618170c485256ae100696f4c/Body/M1

http://www.wildmanstevebrill.com/Plants.Folder/Poison%20Ivy.html

http://library.thinkquest.org/C007974/1_1fox.htm

http://www.helium.com/items/1493911-belladonna

http://botanical.com/botanical/mgmh/i/ivypoi17.html

http://webecoist.momtastic.com/2008/09/16/16-most-unassuming-yet-lethal-killer-plants/