Andersen KG et al. The proximal origin of SARS-CoV-2. Nature Medicine, March 2020.

Cases of Covid-19 first emerged in December 2019, when a mysterious illness was reported in in the city of Wuhan, China. The cause of the disease was soon confirmed as a new kind of coronavirus, and the infection has since caused a large-scale epidemic and spread to more than 70 other countries. Coronaviruses are a large family of viruses that are related to a broad spectrum of illnesses, the first of which was the 2003 Severe Acute Respiratory Syndrome (SARS) epidemic in China. A second outbreak of severe illnesses began in 2012 in Saudi Arabia with the Middle East Respiratory Syndrome (MERS). On December 31 of 2019, Chinese authorities alerted the World Health Organization of an outbreak of a novel strain of coronavirus named SARS-CoV-2 causing severe illness. As of February 20, 2020, nearly 167,500 Covid-19 cases have been reported, though many milder cases have likely gone undiagnosed. More than 6,600 people have already died as a result of contracting this virus – and the numbers will be much higher when you will be reading this article. Chinese scientists sequenced the genome of SARS-CoV-2 very shortly after the epidemic began and made the data available worldwide. The analyses of genomic sequence data have shown that Chinese authorities rapidly detected the epidemic and that the number of Covid-19 cases have been increasing because of human to human transmission after a single introduction into the human population.

Recently, a group of scientists used this sequencing data to explore the origins of SARS-CoV-2 and how it has become the version that it is now. The scientists specifically focused on the genetic codes for spike proteins, the mechanical framework on the outside of the virus that it uses to grab and penetrate the outer walls of human and animal cells. There are 2 major parts of the spike proteins: the receptor-binding domain (RBD), a molecular hook that grips onto host cells, and the cleavage site, a molecular can opener that allows the virus to crack open and enter host cells. The scientists found that the RBD portion of the SARS-CoV-2 spike proteins mutated to effectively target a molecular feature on the outside of human cells called ACE2, a receptor normally involved in regulating blood pressure. The SARS-CoV-2 spike protein was exceptionally effective at binding to human cells, and the scientists concluded this could only be a product after a natural selection process and not the product of human-designed genetic engineering. This evidence was further strengthened by data on SARS-CoV-2’s backbone molecular structure. If someone were to engineer a new coronavirus as a pathogen, they would have constructed it from the backbone of a virus known to cause illness. But the scientists found that the SARS-CoV-2 backbone differed substantially from those of already known coronaviruses and mostly resembled related viruses found in bats and pangolins. These two features of the virus, the mutations in the RBD portion of the spike protein and its distinct backbone, basically ruled out laboratory manipulation as a potential origin for SARS-CoV-2. Based on their genomic sequencing analysis, scientists came up with two possible scenarios as the most likely origins for SARS-CoV-2.

In the first scenario, the current pathogenic state of SARS-CoV-2 has emerged naturally in non-human hosts such as bats or pangolins and then jumped to humans. Coronaviruses are well known to undergo genetic recombination. In fact, this is exactly how previous coronavirus outbreaks have emerged, with humans contracting the virus after direct exposure to civets (SARS) and camels (MERS). The researchers proposed horseshoe bats as the most likely reservoir for SARS-CoV-2 as it is very similar to a bat coronavirus. There are no documented cases of direct bat-human transmission so far, suggesting that an intermediate host was likely involved between bats and humans.

In this particular scenario, both of the distinctive features of SARS-CoV-2’s spike protein and the cleavage site would have mutated to their current pathogenic state prior to entering humans. In this case, the current epidemic would probably have emerged rapidly as soon as humans were infected, as the virus would have already equipped with the features that make it pathogenic and able to spread between people.

In the second proposed scenario, a non-pathogenic version of the virus jumped from an animal host into humans and after a mutation process it has acquired its current pathogenic state within the human population. For instance, some coronaviruses from pangolins, armadillo-like mammals found in Asia and Africa, have a spike protein very similar to that of SARS-CoV-2. A coronavirus from a pangolin could possibly have been transmitted to a human, either directly or through an intermediary host such as civets or ferrets.

In this scenario, only the cleavage site could have mutated within a human host, possibly via limited undetected circulation in the human population for months or maybe years prior to the beginning of the epidemic. The researchers found that the SARS-CoV-2 cleavage sites have similarities that resemble strains of bird flu that can transmit easily between people. In the case of SARS-CoV-2, such a virulent cleavage site could have been formed in human cells and soon the current epidemic got initiated, as the coronavirus would possibly have become far more capable of spreading between people.

At this point, it is almost impossible to know for sure which of the scenarios is most likely. If the SARS-CoV-2 entered humans in its current pathogenic form from an animal source, it raises the probability of future outbreaks, as the illness-causing strain of the virus could still be circulating in those animal populations and might come back to humans again. It is still noteworthy that a non-pathogenic coronavirus entering the human population and then acquiring properties similar to SARS-CoV-2, the second scenario, is less likely than the first scenario.

In conclusion, this study brings an evidence-based view to the baseless rumors and conspiracy theories that the SARS-CoV-2 was deliberately manufactured in a lab and concludes that the virus has emerged after a natural process that took place in multiple hosts over time. These genetic findings are also consistent with how SARS-CoV2 is currently behaving. The virus has a low fatality rate (1% to 3.4%) and does not seem to act like a bioweapon compared to pathogens such as anthrax or Ebola. Given the previous coronavirus epidemics and the persistence of the culture of eating exotic mammals in China and other parts of the world, the current COVID19 epidemic is unfortunately not a big surprise for scientists and experts. We have to take necessary measures to be more prepared for such outbreaks that may take place in future.

If you heard that a very destructive creature was in your village, what would you expect this creature to look like? Perhaps a ferocious cat, or a colossal beast that was capable of leveling whole buildings? Such a creature does exist in Africa, except it is a single celled bacterium by the genus Trypanosome, a microscopic creature with the capacity to strike fear into the heart of virtually an entire continent. Living a segment of its life as a parasite in the bloodstream of humans and other mammals, Trypanosome can trigger a lethal neurological disorder in the circulatory system. It has also been found that it is the cause of a serious sleep disorder in humans. The disease can ruin a person’s circadian cycle, cause fevers, and changes in personality. Unfortunately, about 60 million people in 36 of the 52 countries in Africa are at constant risk.

Another significant role in the lifecycle of trypanosomiasis is the tsetse fly, the bacteria’s most common intermediate host, which transports the Trypanosome from one mammalian host to another. Trypanosomiasis is endemic in a large area of approximately 3.8 million sq. mi. in Africa, where both the parasitic disease and the tsetse fly coexist. Moreover, the danger is not limited to humans because it also affects many other mammal species, most notably livestock and horses. Malnutrition often follows as a direct consequence when large swaths of animals are killed by trypanosomiasis, as there will be less meat and dairy to consume.

The trypanosome parasite invites disease for the host mammal by collapsing or neutralizing its immune system. Let us first remember how the immune system works:

The immune system

Every living thing is provided with two things: food and protective systems. Immune system is one of these vital systems. Most immune systems across mammals function in similar ways; Antibodies are produced to destroy toxic substances and antigens on foreign bacteria, fungal cells, or the virus sheath invading the body. These antigens can be found on the infected foreign cells and have a unique shape and structure according to the organism that causes each disease. The immune system binds to the antigens of the foreign organism in the same manner as a key-lock system with its antibodies produced while fighting against the disease, thus neutralizes the invading organism.

Most of the antigens, which reveal the identity of a foreign being, are structures created of proteins, polysaccharides, or protein-based fats. Our immune system has the sensitivity and the capacity to produce an infinitely diverse variety that can discern even quite identical but foreign substances bearing antigenic properties for our body. To draw an analogy, a specific antibody can be produced for each speck of dust on Jupiter. Our immune system is blessed with the ability to synthesize appropriate antibodies by selecting proteins that differ in type or location of one amino acid.

The mechanism of binding of the antibody to the antigen is carried out with effective economy, because each type of antibody is produced specifically against a particular antigen. This mechanism works like a key-lock system, so the body recognizes its own cells and does not attack them. Each antibody produced in the immune system is created in a three-dimensional, one-to-one compatible structure with the antigen that causes it to be produced, and easily recognizes and locates it, binds as the key fits into the lock, and thus renders it harmless by disrupting the chemical structure of the antigen.

Trypanosome and the immune system

The case of trypanosome vs. the immune system is somewhat exceptional. The abovementioned almost universal immunity principle does not work against trypanosome. Even though parasites are constantly exposed to the mammalian immune system in the blood, they constantly change the antigen that forms the surface sheath. They thwart the host’s defense, as if rapidly changing their password so that it can never be guessed. Until the immune system produces new antibodies to bind to new antigens, some of the trypanosomes discard their sheaths and drape themselves in another one. If this condition persists, the immune system of the host cannot cope with the infection and may succumb to it.

This extraordinary phenomenon astonishes the scientific community and many scientists are investigating the molecular structure of antigen diversity extensively in African, European, and US laboratories. These parasites are only 0.015–0.030 mm in size, and its two most notorious species are Trypanosoma rhodesiense and Trypanosoma gambiense, which inflict serious damage on the human body.

Like many other parasitic species, the life cycle of trypanosomes is very complex. In each phase of this life journey, the parasite takes different forms and exhibits different characteristics in such an unusual way that generates curiosity. The life cycle can be summarized as follows: when the tsetse fly bites a disease-bearing mammal, the trypanosomes in the mammal’s blood are sucked up and settle in the middle intestine of the fly. They undergo a series of complex processes including several structural and biochemical changes. After about three weeks, the trypanosomes appear in the fly’s salivary glands in a disease-bearing form. Meanwhile, they are also draped in new surface sheaths.

When the secondary host fly bites a healthy person, the disease-causing trypanosomes enter the blood of the new host. In this new stopover, parasites are transformed into a form in which they can rapidly multiply. First, they wreak havoc in blood vessels and on lymph nodes, causing fever, marks and swelling in the body. At this stage, a constant struggle with the host’s immune system ensues. A likely invasion the patient’s central nervous system by the trypanosomes can cause intense drowsiness, coma, and eventually death.

In years of research on the trypanosomes, the thick surface sheath covering the cell membrane of the parasite was first described in 1965 by Keith Vickerman of the University of Glasgow. Shortly thereafter, different surface sheaths were discovered in different trypanosome clones. In 1968, Richard W. F. Page from the Molteno Parasitic Research Institute in Cambridge analyzed and decoded the isolated antigenic surface proteins from several clones, revealing that each clone had a biochemically different protein. The clarity of these differences suggests that each antigen is expressed by a different gene. In the 1970s, George Cross and his colleagues found evidence supporting Le Page’s proposal. These antigens are now called Variable Surface Glycoproteins (VSG). As a result of subsequent research, the picture became even more clear.

Once the infection has begun, antibodies are formed in the host’s immune system that bind to the variable surface glycoproteins that appear on the surface sheath of the invading parasites. These antibodies kill most of the initial trypanosomes. Yet interestingly, on a few remaining trypanosomes a new sheath to which antibodies cannot bind is built, and the trypanosomes evade the immune system’s grasp. The survivors induce a new population producing new variable surface glycoproteins. This time, the immune system produces new antibodies against these freshly constructed antigens. Meanwhile, the parasitic population grows. Newly produced antibodies are able to kill 99% of new parasites again. However, until that time, the parasitic group constituted by about 1% of the survivors has already changed its sheath. Hence, another population begins to multiply. This process of life being a struggle unfortunately continues until the host mammal dies.

The mechanisms of antigen diversity in trypanosomes are very complex and variable, and the total capacity to produce varieties is not clearly known. Recombinant DNA technology is used to investigate the structure of the genes for producing variable surface glycoproteins, the mechanism of cell membrane binding, and the selection and expression of one of the codes. In addition to the four licensed medicines produced for the treatment of parasitic diseases, new drugs are being developed.

It is astonishing that this tiny window of invisible dimensions has such a huge potential opening to different branches of science. Many such exceptional and precise situations exist in the universe that may showcase contradicting mechanisms with general principles and procedures. Sometimes we may wonder why God creates such harmful parasites. Since we do not know the performance at every point of an entire ecosystem with our insufficient scientific knowledge, limited sensory organs and temporary observation, we tend to see any seemingly harmful being as futile and devoid of wisdom and immediately raise our voices in protest. However, with new discoveries in science, thousands of wise meanings may be extracted from a creature we generally take for granted.

References

Lori Peacock, Simon Cook, Vanessa Ferris, Mick Bailey, Wendy Gibson (2012): The life cycle of Trypanosoma (Nannomonas) congolense in the tsetse fly, Parasites & Vectors, 5:109 www.parasitesandvectors.com/content/5/1/109.

Michael P Barrett, Richard J S Burchmore, August Stich, Julio O Lazzari, Alberto Carlos Frasch, Juan José Cazzulo, Sanjeev Krishna, (2003): The Trypanosomiases, The Lancet, Vol 362, November 1, Pages 1469-1475, www.thelancet.com.

www.cdc.gov/dpdx/trypanosomiasisafrican/index.html

Meinecke et al. Turbulent amplification of magnetic fields in laboratory laser-produced shock waves, June 2014, Nature Physics.

A supernova is the explosion of a massive star which releases a burst of radiation that can be as bright as 10 billion suns. Such a massive amount of radiation can shine throughout the entire universe for several light-years. Supernovas are triggered either when the fuel within a star ignites or when a star’s core collapses under extreme gravitational forces. Supernovas have already taught us very important lessons about the history of the universe. For example, these explosions have provided solid evidence that the universe is expanding. Supernovas can also tell us a lot about how old stars die and how new stars are born. When a star goes through a supernova explosion, it leaves behind a skeleton made of expanding dust and gas that scientists call a remnant. These star-remnants spread around space. They might end up on earth or other planets, or they could form the energy source of a new star. Since the best way to understand supernovas is to actually explode a star, researchers recently developed a technique to simulate small-scale supernovas in a lab environment. To do this, scientists used lasers that are 60,000 billion times more powerful than a laser pointer. They focused the laser beams on a thin carbon rod inside a gas-filled chamber. The lasers heated the chamber to over 1 million degrees Celsius, which caused the carbon rod to explode and expand out through the low density gas – just like how exploding stars speed through space. The experiment revealed that as the blast passes through the grid, it becomes irregular and turbulent. They also noticed that the magnetic field was dramatically higher within the grid than without, suggesting that the magnetic field was amplified by the generated turbulence. The supernova system developed in this study holds the possibility of helping us better understand how the universe was formed and evolved, and could provide some insight into how magnetic fields were first created.

Young blood: The fountain of youth?

Villeda SA et al. Young blood reverses age-related impairments in cognitive function and synaptic plasticity in mice. June 2014, Nature Medicine.
Sinha M. et al. Restoring systemic GDF11 levels reverses age-related dysfunction in mouse skeletal muscle. June 2014, Science.

Two recent studies of lab mice showed that transfusions of blood from younger individuals reverse the effects of aging in their elders. One research group showed that neural damage of mice with age-related cognitive impairments could be reversed by such transfusions. Alternatively, injecting the younger plasma into the brain was also very effective at repairing neural damage. Another research group showed that blood from younger mice repaired age-related heart defects in older mice. Researchers further discovered that high levels of the protein GDF11, present in the blood of younger mice, were the key for rejuvenation. Researchers proposed that blood from younger mice contains molecules with anti-aging properties that awaken the stem cells of the brain and heart muscles and thus initiate the rejuvenation. These studies are incredibly encouraging for combating Alzheimer’s disease, heart disease, and many other age-related diseases; however, a comprehensive set of clinical tests needs to be conducted before testing the effects in humans.

“Chameleon” plant discovered

Gianoli E. and Carrasco-Urra F. Leaf mimicry in a climbing plant Protects against herbivory. May 2014, Current Biology.

Scientists thought for many years that camouflage and mimicry were only observed in the animal kingdom. A newly discovered wood vine in Chile, Boquila trifoliolata, has been found to transform its leaves to mimic a variety of host trees. B. trifoliolata is the first plant ever shown to imitate multiple hosts. This is a rare trait called “mimetic polymorphism” and it was only previously observed in butterflies. As B. trifoliolata climbs onto a tree’s branches, it changes the color, size, shape, orientation, and even the vein patterns of its leaves to match the surrounding flora. When the same vine crosses over to a second tree, the size of its leaves can even increase 10 times  to match the second host plant. According to scientists, mimicry may protect the vine from plant-eating herbivores such as weevils and leaf beetles. It is perplexing how a plant can distinguish between individual trees and keep changing its physical characteristics. Odors, chemicals, or microbes that are released form host plants are potential candidate mechanisms for this intriguing plant behavior.

Each creation is a work of art. All animals and plants, as well as every human being, are unique and priceless. And those who appreciate their value are like antique dealers as in the passage above. I recently had the chance to listen to such an “antique dealer,” Joanna Aizenberg of Bell Laboratories/Lucent Technologies, and witnessing the appreciation of the valuables she presented to us helped me better understand Said Nursi. Both the valuable object she was talking about and her appreciation of it were equally inspiring for me, and this is the reason why I have decided to share this story with you. Without any further ado, here is the story of a sponge species called the Venus’ Flower Basket and its “eternally” incarcerated residents: a pair of shrimp. Now, you must find what is hiding behind all this; after all, it is the eyes that look but the heart that perceives.

Venus’ Flower Baskets (Figure 1a) are vase-like sponges that grow upright on the sea floor of the Pacific Ocean, mostly around Japan. They have a very sophisticated mesh structure which caused medieval Europeans to assume they were glasswork made in China. In Japan they are called Kairou-Douketsu (together for eternity) and given as wedding gifts, since they generally house a pair of mated shrimp which are trapped in their cavity. As you have probably already understood, our story is about the engineering secrets of these sponges and their relationship with their guests.

The design

The skeleton of the Venus’ Flower Basket is made of silica, which is a very brittle material (remember the glass windows that you broke with your football when you were a kid; they were made with silica). How can these amazing creatures withstand the pressure and the currents present at the sea floor or the disturbance caused by two shrimp? The secret lies in the hierarchical construction of their cylindrical cage-like structure. As can be seen in Figure 1b, their skeleton is made up of beams that run perpendicular and parallel to the axis of the sponge, which forms a rectangular grid. This grid is further supported by beams that run diagonally in both directions. Finally, this whole structure is reinforced by ridges that spiral around. But these are just the macroscopic hierarchical levels of the construction. Now let’s start from the very first level of this hierarchy and try to understand how each level adds to the stability of the sponge.

The basic building block of the Venus’ Flower Baskets is a fiber composed of silica nano-spheres (Figures 1i and 2a) that grows around an organic filament (the black dots at the center of the circles in Figure 1f). Though this fiber is not very stress tolerant, due to the size of the spheres from which it is made, in the next level of hierarchy it is toughened by alternating organic and silica sheets that form a concentric lamellar (fine, alternating layers of different materials) fiber structure. The thickness of each layer in the fiber decreases from 1.5 (: 1/1000 mm) at the center to 0.2 towards the periphery (Figures 1f, 1g and 2b). Hence any crack that is initiated at the periphery is halted at the organic interlayers and while the thinner outer layers lessen the depth of crack propagation, the thicker inner layers enhance mechanical rigidity (in addition to their mechanical stability, these silica fibers are endowed with optical properties which are superior to man-made fibers, which will be discussed later on in the article).

Figure 1. Structural analysis of the mineralized skeletal system of Euplectella sp. (a) Photograph of the entire skeleton, showing cylindrical glass cage. Scale bar, 1 cm. (b) Fragment of the cage structure showing the square-grid lattice of vertical and horizontal struts with diagonal elements arranged in a chessboard manner. Orthogonal ridges on the cylinder surface are indicated by arrows. Scale bar, 5 mm. (c) Scanning electron micrograph (SEM) showing that each strut (enclosed by a bracket) is composed of bundled multiple spicules (the arrow indicates the long axis of the skeletal lattice). Scale bar, 100 mm. (d) SEM of a fractured and partially HF-etched (25) single beam revealing its ceramic fiber-composite structure. Scale bar, 20 mm. (e) SEM of the HF-etched (25) junction area showing that the lattice is cemented with laminated silica layers. Scale bar, 25 mm. (f) Contrast-enhanced SEM image of a cross section through one of the spicular struts, revealing that they are composed of a wide range of different-sized spicules surrounded by a laminated silica matrix. Scale bar, 10 mm. (g) SEM of a cross section through a typical spicule in a strut, showing its characteristic laminated architecture. Scale bar, 5 mm. (h) SEM of a fractured spicule, revealing an organic interlayer. Scale bar, 1 mm. (i) Bleaching of biosilica surface revealing its consolidated nanoparticulate nature (25). Scale bar, 500 nm. Figure and captions from ref. 2.

Fibers of different diameters reinforced this way are then bundled loosely in a silica matrix (Figure 1d and 1f). The different diameter of the fibers in the bundle and the weak lateral bonding between them are essential for increasing the strength of the bundle against crack propagation. At the next level of hierarchy, these bundles are used as building blocks of the cylindrical cage of the sponge, being arranged horizontally and vertically into a square grid. This grid in turn is reinforced by diagonal bundles that run in both directions along every second square lattice. The minimum number of pin-jointed struts (i.e. ones that are free to rotate at the joints) per node needed in order to form a rigid two-dimensional grid has been shown to be six; this is the number present in the skeleton of the Venus’ Flower Basket. In fact, if the diagonal bundles were to run along every square lattice, the number of struts per node would be 8, which would be redundant for the stability in the skeleton.

At the early stages of the growth of the Venus’ Flower Basket the struts are not connected at the nodes. However as the sponge gets older the struts are joined by a silica cement which itself also has a lamellar structure (Figure 1e). Hence, while the younger sponges are flexible, the older ones are stiff; this also has important implications for the symbiotic relation that the sponge has with its guests, the shrimp. (This issue will be discussed in detail when the lifecycle of the shrimp is examined.) While the resulting grid is stable in two dimensions, in three dimensions it may still suffer from exterior effects, such as ovalization. This problem however is solved at the next level of hierarchy by the helical ridges that surround the grid (Figure 1b). The absence of the ridges at the base of the skeleton of the sponge where the cage diameter is small, and their increased density further up the cage where the diameter is much greater is proposed as evidence supporting this argument. Finally, this whole cage structure must be anchored to the sea floor in a way that will withstand the bending stresses caused by the currents. This is managed through the use of the fibers that have been discussed earlier; they are used as connectors between the base of the sponge that is anchored to the sea floor and the vertical struts of the skeleton, resulting in a flexible connection that enables the cage to swing freely in the currents (Figure 1a).

As a conclusion, it can be said that “The resultant structure might be regarded as a textbook sample in mechanical engineering, because the seven hierarchical levels in the sponge skeleton represent major fundamental construction strategies, such as laminated structures, fiber-reinforced composites, bundled beams, and diagonally reinforced square-grid cells to name a few.”

Now let’s concentrate more on the fibers (or spicules) that anchor the cage to the sea floor. These anchorage spicules (a term used for describing the skeletal structures of sponges which comes from the Latin word speculum, meaning the head of a spear or arrow)* are 5-15 cm in length and 40-70 um in diameter. In the above discussion we have briefly discussed the cross-sectional structure of these fibers that gives them their flexible, but resistant nature. Here we will focus on the optical properties of these spicules. But before doing so, let’s briefly explain how optical fibers work.

Optical fibers are silica fibers of a 5 to 80 um diameter that are coated with a cladding layer; light waves can travel in these for long distances by constantly bouncing off the cladding. The reason for this is the refractive index difference between the silica core and the cladding layer. Refractive index (n) is a measure of the ability of a medium to change the phase velocity of light and cause the light waves to bend while leaving one medium and entering another (refraction); in the case of fiber optics, leaving the core and entering the cladding. However, if the refractive index of the second medium is lower than that of the initial one, the incident light waves that have an incidence angle higher than a critical value or critical angle can be reflected back to the first medium and this is what happens in fiber optics (See red ray in figure 2). If the core diameter is small (5-10 um), light rays can propagate only through a single path in the fiber (which runs parallel to the fiber axis), hence these type of fibers are called single-mode fibers (See Figure 2a). If the core diameter is larger however, (60-80 um) several paths are accessible, and more paths will have incidence angles that are greater than the critical angle, hence they are called multi-mode (See Figure 2b).

Now with this information in mind, let’s have a look at the characteristics of the anchoring spicules of the Venus’ Flower Basket. First of all, as mentioned in the previous discussion, the lamellar structure of these spicules prevents crack propagation, which is the main failure mode of commercial silica fibers. This lamellar structure, however, also determines the dependence of the optical behavior of the spicules on the environment in which they are embedded. For instance if the spicules are embedded in an epoxide medium with a refractive index of 1.57, the spicule as a whole would not be able to act as an optical fiber, due to the smaller refractive index of the cladding. However, since the core region of the spicules has a slightly higher refractive index than that of the cladding, the core acts as a single mode fiber in such an environment (see Figure 2a). In sea water-the spicules’ native environment-which has a refractive index of 1.33, the whole spicule acts as a multimode fiber, since the refractive index difference between the core and the cladding is much smaller than that between the cladding and the surrounding sea water.

Another advantage of these spicules over man-made fibers is their formation/production parameters, which are ambient temperature and pressure; these enable the introduction of impurities into the silica. Though at first it may not sound as if impurities are a positive characteristic, these impurities are very important for increasing the refractive index of silica and act as dopants (impurity elements added to a semiconductor lattices in low concentrations in order to alter the optical/electrical properties of the semiconductor). The core section of the spicules, for instance, shows increased sodium concentration, which is the cause of the higher refractive index of this section. Such dopant introduction in the silica during the fabrication process, however, is not possible in the case of man-made fibers, due to the very high processing temperatures.

In addition to this, the spicules have crown-like caps at their base and thorn-like structures throughout their middle section. While the crown-like termini most probably are used to anchor the sponge to the ocean floor, it has also been shown that the waveguiding efficiency of the spicules increases when the illumination comes through the end that has the crown-like structure. Hence, it has been proposed that this structure may be acting as a light harvesting lens. The thorn-like structures, on the other hand, share the lamellar construction of the spicule body, and the light guided through the body branches out to these spines and emerges at the tip. Since sea water comes into contact with the tip at an almost perpendicular angle to the guided light, the coupling is pretty efficient. Hence the combination of crown-like ends and thorn-like structures forms optical networks that collect and distribute light. However, at the depths inhabited by the Venus’ Flower Baskets there is no accessible light source. If one accepts the fact that there is no waste in nature-whether one believes in “creation” or “evolution”-the existence of such an advanced network-like structure as a part of a sponge-the most primitive animal-is at least thought-provoking. In the case of sponges that dwell in shallower waters with similar spicules, it has been postulated that such spicules gather and provide sunlight for the sponge’s endosymbiotic algae. However, at the depths at which the Venus’ Flower Baskets live, direct sunlight is not available. However it has been suggested that if light sources, such as bioluminescent microorganisms (bioluminescence is the production and emission of light by a living organism as the result of a chemical reaction during which chemical energy is converted to light energy) or chemiluminescence (emission of light as the result of a chemical reaction) exist, their light may be efficiently distributed by the sponge and act as an attractant for juvenile shrimp that are searching for a host. But for now these suggestions are just speculation and merit further investigation.

Before concluding this section, we should also note that, as a natural outcome of their construction/composition, these spicules do not have as great a transparency as their industrial counterparts and light cannot be transferred over long distances with them. However, it seems this is not a problem for the Venus’ Flower Basket as, apparently, they just need fibers of 5-15 cm to survive and it is the scientists who need to figure out a way to incorporate the traits of the Venus’ Flower Basket into industrial fibers.

The love

As mentioned in the introduction, the Venus Flower Basket hosts a pair of mated shrimp. These belong to the family of Spongicolidae, the Spongicala japonica. These shrimp, which can be as “big” as 9 mm in length, spend most of their lives in their host sponge. Though studies about them are limited, it is believed that before permanently being entrapped in their host, the shrimp have two free- living periods. The first one is just after hatching when they are small enough to exit through the mesh of the sponge. During this period they exit and re-enter their cages and live in a group with their parents and other juveniles. Studies suggest that the females generally stay with their parents until sexual maturity, whereas the males tend to leave their original host and live a solitary life until they reach a length of about 4 mm.

The second free-living period comes at the time of sexual maturity, when it is believed that the male and female mate outside and then invade a host, or the female searches for a host that is already occupied by a solitary male. During this stage, the shrimp have a body length of 3.5 to 6.5 mm which is bigger than the mesh size of the host sponges. Though this seems puzzling, it is thought that the mated shrimp enter the sponge in its flexible stage-when it may be easier to penetrate through the mesh-and get trapped there “forever” as the sponge grows older and stiffer. In fact this theory is supported by the finding that several flexible sponge specimens host solitary and young mated shrimp, whereas in the stiff specimens only very few solitary and young mated shrimp have been observed.

References

1. “Biological glass fibers: Correlation between optical and structural properties.” J. Aizenberg, V. C. Sundar, A. D. Yablon, J. C. Weaver, and G. Chen, Proc. Nat. Ac. Sci. 101 3358 (2004).

2. “Skeleton of Euplectella sp.: Structural hierarchy from the nanoscale to the macroscale.” J. Aizenberg, J. C. Weaver, M. S. Thanawala, V. C. Sundar, D. E. Morse, P. Fratzl, Science, 309 275 (2005).

3. “Fibre-optical features of a glass sponge – Some superior technological secrets have come to light from a deep-sea organism.” V. C. Sundar, A. D. Yablon, J. L. Grazul, M. Ilan, J. Aizenberg, Nature 424 899 (2003).

4. “Skeletal growth of the deep-sea hexactinellid sponge Euplectella oweni, and host election by the symbiotic shrimp Spongicola japonica” (Crustacea: Decapoda: Spongicolidae). T. Saito, I. Uchida and M. Takeda J. Zool., Lond. 258 521 (2002)

5. “Pair formation in Spongicola japonica (Crustacea: Stenopodidea: Spongicolidae), a shrimp associated with deep-sea hexactinellid sponges.” T. Saito, I. Uchida and M. Takeda J. Mar. Biol. Ass. U.K. 81 789 (2001).

Note

*. Also defined as, one of the minute calcareous or siliceous bodies that support the tissue of various invertebrates (Merriam-Webster’s English dictionary)

Ants are highly social insects and have a complex system of internal communication. It is only by this system that the colonies manage to carry out their collaborative activities like nest- construction, food-gathering, brood-rearing, and defense of the colony. The fact that ants allow some alien species full access to the benefits of their society suggests that the guests must somehow have, in the words of Hölldobler, ‘broken the ant’s code, that is, attained the ability to ‘speak’ the ants’ language, which involves a diversity of visual, mechanical and chemical cues. ’

To support this suggestion, Hölldobler focused mainly on the rove beetle and looked into its communications and relations with certain species of ants. The relations vary considerably with the beetle species. Some live along the ants’ food gathering trail, some at the garbage dump, some in the chambers within the nest and others inside the brood chamber itself.

Atemeles pubicollis, a European species of beetle, is a well-known example of the species that live inside the brood chamber. It lives in the nest of the mound-making wood ant Formica polyetena during its larval stage. Hölldobler found that the ants’ adoption of the beetle larva depends on chemical communication. The larva secretes a substance that apparently acts as an attractant for the ant. The brood-keeping ants respond to the chemical signal with intense grooming of the larvae.

A different kind of communication takes place to elicit the ant’s feeding of the larvae. Hölldobler observed that the beetle larvae imitate certain begging behaviour of ant larvae involving mechanical stimulation of the brood- keeping adults. When the adult ant touches the beetle larva with its mouth or antenna, the larva rears up immediately and tries to make contact with the ant’s head. If the larva succeeds in tapping the ant’s lip with its own mouth, the ant regurgitates a droplet of food. The beetle larvae receive more food than the ant larvae since they perform the begging behaviour more intensely than the ant larvae do.

How does the ant colony manage to survive the beetle larvae’s competition for food? The answer is a simple:The beetle larvae are cannibalistic and unable to distinguish their fellow larvae from ant larvae by odour. Thus, they reduce their own population. That is why we find the ant larvae in clusters while the beetle larvae, having devoured their neighbours, are loners in the brood chamber.

The Atemeles beetles have two different homes with ants; one for the summer and one for winter. In the autumn, the beetles migrate to nests of the dark brown insect eating ants of the genus Myrmica. The reason for their migration is that brood-keeping and the food supply are maintained in Myrmica throughout the winter, whereas Formica ants suspend their raising of young. In the spring the beetles return to Formica nests for mating and the laying of eggs. The Lomechusa beetle are also co-dwellers with Formica ants. However, they do not change their environment for the winter. Instead, after hatching they simply move on to another Formica colony of the same species and share their food supply.

How the migrating beetle find its way to a Myrmica nest is another question. We find Formica nests normally in woodlands, whereas Myrmica are found in the grasslands beyond the woods. Hölldobler suggests that when the beetles leave the Formica nest, they generally move in the direction of increasing light. This may explain how the beetles manage to reach the relatively open grasslands where the Myrmica ants Jive. When they reach open grasslands they use the odour of the host species of ant to find a nest.

The beetle obtains recognition and adoption with a ritual, involving chemical communication, when it finds a Myrimica nest. The beetle first touches the ant lightly with its antenna and raises the tips of lts abdomen towards the host. The ant responds by secretions from glands on the tip of the abdomen. Next the ant is attracted to a series of glands along the sides of the beetle’s abdomen. Hölldobler calls these ‘the adoption glands’ because the ant will not welcome or adopt the beetle unless it senses their secretion. Most probably, the odour of this secretion mimics the odour of the ant can approach, and grasp it in order to carry it into the brood chamber.

The Atemeles care not the only species capable of making themselves at home with more than one kind of ant. Xenodusa beetles also change their nests with the seasons. The larvae live in Formica nests through the summer and live in the carpenter (Campotonus) ant nests in winter time. It is interesting that the carpenter ants also maintain larvae throughout the winter. Except for above mentioned beetles do not have the command of the ant language required to gain acceptance to the brood chamber. Some species of European beetles like Dinarda are limited to peripheral chambers of the nest of their host. Dinarda offers secretions from glands similar to Atemeles’ glands, but these secretions only induce the ant to tolerate the beetle, not to adopt it and take it into the brood chamber. Therefore Dinarda can only live on such food as it can find in the peripheral chambers. Other groups of beetles have communication sufficient only to allow the beetle to feed at the ants’ garbage dumps.

Many beetles closely resemble their ant hosts in appearance. This is particularly true of guests of the army ants. Some scientists concluded that the factor inducing the ants to accept the beetles as nest-mates was the beetles’ morphological resemblance to themselves. It was even thought to be case with Atemeles, although they do not particularly resemble their hosts. Hölldobler altered the shape ond the collar of these beetles artificially and found that morphological features do not contribute to the success of their relationship with their host. Instead it appears that communicative behaviour remains the essential requirement for acceptance. The guests’ mimicry of their hosts’ appearance, probably serves as a protection against predation by birds.

There are some questions still to be answered about ants and their hosts: How did the fascinating, effective system of communication between the beetles and their hosts develop?Why do only some species of beetles have this ability while the rest do not?

REFERENCES 

• ATKINS, M. D. (1980) Introduction la Insect Behaviour, Macmillan Publishing Co. Inc. , New York, pp. 100-2.
• HÖLLDOBLER, B. (1971) ‘Communication between Ants and their Hosts’, Scientific American, January, pp. 86-93.
• WIGGLESWORTH, V B. (1964) The Life of lnsects, The New American Library, New York