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Half duck, half beaver: the astonishing platypus

In recent years a strange assortment of animals, some familiar and some obscure, have enjoyed a brief moment of scientific attention. In each case, the occasion for this special fame was the publication of the genome – the complete DNA sequence – of that organism. In May 2008, the genome of Australia’s platypus was published. This creature is justly famous anyway, but the genome studies have helped focus attention on why this is so.

Not a hoax

When British naturalists first saw a pelt of a platypus, they were sure it was a hoax. With its thick fur, webbed front feet and duck bill-like snout, it certainly did not resemble any other animal known at the time. Further study showed however that the animal is perfectly genuine. Eventually, naturalists discovered that this animal lays eggs, but yet it suckles its young with genuine mother’s milk. It seemed as if this creature was a strange jumble of bird, reptile and mammalian (feeds milk to young) characteristics. More careful study however reveals that this organism is actually a beautifully designed entity.

The duckbilled platypus remains a highly unusual creature. Not only its appearance, but many aspects of its biology are unique. These small animals (up to 60 cm long) spend most of their time underwater. Indeed they are able to find food only when submerged. Amazingly, however, they swim blind, deaf and without the normal opportunity to detect odors since flaps cover their eyes, ears and nose while they are submerged. Recent research however has revealed that they have some unique abilities to compensate for lack of sight, hearing and smell.

Once the genome data has been collected, there is nothing obvious to show what stretches of DNA contain genes of interest. The number of nucleotides in the platypus genome is 2.3 billion, quite close to the 3 billion contained in the human genome. The number of protein-coding genes thus far identified in platypus is also similar to the number in humans: 18,600 for platypus compared to about 25,000 for humans. Faced with endless arrangements of nucleotides, how do scientists “read” the information contained therein?

What scientists did was to start slowly in their early genome studies with attempts to identify sections coding for certain basic genes. Gradually they built up a computerized repertoire of DNA coding which identifies important genes in at least one organism. Then when they wish to study a different organism, they use huge computers to look for similar stretches of DNA in the new organism. Fancy mathematics allows the computer to decide whether similar sequences are close enough to represent the same gene or not.

Since the genomes of many organisms have now been documented, scientists now have a large collection of nucleotide sequences that code for important genes.  The interesting thing then is to compare how the new organism resembles other creatures and ways in which it differs. Does it have similar genes or different ones? This analysis certainly reveals interesting things about the platypus.

Gender and reproduction

Genome analysis shows that gender determination in platypus is unique among milk-producing organisms. Rather than X and Y chromosomes such as we normally see in milk producers, gender in platypus is determined by chains of tiny chromosomes. Females have five pairs of tiny X chromosomes, while males have 5 pairs of X chromosomes plus five tiny Y chromosomes.

The really interesting thing is that the genetic information on the X chromosomes is nothing like that in other milk-producing creatures. The information, in fact, is faintly similar to the Z chromosome which determines gender in birds. Scientists are totally astonished by this feature of the platypus genome.

Unlike other milk producers, platypus and echidnas have just one opening at the rear end of the body. Other milk producers have an opening from the digestive system plus a combined one for urine and reproduction. Platypus and echidnas have one combined opening for everything called the cloaca (like birds and reptiles).

But platypus has a unique way of producing young, not at all like birds or reptiles. The female keeps the fertilized eggs inside her body for 21 days. Meanwhile, she seals herself into a small chamber lined with vegetation at the end of an 8-meter long tunnel dug into the bank of a lake or stream. There she lays 1 or 2 tiny sticky, leathery eggs. These she incubates until they hatch in about 11 days.

Initially only about the size of jelly beans and lacking developed organs and an immune system, the young suckle milk through pores on their mother’s abdomen. After 4 months, the young become independent. The eggs, it is well known, divide in a manner similar to birds and reptiles and as a result, contain a yolk. However recent genome research reveals that the milk is very similar in composition to that of other mammals.

Underwater navigation

Recent research has revealed how the platypus is able to find food despite the fact that its ears, nose and eyes are closed underwater. Obviously the creature needs special hardware and talents designed for navigation. Thus it was that in 1985 German scientist Henning Scheich discovered some highly unusual properties of the platypus. This animal reacts to weak electrical fields in water.

What this scientist did was bury a small charged battery under a brick in the water. In addition, he placed a similar, but dead battery under another brick. The platypus dislodged the brick sitting on top of the charged battery, but it ignored the other brick/battery site. Later, the platypus avoided a mesh screen placed in front of a charged battery, but it collided with a screen placed in front of a dead battery. Further studies have amply confirmed that platypus have electroreceptors in their bills.

As sensitive as a star-nosed mole

Since the late 1980s, scientists have discovered that there are two kinds of electroreceptor and one type of touch receptor in the platypus snout.

At the front edges of the bill, there are tiny pores containing a membranous receptor. Moreover, over the main surface of the bill there are oblique stripe-like arrays of pores which are mucous-filled. The mucous serves to enhance transmission of a signal to the nerve at the bottom of the pit.

The bill of the platypus has 40,000 electroreceptors, while in comparison the 2 species of its closest cousin, the echidna, boast only 2000 and 400 respectively. Mapping of sensors was conducted on anesthetized animals. Electrical sensors were attached to the exposed cortex of the brain, and electrical and mechanical stimuli were applied to the bill. The resulting signals in the cortex were duly noted as were the locations in the bill where the sensitive pores were located.

The push-rod mechanical (touch) receptors in the bill are remarkable in their own right. Inside the pore is a compacted column of skin which can rotate about its base or move up and down.

These very sensitive touch receptors are similar to the highly unusual touch receptors in the nose of the star-nosed mole. The organ of touch in the snout of the star-nosed mole is so sensitive, that the information obtained from it is almost as detailed as vision. This animal also spends most of its time foraging for food in the water. Until recently, scientists knew of no other creatures with as sensitive a sense of touch. Now it appears that the mechanoreceptors in the bill of platypus are of even more sophisticated design.

There is yet another interesting feature of these sensory pores on the bill of the platypus – each is surrounded by petal-like skin flaps which open when the animal is underwater. When the animal emerges from the water, however, tiny sphincters around each pore close the flaps so that the sensors will not dry out.

The food which the platypus seeks are small animals living near or in the bottom sediments of lakes, ponds, or rivers. These animals favor some larvae of insects, worms, small crustaceans and other invertebrates. Apparently, these small creatures generate weak electrical fields as they move or simply maintain the processes of life in their bodies. With its electroreceptor capabilities, it seems that platypus can detect the field generated by a freshwater shrimp that is 10 centimeters away. Scientists suspect that the platypus knows how far away an electrical source is, whether it is moving, and in what direction it is proceeding.

More and more talents

The remarkable thing is that these sensory talents of platypus are so unique. As far as electrical sensing of the environment is concerned, some fish also exhibit this ability. However, in the case of fish, the sensors are all over the body and they are not nearly so sensitive.

But platypus has more talents yet! One might have imagined that platypus would not need much in the way of a sense of smell since their noses are closed under water. This conclusion is partly right and partly wrong. As far as genes for normal smell (chemical receptors) are concerned, the genome project shows that platypus has a reduced number of receptor types (only about half of what most mammals exhibit). However, there are chemical receptors called vomeronasal receptors which may be located in the mouth or the nose and surprise, surprise, platypus has the largest variety of vomeronasal type 1 receptors known. At 950 different variations on the vomeronasal type 1 receptor (V1R) the platypus has 50% more than the mouse. Compare this to the chicken, which has no such receptors. Nor, for that matter, do people.

The platypus thus has very special electrical, touch and chemical (taste) receptors. The article on the platypus genome published in Nature (May 8/08) discusses the large number of genes which code for the special chemical receptors (V1R). But the article makes no mention of genes for electrical and touch receptors. Obviously, there must be quite a number of genes in the platypus coding for components of these sophisticated sensors. However, the sequence (order) of nucleotides does not come with labels identifying which sections code for what. Scientists need an already established standard order of nucleotides coding for such genes from another, not too different creature. Since these talents are highly unusual, however, no comparison with a similar gene in a similar creature can as yet be made. Thus we don’t hear about how many genes code for electrosensory abilities and for extremely sensitive touch.

Defense: immunity and venom

Besides food and reproduction, an animal in nature needs to defend itself against larger animals and against microbes. The newly hatched young have only partially developed organs. They have no spleen, no thymus and no killer T and B cells which provide acquired immunity.

They do, however, exhibit a very unusual number of natural killer receptor genes. A natural killer is a precisely shaped molecule which is able to recognize other types of molecules characteristically produced by disease-causing organisms but not by the host organism itself. This capacity to stop a large number of common disease agents in their tracks is programmed into the genes of platypus and most other organisms as well.

However, since the platypus young are so small and vulnerable, it makes sense that these animals are provided with an unusually large variety of natural killer-type molecules (coded for on appropriate genes). The platypus thus has 214 genes for different variations on the natural killer theme compared to only 45 for rat, 9 for opossum and 15 for humans.

In addition, platypus is unusual among mammals in that the male is able to deliver a venom potent enough to kill a dog. There are only a few mammals which are venomous, but all of the others transmit the venom by means of a bite. The platypus, on the other hand, has spurs on its hind legs which deliver the venom. That venom is a cocktail of at least 19 different substances which exert various nasty effects on the victim.

God’s creativity and intricate design

Secular scientists have long declared platypus to be a strange blend of reptilian, bird and mammal (milk producer) characteristics. Such people consider that the genome study has further confirmed this view.

They are wrong. What that study has shown is that this animal is not a jumble of features from a broad assortment of organisms, but rather a wonderfully integrated collection of unusual anatomy and attributes. Certain features may remind us of birds and reptiles, but the similarities are merely superficial. The platypus truly is unique in its navigational abilities and in all the other features. Obviously, this unusual creature was designed to pursue its unique but effective lifestyle and designed to delight us in yet another aspect of God’s amazing creation. So give three cheers for a weird but wonderful inhabitant of Australia!!

This first appeared in the September 2008 issue under the title “Awesome Aussie: the platypus looks fascinating from the outside, but a look at its inside – its DNA – is just as intriguing.” Dr. Margaret Helder is the President of the Creation Science Association of Alberta and the author of “No Christian Silence on Science.” For more on the platypus, check out the great video below.

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Science - General

Why animals don’t get lost (and no, it’s not because they’re willing to ask for directions)

Since the advent of global positioning satellites, or at least since their availability for civilians, scientists have found many uses for these devices. One of the more interesting applications is to track animals. Of obvious popular appeal are programs such as “fish with chips.” A multimillion-dollar "Census of Marine Life" project fitted marine animals in the Pacific Ocean with electronic surveillance tags. As of 2005, about 1,800 sharks, tuna and turtles had been fitted with transmitting devices which relayed information to a satellite when the animal surfaced. By this means, a bluefin tuna was tracked as it crossed the Pacific Ocean three times in 600 days! This fish swam 40,000 kilometers (km) with an average of 66 km/day. More dramatic still, were the exploits of Nicole, a 3.5 meter long great white shark. This specimen swam 11,000 km from South Africa to Australia and back within three months. Nicole averaged 122 km/day! She swam in a straight line, never less than 5 km/hr, and 60% of the time she stayed within one meter of the surface. It's obvious she knew where she was going. Scientists have been astonished to discover how far these and many other animals migrate. Another interesting study involved young fingerling salmon emerging from 16 river systems on the Pacific coast of North America. The tags on several thousand of these fish were scanned as they passed over special receivers placed on the ocean floor from Washington State up to Alaska. This study revealed that the young salmon follow precise migration paths which vary depending upon their river of origin. The results of these tracking studies intensify the question, long pondered, as to how animals navigate long precise routes through the oceans or skies. As our tools for study become ever more sophisticated, our insights might be expected to increase too. This may be, but the more famous cases still abound in unanswered questions.  Sea turtles Most of the seven species of sea turtle can be found throughout the world’s tropical and subtropical seas. Despite this wide range, local populations exhibit very specific nesting site preferences and sometimes even a specific preference in feeding sites as well. This might not seem remarkable, until we realize that the nesting and feeding sites may be thousands of kilometers apart. After decades of ecological studies, scientists still have only a poor understanding of the wonders of sea turtle navigation. Green turtles are a rugged, long-lived species (up to 70 years). As is typical with sea turtles, the female lays her eggs at night in the sand of a wide beach along the seashore. She digs a pit and lays as many as one hundred eggs. After covering the eggs, the mother then retreats into the sea. Several weeks later, all the eggs hatch at the same time. The hatchlings emerge from the sand and head straight for the ocean. Once immersed, they swim straight out, farther and farther from land with its multitude of avian, crustacean, and human predators. Only about one in one thousand hatchlings survives long enough to mature. Once in the open sea, young turtles apparently set out for the feeding grounds. Green turtles hatched on beaches of Costa Rica later turn up in Spain, Chile, and Brazil. Then, once mature, females return to the very same beaches from which they hatched fifteen to thirty years previously. Tagging programs with young turtles have never revealed an adult female nesting on a beach other than the one from which she emerged. How do these turtles, out at sea, navigate towards the appropriate beach? Ascension Island One of the more remote destinations on earth is Ascension Island. Situated in the mid South Atlantic Ocean, this island of 88 square kilometers lies about 1100 kilometers northwest of Saint Helena, itself an island famous for its remote location. (Napoleon Bonaparte spent his last days on Saint Helena, a site chosen as his prison because its distance from everywhere made escape impossible). However Ascension Island is even more isolated than Saint Helena. Nevertheless green turtles, feeding in shallow waters along the Brazilian coast, and others in similar habitats near Gabon (Africa), swim due east or west (respectively) to nest on the beaches of Ascension Island. The journey from Africa to the island is 2,500 km and from Brazil to the island is 2,250 km. It is like finding a needle in a haystack. Nevertheless adult female turtles make the journey once every three to four years. Moreover, they do not eat at all during the entire eight month return trip. Leatherback Amazing skills in navigation are not unique to green sea turtles. Studies on the largest turtle of all, the leatherback, reveal some interesting details too. Unlike the green turtle, the leatherback forages for food in the deep ocean so they are less tied to specific feeding grounds. Nevertheless, there are only a few dozen places in the world where these turtles lay eggs. Of these, only four beaches attract large numbers of nesting leatherbacks. One of these four beaches is Playa Grande Beach on the west coast of Costa Rica. Tagging studies have revealed that these turtles travel 2,500 km west from Costa Rica toward the Galapagos Islands and beyond into deeper waters. They confine this travel to a narrow corridor up to 480 km wide. The females return to Playa Grande to lay eggs up to ten times per season. The females of another leatherback population, which feeds on jellyfish in the waters off Canada’s Nova Scotia coast, later proceed to beaches within the Caribbean Sea in order to nest. Studies on turtle navigation have revealed that young hatchlings react positively to wave direction, the earth’s magnetic field, moonlight, and perhaps chemical gradients. Nobody has, however, established precisely how adult turtles navigate thousands of kilometers in the open ocean, or even why they do so. Even if turtles are able to orient themselves in a specific direction, how do they locate the particular beach from which they hatched so many years previously and on which they spent so short a time?  Freshwater eels Eels are long snake-like fish which can grow up to 3 meters long. While some might consider such creatures ugly, many in Europe and North America consider them very tasty snacks. However, there was one longstanding mystery concerning the freshwater eels of eastern North America and Europe. Why were no young eels ever observed? Did they spring fully grown from their parents, like the mythical goddess Minerva who was imagined to have sprung mature and fully clothed from Jupiter’s brain? A Danish biologist solved the problem early in the twentieth century. Johannes Schmidt discovered that freshwater eels from both sides of the Atlantic spawn in a remote region of the Atlantic Ocean east of the Bahamas Islands. As is typical when one mystery is solved, this answer raised many new questions. How and why do all these eels navigate so far? Sargasso Sea The Sargasso Sea, a region of the Atlantic Ocean where water currents slowly move in a gigantic gyre (whirlpool), is roughly the size of Australia. Its existence is a byproduct of the Gulf Stream which carries warm water north along the eastern coast of North America and then eastward toward Europe, and the North Equatorial Current which carries cold water south towards Africa and then west towards the Caribbean. It so happens that this sluggish whirlpool region of the Atlantic is very rich in mineral nutrients. Sargassum, a distinctive floating brown seaweed, grows so thickly there that the sea surface sometimes looks more like a meadow than like open water. Naturally this region is a wonderful habitat for sea life and there the eels go to mate. In the fall, eels which are about ten years old, undergo physical and physiological changes. They stop eating as their stomachs shrink, and their reproductive organs expand. These mature specimens then move from their preferred freshwater habitats down streams to rivers, and from rivers to the sea. They proceed from far inland along the Atlantic coast from Mexico up to Labrador, from Greenland’s coast and Iceland, from the British Isles, from Scandinavia and from lands bordering the Mediterranean and Black Seas. As these eels converge on the Sargasso Sea, they show no specific preference to mate with specimens from their part of the world. Each female then lays up to twenty million eggs. These hatch into thin, flat, almost transparent creatures about one half cm long. As they move north in the Gulf Stream, those which mature first, apparently stop off in the fresh waters of North America. Others may take longer to mature, up to two or three years and these drift towards Europe. The American and European populations look different, but biologists think that genetically they may be almost identical. It is apparent that we know some of the story concerning eels but there are obviously many blanks yet to fill. What causes the eels to migrate to a common area in the open ocean? Why do they not spawn closer to their feeding grounds? Drifting towards coastal areas is obviously easy enough, but how do the eels navigate their way back to the Sargasso Sea? There obviously is more to freshwater eels than a tasty snack. Monarch butterflies One of the most amazing examples of navigation is that of the monarch butterfly. During the spring, these insects leave tiny stands of trees in Mexico where they spent the winter. They fly northeast to destinations throughout eastern North America. Then in the fall, several generations later, these butterflies head back to the very same stands of trees from which their great great grandparents had emerged the previous spring. Several questions naturally arise. It may be that day length triggers the instinct to fly southwest in the fall, but how do these tiny brains identify the appropriate direction? Laboratory studies have shown that adult butterflies emerge at dawn from the chrysalis. This time is apparently internalized within each insect’s 24 hour physiological clock. (Your own physiological clock tells you, for example, when it is time to sleep and time to eat.) It is the insect’s awareness of passing time which allows these butterflies to navigate with the sun as their reference point. As the sun moves across the sky, the butterflies automatically adjust their orientation to the sun according to the time of day and thus they maintain a constant southwest direction. If any butterflies are artificially caused to emerge from the chrysalis at a different point in the day, they cannot navigate according to the sun’s position and consequently they get lost. Imagine a navigating system that automatically adjusts for time of day! This is a fancy computer to cram into a very small insect brain. Obviously the whole system was designed to function in a sophisticated manner while using on a few simple cues. In the spring after over wintering, these very same butterflies will fly toward the northwest. Arctic birds In certain instances a much simpler navigating system than that of the butterflies may suit the needs of an animal. This situation applies to arctic birds on their annual migration south. Navigation apparently is most difficult near the poles since many useful parameters, like magnetic field, all converge. During the late summer of 2005, scientists carried out a study of arctic bird navigation. As flocks of birds passed over the Bering Strait between Alaska and Siberia, scientists briefly tracked them by radar. From hundreds of such tracks, the travel trajectories (direction) could be calculated. The scientists had calculated the various routes that birds would follow if they were using one or other navigational cues. If the birds were navigating by means of a magnetic compass, for example, they would proceed towards the northeast (not an ideal direction). If they used the sun as their reference point, adjusting their calculations according to time of day, they would proceed towards the east. However if they followed the sun without adjusting direction for time of day, they would proceed in a southeast direction. This was indeed the path these birds appeared to follow. The end result of this strategy is that their route then traces an arc, part of a great circle. Such a route is by definition the shortest distance connecting two points on the globe. For people relying on technology, a great arc requires continuous changes in compass direction. Navigating by compass (magnetic field) is longer but much easier. Obviously, however, one expends less energy on a shorter route. In the case of arctic birds, lacking complex computer programs, they nevertheless manage to follow a sophisticated path out of the arctic. Scientists cannot refrain from asking how these birds learned such a navigational strategy. Conclusion There is no doubt that tracking studies have revealed exciting details about animal navigation. In addition, physiological studies continue to give us glimpses into methods that these creatures use to plot their routes. But none of these environmental cues would be any help at all without senses designed to perceive them, and brains to interpret the data correctly, and to act upon it. Secular scientists may eventually describe the tracking mechanisms ever so precisely, but they will never be able to tell us why or how these remarkable designs were conferred on these creatures. Christians know. Dr. Margaret Helder is the President of the Creation Science Association of Alberta. This article first appeared in the January 2006 issue....