Category Nature Science & Wildlife

Beavers are rodents with very long, sharp front teeth. They use their teeth to gnaw down small trees for use in dam building or for food. Beavers build dams of sticks and mud across a river. This makes a calm pool the other side of the dam in which the beaver can build its home, or lodge. The inside of the lodge is reached by means of underwater tunnels. This keeps the beaver safe from predators such as wolves, even when the surface of the water is frozen in winter.

Dam-building is synonymous with beavers, the ultimate aquatic engineers. Using branches from trees they have felled, these large rodents dam lakes to create moat-like ponds of still water where they construct islands known as ‘conical lodges’ out of timber, mud and rocks. The body of water surrounding the lodges provides protection from predators – resident beavers enter and exit their sophisticated homes incognito via water-filled tunnels leading from the lodges to the pond. The largest lodge, found in Alberta, Canada, measures over 500m in length – though contrary to a widely circulated myth, it is not visible from space! In deep or fast-moving water areas, beavers simply excavate into river banks and set up home there instead.

Beaver dam building is a pretty fascinating topic. Unfortunately, no-one really knows how beavers evolved, let alone how dam building behaviour evolved. Beavers appear to build dams for two main reasons: protection from predators and to provide a stable source of food and easy access to it for themselves.

This offers some clues about how they evolved – almost certainly as a response to selection pressures for these two reasons avoid predation, obtain food. These dams are made of branches stuck down into the stream bed and then built up with a thick mortar of mud, gravel and interwoven branches.

The dam is constantly maintained to keep the water at the same level for beaver comfort and security. Beaver dams are sometimes maintained and expanded over many generations. They can be up to 1,000 feet long and 15-20 feet high.

Beavers are famous for their logging skills, chiseling down trees up to 3 feet in diameter. However, they are not clever enough to aim a tree’s fall and on rare occasions a beaver has been crushed by a tree trunk. The beaver is a very powerful animal, capable of dragging a heavy log through the woods and down into the water.

Although they often lay hundreds or even thousands of eggs, some fish do build nests to protect their young. The stickleback, found in European ponds and rivers, builds a nest of plant fibres in which the male guards the eggs until they have hatched, chasing away even the female that laid them.

The most interesting habits of fishes are their parental behavior in guarding the eggs and caring the young ones. In Chondrichthyes, young ones hatch out in a fully developed condition. But, in Osteichthyes larvae hatch out from eggs and then metamorphose to young adults. In most cases these larvae are quite numerous and so chance will favor at least few of them to tide over adverse condition.

Nest and nursery building Nest building is the commonest method adopted by fishes to protect their eggs and young ones. It is exhibited mostly by fresh water fishes and also by marine fishes having demersal eggs. Nest building involves active participation of either males or females or both. The simplest form of nest building is exhibited by salmons, darters, sunfishes, cichlids, etc. Salmons select gravelly shallows of running streams as their spawning ground. Here they assemble in shoals. Female will make a nursery in the form of pit to lay eggs. After fertilization, she will cover them with layer of gravel. Similar method is adopted by Australian fresh water, Arius. In case of darters , sun fishes and cichlids males make shallow basin like dipressions on the bottom.

The male of N. American bowfin (Amia calva) constructs a crude circular nest of soft weeds and rootless amidst aquatic vegetation. Spawning takes place in the “weedy castle”. Sometimes later the young ones leave the nest in a swarm escorted by their watchful father. The male of N. American bowfin (Amia calva) constructs a crude circular nest of soft weeds and rootless amidst aquatic vegetation. Spawning takes place in the “weedy castle”. Sometimes later the young ones leave the nest in a swarm escorted by their watchful father.

The male of two-spinned stickle back builds an elaborate nest in fresh water, using twigs and weeds, fastened together by the threads of a sticky secretion from the kidney.

Nest building by female is rarely known. Female Heterotis has been shown to make nests in swamps. There are instances in which both the parents take part in nest building. Eg: Labrus Labrus.

Carrying the eggs on the body some fishes ensure protection to their eggs by carrying them safely either in the mouth or anywhere in the body. In Aspredo and Platystacus, the skin of the lower part of the female becomes smooth and spongy during breeding seasons. Fertilized eggs get attached to it.

 In some fishes like Arius and Tilapia mouth-brooding or buccal incubation is a characteristic property both the male and female carries eggs and young ones in their mouth. In oral incubation, the parent will not feed until young ones hatch out. male nursery fish krutus has a cephalic horn upon which female deposits grape like egg clusters.

Keeping the eggs in brood chambers in most species of Syngnathus, Hippocampus, siphonostoma, male has a brood pouch for the deposition of eggs. In Hippocampus, some sort of” placenta” may be formed for gas exchange between the father and the developing young ones. In syngnathus, brood pouch has a highly vascular spongy lining from which the developing young ones may draw nourishment. in unique pipe fish of Indian and pacific oceans, Salenostomus the inner side of the ventral fin of female coalesces with the integument forming a large pouch for keeping the eggs.

Coiling round the eggs The British gunnel or the butter fish has a peculiar way of parental care. The female roll the eggs to a ball and then curls around them. Often male may assist her in this process. Butter Fish.

Keeping the eggs in egg capsules Some chondrichthyes, gives maximum protection to eggs by enclosing them in an egg capsule. In Scyllium, Raja etc, fertilized eggs are kept in a specially designed horny egg capsule, popularly called “Mermaid’s purse”. Egg filled capsules get attached to aquatic weeds with the help of tendril like filaments. Development is completed inside the capsule, utilizing the yolk reserve. Young ones hatch out by breaking the capsule.

Oviposition means, act of laying or depositing eggs. It is mostly exhibited by central European bitterling. In this the genital papilla of the female serves as an ovipositor. With its help eggs may be introduced to the gill chamber of a pond mussel.  During this female takes to a vertical posture and spawning. Male swims around her and discharges sperms in to the mussel. Fertilization and development take place in the gill chamber and young ones leave the host later.

Several fishes provide maximum pre-natal protection to their embryos by adopting ovoviviparity. Here the development is internal and the special portion of the oviduct serves as an unspecialized uterus.  A true mammalian type of placenta is absent. Nutrition is given either by yolk reserve or the uterine milk which is secreted by uterine wall. Eg: for ovoviviparous chondrichthyes are scoliodon, sphyrna, pristis, stegastoma, squalus, mustelus, myliobatis, trygon pteroplatea,etc. Eg: for ovoviviparous osteichthyes are Gambusia,poicilia,blennis,allis,zoarces,cymogaster etc.

Freshwater habitats include both still and moving water. Living things within rivers and streams can travel through the water to different areas. Many underwater inhabitants of ponds and Lakes, however, cannot escape from what may be quite a small area of water. However, even a tiny pool may have a complete, self-contained ecosystem. As well as plants and fish, freshwater ecosystems support living things that visit the water but spend part of their lives on land, such as amphibians, birds and insects. Many mammals also spend time in and around the water. Finally, the kinds of wildlife found in freshwater ecosystems will be affected by the climate and landscape around it. For example, the crocodile may be the fiercest predator in an African river, but its place may be taken by an otter in a European stream.

Cast out your fishing line or scoop your net through the water. You are bound to catch something when you are along the river’s edge or at the lake. Catching fish is always exciting, but while you wait for that fish to come along.

Freshwater ecosystems include lakes, ponds, rivers, streams, springs, and wetlands. You will find them in many different sizes, from very small to very large. The water within the ecosystem can be still (not moving), like in a pond, or it can be running (moving), like a river or stream.

Freshwater ecosystems are broken into three zones: littoral, open water and deep water – we’ll talk more about these below. The plants and animals within the ecosystem interact with light, food, oxygen, weather, and climate in different ways.

Plants and animals grow in different zones in freshwater ecosystems. The littoral (or marsh) zone refers to the plants and animals that grow closest to the edge of the water. The plants in this area can make great hiding spots for animals to hide from predators. You might find snails, clams, or even eggs and larvae from reptiles and insects in this area. Common predators (animals who prey, or feed, on other animals) in this zone include snakes, ducks and swans.

The open water zone refers to plants and animals that live near the top of the water. Some float on top of the water and have tiny roots that go down into the water, like duckweed. Others have their roots down in the mud at the bottom of the pond and leaves that float at the top of the pond, like water lilies. These plants get lots of sunlight, which makes them the top energy producers for the animals in the water. Many fish also swim in this open water zone.

Freshwater ecosystems play a fundamental ecological role and provide economically important products and services. They provide critical habitats for a large number of aquatic plants, fishes, reptiles, birds and mammals. They host many migratory and threatened species of birds, reptiles and fish. The freshwater ecosystems are areas of tourist attraction by providing recreation sites for game and bird watching.

Freshwater ecosystems, especially vegetated wetlands, play an important role in mitigation against climate variability. They do so through a number of ecosystem functions including flood control, water purification, shoreline stabilization and sequestration of carbon dioxide. At landscape level, wetlands control soil erosion and retain sediments and in so doing concentrate nutrients in the wetland soil. They also provide economic benefits such as fresh water, fisheries, fuel-wood, building material, medicinal products, honey and foliage for livestock and wildlife. Wetlands provide fertile land for agricultural, mineral salts, sand and soil for making pottery and building bricks. Wetlands are central to rural subsistence economies and livelihood activities of many rural communities in Kenya. Freshwater ecosystems in general are critical to poverty alleviation and creation of employment and wealth.

Oceans offer various habitats at different depths below the surface. These are called zones. The euphotic zone is at the top, ending at a depth of about 200m (660ft). Below this, very little light from the Sun can reach. The bathypelagic zone below is totally dark, so no plants can live there, but a number of fish, squid and crustaceans do make this zone their home, feeding on waste material that sinks down from above and on each other. Deep-sea creatures cannot see in total darkness, but their other senses help them to find food. Some, such as angler fish, carry their own lights. They are not bright enough to search for food by, but they may lure other fish towards them and help fish of the same species to recognize each other.

When the ancestors of cave fish and certain crickets moved into pitch-black caverns, their eyes virtually disappeared over generations. But fish that ply the sea at depths greater than sunlight can penetrate have developed super-vision, highly attuned to the faint glow and twinkle given off by other creatures. They owe this power, evolutionary biologists have learned, to an extraordinary increase in the number of genes for rod opsins, retinal proteins that detect dim light. Those extra genes have diversified to produce proteins capable of capturing every possible photon at multiple wavelengths—which could mean that despite the darkness, the fish roaming the deep ocean actually see in color.

The finding “really shakes up the dogma of deep-sea vision,” says Megan Porter, an evolutionary biologist studying vision at the University of Hawaii in Honolulu who was not involved in the work. Researchers had observed that the deeper a fish lives, the simpler its visual system is, a trend they assumed would continue to the bottom. “That [the deepest dwellers] have all these opsins means there’s a lot more complexity in the interplay between light and evolution in the deep sea than we realized,” Porter says.

At a depth of 1000 meters, the last glimmer of sunlight is gone. But over the past 15 years, researchers have realized that the depths are pervaded by faint bioluminescence from flashing shrimp, octopus, bacteria, and even fish. Most vertebrate eyes could barely detect this subtle shimmer. To learn how fish can see it, a team led by evolutionary biologist Walter Salzburger from the University of Basel in Switzerland studied deep-sea fishes’ opsin proteins. Variation in the opsins’ amino acid sequences changes the wavelength of light detected, so multiple opsins make color vision possible. One opsin, RH1, works well in low light. Found in the eye’s rod cells, it enables humans to see in the dark—but only in black and white.

Salzburger and his colleagues searched for opsin genes in 101 fish species, including seven Atlantic Ocean deep-sea fish whose genomes they fully sequenced. Most fish have one or two RH1 opsins, like many other vertebrates, but four of the deep-se species stood apart, the researchers report this week in Science. Those fish—the lantern-fish, a tube-eye fish, and two spinyfins—all had at least five RH1 genes, and one, the silver spinyfin (Diretmus argenteus), had 38. “This is unheard of in vertebrate vision,” says K. Kristian Donner, a sensory biologist at the University of Helsinki.

To make sure the extra genes weren’t just nonfunctional duplicates, the team measured gene activity in 36 species, including specimens of 11 deep-sea fish. Multiple RH1 genes were active in the deep-sea species, and the total was 14 in an adult silver spinyfin, which thrives down to 2000 meters. “At first it seems paradoxical—this is where there’s the least amount of light,” Salzburger says.