The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own. An egg results from fertilization of an egg cell. Most arthropods and mollusks lay eggs, although some, such as scorpions do not. Reptile eggs, bird eggs, monotreme eggs are laid out of water, are surrounded by a protective shell, either flexible or inflexible. Eggs laid on land or in nests are kept within a warm and favorable temperature range while the embryo grows; when the embryo is adequately developed it hatches, i.e. breaks out of the egg's shell. Some embryos have a temporary egg tooth they use to pip, or break the eggshell or covering; the largest recorded egg is from a whale shark, was 30 cm × 14 cm × 9 cm in size. Whale shark eggs hatch within the mother. At 1.5 kg and up to 17.8 cm × 14 cm, the ostrich egg is the largest egg of any living bird, though the extinct elephant bird and some dinosaurs laid larger eggs. The bee hummingbird produces the smallest known bird egg; some eggs laid by reptiles and most fish, amphibians and other invertebrates can be smaller.
Reproductive structures similar to the egg in other kingdoms are termed "spores," or in spermatophytes "seeds," or in gametophytes "egg cells". Several major groups of animals have distinguishable eggs; the most common reproductive strategy for fish is known as oviparity, in which the female lays undeveloped eggs that are externally fertilized by a male. Large numbers of eggs are laid at one time and the eggs are left to develop without parental care; when the larvae hatch from the egg, they carry the remains of the yolk in a yolk sac which continues to nourish the larvae for a few days as they learn how to swim. Once the yolk is consumed, there is a critical point after which they must learn how to hunt and feed or they will die. A few fish, notably the rays and most sharks use ovoviviparity in which the eggs are fertilized and develop internally; however the larvae still grow inside the egg consuming the egg's yolk and without any direct nourishment from the mother. The mother gives birth to mature young.
In certain instances, the physically most developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as intrauterine cannibalism. In certain scenarios, some fish such as the hammerhead shark and reef shark are viviparous, with the egg being fertilized and developed internally, but with the mother providing direct nourishment; the eggs of fish and amphibians are jellylike. Cartilagenous fish eggs are fertilized internally and exhibit a wide variety of both internal and external embryonic development. Most fish species spawn eggs that are fertilized externally with the male inseminating the eggs after the female lays them; these eggs would dry out in the air. Air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, Chiromantis xerampelina. Bird eggs are incubated for a time that varies according to the species. Average clutch sizes range from one to about 17; some birds lay eggs when not fertilized.
The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, but some birds passerines, produce colored eggs. The pigment biliverdin and its zinc chelate give a green or blue ground color, protoporphyrin produces reds and browns as a ground color or as spotting. Non-passerines have white eggs, except in some ground-nesting groups such as the Charadriiformes and nightjars, where camouflage is necessary, some parasitic cuckoos which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs if there is no need of cryptic colors; however some have suggested that the protoporphyrin markings on passerine eggs act to reduce brittleness by acting as a solid state lubricant. If there is insufficient calcium available in the local soil, the egg shell may be thin in a circle around the broad end. Protoporphyrin speckling compensates for this, increases inversely to the amount of calcium in the soil. For the same reason eggs in a clutch are more spotted than early ones as the female's store of calcium is depleted.
The color of individual eggs is genetically influenced, appears to be inherited through the mother only, suggesting that the gene responsible for pigmentation is on the sex determining W chromosome. It used to be thought that color was applied to the shell before laying, but this research shows that coloration is an integral part of the development of the shell, with the same protein responsible for depositing calcium carbonate, or protoporphyrins when there is a lack of that mineral. In species such as the common guillemot, which nest in large groups, each female's eggs have different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed. Bird eggshells are diverse. For example: cormorant eggs are rough and chalky tinamou eggs are shiny duck eggs are oily and waterproof cassowary eggs are pittedTiny pores in bird eggshells allow the embryo to breathe; the domestic
Fresh water is any occurring water except seawater and brackish water. Fresh water includes water in ice sheets, ice caps, icebergs, ponds, rivers and underground water called groundwater. Fresh water is characterized by having low concentrations of dissolved salts and other total dissolved solids. Though the term excludes seawater and brackish water, it does include mineral-rich waters such as chalybeate springs. Fresh water is not the same as potable water. Much of the earth's fresh water is unsuitable for drinking without some treatment. Fresh water can become polluted by human activities or due to occurring processes, such as erosion. Water is critical to the survival of all living organisms; some organisms can thrive on salt water, but the great majority of higher plants and most mammals need fresh water to live. Fresh water can be defined as water with less than 500 parts per million of dissolved salts. Other sources give higher upper salinity limits for e.g. 1000 ppm or 3000 ppm. Fresh water habitats are classified as either lentic systems, which are the stillwaters including ponds, lakes and mires.
There is, in addition, a zone which bridges between groundwater and lotic systems, the hyporheic zone, which underlies many larger rivers and can contain more water than is seen in the open channel. It may be in direct contact with the underlying underground water; the majority of fresh water on Earth is in ice caps. The source of all fresh water is precipitation from the atmosphere, in the form of mist and snow. Fresh water falling as mist, rain or snow contains materials dissolved from the atmosphere and material from the sea and land over which the rain bearing clouds have traveled. In industrialized areas rain is acidic because of dissolved oxides of sulfur and nitrogen formed from burning of fossil fuels in cars, factories and aircraft and from the atmospheric emissions of industry. In some cases this acid rain results in pollution of rivers. In coastal areas fresh water may contain significant concentrations of salts derived from the sea if windy conditions have lifted drops of seawater into the rain-bearing clouds.
This can give rise to elevated concentrations of sodium, chloride and sulfate as well as many other compounds in smaller concentrations. In desert areas, or areas with impoverished or dusty soils, rain-bearing winds can pick up sand and dust and this can be deposited elsewhere in precipitation and causing the freshwater flow to be measurably contaminated both by insoluble solids but by the soluble components of those soils. Significant quantities of iron may be transported in this way including the well-documented transfer of iron-rich rainfall falling in Brazil derived from sand-storms in the Sahara in north Africa. Saline water in oceans and saline groundwater make up about 97% of all the water on Earth. Only 2.5–2.75% is fresh water, including 1.75–2% frozen in glaciers and snow, 0.5–0.75% as fresh groundwater and soil moisture, less than 0.01% of it as surface water in lakes and rivers. Freshwater lakes contain about 87% of this fresh surface water, including 29% in the African Great Lakes, 22% in Lake Baikal in Russia, 21% in the North American Great Lakes, 14% in other lakes.
Swamps have most of the balance with only a small amount in rivers, most notably the Amazon River. The atmosphere contains 0.04% water. In areas with no fresh water on the ground surface, fresh water derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers. Most of the world's fresh water is frozen in ice sheets. Many areas suffer from lack of distribution such as deserts. Water is a critical issue for the survival of all living organisms; some can use salt water but many organisms including the great majority of higher plants and most mammals must have access to fresh water to live. Some terrestrial mammals desert rodents, appear to survive without drinking, but they do generate water through the metabolism of cereal seeds, they have mechanisms to conserve water to the maximum degree. Fresh water creates a hypotonic environment for aquatic organisms; this is problematic for some organisms with pervious skins or with gill membranes, whose cell membranes may burst if excess water is not excreted.
Some protists accomplish this using contractile vacuoles, while freshwater fish excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, diadromous fish have the ability to migrate between fresh water and saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; the eel uses the hormone prolactin, while in salmon the hormone cortisol plays a key role during this process. Many sea birds have special glands at the base of the bill; the marine iguanas on the Galápagos Islands excrete excess salt through a nasal gland and they sneeze out a salty excretion. Freshwater molluscs include freshwater snails and freshwater bivalves. Freshwater crustaceans include crayfish. Freshwater biodiversity faces many threats; the World Wide Fund for Nature's Living Planet Index noted an 83% decline in the populations of freshwater vertebrates between 1970 and 2014.
These declines continue to outpace
The Chinese goose is a breed of domesticated goose descended from the wild swan goose. Chinese geese differ from the wild birds in much larger size, in having an strongly developed basal knob on the upper side of the bill; the knob at the top of the beak is more prominent on males than females. It takes several months for the knob to become pronounced enough that it can be used for determining gender. Chinese geese are a close cousin of the African goose, a heavier breed descended from the swan goose. Chinese geese appear in two varieties: white. While many domestic Chinese geese have a similar body type to other breeds, the breed standards as defined in the American Poultry Association's Standard of Perfection and other sources call for a slimmer, taller fowl. Chinese geese are among the better laying breeds of goose. A female Chinese goose can lay 50–60 eggs over the course of the breeding season, although there are reports of Chinese geese laying up to 100 eggs during that time. Ekarius, Carol.
Storey's Illustrated Guide to Poultry Breeds. 210 MAS MoCA Way, North Adams MA 01247: Storey Publishing. ISBN 978-1-58017-667-5. Buckland, Roger & Guy, Gérard: Goose Production. FAO Animal Production and Health Papers 154. ISBN 92-5-104862-2 PDF fulltext "Chinese Geese". Feathersite.com. Retrieved 2008-07-02. List of goose breeds
Flight feathers are the long, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird. The primary function of the flight feathers is to aid in the generation of both thrust and lift, thereby enabling flight; the flight feathers of some birds have evolved to perform additional functions associated with territorial displays, courtship rituals or feeding methods. In some species, these feathers have developed into long showy plumes used in visual courtship displays, while in others they create a sound during display flights. Tiny serrations on the leading edge of their remiges help owls to fly silently, while the extra-stiff rectrices of woodpeckers help them to brace against tree trunks as they hammer on them. Flightless birds still retain flight feathers, though sometimes in radically modified forms; the moult of their flight feathers can cause serious problems for birds, as it can impair their ability to fly. Different species have evolved different strategies for coping with this, ranging from dropping all their flight feathers at once to extending the moult over a period of several years.
Remiges are located on the posterior side of the wing. Ligaments attach the long calami to the wing bones, a thick, strong band of tendinous tissue known as the postpatagium helps to hold and support the remiges in place. Corresponding remiges on individual birds are symmetrical between the two wings, matching to a large extent in size and shape, though not in pattern, they are given different names depending on their position along the wing. Primaries are connected to the manus; these feathers are important for flapping flight, as they are the principal source of thrust, moving the bird forward through the air. The mechanical properties of primaries are important in supporting flight. Most thrust is generated on the downstroke of flapping flight. However, on the upstroke, the primaries are separated and rotated, reducing air resistance while still helping to provide some thrust; the flexibility of the remiges on the wingtips of large soaring birds allows for the spreading of those feathers, which helps to reduce the creation of wingtip vortices, thereby reducing drag.
The barbules on these feathers, friction barbules, are specialized with large lobular barbicels that help grip and prevent slippage of overlying feathers and are present in most of the flying birds. Species vary somewhat in the number of primaries they possess; the number in non-passerines varies between 9 and 11, but grebes and flamingos have 12, ostriches have 16. While most modern passerines have ten primaries, some have only nine; those with nine are missing the most distal primary, very small and sometimes rudimentary in passerines. The outermost primaries—those connected to the phalanges—are sometimes known as pinions. Secondaries are connected to the ulna. In some species, the ligaments that bind these remiges to the bone connect to small, rounded projections, known as quill knobs, on the ulna. Secondary feathers remain close together in flight and help to provide lift by creating the airfoil shape of the bird's wing. Secondaries tend to be shorter and broader with blunter ends, they vary in number from 6 in hummingbirds to as many as 40 in some species of albatross.
In general and longer-winged species have a larger number of secondaries. Birds in more than 40 non-passerine families seem to be missing the fifth secondary feather on each wing, a state known as diastataxis. In these birds, the fifth set of secondary covert feathers does not cover any remiges due to a twisting of the feather papillae during embryonic development. Loons, pelicans and eagles, sandpipers, gulls and owls are among the families missing this feather. Tertials arise in the brachial region and are not considered true remiges as they are not supported by attachment to the corresponding bone, in this case the humerus; these elongated "true" tertials act as a protective cover for all or part of the folded primaries and secondaries, do not qualify as flight feathers as such. However, many authorities use the term tertials to refer to the shorter, more symmetrical innermost secondaries of passerines in an effort to distinguish them from other secondaries; the term humeral is sometimes used for birds such as the albatrosses and pelicans that have a long humerus.
The calami of the flight feathers are protected by a layer of non-flight feathers called covert feathers or tectrices, at least one layer of them both above and beneath the flight feathers of the wings as well as above and below the rectrices of the tail. These feathers may vary in size — in fact, the upper tail tectrices of the male peafowl, rather than its rectrices, are what constitute its elaborate and colorful "train"; the outermost primaries of large soaring birds ra
In biology, a mutation is the permanent alteration of the nucleotide sequence of the genome of an organism, virus, or extrachromosomal DNA or other genetic elements. Mutations result from errors during DNA replication or other types of damage to DNA, which may undergo error-prone repair, or cause an error during other forms of repair, or else may cause an error during replication. Mutations may result from insertion or deletion of segments of DNA due to mobile genetic elements. Mutations may or may not produce discernible changes in the observable characteristics of an organism. Mutations play a part in both normal and abnormal biological processes including: evolution and the development of the immune system, including junctional diversity; the genomes of RNA viruses are based on RNA rather than DNA. The RNA viral genome can be double single stranded. In some of these viruses replication occurs and there are no mechanisms to check the genome for accuracy; this error-prone process results in mutations.
Mutation can result in many different types of change in sequences. Mutations in genes can either have no effect, alter the product of a gene, or prevent the gene from functioning properly or completely. Mutations can occur in nongenic regions. One study on genetic variations between different species of Drosophila suggests that, if a mutation changes a protein produced by a gene, the result is to be harmful, with an estimated 70 percent of amino acid polymorphisms that have damaging effects, the remainder being either neutral or marginally beneficial. Due to the damaging effects that mutations can have on genes, organisms have mechanisms such as DNA repair to prevent or correct mutations by reverting the mutated sequence back to its original state. Mutations can involve the duplication of large sections of DNA through genetic recombination; these duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years.
Most genes belong to larger gene families of shared ancestry. Novel genes are produced by several methods through the duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions. Here, protein domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties. For example, the human eye uses four genes to make structures that sense light: three for cone cell or color vision and one for rod cell or night vision. Another advantage of duplicating a gene is. Other types of mutation create new genes from noncoding DNA. Changes in chromosome number may involve larger mutations, where segments of the DNA within chromosomes break and rearrange. For example, in the Homininae, two chromosomes fused to produce human chromosome 2. In evolution, the most important role of such chromosomal rearrangements may be to accelerate the divergence of a population into new species by making populations less to interbreed, thereby preserving genetic differences between these populations.
Sequences of DNA that can move about the genome, such as transposons, make up a major fraction of the genetic material of plants and animals, may have been important in the evolution of genomes. For example, more than a million copies of the Alu sequence are present in the human genome, these sequences have now been recruited to perform functions such as regulating gene expression. Another effect of these mobile DNA sequences is that when they move within a genome, they can mutate or delete existing genes and thereby produce genetic diversity. Nonlethal mutations increase the amount of genetic variation; the abundance of some genetic changes within the gene pool can be reduced by natural selection, while other "more favorable" mutations may accumulate and result in adaptive changes. For example, a butterfly may produce offspring with new mutations; the majority of these mutations will have no effect. If this color change is advantageous, the chances of this butterfly's surviving and producing its own offspring are a little better, over time the number of butterflies with this mutation may form a larger percentage of the population.
Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can increase in frequency over time due to genetic drift, it is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. DNA repair mechanisms are able to mend most changes before they become permanent mutations, many organisms have mechanisms for eliminating otherwise-permanently mutated somatic cells. Beneficial mutations can improve reproductive success. Mutationism is one of several alternatives to evolution by natural selection that have existed both before and after the publication of Charles Darwin's 1859 book, On the Origin of Species. In the theory, mutation was the source of novelty
Carl Linnaeus known after his ennoblement as Carl von Linné, was a Swedish botanist and zoologist who formalised binomial nomenclature, the modern system of naming organisms. He is known as the "father of modern taxonomy". Many of his writings were in Latin, his name is rendered in Latin as Carolus Linnæus. Linnaeus was born in the countryside of Småland in southern Sweden, he received most of his higher education at Uppsala University and began giving lectures in botany there in 1730. He lived abroad between 1735 and 1738, where he studied and published the first edition of his Systema Naturae in the Netherlands, he returned to Sweden where he became professor of medicine and botany at Uppsala. In the 1740s, he was sent on several journeys through Sweden to find and classify plants and animals. In the 1750s and 1760s, he continued to collect and classify animals and minerals, while publishing several volumes, he was one of the most acclaimed scientists in Europe at the time of his death. Philosopher Jean-Jacques Rousseau sent him the message: "Tell him I know no greater man on earth."
Johann Wolfgang von Goethe wrote: "With the exception of Shakespeare and Spinoza, I know no one among the no longer living who has influenced me more strongly." Swedish author August Strindberg wrote: "Linnaeus was in reality a poet who happened to become a naturalist." Linnaeus has been called Princeps botanicorum and "The Pliny of the North". He is considered as one of the founders of modern ecology. In botany and zoology, the abbreviation L. is used to indicate Linnaeus as the authority for a species' name. In older publications, the abbreviation "Linn." is found. Linnaeus's remains comprise the type specimen for the species Homo sapiens following the International Code of Zoological Nomenclature, since the sole specimen that he is known to have examined was himself. Linnaeus was born in the village of Råshult in Småland, Sweden, on 23 May 1707, he was the first child of Christina Brodersonia. His siblings were Anna Maria Linnæa, Sofia Juliana Linnæa, Samuel Linnæus, Emerentia Linnæa, his father taught him Latin as a small child.
One of a long line of peasants and priests, Nils was an amateur botanist, a Lutheran minister, the curate of the small village of Stenbrohult in Småland. Christina was the daughter of the rector of Samuel Brodersonius. A year after Linnaeus's birth, his grandfather Samuel Brodersonius died, his father Nils became the rector of Stenbrohult; the family moved into the rectory from the curate's house. In his early years, Linnaeus seemed to have a liking for plants, flowers in particular. Whenever he was upset, he was given a flower, which calmed him. Nils spent much time in his garden and showed flowers to Linnaeus and told him their names. Soon Linnaeus was given his own patch of earth. Carl's father was the first in his ancestry to adopt a permanent surname. Before that, ancestors had used the patronymic naming system of Scandinavian countries: his father was named Ingemarsson after his father Ingemar Bengtsson; when Nils was admitted to the University of Lund, he had to take on a family name. He adopted the Latinate name Linnæus after a giant linden tree, lind in Swedish, that grew on the family homestead.
This name was spelled with the æ ligature. When Carl was born, he was named Carl Linnæus, with his father's family name; the son always spelled it with the æ ligature, both in handwritten documents and in publications. Carl's patronymic would have been Nilsson, as in Carl Nilsson Linnæus. Linnaeus's father began teaching him basic Latin and geography at an early age; when Linnaeus was seven, Nils decided to hire a tutor for him. The parents picked a son of a local yeoman. Linnaeus did not like him, writing in his autobiography that Telander "was better calculated to extinguish a child's talents than develop them". Two years after his tutoring had begun, he was sent to the Lower Grammar School at Växjö in 1717. Linnaeus studied going to the countryside to look for plants, he reached the last year of the Lower School when he was fifteen, taught by the headmaster, Daniel Lannerus, interested in botany. Lannerus gave him the run of his garden, he introduced him to Johan Rothman, the state doctor of Småland and a teacher at Katedralskolan in Växjö.
A botanist, Rothman broadened Linnaeus's interest in botany and helped him develop an interest in medicine. By the age of 17, Linnaeus had become well acquainted with the existing botanical literature, he remarks in his journal that he "read day and night, knowing like the back of my hand, Arvidh Månsson's Rydaholm Book of Herbs, Tillandz's Flora Åboensis, Palmberg's Serta Florea Suecana, Bromelii Chloros Gothica and Rudbeckii Hortus Upsaliensis...."Linnaeus entered the Växjö Katedralskola in 1724, where he studied Greek, Hebrew and mathematics, a curriculum designed for boys preparing for the priesthood. In the last year at the gymnasium, Linnaeus's father visited to ask the professors how his son's studies were progressing. Rothman believed otherwise; the doctor offered to have Linnaeus live with his family in Växjö and to teach him physiology and botany. Nils accepted this offer. Rothman showed Linnaeus that botany was a serious sub