Egg (biology) 484939 225797626 2008-07-15T13:20:54Z 83.227.157.212 {{Mergefrom|Ovum|date=May 2008}} [[Image:Oeufs002b.jpg|Bird eggs and others (click on image for key)|right|200px|thumb]] In most [[bird]]s and [[reptile]]s, an '''egg''' ([[Latin language|Latin]] ''ovum'') is the [[zygote]], resulting from [[fertilization]] of the [[ovum]]. To enable incubation the egg is usually kept within a favourable temperature range as it nourishes and protects the growing [[embryo]]. When the embryo is adequately developed it breaks out of the egg in the process of hatching. Some embryos have a temporary [[egg tooth]] with which to crack or pip the eggshell or covering. [[Oviparous]] animals are animals that lay eggs, with little or no other development within the mother. The study or collecting of eggs, particularly bird eggs, is called [[oology]]. Reptile eggs, bird eggs, and monotreme eggs, which are laid out of water, are surrounded by a protective [[Eggshell|shell]], either flexible or inflexible. The special membranes that support these eggs are traits of all [[amniotes]], including [[mammal]]s. The 1.5 kg [[ostrich]] egg contains the largest existing single cell currently known, though the extinct ''[[Aepyornis]]'' and some [[dinosaur]]s had larger eggs. The [[Bee Hummingbird]] produces the smallest known bird egg, which weighs half a gram. The eggs laid by some reptiles and most fish can be even smaller, and those of insects and other [[invertebrate]]s can be much smaller still. [[Image:Editing Image-Acanthodoris lutea laying eggs 2.jpg|[[Nudibranch]] [[Orange-peel doris]] ''Acanthodoris lutea '' in [[California]] [[tide pools]] laying eggs|right|200px|thumb]] ==Bird eggs== Bird eggs are laid by females and [[Incubate (bird)|incubated]] for a time that varies according to the species; a single young hatches from each egg. Average [[clutch (eggs)|clutch size]]s range from one (as in [[condor]]s) to about 17 (the [[Grey Partridge]]). Some birds lay eggs even when not fertilized; it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are also called wind-eggs. ===Colors=== [[Image:Murre Eggs.jpg|thumb||250px|Guillemot eggs]] The default color of vertebrate eggs is the white of the [[calcium carbonate]] from which the shells are made, but some birds, mainly [[passerine]]s, produce colored eggs. The pigments [[biliverdin]] and its zinc [[chelate]] give a green or blue ground color, and [[protoporphyrin]] produces reds and browns as a ground color or as spotting. Non-passerines typically have white eggs, except in some ground-nesting groups such as the [[Charadriiformes]], [[sandgrouse]] and [[nightjar]]s, where camouflage is necessary, and some [[brood parasite|parasitic]] [[cuckoo]]s which have to match the passerine host's egg. Most passerines, in contrast, lay colored eggs, even if there is no need of cryptic colors. However, a recent study{{Fact|date=September 2007}} suggests that the protoporphyrin markings on passerine eggs actually 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, especially in a circle around the broad end. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil. For the same reason, later 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 also genetically influenced, and appears to be inherited through the mother only, suggesting that the [[gene]] responsible for pigmentation is on the sex determining [[W chromosome]] (female birds are WZ, males ZZ). It used to be thought that color was applied to the shell immediately 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 very different markings, making it easier for females to identify their own eggs on the crowded cliff ledges on which they breed. ===Shell=== 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 heavily pitted Tiny [[pore]]s in bird eggshells allow the embryo to breathe. The [[chicken|domestic hen]]'s egg has around 7500 pores. ===Shape=== Most bird eggs have an [[Oval (geometry)|oval shape]], with one end rounded and the other more pointy. This shape results from the egg being forced through the [[oviduct]]. Muscles contract the oviduct behind the egg, pushing it forward. The egg's wall is still shapeable, and the pointy end develops at the back side. Cliff-nesting birds often have highly conical eggs. They are less likely to roll off, tending instead to roll around in a tight circle; this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs. ===Predation=== Many animals feed on eggs. For example, principal predators of the [[American Black Oystercatcher|Black Oystercatcher]]'s eggs include [[raccoon]]s, [[skunk]]s, [[mink]], river and sea [[otter]]s, [[gull]]s, [[crow]]s and [[fox]]es. The [[stoat]] (''Mustela erminea'') and [[long-tailed weasel]] (''M. frenata'') steal ducks' eggs. Snakes of the genera ''[[Dasypeltis]]'' and ''[[Elachistodon]]'' specialize in eating eggs. [[Brood parasitism]] occurs in birds when one species lays its eggs in the nest of another. In some cases, the host's eggs are removed or eaten by the female, or expelled by her chick. Brood parasites include the [[cowbird]]s and many Old World [[cuckoo]]s. ===Various bird eggs=== <gallery> Image:Egg125o.gif|An average [[Whooping Crane]] egg is 102 mm long, and weighs 208 grams Image:Nest Eggs.jpg|Eggs in a nest Image:Eggs of hummingbird, hen, and ostrich.jpg|Eggs of hummingbird, hen, and ostrich Image:Senegal egg 10s06.JPG|Senegal Parrot egg (on 1cm grid). A bird that nests in tree holes. </gallery> ==Fish eggs (amniotic egg)== [[Image:Salmonlarvakils.jpg|thumb|right|150px|[[Salmon]] fry hatching - the larva has grown around the remains of the yolk and the remains of the soft, transparent egg are discarded.]] [[Image:Salmoneggskils.jpg|left|thumb|200px|Salmon eggs in different stages of development. In some only a few cells grow on top of the [[yolk]], in the lower right the blood vessels surround the yolk and in the upper left the black eyes are visible.]] 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. Typically large numbers of eggs are laid at one time (an adult female [[cod]] can produce 4&ndash;6 million eggs in one spawning) and the eggs are then left to develop without parental care. When the larvae hatch from the egg, they often 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 [[ray (fish)|ray]]s and most [[shark]]s 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 then gives birth to relatively mature young. In certain instances, the most physically-developed offspring will devour its smaller siblings for further nutrition while still within the mother's body. This is known as [[Cannibalism (zoology)#Intrauterine cannibalism|intrauterine cannibalism]]. In certain rare scenarios, some fish such as the [[hammerhead shark]] and [[reef shark]] are [[Viviparity|viviparous]], with the egg being fertilized and developed internally, but with the mother also providing direct nourishment. <br clear="both"> ==Other eggs== [[Image:Snapping turtle eggs md.jpg|thumb|right|200px|Turtle eggs in a nest dug by a female common snapping turtle (''[[Common Snapping Turtle|Chelydra serpentina]]'')]] [[Image:Frog in frogspawn.jpg|thumb|150px|left|A frog amongst frogspawn]] ===Invertebrate eggs=== Eggs are common among invertebrates, including [[insect]]s, [[mollusk]]s, and [[crustacean]]s. ===Fish and amphibian eggs=== The eggs of [[fish]] and [[amphibian]]s are jellylike. Fish eggs are fertilized externally, typically with the male inseminating the eggs after the female lays them. These eggs do not have a shell and would dry out in the air. Even air-breathing amphibians lay their eggs in water, or in protective foam as with the Coast foam-nest treefrog, ''[[Chiromantis xerampelina]]''. ===Amniote eggs and embryos=== Like amphibians, [[amniotes]] are air-breathing vertebrates, but they have complex eggs or embryos, including an amniotic membrane. Amniotes include [[reptile]]s, [[dinosaur]]s, [[bird]]s, and [[mammal]]s. Reptile eggs are often rubbery and are always initially white. They are able to survive in the air. Often the sex of the developing embryo is determined by the temperature of the surroundings, with cooler temperatures favouring males. Not all reptiles lay eggs; some are [[viviparous]] ("live birth"). Dinosaurs laid eggs, some of which have been preserved as petrified fossils. Among mammals, early extinct species laid eggs, as do [[platypus]]es and [[echidna]]s (spiny anteaters). Platypuses and two genera of [[echidna]] are Australian [[monotremes]]. [[Marsupial]] and [[placental]] mammals do not lay eggs, but their unborn young do have the complex tissues that identify amniotes. <gallery> Image:Tortoise-Hatchling.jpg|A baby [[tortoise]] emerges from its egg. Image:Emperor Gum Moth eggs2.jpg|Insect eggs, in this case those of the [[Opodiphthera eucalypti|Emperor Gum Moth]], are often laid on the underside of leaves. Image:Clupeaharenguskils2.jpg|Fish eggs, such as these [[herring]] eggs are often transparent and fertilized after laying Image:Skate egg case (Raja binoculata) 01.jpg|[[Skate]]s (and [[shark]]s) have a uniquely shaped egg case called a [[mermaid's purse]] </gallery> ==References== *[http://www.lifesciences.napier.ac.uk/teaching/MB/Fish02.html Marine Biology notes] from School of Life Sciences, Napier University. *[http://news.nationalgeographic.com/news/2005/10/1011_051011_speckled_eggs.html Speckles Make Bird Eggs Stronger, Study Finds] John Pickrell, National Geographic News, 11 Oct 2005. *Andrew Gosler, ''Yet even more ways to dress eggs'' in British Birds, vol 99 no 7, July 2006 ==See also== {{commons|Egg}} *[[Egg (food)]] *[[Egg yolk]] *[[Egg white]] *[[Trophic egg]] *[[Animal shell]] [[Category:reproductive system]] [[Category:Oology]] [[Category:Aviculture]] [[af:Eier]] [[ar:بيضة (أحياء)]] [[ast:Güevu (bioloxía)]] [[ay:K'awna]] [[bm:Syɛfan]] [[bs:Jaje]] [[bg:Яйце]] [[ca:Ou (biologia)]] [[cs:Vejce]] [[cy:Ŵy]] [[da:Æg]] [[pdc:Oi]] [[de:Ei]] [[eml:Óv]] [[es:Huevo (biología)]] [[eo:Ovo]] [[fa:تخم مرغ]] [[fr:Œuf (biologie)]] [[gd:Ugh]] [[gl:Ovo (alimento)]] [[ko:알]] [[hr:Jaje]] [[id:Telur]] [[is:Egg (matvæli)]] [[it:Uovo (biologia)]] [[he:ביצה]] [[ku:Hêk]] [[la:Ovum]] [[lb:Ee]] [[lt:Kiaušinis]] [[ml:മുട്ട]] [[nl:Ei (dier)]] [[nds-nl:Tudeaai]] [[ja:卵]] [[no:Egg]] [[nn:Egg]] [[nrm:Oeu]] [[oc:Uòu]] [[pl:Jajo (biologia)]] [[pt:Ovo]] [[qu:Runtu]] [[ru:Яйцо]] [[simple:Egg (biology)]] [[sl:Jajce]] [[sr:Јаје]] [[su:Endog]] [[fi:Muna]] [[sv:Ägg]] [[ta:முட்டை]] [[vi:Trứng gà]] [[tr:Yumurta]] [[uk:Яйце]] [[zh:蛋]] [[hu:Tojás (biológia)]]