Misplaced Pages

#834165

74-604: See text . Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian ( Wuchiapingian ), They have typically been classified as advanced reptiliomorphs (transitional between " amphibians " sensu lato and amniotes ) positioned close to, but outside of the clade Amniota, though some recent research has recovered them as

148-588: A population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of

222-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it

296-446: A branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"

370-464: A breeding site. The females choose large males that are successfully defending prime breeding sites which the females find attractive. For example, sculpin males defend "caves" underneath rocks which are suitable for the incubation of embryos. Another way males get to mate with several females is through the use of leks. Leks are places where many fish come together, and the males display to each other. Based on these displays, each female then selects

444-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking

518-480: A classification of the spawning behaviours of fish by Balon (1975, 1984) into reproductive guilds . This classification is based on how the eggs are fertilized (internal or external spawners), where the eggs are deposited ( pelagic or benthic spawners), and whether and how the parents look after the eggs after spawning (bearers, guarders and nonguarders). Nonguarders do not protect their eggs and offspring after spawning Open substrate spawners scatter their eggs in

592-772: A few days and replace the dominant male. This is found amongst coral reef fishes such as groupers , parrotfishes and wrasses . It is less common for a male to switch to a female ( protandry ). As an example, most wrasses are protogynous hermaphrodites within a haremic mating system. Hermaphroditism allows for complex mating systems. Wrasses exhibit three different mating systems: polygynous, lek-like , and promiscuous mating systems. Group spawning and pair spawning occur within mating systems. The type of spawning that occurs depends on male body size. Labroids typically exhibit broadcast spawning, releasing high amounts of planktonic eggs, which are broadcast by tidal currents; adult wrasses have no interaction with offspring. Wrasse of

666-840: A forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, they graze on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat krill and other crustaceans . The capelin move inshore in large schools to spawn and migrate in spring and summer to feed in plankton rich areas between Iceland , Greenland , and Jan Mayen . The migration is affected by ocean currents . Around Iceland maturing capelin make large northward feeding migrations in spring and summer. The return migration takes place in September to November. The spawning migration starts north of Iceland in December or January. The diagram on

740-400: A pair of gonads , which release sperm in response to hormones in the female's bloodstream indicating egg release. This ensures that, when the female is ready to spawn, she has a mate immediately available. A single anglerfish female can "mate" with many males in this manner. Polygynandry occurs when multiple males mate indiscriminately with multiple females. This mutual promiscuity is

814-503: A particular subgroup of the family Labridae , Labrini, do not exhibit broadcast spawning. Less commonly hermaphrodites can be synchronous , meaning they simultaneously possess both ovaries and testicles and can function as either sex at any one time. Black hamlets "take turns releasing sperm and eggs during spawning. Because such egg trading is advantageous to both individuals, hamlets are typically monogamous for short periods of time–an unusual situation in fishes." The sex of many fishes

SECTION 10

#1732802420835

888-501: A phylogenetic analysis, and in this study the analysis resulted in Diadectomorpha being inside amniota as a sister taxon to Synapsida. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos)  'branch'), also known as a monophyletic group or natural group ,

962-488: A relatively small number of embryos and retain them for a few weeks to 16 months or longer. The shorter times spans are characteristic of species that eventually deposit their embryos in the environment, surrounded by a horny capsule; whereas the longer periods are characteristic of sharks that retain the embryos until they are ready to emerge as actively swimming young." However, some fish do not fit these categories. The livebearing largespring gambusia ( Gambusia geiseri )

1036-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on

1110-400: A significant temperature change, often in spring. Males chase females, prompting them to release their eggs by bumping and nudging them. As the female goldfish spawns her eggs, the male goldfish stays close behind fertilizing them. Their eggs are adhesive and attach to aquatic vegetation. The eggs hatch within 48 to 72 hours. Within a week or so, the fry begins to assume its final shape, although

1184-605: A species is all-male or all-female. Unisexuality occurs in some fish species, and can take complex forms. Squalius alburnoides , a minnow found in several river basins in Portugal and Spain, appears to be an all-male species. The existence of this species illustrates the potential complexity of mating systems in fish. The species originated as a hybrid between two species, and is diploid , but not hermaphroditic. It can have triploid and tetraploid forms, including all-female forms that reproduce mainly through hybridogenesis . It

1258-423: A species is either male or female, and remains that way throughout their lives. Most fish are gonochorists, but hermaphroditism is known to occur in 14 families of teleost fishes. Usually hermaphrodites are sequential , meaning they can switch sex, usually from female to male ( protogyny ). This can happen if a dominant male is removed from a group of females. The largest female in the harem can switch sex over

1332-438: A substrate and guard them until the eggs hatch. After hatching, the female picks up the fry and keeps them in her mouth. When the fry can fend for themselves, they are released. Some eartheaters are larvophile mouthbrooders. The beginning of the evolutionary process of livebearing starts with facultative (optional) internal bearing. The process occurs in several species of oviparous (egg-laying) killifishes which spawn in

1406-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,

1480-437: A year may pass before they develop a mature goldfish colour; until then they are a metallic brown like their wild ancestors. In their first weeks of life, the fry grow quickly—an adaptation born of the high risk of getting devoured by the adult goldfish. Carp typically spawn in the spring and summer, depending on the climate and conditions. Oxygen levels of the water, availability of food, size of each fish, age, number of times

1554-546: Is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual,

SECTION 20

#1732802420835

1628-438: Is also true of cartilaginous fishes (such as sharks , rays and skates ). Spawn consists of the reproductive cells ( gametes ) of many aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing ova (unfertilized eggs) into the water, often in large quantities, while males simultaneously or sequentially release spermatozoa ( milt ) to fertilize

1702-444: Is an "investment by parents in offspring that increases the offspring's chances of surviving (and hence reproducing). In fish, parental care can take a variety of forms including guarding, nest building, fanning, splashing, removal of dead eggs, retrieval of straying fry, external egg carrying, egg burying, moving eggs or young, ectodermal feeding, oral brooding, internal gestation, brood-pouch egg carrying, etc." Territorial behaviour

1776-441: Is an external method of reproduction where the female releases many unfertilised eggs into the water. At the same time, a male or many males release a lot of sperm into the water which fertilises some of these eggs. The eggs contain a drop of nutrient oil to sustain the embryo as it develops inside the egg case. The oil also provides buoyancy, so the eggs float and drift with the current. The strategy for survival of broadcast spawning

1850-615: Is called coral because it turns bright red when cooked. Roe (reproductive organs) are usually eaten either raw or briefly cooked. "The reproductive behaviour of fishes is remarkably diversified: they may be oviparous (lay eggs), ovoviviparous (retain the eggs in the body until they hatch), or viviparous (have a direct tissue connection with the developing embryos and give birth to live young). All cartilaginous fishes—the elasmobranches (e.g., sharks, rays, and skates)—employ internal fertilization and usually lay large, heavy-shelled eggs or give birth to live young. The most characteristic features of

1924-408: Is difficult for fish to find partners, or when both sexes look after the young. Many tropical cichlids , which rear their young together in locations where they must fiercely defend against competitors and predators are monogamous. "In some pipefishes and seahorses , development of eggs takes a long time before the female can place them in the brood pouch of a male, where they are fertilized. While

1998-610: Is dominated by large and aggressive males. Cuckoldry is a variant of polyandry, and can occur with sneak spawners (sometimes called streak spawners ). A sneak spawner is a male that rushes in to join the spawning rush of a spawning pair. A spawning rush occurs when a fish makes a burst of speed, usually on a near vertical incline, releasing gametes at the apex, followed by a rapid return to the lake or sea floor or fish aggregation. Sneaking males do not take part in courtship. In salmon and trout, for example, jack males are common. These are small silvery males that migrate upstream along with

2072-489: Is generally necessary for guarders, and the embryos are almost always guarded by males (apart from cichlids). There is a need to be territorial because looking after embryos usually includes defending the site where they are being looked after. It also often means there is competition for the best egg-laying sites. Elaborate courtship behaviour is usual among guarders. Guarding males keep the embryos safe from predators, keep oxygen levels high by fanning water currents, and keep

2146-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution

2220-646: Is known. Whether this is due to an actual lack of tadpole stage or taphonomy (many diadectomorphs were upland creatures where tadpoles would have a poor probability of being fossilized) is uncertain. Alfred Romer indicated that the anamniote/amniote divide might not have been very sharp, leaving the question of the actual mode of reproduction of these large animals unanswered. Possible reproductive modes include full amphibian spawning with aquatic tadpoles, internal fertilization with or without ovoviviparity , aquatic eggs with direct development or some combination of these. The reproductive mode might also have varied within

2294-450: Is not fixed, but can change with physical and social changes to the environment where the fish lives. Particularly among fishes, hermaphroditism can pay off in situations where one sex is more likely to survive and reproduce, perhaps because it is larger. Anemone fishes are sequential hermaphrodites which are born as males, and become females only when they are mature. Anemone fishes live together monogamously in an anemone , protected by

Diadectomorpha - Misplaced Pages Continue

2368-517: Is often associated with r-strategists . However, most fish and other spawning animals are iteroparous. When the internal ovaries or egg masses of fish and certain marine animals are ripe for spawning they are called roe . Roe from certain species, such as shrimp , scallop , crab and sea urchins , are sought as human delicacies in many parts of the world. Caviar is a name for the processed, salted roe of non-fertilized sturgeon . The term soft roe or white roe denotes fish milt . Lobster roe

2442-494: Is often necessary to construct fish ladders and other bypass systems so salmon can navigate their way past hydroelectric dams or other obstructions such as weirs on their way to spawning grounds. Coastal fish often use mangroves and estuaries as spawning grounds, while reef fish can find adjacent seagrass meadows that make good spawning grounds. Short-finned eels can travel anything up to three or four thousand kilometres to their spawning ground in deep water somewhere in

2516-509: Is rare to find true parthenogenesis in fishes, where females produce female offspring with no input from males. All-female species include the Texas silverside , Menidia clarkhubbsi as well as the Amazon molly . Parthenogenesis has been recently observed in hammerhead sharks and blacktip sharks . It is also known to occur in crayfish and amphibians. This section is patterned after

2590-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed

2664-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with

2738-503: Is the egg yolk, as in externally spawned eggs. This situation, also referred to as ovoviviparity , is characteristic of marine rock fishes and the Lake Baikal sculpins . This strategy allows these fish to have fecundities approaching those of pelagic fish with external fertilization, but it also enables them to protect the young during their most vulnerable stage of development. By contrast, sharks and rays using this strategy produce

2812-476: Is to disperse the fertilised eggs, preferably away from the coast into the relative safety of the open ocean. There the larvae develop as they consume their fat stores, and eventually hatch from the egg capsule into miniature versions of their parents. To survive, they must then become miniature predators themselves, feeding on plankton. Fish eventually encounter others of their own kind ( conspecifics ), where they form aggregations and learn to school. Internally,

2886-618: The Coral Sea . Forage fish often make great migrations between their spawning, feeding and nursery grounds. Schools of a particular stock usually travel in a triangle between these grounds. For example, one stock of herrings have their spawning ground in southern Norway , their feeding ground in Iceland , and their nursery ground in northern Norway. Wide triangular journeys such as these may be important because forage fish, when feeding, cannot distinguish their own offspring. Capelin are

2960-516: The Late Pennsylvanian and Early Permian periods. Diadectomorphs possessed both amphibian -like and amniote -like characteristics. Originally these animals were included under the order Cotylosauria , and were considered the most primitive and ancestral lineage of reptiles . More recently they have been reclassified either as non-amniote reptiliomorphs lying just outside the clade Amniota, or as early-diverging synapsids (members of

3034-570: The bluegill sunfish in fresh water. Sneaker males that become too large to hide effectively become satellite males . With bluegill sunfish, satellite males mimic the behaviour and colouration of the females. They hover over a nest containing a pair of courting sunfish, and gradually descend to reach the pair just as they spawn. Males may need to be 6 or 7 years old to function capably as parental males, but may be able to function as sneaker or satellite males when they are as young as 2 or 3 years old. The smaller satellite and sneaker males may get mauled by

Diadectomorpha - Misplaced Pages Continue

3108-662: The sardine run occurs when millions of sardines migrate from their spawning grounds south of the southern tip of Africa northward along the Eastern Cape coastline. Chinook salmon make the longest freshwater migration of any salmon, over 3,000 kilometres (1,900 mi) up the Yukon River to spawning grounds upstream of Whitehorse , Yukon. Some green sea turtles swim more than 2,600 kilometres (1,600 mi) to reach their spawning grounds. Goldfish , like all cyprinids , are egg-layers. They usually start breeding after

3182-632: The Diadectomorphs has been the matter of some debate. If their group lay within the Amniota as has at times been assumed, they would have laid an early version of the amniote egg. Current thinking favours the amniote egg being evolved in very small animals, like Westlothiana or Casineria , leaving the bulky Diadectomorphs just on the amphibian side of the divide. This would indicate the large and bulky diadectomorphs laid anamniote eggs (in water). However, no unambiguously diadectomorph tadpole

3256-421: The abdomen. Male sharks and rays can pass sperm along a duct into a seminal vesicle , where they store it for a while before it is expelled, while teleosts usually employ separate sperm ducts. Externally, many marine animals, even when spawning, show little sexual dimorphism (difference in body shape or size) or little difference in colouration . Where species are dimorphic, such as sharks or guppies ,

3330-533: The amniote group containing mammals and their extinct relatives). Contrary to other non-amniote reptiliomorphs, the teeth of the Diadectomorpha lacked the infolding of the dentine and enamel that account for the name Labyrinthodontia for the non-amniote tetrapods . Diadectomorpha is most commonly given the rank of order when formal taxonomic ranks are applied. It is further divided into three families , representing specialization into different ecological niches . The exact phylogenetic relationship between

3404-472: The anemone stings. The males do not have to compete with other males, and female anemone fish are typically larger. When a female dies a juvenile (male) anemone fish moves in, and "the resident male then turns into a female and reproductive advantages of the large female–small male combination continue". In other fishes sex changes are reversible. For example, if some gobies are grouped by sex (male or female), some will switch sex. Unisexuality occurs when

3478-420: The approach most commonly used by spawning animals, and is perhaps the "original fish mating system." Common examples are forage fish , such as herrings , which form huge mating shoals in shallow water. The water becomes milky with sperm and the bottom is draped with millions of fertilized eggs. Alternate male strategies which allow small males to engage in cuckoldry can develop in species where spawning

3552-448: The area free from dead embryos and debris. They protect the embryos until they hatch, and often look after the larval stages as well. The time spent guarding can range from a few days to several months. Some guarders build nests ( nest spawners ) and some do not ( substrate spawners ), though the difference between the two groups can be small. Substrate spawners clean off a suitable area of surface suitable for egg laying, and look after

3626-432: The area, but they do not actively build a nest. Bearers are fish that carry their embryos (and sometimes their young) around with them, either externally or internally. Mouth brooders - carry eggs or larvae in their mouth. Mouth brooders can be ovophiles or larvophiles. Ovophile or egg-loving mouth-brooders lay their eggs in a pit, which are sucked up into the mouth of the female. The small number of large eggs hatch in

3700-477: The brooding but cannot handle all the eggs the female produce, such as with some pipefish . The males in some deep sea anglerfishes are much smaller than the females. When they find a female they bite into her skin, releasing an enzyme that digests the skin of their mouth and her body and fusing the pair down to the blood-vessel level. The male then slowly atrophies , losing first his digestive organs, then his brain, heart, and eyes, ending as nothing more than

3774-476: The eggs. The fungi ( mushrooms ), are also said to "spawn" when they release a white, ‘fibrous’ matter, forming the matrix from-which they grow. There are many variations in the way spawning occurs, depending on sexual differences in anatomy, how the sexes relate to each other, where and how the spawn is released and whether or how the spawn is subsequently guarded. Marine animals, and particularly bony fish , commonly reproduce by broadcast spawning . This

SECTION 50

#1732802420835

3848-507: The environment. They usually spawn in shoals without complex courtship rituals, and males outnumber females. Broadcast spawners : release their gametes (sperm and eggs) into open water for external fertilisation. There is no subsequent parental care. About 75% of coral species are broadcasters, the majority of which are hermatypic, or reef-building corals. Brood hiders hide their eggs but do not give parental care after they have hidden them. Brood hiders are mostly benthic spawners that bury

3922-532: The fertilized eggs. For example, among salmon and trout the female digs a nest with her tail in gravel. These nests are called redds . The female then lays her eggs while the male fertilizes them, while both fish defend the redd if necessary from other members of the same species. Then the female buries the nest, and the nest site is abandoned. In North America, some minnows build nests out of piles of stones rather than dig holes. The minnow males have tubercles on their head and body which they use to help them defend

3996-435: The group. Lee and Spencer (1997) argued diadectomorphs probably laid amniote eggs because their adaptations to feed on terrestrial plants rich on fiber mean they were adapted to a niche not seen in unambiguous 'amphibians', and would have required an early acquisition of terrestrial endosymbionts necessary for this diet that supposedly could not have happened if young diadectomorphs were aquatic larvae. David Berman (2013) ran

4070-415: The host. The same female may use a number of mussels, and she deposits only one or two yellow, oval eggs into each. Early developmental stages are protected from predation within the body of the mussel. After 3 to 4 weeks larvae swim away from the host to continue life on their own. Guarders protect their eggs and offspring after spawning by practicing parental care (also called brood care ). Parental care

4144-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of

4218-470: The male is pregnant, the female starts a new batch of eggs, which are ready at about the same time that the male gives birth to the young from the previous mating. This close timing of development promotes monogamy, especially if the likelihood of encountering another potential mate is low." Polygyny occurs when one male gets exclusive mating rights with multiple females. In polygyny, a large conspicuous male usually defends females from other males or defends

4292-533: The male they want to be their mate. For example, among the cichlid Cyrtocara eucinostomus in Lake Malawi , up to 50,000 large and colourful males display together on a lek four kilometres long. The females, which are mouth brooders, choose which male they want to fertilize their eggs. Polyandry occurs when one female gets exclusive mating rights with multiple males. This happens among fish like clownfish that change their sex. It can also happen when males do

4366-447: The males often have penis-like intromittent organs in the form of a modified fin. A species is semelparous if its individuals spawn only once in their lifetime, and iteroparous if its individuals spawn more than once. The term semelparity comes from the Latin semel , once, and pario , to beget, while iteroparity comes from itero , to repeat, and pario , to beget. Semelparity is sometimes called "big bang" reproduction, since

4440-437: The more powerful parental males, but they spawn when they are younger and they do not put energy into parental care. Hermaphroditism occurs when a given individual in a species possesses both male and female reproductive organs, or can alternate between possessing first one, and then the other. Hermaphroditism is common in invertebrates but rare in vertebrates. It can be contrasted with gonochorism , where each individual in

4514-581: The more primitive bony fishes is the assemblage of polyandrous (many males) breeding aggregations in open water and the absence of parental care..." There are two main reproduction methods in fish. The first method is by laying eggs and the second by live-bearing (producing their young alive). Monogamy occurs when one male mates with one female exclusively. This is also called pair spawning . Most fish are not monogamous, and when they are, they often alternate with non-monogamous behaviours. Monogamy can occur when feeding and breeding grounds are small, when it

SECTION 60

#1732802420835

4588-434: The mother's mouth, and the fry remain there for a period of time. Fertilization often occurs with the help of egg-spots, which are colorful spots on the anal fin of the male. When the female sees these spots, she tries to pick up the egg-spots, but instead gets sperm that fertilizes the eggs in her mouth. Many cichlids and some labyrinth fish are ovophile mouthbrooders. Larvophile or larvae-loving mouth-brooders lay their eggs on

4662-399: The nest site. Bitterlings have a remarkable reproduction strategy where parents transfer responsibility for the care of their young to mussels . The female extends her ovipositor into the mantle cavity of the mussel and deposits her eggs between the gill filaments. The male then ejects his sperm into the mussel's inhalant water current and fertilization takes place within the gills of

4736-415: The normal way on the substrate, but in the process accidentally fertilize eggs that the female retains and does not spawn. These eggs are spawned later, usually without allowing much time for embryonic development. The next step in the evolution of livebearing is obligate (by necessity) internal bearing, where the female retains all the embryos. "The only source of nutrition for these embryos, however,

4810-482: The relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade" is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade"

4884-458: The right shows the main spawning grounds and larval drift routes. Capelin on the way to feeding grounds is coloured green, capelin on the way back is blue, and the breeding grounds are red. In a paper published in 2009, researchers from Iceland recount their application of an interacting particle model to the capelin stock around Iceland, successfully predicting the spawning migration route for 2008. Referred to as "the greatest shoal on earth",

4958-412: The sexes of most marine animals can be determined by looking at the gonads . For example, male testes of spawning fish are smooth and white and account for up to 12% of the mass of the fish, while female ovaries are granular and orange or yellow, accounting for up to 70% of the fish's mass. Male lampreys, hagfish and salmon discharge their sperm into the body cavity where it is expelled through pores in

5032-482: The single reproductive event of semelparous organisms is usually large and fatal to the spawners. The classic example of a semelparous animal is the Pacific salmon , which lives for many years in the ocean before swimming to the freshwater stream of its birth, spawning, and then dying. Other spawning animals which are semelparous include mayflies , squid , octopus , smelt , capelin and some amphibians. Semelparity

5106-509: The sister group to the traditional Synapsida within Amniota, based on inner ear anatomy and cladistic analyses. They include both large (up to 2 meters long) carnivorous and even larger (to 3 meters) herbivorous forms, some semi-aquatic and others fully terrestrial. The diadectomorphs seem to have originated during late Mississippian times, although they only became common after the Carboniferous rainforest collapse and flourished during

5180-577: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Spawn (biology) As a general rule, aquatic or semiaquatic reptiles , birds , and mammals do not reproduce through spawning, but rather through copulation like their terrestrial counterparts. This

5254-427: The standard, large, hook-nosed males and that spawn by sneaking into a redd (spawning nest) to release sperm simultaneously with a mated pair. This behaviour is an evolutionarily stable strategy for reproduction, because it is favoured by natural selection just like the "standard" strategy of large males. Cuckoldry occurs in many fish species, including dragonets , parrotfishes and wrasses on tropical reefs and

5328-463: The three is disputed. Below is a cladogram modified from the 2010 analysis: Limnoscelidae [REDACTED] Tseajaiidae [REDACTED] Ambedus pusillus ? Oradectes sanmiguelensis Orobates pabsti [REDACTED] Alveusdectes fenestralis Desmatodon hesperis Silvadectes absitus Diadectes tenuitectes Diadectes sideropelicus [REDACTED] Diasparactus zenos [REDACTED] The reproduction of

5402-423: Was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case, the group consists of a common ancestor with all its descendant branches. Rodents, for example, are

5476-548: Was thought to be ovoviviparous until it was shown in 2001 that the embryos received nutrients from the mother. Spawning grounds are the areas of water where aquatic animals spawn, or produce their eggs. After spawning, the spawn may or may not drift to new grounds which become their nursery grounds. Many species undertake migrations each year, and sometimes great migrations, to reach their spawning grounds. For example, lakes and river watersheds can be major spawning grounds for anadromous fish such as salmon . These days, it

#834165