Spawn (biology) | Wikipedia audio article

Spawn (biology) | Wikipedia audio article


Spawn is the eggs and sperm released or deposited
into water by aquatic animals. As a verb, to spawn refers to the process
of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquatic mammals
and reptiles, reproduce through the process of spawning. 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 the
eggs.Most fish reproduce by spawning, as do most other aquatic animals, including crustaceans
such as crabs and shrimps, molluscs such as oysters and squid, echinoderms such as sea
urchins and sea cucumbers, amphibians such as frogs and newts, aquatic insects such as
mayflies and mosquitoes and corals, which are actually small aquatic animals—not plants. Fungi, such as mushrooms, are also said to
“spawn” a white, fibrous matter that forms 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.==Overview==Marine animals, and particularly bony fish,
commonly reproduce by broadcast spawning. This 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
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, 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 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, 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 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 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 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), ovoviparous (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 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). In the first method, the female fish lays
eggs either on the sea floor or on the leaves of an aquatic plant. A male fish fertilizes the eggs, and both
then work together to protect the eggs/babies from danger until they can defend themselves. In the second method, the male fish uses its
anal fin to transmit sperm into the female fish and fertilize the fish eggs. Later, the female gives live birth to her
fry.==Sexual strategies=====Basic strategies===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 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 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 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 another. Based on these displays, each female then
selects 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 the brooding
but can 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 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 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.===Cuckoldry===Alternate male strategies which allow small
males to engage in cuckoldry can develop in species where spawning 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 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 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 the more powerful parental males, but they spawn when they are younger and they
do not put energy into parental care.===Hermaphroditism===
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 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 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 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 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 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===
Unisexuality occurs when 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 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 a complex of Mexican mollies. Parthenogenesis has been recently observed
in hammerhead sharks and blacktip sharks. It is also known to occur in crayfish and
amphibians.==Spawning strategies==
This section is patterned after 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===
Nonguarders do not protect their eggs and offspring after spawning====Open substrate spawners====Open substrate spawners scatter their eggs
in 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. Pelagic spawners: a type of broadcast spawners,
spawn in the open sea, mostly near the surface. They are usually pelagic fish such as tuna
and sardines. Some demersal fish leave the bottom to spawn
pelagically, particularly coral reef fish such as parrotfish and wrasses. Pelagic spawning means water currents widely
disperse the young. The eggs, embryos and larvae of pelagic spawners
contain oil globules or have a high water content. As a result, they are buoyant and are widely
dispersed by currents. The downside is that mortality is high, because
they can be eaten so easily by pelagic predators or they can drift into unsuitable areas. Females compensate by spawning large numbers
of eggs and extending their spawning periods. Pelagic spawners that live in or around coral
reefs can spawn a small number of eggs almost daily over a period of months. These fishes have complex breeding behaviours
including sex changes, harems, leks and territoriality. See also: Coral reef fish. Benthic spawners: deposit their spawn on or
near the bottom of the sea (or lake). They are usually demersal fish such as cod
and flatfish. These species typically spawn without ceremony;
they do not engage in elaborate courtship rituals. Each female is usually followed by several
males who fertilize the eggs as they are released. Various strategies ensure the eggs and embryos
remain in place, and do not drift with the current. The eggs can adhere to other eggs or to whatever
they are deposited on, or the eggs can be laid in long strings which are wrapped around
plants or rocks. Some eggs take on water after they are released,
so they can be dropped into cracks where they swell and wedge themselves in place. Egg scatterers: scatter adhesive or non-adhesive
eggs to fall to the substrate, into plants, or float to the surface. These species do not look after their brood
and even eat their own eggs. These are often schooling fish which spawn
in groups or pairs, often laying a large number of small eggs. The fry hatch quickly. Egg depositers: deposit eggs on a substrate
(tank glass, wood, rocks, plants). Egg depositors usually lay fewer eggs than
egg-scatterers, although the eggs are larger. Egg depositors fall into two groups: those
that care for their eggs, and those that do not. Among egg depositors that care for their eggs
are cichlids and some catfish. Egg depositors that care for their young can
be divided into two groups: cavity spawners and open spawners. Cavity spawners: lay eggs in a cave or cavity. These fish form pairs and have advanced brood
care where the eggs are defended and cleaned. The eggs take a few days to hatch, and the
fry are often guarded by the parents. Various catfish, Cyprinidae, and killifish
make up the majority. Cavity spawners can be contrasted with open
(shelter) spawners, which lay their eggs on an open surface.====Brood hiders====
Brood hiders hide their eggs but do not give parental care after they have hidden them. Brood hiders are mostly benthic spawners that
bury 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 the nest site. Egg buriers – can inhabit waters that dry
up at some time of the year. An example are annual killifish which lay
their eggs in mud. The parents mature quickly and lay their eggs
before dying when the water dries up. The eggs remain in a dormant stage until rains
stimulate hatching.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 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===Guarders protect their eggs and offspring
after spawning by practicing parental care (also called brood care). Parental care is an “investment by parents
in offspring that increases the offsprings’ 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 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 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.====Substrate spawners====
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 the area, but they do not actively build
a nest.===Bearers===Bearers are fish that carry their embryos
(and sometimes their young) around with them, either externally or internally.====External bearers====
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 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 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.====Internal bearers=========
Facultative internal bearers=====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 the normal way on the substrate, but in the process
accidentally fertilize eggs which the female retains and does not spawn. These eggs are spawned later, usually without
allowing much time for embryonic development.=====Obligate internal bearers=====
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, 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 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.”=====Viviparous fish=====
However, some fish do not fit these categories. The livebearing largespring gambusia (Gambusia
geiseri) was thought to be ovoviviparous until it was shown in 2001 that the embryos received
nutrients from the mother.==Spawning grounds==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 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
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 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 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”, 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.==Examples=====
Fish=======
Goldfish====Goldfish, like all cyprinids, are egg-layers. They usually start breeding after 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 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====
A member of the Cyprinidae, carp spawn in times between April and August, largely dependent
upon the climate and conditions they live in. Oxygen levels of the water, availability of
food, size of each fish, age, number of times the fish has spawned before and water temperature
are all factors known to effect when and how many eggs each carp will spawn at any one
time.=====Siamese fighting fish=====
Prior to spawning, male Siamese fighting fish build bubble nests of varying sizes at the
surface of the water. When a male becomes interested in a female,
he will flare his gills, twist his body, and spread his fins. The female darkens in colour and curves her
body back and forth. The act of spawning takes place in a “nuptial
embrace” where the male wraps his body around the female, each embrace resulting in the
release of 10-40 eggs until the female is out of eggs. The male, from his side, releases milt into
the water and fertilization takes place externally. During and after spawning, the male uses his
mouth to retrieve sinking eggs and deposit them in the bubble nest (during mating the
female sometimes assists her partner, but more often she will simply devour all the
eggs that she manages to catch). Once the female has released all of her eggs,
she is chased away from the male’s territory, as it is likely that she’ll eat the eggs due
to hunger. The eggs then remain in the male’s care. He keeps them in the bubble nest, making sure
none fall to the bottom and repairing the nest as needed. Incubation lasts for 24–36 hours, and the
newly hatched larvae remain in the nest for the next 2–3 days, until their yolk sacs
are fully absorbed. Afterwards the fry leave the nest and the
free-swimming stage begins.===Crustaceans=======
Copepods====Copepods are tiny crustaceans which usually
reproduce either by broadcast spawning or by sac spawning. Broadcasting copepods scatter their eggs into
the water, but sac spawners lay their eggs into an ovigerous sac. Sac spawners spawn few but relatively large
eggs that develop slowly. By contrast, broadcast spawners spawn numerous
small eggs that develop rapidly. However, the shorter hatch times that result
from broadcasting are not short enough to compensate for the higher mortality compared
to sac spawners. To produce a given number of hatched eggs,
broadcasters must spawn more eggs than sac spawners.====Spiny lobsters====
After mating, the fertilized eggs of the California spiny lobster are carried on the female’s
pleopods until they hatch, with between 120,000 and 680,000 carried by a single female. The eggs begin coral red, but darken as they
develop to a deep maroon. When she is carrying the eggs, the female
is said to be “berried”. The eggs are ready to hatch after 10 weeks,
and spawning takes place from May to August. The larvae that hatch (called phyllosoma larvae)
do not resemble the adults. Instead, they are flat, transparent animals
around 14 mm (0.55 in) long, but as thin as a sheet of paper. The larvae feed on plankton, and grow through
ten molts into ten further larval stages, the last of which is around 30–32 mm (1.2–1.3
in) long. The full series of larval molts takes around
7 months, and when the last stage molts, it metamorphoses into the puerulus state, which
is a juvenile form of the adult, though still transparent. The puerulus larvae settle to the sea floor
when the water is near its maximum temperature, which in Baja California is in the fall.Egg-bearing
female lobsters migrate inshore from deeper waters to hatch their eggs, though they do
not have specific spawning grounds. These lobster migrations can occur in close
single-file formation “lobster trains”.===Molluscs=======
Pacific oysters====Oysters are broadcast spawners, that is, eggs
and sperm are released into open water where fertilisation occurs. They are protandric; during their first year
they spawn as males by releasing sperm into the water. As they grow over the next two or three years
and develop greater energy reserves, they spawn as females by releasing eggs. Bay oysters usually spawn by the end of June. An increase in water temperature prompts a
few oysters to spawn. This triggers spawning in the rest, clouding
the water with millions of eggs and sperm. A single female oyster can produce up to 100
million eggs annually. The eggs become fertilized in the water and
develop rapidly into planktonic larvae. which eventually find suitable sites, such as another
oyster’s shell, on which to settle. Attached oyster larvae are called spat. Spat are oysters less than 25 millimetres
(0.98 in) long. The Pacific oyster usually has separate sexes. Their sex can be determined by examining the
gonads, and it can change from year to year, normally during the winter months. In certain environmental conditions, one sex
is favoured over the other. Protandry is favoured in areas of high food
abundance and protogyny occurs in areas of low food abundance. In habitats with a high food supply, the sex
ratio in the adult population tends to favour females, and areas with low food abundances
tend to have a larger proportion of male adults. Spawning in the Pacific oyster occurs at 20
°C (68 °F). This species is very fecund, with females
releasing about 50–200 million eggs in regular intervals (at a rate of 5–10 times a minute)
in a single spawning. Once released from the gonads, the eggs move
through the suprabranchial chambers (gills), are then pushed through the gill ostia into
the mantle chamber, and are finally released in the water, forming a small cloud. In males, the sperm is released at the opposite
end of the oyster, along with the normal exhalent stream of water. A rise in water temperature is thought to
be the main cue in the initiation of spawning, as the onset of higher water temperatures
in the summer results in earlier spawning in the Pacific oyster.The larvae of the Pacific
oyster are planktotrophic, and are about 70 µm at the prodissoconch 1 stage. The larvae move through the water column via
the use of a larval foot to find suitable settlement locations. They can spend several weeks at this phase,
which is dependent on water temperature, salinity and food supply. Over these weeks, larvae can disperse great
distances by water currents before they metamorphose and settle as small spat. Similar to other oyster species, once the
Pacific oyster larvae find a suitable habitat, they attach to it permanently using cement
secreted from a gland in their foot. After settlement, the larvae metamorphose
into juvenile spat. The growth rate is very rapid in optimum environmental
conditions, and market size can be achieved in 18 to 30 months.====Cephalopods====
Cephalopods, such as squid and octopuses, have prominent heads and a set of arms (tentacles)
modified from the primitive foot of molluscs. All cephalopods are sexually dimorphic. However, they lack external sexual characteristics,
so they use colour communication. A courting male approaches a likely looking
mate flashing his brightest colours, often in rippling displays. If the other cephalopod is female and receptive,
her skin will change colour to become pale, and mating will occur. If the other cephalopod remains brightly coloured,
it is taken as a warning.All cephalopods reproduce by spawning eggs. Most cephalopods use semi-internal fertilization
where the male places his gametes inside the female’s mantle cavity to fertilize the ova
in the female’s single ovary. The “penis” in most male cephalopods is a
long and muscular end of the gonoduct used to transfer spermatophores to a modified sperm-carrying
arm called a hectocotylus. That in turn is used to transfer the spermatophores
to the female. In species where the hectocotylus is missing,
the “penis” is long and able to extend beyond the mantle cavity and transfers the spermatophores
directly to the female. In many cephalopods, mating occurs head to
head and the male may simply transfer sperm to the female. Others may detach the sperm-carrying arm and
leave it attached to the female. Deep water squid have the greatest known penis
length relative to body size of all mobile animals, second in the entire animal kingdom
only to certain sessile barnacles. Penis elongation in the greater hooked squid
may result in a penis that is as long as the mantle, head and arms combined. Some species brood their fertilized eggs:
female paper nautilus construct shelters for the young, while Gonatiid squid carry a larva-laden
membrane from the hooks on their arms. Other cephalopods deposit their young under
rocks and aerate them with their tentacles hatching. Mostly the eggs are left to their own devices;
many squid lay sausage-like bunches of eggs in crevices or occasionally on the sea floor. Cuttlefish lay eggs separately in cases and
attach them to coral or algal fronds. Like Pacific salmon, cephalopods are mostly
semelparous, spawning many small eggs in one batch and then dying. Cephalopods usually live fast and die young. Most of the energy extracted from their food
is used for growing, and they mature rapidly to their adult size. Some gain as much as 12% of their body mass
each day. Most live for one to two years, reproducing
and then dying shortly thereafter.===Echinoderms===Echinoderms are marine animals, widespread
in all oceans, but not found in fresh water. Just below their skin is an endoskeleton composed
of calcareous plates or ossicles.====Sea urchins====
Sea urchins are spiky echinoderms with spherical bodies which usually contain five gonads. They move slowly, feed mostly on seaweed,
and are important for the diet of sea otters. Sea urchins are dioecious, having separate
male and female sexes, although there is generally no easy way to distinguish the two. The gonads are lined with muscles underneath
the peritoneum, and these allow the animal to squeeze its gametes through the duct and
into the surrounding sea water, where fertilization takes place. Their roe (male and female gonads) is soft
and melting, with a colour ranging from orange to pale yellow, and is sought after as a human
delicacy in many parts of the world.====Sea cucumbers====
Sea cucumbers are leathery echinoderms with elongated bodies which contain a single, branched
gonad. They are found on the sea floor worldwide,
and occur in great numbers on the deep sea floor where they often make up the majority
of the animal biomass. They feed on plankton and decaying organic
debris found at the sea bottom, catching food that flows by with their open tentacles or
sifting through bottom sediments. Like sea urchins, most sea cucumbers reproduce
by releasing sperm and ova into the ocean water. Depending on conditions, one organism can
produce thousands of gametes. Sea cucumbers are typically dioecious, with
separate male and female individuals. The reproductive system consists of a single
gonad, consisting of a cluster of tubules emptying into a single duct that opens on
the upper surface of the animal, close to the tentacles. Many species fertilise their eggs internally. The fertilised egg develops in a pouch on
the adult’s body and eventually hatches as a juvenile sea cucumber. A few species brood their young inside the
body cavity, giving birth through a small rupture in the body wall close to the anus. The remaining species develop their eggs into
a free-swimming larva, usually after about three days of development. This larva swims by means of a long band of
cilia wrapped around its body. As the larva grows it transforms into a barrel-shaped
body with three to five separate rings of cilia. The tentacles are usually the first adult
features to appear, before the regular tube feet.===Amphibious animals===Amphibians are found in and around fresh water
lakes and ponds, but not in marine environments. Examples are frogs and toads, salamanders,
newts and caecilians (which resemble snakes). They are cold-blooded animals that metamorphose
from a juvenile water-breathing form, usually to an adult air-breathing form, though mudpuppies
retain juvenile gills in adulthood.====Frogs and toads====
Female frogs and toads usually spawn gelatinous egg masses containing thousands of eggs in
water. Different species lay eggs in distinctive
and identifiable ways. For example, the American toad lays long strings
of eggs. The eggs are highly vulnerable to predation,
so frogs have evolved many techniques to ensure the survival of the next generation. In colder areas the embryo is black to absorb
more heat from the sun, which speeds up development. Most commonly, this involves synchronous reproduction. Many individuals will breed at the same time,
overwhelming the actions of predators; the majority of the offspring will still die due
to predation, but there is a greater chance some will survive. Another way in which some species avoid predators
and the pathogens eggs are exposed to in ponds is to lay eggs on leaves above the pond, with
a gelatinous coating designed to retain moisture. In these species the tadpoles drop into the
water upon hatching. The eggs of some species laid out of water
can detect vibrations of nearby predatory wasps or snakes, and will hatch early to avoid
being eaten.While the length of the egg stage depends on the species and environmental conditions,
aquatic eggs generally hatch within one week. Unlike salamanders and newts, frogs and toads
never become sexually mature while still in their larval stage. The hatched eggs continue life as tadpoles,
which typically have oval bodies and long, vertically flattened tails. As a general rule, free living larvae are
fully aquatic. They lack eyelids and have a cartilaginous
skeleton, a lateral line system, gills for respiration (external gills at first, internal
gills later) and tails with dorsal and ventral folds of skin for swimming. They quickly develop a gill pouch that covers
the gills and the front legs; the lungs are also developed at an early stage as an accessory
breathing organ. Some species which go through the metamorphosis
inside the egg and hatch to small frogs never develop gills; instead there are specialised
areas of skin that take care of respiration. Tadpoles also lack true teeth, but the jaws
in most species usually have two elongate, parallel rows of small keratinized structures
called keradonts in the upper jaw while the lower jaw has three rows of keradonts, surrounded
by a horny beak, but the number of rows can be lower (sometimes zero), or much higher. Tadpoles feed on algae, including diatoms
filtered from the water through the gills. Some species are carnivorous at the tadpole
stage, eating insects, smaller tadpoles, and fish. Cannibalism has been observed among tadpoles. Early developers who gain legs may be eaten
by the others, so the late bloomers survive longer.====Sea turtles====Sea turtles are amphibious reptiles, but they
are not amphibians. Reptiles belong to the class Reptilia while
amphibians belong to the class Amphibia. These are two distinct taxonomic groups. Reptiles have scales and leathery skins, while
the skins of amphibians are smooth and porous. Unlike frogs, sea turtle eggs have tough,
leathery shells which allow them to survive on land without drying out. Some sea turtles migrate long distances between
feeding and spawning grounds. Green turtles have feeding grounds along the
Brazilian coast. Each year, thousands of these turtles migrate
about 2,300 kilometres (1,400 mi) to their spawning ground, Ascension Island in the Atlantic,
an island only 11 kilometres (6.8 mi) across. Each year the returning turtles dig between
6,000 and 15,000 nests, often returning to the same beach from where they hatched. Females usually mate every two to four years. Males on the other hand visit the breeding
areas every year, attempting to mate. Green sea turtles’ mating is similar to other
marine turtles. Female turtles control the process. A few populations practice polyandry, although
this does not seem to benefit hatchlings. After mating in the water, the female moves
above the beach’s high tide line where she digs a hole with her hind flippers and deposits
her eggs. Litter size depends on the age of the female
and species, but green turtle clutches range between 100 and 200. She then covers the nest with sand and returns
to the sea. At around 45 to 75 days, the eggs hatch during
the night and the hatchlings instinctively head directly into the water. This is the most dangerous time in a turtle’s
life. As they walk, predators such as gulls and
crabs grab them. A significant percentage never make it to
the ocean. Little is known of the initial life history
of newly hatched sea turtles. Juveniles spend three to five years in the
open ocean before they settle as still-immature juveniles into their permanent shallow-water
lifestyle. It is speculated that they take twenty to
fifty years to reach sexual maturity. Individuals live up to eighty years in the
wild. They are among the larger sea turtles, many
more than a meter long and weighing up to 300 kilograms (660 lb).===Aquatic insects===
Aquatic insects also spawn. Mayflies “are famed for their short adult
life. Some species have under an hour to mate and
lay their eggs before they die. Their pre-adult stage, known as the subimago,
may be even shorter – perhaps lasting just a few minutes before they moult into their
adult form. Therefore a mayfly spends most of its life
as a nymph, hidden from view under the water.”===Corals===Corals can be both gonochoristic (unisexual)
and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows corals to settle
new areas. Corals predominantly reproduce sexually. 25% of hermatypic corals (stony corals) form
single sex (gonochoristic) colonies, while the rest are hermaphroditic. About 75% of all hermatypic corals “broadcast
spawn” by releasing gametes—eggs and sperm—into the water to spread offspring. The gametes fuse during fertilization to form
a microscopic larva called a planula, typically pink and elliptical in shape. A typical coral colony form several thousand
larvae per year to overcome the odds against formation of a new colony.Planulae exhibit
positive phototaxis, swimming towards light to reach surface waters where they drift and
grow before descending to seek a hard surface to which they can attach and establish a new
colony. They also exhibit positive sonotaxis, moving
towards sounds that emanate from the reef and away from open water. High failure rates afflict many stages of
this process, and even though millions of gametes are released by each colony very few
new colonies form. The time from spawning to settling is usually
2–3 days, but can be up to 2 months. The larva grows into a polyp and eventually
becomes a coral head by asexual budding and growth. Synchronous spawning is very typical on the
coral reef and often, even when multiple species are present, all corals spawn on the same
night. This synchrony is essential so that male and
female gametes can meet. Corals must rely on environmental cues, varying
from species to species, to determine the proper time to release gametes into the water. The cues involve lunar changes, sunset time,
and possibly chemical signalling. Synchronous spawning may form hybrids and
is perhaps involved in coral speciation. In some places the spawn can be visually dramatic,
clouding the usually clear water with gametes, typically at night. Corals use two methods for sexual reproduction,
which differ in whether the female gametes are released: Broadcasters, the majority of which mass spawn,
rely heavily on environmental cues, because they release both sperm and eggs into the
water. The corals use long-term cues such as day
length, water temperature, and/or rate of temperature change. The short-term cue is most often the lunar
cycle, with sunset cuing the release. About 75% of coral species are broadcasters,
the majority of which are hermatypic, or reef-building corals. The positively buoyant gametes float towards
the surface where fertilization produces planula larvae. The larvae swim towards the surface light
to enter into currents, where they usually remain for two days, but sometimes up to three
weeks, and in one known case two months, after which they settle and metamorphose into polyps
and form colonies. Brooders are most often ahermatypic (non-reef
building) in areas of high current or wave action. Brooders release only sperm, which is negatively
buoyant, and can harbor unfertilized eggs for weeks, lowering the need for mass synchronous
spawning events, which do sometimes occur. After fertilization the corals release planula
larvae which are ready to settle.==Fungi==Fungi are not plants, and require different
conditions for optimal growth. Plants develop through photosynthesis, a process
that converts atmospheric carbon dioxide into carbohydrates, especially cellulose. While sunlight provides an energy source for
plants, mushrooms derive all of their energy and growth materials from their growth medium,
through biochemical decomposition processes. This does not mean that light is an unnecessary
requirement, since some fungi use light as a signal to induce fruiting. However, all the materials for growth must
already be present in the growth medium. Instead of seeds, mushrooms reproduce sexually
during underground growth, and asexually through spores. Either of these can be contaminated with airborne
microorganisms, which will interfere with mushroom growth and prevent a healthy crop. Mycelium, or actively growing mushroom culture,
is placed on growth substrate to seed or introduce mushrooms to grow on a substrate. This is also known as inoculation, spawning
or adding spawn. Its main advantages are to reduce chances
of contamination while giving mushrooms a firm beginning.==Gallery====
See also====
Notes====
Further reading==Cole, Kathleen S (2010) Reproduction and Sexuality
in Marine Fishes: Patterns and Processes University of California Press. ISBN 978-0-520-26433-5.==External links==
Reproduction FAO, Rome.

Leave a Reply

Your email address will not be published. Required fields are marked *