What Two Ways Do We Classify Reproduction In Animals?

Chapter 13: Introduction to Fauna Reproduction and Development

13.1 How Animals Reproduce

Learning Objectives

By the end of this section, y'all will be able to:

• Describe advantages and disadvantages of asexual and sexual reproduction
• Talk over asexual reproduction methods
• Discuss sexual reproduction methods
• Discuss internal and external methods of fertilization

Some animals produce offspring through asexual reproduction while other animals produce offspring through sexual reproduction. Both methods have advantages and disadvantages. Asexual reproduction produces offspring that are genetically identical to the parent because the offspring are all clones of the original parent. A single individual tin produce offspring asexually and large numbers of offspring tin can be produced quickly; these are ii advantages that asexually reproducing organisms have over sexually reproducing organisms. In a stable or predictable environs, asexual reproduction is an constructive means of reproduction because all the offspring volition be adapted to that environment. In an unstable or unpredictable surround, species that reproduce asexually may be at a disadvantage because all the offspring are genetically identical and may not exist adapted to unlike weather.

During sexual reproduction, the genetic fabric of two individuals is combined to produce genetically various offspring that differ from their parents. The genetic variety of sexually produced offspring is thought to give sexually reproducing individuals greater fitness considering more than of their offspring may survive and reproduce in an unpredictable or changing environment. Species that reproduce sexually (and take divide sexes) must maintain ii different types of individuals, males and females. Only half the population (females) tin produce the offspring, so fewer offspring will be produced when compared to asexual reproduction. This is a disadvantage of sexual reproduction compared to asexual reproduction.

Asexual Reproduction

Asexual reproduction occurs in prokaryotic microorganisms (bacteria and archaea) and in many eukaryotic, single-celled and multi-celled organisms. In that location are several ways that animals reproduce asexually, the details of which vary amid individual species.

Fission

Fission, also called binary fission, occurs in some invertebrate, multi-celled organisms. It is in some means coordinating to the process of binary fission of single-celled prokaryotic organisms. The term fission is applied to instances in which an organism appears to dissever itself into ii parts and, if necessary, regenerate the missing parts of each new organism. For case, species of turbellarian flatworms usually called the planarians, such as Dugesia dorotocephala, are able to dissever their bodies into caput and tail regions and so regenerate the missing half in each of the two new organisms. Bounding main anemones (Cnidaria), such as species of the genus Anthopleura (Effigy thirteen.2), will divide along the oral-aboral axis, and bounding main cucumbers (Echinodermata) of the genus Holothuria, will dissever into two halves across the oral-aboral axis and regenerate the other half in each of the resulting individuals.

Figure thirteen.two  The Anthopleura artemisia ocean anemone can reproduce through fission.

Budding

Budding is a form of asexual reproduction that results from the outgrowth of a part of the torso leading to a separation of the "bud" from the original organism and the germination of ii individuals, one smaller than the other. Budding occurs commonly in some invertebrate animals such as hydras and corals. In hydras, a bud forms that develops into an adult and breaks away from the chief body (Figure 13.3).

Figure 13.three (a) Hydra reproduce asexually through budding: a bud forms on the tubular body of an adult hydra, develops a rima oris and tentacles, and then detaches from its parent. The new hydra is fully developed and volition discover its own location for zipper. (b) Some coral, such as the Lophelia pertusa shown here, can reproduce through budding. (credit b: modification of piece of work by Ed Bowlby, NOAA/Olympic Declension NMS; NOAA/OAR/Office of Sea Exploration) Part a: This shows a hydra, which has a stem-like body with tentacles growing out the peak. A smaller hydra is budding from the side of the stalk. Function b: This photo shows branching white coral polyps.

Concept in Activeness

View this video to run across a hydra budding.

Fragmentation

Fragmentation is the breaking of an individual into parts followed by regeneration. If the creature is capable of fragmentation, and the parts are large enough, a dissever individual will regrow from each part. Fragmentation may occur through accidental damage, damage from predators, or as a natural form of reproduction. Reproduction through fragmentation is observed in sponges, some cnidarians, turbellarians, echinoderms, and annelids. In some sea stars, a new private can exist regenerated from a cleaved arm and a piece of the central disc. This ocean star (Figure xiii.4) is in the process of growing a complete sea star from an arm that has been cutting off. Fisheries workers accept been known to try to kill the sea stars eating their clam or oyster beds by cutting them in one-half and throwing them back into the ocean. Unfortunately for the workers, the two parts can each regenerate a new one-half, resulting in twice equally many body of water stars to prey upon the oysters and clams.

Figure thirteen.4 (a) Linckia multifora is a species of sea star that tin reproduce asexually via fragmentation. In this procedure, (b) an arm that has been shed grows into a new bounding main star. (credit a: modifiction of work by Dwayne Meadows, NOAA/NMFS/OPR)

Parthenogenesis

Parthenogenesis is a grade of asexual reproduction in which an egg develops into an individual without being fertilized. The resulting offspring can be either haploid or diploid, depending on the process in the species. Parthenogenesis occurs in invertebrates such as h2o fleas, rotifers, aphids, stick insects, and ants, wasps, and bees. Ants, bees, and wasps use parthenogenesis to produce haploid males (drones). The diploid females (workers and queens) are the result of a fertilized egg.

Some vertebrate animals—such every bit certain reptiles, amphibians, and fish—also reproduce through parthenogenesis. Parthenogenesis has been observed in species in which the sexes were separated in terrestrial or marine zoos. Two female person Komodo dragons, a hammerhead shark, and a blacktop shark have produced parthenogenic immature when the females take been isolated from males. It is possible that the asexual reproduction observed occurred in response to unusual circumstances and would normally not occur.

Sexual Reproduction

Sexual reproduction is the combination of reproductive cells from two individuals to form genetically unique offspring. The nature of the individuals that produce the two kinds of gametes tin vary, having for case separate sexes or both sexes in each individual. Sex conclusion, the mechanism that determines which sexual practice an individual develops into, also can vary.

Hermaphroditism

Hermaphroditism occurs in animals in which one individual has both male and female reproductive systems. Invertebrates such as earthworms, slugs, tapeworms, and snails (Effigy 13.5) are often hermaphroditic. Hermaphrodites may cocky-fertilize, merely typically they will mate with another of their species, fertilizing each other and both producing offspring. Cocky-fertilization is more common in animals that have limited mobility or are non motile, such every bit barnacles and clams. Many species have specific mechanisms in place to prevent self-fertilization, because it is an farthermost form of inbreeding and ordinarily produces less fit offspring.

Figure 13.5 Many (a) snails are hermaphrodites. When two individuals (b) mate, they can produce upward to 100 eggs each. (credit a: modification of work by Assaf Shtilman; credit b: modification of piece of work by "Schristia"/Flickr)

Sex Determination

Mammalian sex activity is determined genetically by the combination of X and Y chromosomes. Individuals homozygous for X (XX) are female and heterozygous individuals (XY) are male. In mammals, the presence of a Y chromosome causes the development of male characteristics and its absence results in female characteristics. The XY system is as well found in some insects and plants.

Bird sex conclusion is dependent on the combination of Z and West chromosomes. Homozygous for Z (ZZ) results in a male and heterozygous (ZW) results in a female. Notice that this organization is the opposite of the mammalian system because in birds the female person is the sex with the different sexual activity chromosomes. The W appears to exist essential in determining the sex of the individual, like to the Y chromosome in mammals. Some fish, crustaceans, insects (such as butterflies and moths), and reptiles use the ZW system.

More than complicated chromosomal sex determining systems as well exist. For example, some swordtail fish have 3 sexual practice chromosomes in a population.

The sex of another species is not determined past chromosomes, but past some aspect of the surround. Sex decision in alligators, some turtles, and tuataras, for example, is dependent on the temperature during the middle 3rd of egg development. This is referred to every bit ecology sex decision, or more specifically, every bit temperature-dependent sex determination. In many turtles, cooler temperatures during egg incubation produce males and warm temperatures produce females, while in many other species of turtles, the opposite is true. In some crocodiles and some turtles, moderate temperatures produce males and both warm and cool temperatures produce females.

Individuals of some species change their sex during their lives, switching from one to the other. If the individual is female commencement, it is termed protogyny or "get-go female," if it is male beginning, information technology is termed protandry or "first male person." Oysters are born male, abound in size, and become female and lay eggs. The wrasses, a family of reef fishes, are all sequential hermaphrodites. Some of these species live in closely coordinated schools with a dominant male person and a large number of smaller females. If the male person dies, a female increases in size, changes sexual practice, and becomes the new ascendant male.

Fertilization

The fusion of a sperm and an egg is a process called fertilization. This can occur either within (internal fertilization) or exterior (external fertilization) the body of the female. Humans provide an example of the erstwhile, whereas frog reproduction is an example of the latter.

External Fertilization

External fertilization unremarkably occurs in aquatic environments where both eggs and sperm are released into the water. After the sperm reaches the egg, fertilization takes place. Nearly external fertilization happens during the process of spawning where one or several females release their eggs and the male person(s) release sperm in the same area, at the same time. The spawning may be triggered by environmental signals, such as water temperature or the length of daylight. Nigh all fish spawn, as do crustaceans (such as crabs and shrimp), mollusks (such as oysters), squid, and echinoderms (such as ocean urchins and sea cucumbers). Frogs, corals, mayflies, and mosquitoes also spawn (Figure xiii.6).

Effigy 13.6 During sexual reproduction in toads, the male grasps the female from behind and externally fertilizes the eggs as they are deposited. (credit: Bernie Kohl)

Internal Fertilization

Internal fertilization occurs most often in terrestrial animals, although some aquatic animals also use this method. Internal fertilization may occur by the male person directly depositing sperm in the female during mating. It may besides occur by the male person depositing sperm in the environment, usually in a protective construction, which a female picks up to deposit the sperm in her reproductive tract. There are 3 ways that offspring are produced post-obit internal fertilization. In oviparity, fertilized eggs are laid outside the female'southward torso and develop there, receiving nourishment from the yolk that is a part of the egg (Effigy 13.seven a). This occurs in some bony fish, some reptiles, a few cartilaginous fish, some amphibians, a few mammals, and all birds. Most not-avian reptiles and insects produce leathery eggs, while birds and some turtles produce eggs with high concentrations of calcium carbonate in the trounce, making them hard. Chicken eggs are an example of a hard shell. The eggs of the egg-laying mammals such as the platypus and echidna are leathery.

In ovoviparity, fertilized eggs are retained in the female, and the embryo obtains its nourishment from the egg's yolk. The eggs are retained in the female's body until they hatch within of her, or she lays the eggs correct earlier they hatch. This procedure helps protect the eggs until hatching. This occurs in some bony fish (like the platyfish Xiphophorus maculatus, Effigy 13.7 b), some sharks, lizards, some snakes (garter snake Thamnophis sirtalis), some vipers, and some invertebrate animals (Madagascar hissing cockroach Gromphadorhina portentosa).

In viviparity the young are born live. They obtain their nourishment from the female and are born in varying states of maturity. This occurs in most mammals (Figure 13.7 c), some cartilaginous fish, and a few reptiles.

Figure 13.seven In (a) oviparity, young develop in eggs outside the female body, as with these Harmonia axydridis beetles hatching. Some aquatic animals, like this (b) pregnant Xiphophorus maculatus are ovoviparous, with the egg developing inside the female and nutrition supplied primarily from the yolk. In mammals, nutrition is supported by the placenta, as was the example with this (c) newborn squirrel. (credit b: modification of piece of work by Gourami Watcher; credit c: modification of work by "audreyjm529″/Flickr)

Section Summary

Reproduction may exist asexual when 1 individual produces genetically identical offspring, or sexual when the genetic material from two individuals is combined to produce genetically various offspring. Asexual reproduction in animals occurs through fission, budding, fragmentation, and parthenogenesis. Sexual reproduction may involve fertilization inside the body or in the external environment. A species may accept separate sexes or combined sexes; when the sexes are combined they may be expressed at dissimilar times in the life cycle. The sex activity of an individual may be determined by various chromosomal systems or environmental factors such equally temperature.

Sexual reproduction starts with the combination of a sperm and an egg in a process called fertilization. This can occur either outside the bodies or within the female person. The method of fertilization varies amongst animals. Some species release the egg and sperm into the environment, some species retain the egg and receive the sperm into the female trunk and and then miscarry the developing embryo covered with shell, while all the same other species retain the developing offspring throughout the gestation menstruum.

Exercises

1. In which group is parthenogenesis a normal event?
   1. chickens
   2. bees
   3. rabbits
   4. sea stars
2. Genetically unique individuals are produced through ________.
   1. sexual reproduction
   2. parthenogenesis
   3. budding
   4. fragmentation
3. External fertilization occurs in which type of surroundings?
   1. aquatic
   2. forested
   3. savanna
   4. steppe
4. What might exist a disadvantage to temperature-dependent sex determination?
5. Compared to split up sexes and assuming self-fertilizing is not possible, what might be one advantage and one disadvantage to hermaphroditism?

Answers

1. B
2. A
3. A
4. Temperatures tin can vary from year to year and an unusually cold or hot yr might produce offspring all of one sex, making it difficult for individuals to discover mates.
5. A possible reward of hermaphroditism might be that anytime an private of the same species is encountered a mating is possible, different separate sexes that must find an individual of the correct sexual activity to mate. (Also, every individual in a hermaphrodite population is able to produce offspring, which is non the instance in populations with divide sexes.) A disadvantage might be that hermaphrodite populations are less efficient because they do not specialize in one sexual activity or some other, which means a hermaphrodite does not produce as many offspring through eggs or sperm as practice species with separate sexes. (Other answers are possible.)

Glossary

asexual reproduction:a mechanism that produces offspring that are genetically identical to the parent

budding:a form of asexual reproduction that results from the outgrowth of a part of an organism leading to a separation from the original animal into two individuals

external fertilization:the fertilization of eggs by sperm outside an animal's body, often during spawning

fission:(also, binary fission) a course of asexual reproduction in which an organism splits into two divide organisms or two parts that regenerate the missing portions of the torso

fragmentation:the breaking of an organism into parts and the growth of a separate individual from each office

hermaphroditism:the state of having both male and female reproductive structures within the aforementioned individual

internal fertilization:the fertilization of eggs by sperm inside the body of the female

oviparity:a process by which fertilized eggs are laid outside the female's torso and develop at that place, receiving nourishment from the yolk that is a part of the egg

ovoviparity:a process by which fertilized eggs are retained within the female; the embryo obtains its nourishment from the egg's yolk, and the young are fully developed when they are hatched

parthenogenesis:a form of asexual reproduction in which an egg develops into a complete individual without being fertilized

sexual activity determination:the mechanism by which the sex of individuals in sexually reproducing organisms is initially established

sexual reproduction:a form of reproduction in which cells containing genetic material from two individuals combines to produce genetically unique offspring

viviparity:a process in which the immature develop within the female and are built-in in a nonembryonic state

Source: https://opentextbc.ca/biology/chapter/13-1-how-animals-reproduce/

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