The different modes of asexual reproduction in animals are parthenogenesis, budding, polyembryony, fragmentation, etc. Some examples are provided in the article below, regarding this type of reproduction. It helps in understanding the concept in a better manner.
A form of reproduction that takes place without gamete fusion is termed as asexual reproduction. The general definition is as follows: the method, in which fertilization, ploidy reduction, or meiosis doesn't take place is known as asexual reproduction.
There are different modes, by which animals reproduce asexually, and their explanations are provided below.
It is the process, in which cells of an organism split into parent and daughter cells. For example, organisms like sponges and hydra reproduce by means of budding. In hydra, this process is similar to that of reproduction in yeasts. Initially, a small bud is formed on the side of the body, which enlarges and develops tentacles, which help in feeding the daughter bud that breaks off from the parent body. In organisms like echinoderms and jellyfish, the buds break off and form their independent bases. The mechanism is different in corals, and their buds do not detach from their parent body, leading to formation of large colonies.
Eggs produced by females develop into adult individuals without getting fertilized; this process is known as parthenogenesis. Some species of fish, frogs, and insects reproduce by means of this method. In few organisms, this process occurs under specific conditions. For example, when aphids get enough food to eat in the spring season, they resort to asexual reproduction; it is a quicker means of producing offspring. However, these creatures can also undergo sexual reproduction.
Animals that reproduce by means of gemmules (internal buds) release cell masses from their body. Sponges reproduce by means of budding, along with gemmule reproduction, and produce external buds. Later, these cells develop into independent offspring.
It is a condition, in which a single egg leads to the development of two or more embryos. By this method, a large number of propagules are produced in the organism's body. As they are released, they directly develop and enter the next phase of their life cycle. The flukes belonging to class Trematoda reproduce by means of polyembryony.
Asexual reproduction in animals doesn't take place on a large scale in nature, and it gives rise to homozygosity. The harmful mutations of the organisms (reproducing by asexual reproduction) get exposed to natural selection. Thus, weeding out of such animals (by natural selection) happens easily. In sexual reproduction, owing to heterozygosity, harmful mutations may not get exposed, and hence, animals stay unaffected from natural selection.