Which sea stars carry out the fissiparism form of asexual reproduction?
Which sea stars carry out the fissiparism form of asexual reproduction?
From the results of research studies, it appears that it is mostly small sea stars that carry out fissiparism, for example Nepanthia belcheri and Asterina anomala. A possible explanation is that small sea stars have less tissue and smaller organs. Thus, they are able to regenerate faster. Some small to medium-sized sea stars also carry out fissiparism such as the multi-armed sea star and orange sea star.
【Extended Reading: Fissiparism in指海星】
Organisms mainly carry out two types of reproduction. The first type is sexual reproduction. Females and males produce ova and sperm, which result in offspring through the process of fertilization. Examples include humans and other terrestrial large, higher animals. The second type is referred to as asexual reproduction. In this type of reproduction, no ova or sperm are produced. Instead, an outgrowth or bud is produced on the body of the parent (referred to as budding) or fission is carried out (referred to as fissiparism). The fissiparism of 指蛇星 is commonly observed among sea stars and is a very effective form of asexual reproduction.
When the arms of 指蛇星 grow to about 2 centimeters, some will automatically fall off. Usually 2 or 3 of the 5 arms will drop off. Each of the arms that drops off slowly grows 4 other new arms. Each arm can become a complete 指蛇星. Once mature, it can continue the fissiparism form of asexual reproduction.
What are the advantages of fissiparism? The advantage of this type of asexual reproduction is that a sea star can produce offspring on its own. The individuals that are produced via fissiparism are thousands of times larger than those produced by the fertilization of an ovum by a sperm. This means that they are less prone to being eaten by predators and have better resistance to disease. In addition, individuals that are produced by sexual reproduction have to undergo a long and slow process of development and growth. Larvae require a long period of growth in ocean waters and are at great risk of being eaten, especially when small.
What are the disadvantages of fissiparism? The major disadvantage of this form of reproduction is that the individuals that are produced are genetically identical to the parent. There is no genetic variation. Instead the individuals that are produced are clones of the parents. Thus, the adaptability of the offspring is the same as that of the parents. When there is a large change in the environment, such as increase in water temperature, the cloned offspring do not have the ability to adapt and are at risk of dying off. Offspring produced through sexual reproduction are at much less risk. That is because the combination of ovum and sperm provides for a number of genetic variations among the offspring. Thus, some of the offspring are stronger and more resistant to adverse environments and can survive or move to a suitable area where they can continue to reproduce.
Two of the arms from 指海星 have broken off and are undergoing asexual reproduction. After a period of time, each arm produces new arms. Each of these arms can produce a complete sea star. This is a type of asexual reproduction.