Question

Populations of some species of fish, insects, and crustaceans consist of both sexually and obligately asexually reproducing individuals. Would you expect such populations to become entirely asexual or sexual? What factors might maintain both reproductive modes? How might studies shed light on the factors that maintain sexual reproduction? The text says that “the recency of most parthenogenetic lineages suggests that sex reduces the risk of extinction.” Explain why.

Answer 1

Sexual reproduction is the method which requires two individuals to come together for reproduction. Male gamete from male individual and female gamete from female individual fuse to form a zygote. Formation of gametes requires a type of cell division which is called meiosis. Meiosis brings number of new gene combination because of a phenomenon called crossing over. The recombination of genes brings new variety of individuals in the population. Variety in the popuation is important for the population to survive. Because any changes in the surroundings, atleast some variant will be able to survive. Fusion of gametes from two individuals and crossing over bring many variations in population. This gives advatage to the population because variants can be subjected to natural selection and the best variant will survive and adapt.

Asexual reproduction involves only one individual. There is no need for searching the mate. It is also a very fast method of reproduction. But asexual reproduction does not bring varations in the population. The rate at which variants are formed are due to some minor DNA changes only. That is very slow process. If variants are not there in the population, survival of such a population when the surrounding environment changes is difficult. The population may get extinct if there are no variants in the population.

Sexual reproduction is more advantageous than the asexual reproduction though asexual reproduction is less time consuming and produces large number of individuals. Such populations where some individuals are obligate asexual organisms will never become asexual because of the advatages of sexual reproduction. FAst reproductive strategy helps in maintaining asexula organism numbers, variations in offspring maintain the sexual organisms.

Sexual reproduction gives the population lot of survival adbatage during harsh environmental conditions. Huge variants the sexual reproduction brings prevents the population form extinction. Parthenogenetic organism is produced by female gamete developing in to an organism without fertilization. Here only one individual is involved. So variability is comparatively less in such organisms also.