Long answer question.
Describe the different types of reproductive isolations.
A number of isolating mechanisms are operated in nature and therefore divergence and speciation may occur.
The isolating mechanisms are of two types namely, geographical isolation and reproductive isolation.
1. Geographical Isolation:
It is also called as physical isolation. It occurs when an original population is divided into two or more groups by geographical barriers such as rivers, oceans, mountains, glaciers, etc. These barriers prevent interbreeding between isolated groups.
The separated groups are exposed to different kinds of environmental factors and they acquired new traits by mutations. The separated populations develop distinct gene pool and they do not interbreed. Thus, new species have been formed by geographical isolation. e.g. Darwin’s Finches.
2. Reproductive Isolation:
Reproductive isolation occurs due to change in genetic material, gene pool and structure of genital organs. It prevents interbreeding between populations. Types of Isolating Mechanisms:
a. Pre-mating or pre-zygotic isolating mechanism:
This mechanism prevents fertilization and zygote formation.
i. Habitat isolation or (Ecological isolation): Members of a population living in the same geographic region but occupying separate habitats in such a way that potential mate do not meet.
ii. Seasonal or temporal isolation: Members of a population living in the same geographic region but are sexually mature at different years or different times of the year.
iii. Ethological isolation: Due to specific mating behavior the members of the population do not mate.
iv. Mechanical Isolation: Members of two populations have a difference in the structure of reproductive organs.
2. Post-mating or Post-zygotic barriers:
i. Gamete mortality: Gametes have a limited life span. Due to one or the other reasons, if the union of the two gametes does not occur in the given time, it results in gamete mortality.
ii. Zygote mortality: Here, egg is fertilized but the zygote dies due to one or the other reasons.
iii. Hybrid sterility: Hybrids develop to maturity but become sterile due to the failure of proper gametogenesis (meiosis).
e.g. Mule is an inter-generic hybrid that is sterile.