Significance of isolating mechanism

- • courtship is avoided. If isolating mechanisms are distinct and specific only individuals • courtship is avoided. If isolating mechanisms are distinct and specific only individuals of the same species indulge in courtship.
- • mechanism protects gene pool of a species and prevents hybridization. • mechanism protects gene pool of a species and prevents hybridization.
- • prevents wastage of gametes and energy. • prevents wastage of gametes and energy.
- • weak isolating mechanism leads to production of new species through hybridization. • weak isolating mechanism leads to production of new species through hybridization.
- • of isolating mechanism leads to production of new species by instant speciation. • of isolating mechanism leads to production of new species by instant speciation.
- • isolation followed by reproductive isolation ultimately leads to production of • isolation followed by reproductive isolation ultimately leads to production of new species.
- • mechanisms protect the identity of a species, which all species fiercely guard. • mechanisms protect the identity of a species, which all species fiercely guard.

## SPECIATION

Speciation is the evolution of a new species from the pre-existing one by gradual modification. Since species are reproductively isolated populations, creation of a new species demands a mechanism that will produce reproductive isolation between two populations. Speciation can be classified into two categories as follows: Convergent speciation: speciation: Two species that have not developed enough reproductive isolation but have maintained their independent existence owing to the geographical isolation can merge and produce a new species by hybridization should the geographical barrier separating them is removed. Sometimes migrations or accidental carriage by wind or storm can also make the two populations merge into one species. · Divergent speciation: speciation: When two or more species are produced by splitting of a single species, either by migration or adaptive radiation. Gradually each population gives rise to an independent species, as happened in the case of Darwin’s finches. When a population enters a new ecological zone evolution is generally quick to produce new species by adaptation to new environment. · Phyletic speciation: speciation: This is also called sequential evolution or transformation, in which a species changes gradually over a long period of time to become entirely different from the ancestor. Evolution of horse from Hyracotherium and elephant from Moeritherium are excellent examples of phyletic speciation. Darwin’s theory is based on this concept of gradualism. · Quantum speciation: speciation: This involves sudden formation of a new species by rapid changes or saltation, caused by mega-mutation and disruptive selection, hybridization or polyploidy. When new areas are colonized, all niches are vacant that forces the isolating mechanism to set in rather rapidly to produce new types. Based on the mode, habitat and geographical distribution, speciation can be of several types as follows: 1. Allopatric speciation: Allopatric speciation: Also called geographical speciation. A physical barrier divides the population into smaller units, as happens during interglacial period when sea level rises and separates islands from the mainland. The separated populations on the islands evolve differently by constant genetic changes, translocations, inversions etc. They change into races, then subspecies and if time is long enough, into species.