The species of some genera are reproductively isolated but are similar in outward appearance or morphology. These are called sibling species. They live in the same geographical area. They can be identified by their breeding time, preferred habitats and behavior.
Examples of Sibling Species:
(i) The Malaria carrying mosquito of Europe, Anopheles maculipennis and Atroparrus are morphologically similar but they are reproductively isolated and they are unable to produce fertile hybrids.
(ii) Another example of sibling species is illustrated by genus Drosophila. Drosophila pseudoobscura and D. persimilis are structurally similar except minor differences in wing size, genitalia and sex comb, gene arrangement.