Q.Define isolating mechanism and explain its types with suitable examples.

Step 1. An isolating mechanism (isolating barrier) is defined as any evolved character of two species that stops them from interbreeding, thereby preserving each species' separate genetic integrity even when they live in the same area.

Step 2. Prezygotic mechanisms prevent the two species from ever coming into reproductive contact: (i) Ecological/habitat isolation — different microhabitats, e.g. Rana areolata (shallow ponds) vs Rana grylio (deep water); (ii) Seasonal isolation — different breeding times, e.g. Bufo americanus (early spring) vs Bufo fowleri (late season); (iii) Sexual/ethological isolation — different mating calls/behaviour, e.g. Hyla versicolor vs Hyla femoralis tree frogs; (iv) Morphological/mechanical isolation — incompatible genitalia size, e.g. Bufo quercicus vs Bufo valliceps; (v) Physiological isolation — gamete incompatibility despite mating, e.g. Drosophila virilis sperm surviving only about a day inside D. americana; (vi) Cytological isolation — differing chromosome numbers block fertilisation, e.g. Rana catesbeiana vs Rana areolata. …

Define the term, then work through all nine types under the prezygotic/postzygotic g …

• Confusing physiological isolation (gametes fail after mating occurs) with hybrid inviability (a postzygotic mechanism where fertilisation has already succeeded). …