Isolation mechanisms in evolution

An isolating mechanism is a mean of producing and maintaining isolation within a population. This can be brought about by mechanisms acting before or after fertilization.

1. Prezygotic mechanism [barrier to the formation of hybrids]

• Seasonal isolation; occurs when two species mate or flower at different time of the year. E.g., California Pinus radiata flowers in February whereas Pinus attenuata flowers in April
• Ecological isolation: occurs where two species inhabit the similar regions but have difference habitat preference e.g., Viola arvensis grows on calcareous soil whereas viola tricolor prefers.
• Behavioral isolation: occurs where animals exhibit courtship patterns, that attract one individual for sex but not another.
• Mechanical isolation: occur in animal where difference in genitalia prevent successful copulation and in plant where related species of flower are pollinated by different animals.

2. Postzygotic mechanism [barrier affecting hybrids]

• Hybrid in-viability; Hybrid are produced but fail to develop to maturing. E.g. hybrid formed between northern and southern race of the leopard frog [Rana pipens] in North America.
• Hybrid sterility: hybrid fail to reproduce functional gametes, e.g., the male [2n= 63] result from the cross between the horse [Equus hernionus 2n = 66]
• Hybrid breakdown: F1 hybrid are fertile but the F2 generation and back crosses between F1 hybrid and parental stock fail to develop or and infertile i.e., hybrid formed between species [genus Gossypium].

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Dr. Bbosa Science