In both cases, populations become reproductively isolated.

the reproductive isolation might lead to a new species.

Reproductive isolation may lead to the evolution of new species.

One concept of species holds that species are defined in terms of reproductive isolation.

Reproductive isolation (Biology) A mechanism that prevents, or severely limits, the hybridization of two species living in the same region, even when they are closely related.

The barriers prevent the exchange of genetic information between the two populations leading to reproductive isolation.

Reproductive isolation is the existence of biological factors (barriers) that impede two different species from producing viable, fertile offspring.

Reproductive isolation: the existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring.

When the two varieties were cross-bred the eggs were infertile suggesting reproductive isolation.[234][236]

These show differences in their morphology and flowering phenology that could contribute to their reproductive isolation.

Reproductive isolation: Mechanisms that prevent two or more populations from interbreeding with each other and forming viable, fertile offspring.

A species is defined in terms of its reproductive isolation, meaning that members from different species cannot interbreed.

For speciation to occur, there must be some reproductive isolation that occurs between formerly reproducing members of the original ancestor species.

The establishment of reproductive isolation is a critical component of species formation because it is required for the initial divergence and for the subsequent maintenance of different species.

The establishment of reproductive isolation is a critical component of species formation because it is required for the initial divergence and for the subsequent maintenance of different species.