Which of the following could be an example of instant speciation?

Instant speciation refers to the rapid formation of new species, often as a result of significant genetic changes that lead directly to reproductive isolation without the gradual processes typical of traditional speciation. The phenomenon can occur suddenly through mechanisms like polyploidy in plants, where the doubling of chromosomes can create an instant barrier to reproduction with the parent species.

In this context, mutations that lead to reproductive isolation directly create a situation where individuals from different populations can no longer interbreed, thus forming distinct species practically instantaneously. This contrasts with processes like habitat differentiation or geographic barriers, which usually involve more gradual changes and are often associated with longer evolutionary timeframes.

While habitat differentiation and geographic barriers can contribute to speciation, they typically require extended periods to develop into fully realized reproductive isolation. Enhanced survival in a new niche, while advantageous for species adaptive evolution, does not inherently equate to immediate speciation unless it concurrently results in reproductive isolation. Hence, the instance of mutations leading to reproductive isolation serves as the clearest example of instant speciation.