Reproductive isolation in sympatric speciation develops without a geographic barrier.

Speciation occurs due to reproductive isolation. This can be caused by mating differences, sterility or environmental barriers that eventually lead to the adaptive splitting into two species.Reproductive isolation is the inability of a species to breed successfully with related species due to geographical, behavioural, physiological or genetic barriers.Sympatric speciation refers to the formation of two or more descent species from a single ancestral species all occupying the same geographic location. It also results from the sexual conflict.So, the correct answer is option A.