Nicotiana sylvestris flowers only during long days and N.tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be induced to flower at the same time and can be cross-fertilized to produce self-fertile offspring. What is the best reason for considering N.sylvestris and N.tabacum to be separation species?
(1) They cannot interbreed in nature
(2) They are reproductively distinct
(3) They are physiologically distinct
(4) They are morphologically distinct