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 separate species?
- They cannot interbreed in nature
- They are reproductively distinct
- They are physiologically distinct
- They are morphologically distinct
Answer
(1) They cannot interbreed in nature
Solution
A biological species is a group of natural populations that interbreed among themselves and are reproductively isolated from other such groups in nature.
⇒ The two plants flower at different times (long day vs short day), so in nature their pollen never meets — temporal (seasonal) reproductive isolation.
⇒ They can be crossed only under artificial laboratory conditions, which does not count for species status.
∴ The best reason is that they cannot interbreed in nature.
Answer: (1)