[Campbell Biology P.918] Wild tobacco Nicotiana attenuata adjusts its flowering time in resp... | Practice Question

Wild tobacco Nicotiana attenuata adjusts its flowering time in response to herbivory. Normally, it flowers at night, attracting hawk-moths. However, when heavily infested by hawk-moth larvae, it shifts to flowering at dawn, attracting hummingbirds. What specifically triggers this shift, and what is the primary benefit for the plant?

  • A: The plant detects physical damage, shifting to dawn flowering to simply avoid hawk-moths.
  • B: Oral secretions from the munching larvae trigger the shift. This allows hummingbirds to pollinate the flowers at dawn, avoiding hawk-moths that lay eggs on the leaves.
  • C: The plant starts producing a new chemical repellent against hawk-moths, which coincidentally leads to dawn flowering.
  • D: The shift is a direct response to a lack of night-time pollinators, indicating a failure of hawk-moths to visit.

Explanation

The text explicitly states that 'oral secretions from the munching larvae trigger the dramatic shift in the timing of flower opening.' The purpose is to avoid the hawk-moths, which lay eggs on the leaves, and instead be pollinated by hummingbirds at dawn.