Question

1. The alpine sky pilot, Polemonium viscosum is a common flowering plant in the Rocky Mountains. At high elevations, P. viscosum is pollinated mainly by B. kirbyellus bumblebees; At lower elevations, it is pollinated mainly by flies. A biologist observed that alpine sky pilot populations growing at higher elevations had significantly larger flower corollas than those growing at lower elevations.

a) Explain why flower size would be likely to affect the fitness of sky pilots at different elevations.

b) Explain why, based on fitness differences, average flower size has become different at high and low elevations.

2. A biologist claims that although the two sky pilot populations have different flower sizes, they are the same biological species.

a) How would the biologist test this hypothesis?

b) What experimental outcome would support the hypothesis that the two populations are the same biological species?

Answer 1

1a. Bumblebees preferentially visit plants with large, long-tubed, broadly flared corollas, bypassing neighbouring individuals with smaller Corolla. Thus explanation is sufficient to explain the evolution of large, broadly flared flowers in high-tundra sky pilot.

b. The decrease in flower size at lower elevations could simply reflect the reduced importance of bumblebees as pollinators. Also, plants with less conspicuous flowers have functional advantages near timberline i.e lower elevations that compensate for their reduced attractiveness to pollinators like flies.

2a. He can test this hypothesis by making the two species interbreed together. If they produce fertile and viable offsprings capable of reproducing the original parents belong to the same species. This whole concept is called a biological species concept.

b. Production of fertile and viable offsprings would support the hypothesis that the two populations are the same biological species.