Q44 - Pollen Donor Competition on the Stigma

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Flower Anatomy & Reproductive Structures

Plants compete as pollen donors for siring offspring, i.e. becoming fathers. The stigma becomes an arena, where pollen donors/fathers “fight” for fertilization (paternity), and where the females “choose” fathers of their seeds. This was studied in the plant Purple Chinese Houses (Collinsia heterophylla) (Fig.).

Proportion of seeds sired by either a dark (D) or a white pollen donor (W): A, pollen deposited on stigma in succession (1: D → W, i.e. first D and then W, or 3: W → D) or simultaneously as a mixture (2: D + W); B, size of deposited pollen load (D and W added simultaneously): L and H = low and high pollen load, respectively; and C, two or four donors (i.e. first 2D and then 1–2 days later 2W or vice versa) (from Lankinen & Madjidian 2011).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. There is a first-donor advantage

B. No competitive effect of high pollen load is observed

C. Increase in number of fathers increases competition

D. If lots of pollen from the first donor is deposited, pollen added 2 days later from a second donor does not sire seeds

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Question reproduced from IBO 2015, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)