Question

directions
observed traits in a population of broadleaf arrowhead, by flowering date
trait | day 5 | day 10 | day 15 | day 20
total number of open male and female flowers per growth unit | 25 | 65 | 110 | 45
estimated reproductive success rate of male flowers | 0.29 | 0.29 | 0.29 | 0.29
proportion of male flowers | 0.45 | 0.50 | 0.48 | 0.13
the mating environment hypothesis predicts that populations of flowering plants compensate for reduced mating opportunities due to dichogamy (a plant’s expression of male and female functions at separate times to prevent self - pollination) by adjusting the bias of floral sex allocation during the flowering period, increasing the probability of successful cross - plant pollination.
researchers tested the hypothesis by examining a population of broadleaf arrowhead, a plant for which bloom onset generally takes longer for male flowers than for female flowers, during the flowering season. they concluded that the mating environment hypothesis is not well supported by their observational data.
12 mark for review
which choice best describes data from the table that support the researchers’ conclusion?
a whereas the total number of open flowers per growth unit peaked on day 15, the proportion of male flowers experienced a peak earlier in the flowering season, on day 10.
b despite the sharp reduction in the total number of open flowers per growth unit from day 15 to 20, there was no decline in the estimated reproductive success rate of male flowers in that interval.
c sex allocations were largely evenly distributed on days 10 and 15 but were female biased on days 5 and 20.
d although sex allocations became overwhelmingly female biased by day 20, male flowers’ estimated reproductive success rate did not vary from day 5 to 20.

Explanation:

To solve this, we analyze each option against the table data and the hypothesis:

• Option A: The "proportion of male flowers" peaks at Day 10 (0.50), but the total flowers peak at Day 15. However, the hypothesis is about compensating for reduced mating opportunities via floral sex allocation adjustment. This option doesn't directly relate to supporting the "not well supported" conclusion.
• Option B: The total flowers drop from Day 15 (110) to Day 20 (45), but male reproductive success rate stays 0.29. The hypothesis predicts adjustment of sex allocation to increase cross - pollination success. If the rate doesn't change despite the drop in total flowers, it doesn't support the idea of adjustment, but let's check other options.
• Option C: On Day 5, proportion of male flowers is 0.45 (so female - biased? 1 - 0.45 = 0.55), Day 10: 0.50 (near even), Day 15: 0.48 (near even), Day 20: 0.13 (female - biased). But the hypothesis is about compensating for reduced mating opportunities. This doesn't clearly relate to the conclusion.
• Option D: By Day 20, proportion of male flowers is 0.13 (overwhelmingly female - biased). The male reproductive success rate is 0.29 every day (Day 5 - 20). The hypothesis predicts that plants adjust sex allocation to increase cross - pollination success. If the reproductive success rate doesn't change even with a huge shift in sex allocation (towards female), it means the adjustment (if any) didn't affect success, so the data doesn't support the hypothesis. This matches the researchers' conclusion that the hypothesis is not well supported.

Answer:

D. Although sex allocations became overwhelmingly female biased by day 20, male flowers’ estimated reproductive success rate did not vary from day 5 to 20.