Monthly Temperatures and Wing Centroid Sizes of Fruit Fly Specimens
| Month | Average high (°F) | Average low (°F) | Average male wing centroid size (mm) | Average female wing centroid size (mm) |
|---|---|---|---|---|
| September | 80 | 54 | 1.98 | 2.27 |
| October | 67 | 44 | 1.98 | 2.27 |
| May | 73 | 50 | 1.98 | 2.29 |
| July | 87 | 62 | 2.02 | 2.31 |
Drosophila (fruit flies) have generation times of 10–12 days, so seasonal changes in humidity and other environmental conditions can drive seasonal fluctuations in chromosome rearrangements in species such as D. persimilis and D. mediopunctata. Drosophila body size (for which wing centroid size serves as a proxy measure) correlates with life span. Banu Şebnem Önder and Cansu Fidan Aksoy measured the wing sizes of members of a D. melanogaster population in Yeşilöz, Turkey, that were collected monthly between May and October over three years. Their research suggests that Drosophila collected in relatively cooler months should tend to have a shorter life span, as is illustrated by the finding that_______
Which choice most effectively uses data from the table to complete the assertion?
Explanation
Context: Wing centroid size stands in for body size, which correlates with life span. To illustrate that flies collected in cooler months are shorter lived, the blank needs a smaller wing measurement attached to the cooler month.
Answer: B) the average female wing centroid size was smaller in September than in July.
Why? July averages 87°F high and 62°F low against September's 80°F and 54°F, so September is the cooler month. Average female wing centroid size falls from 2.31 mm in July to 2.27 mm in September, giving a smaller body proxy in the cooler month and therefore the shorter predicted life span.
Traps:
- A) male size 1.98 mm in September but 2.31 mm in July → misreads the table; 2.31 mm is July's female value, while July's male value is 2.02 mm.
- C) lower average low in May than in September → matches the table (50°F versus 54°F) but reports temperature only, with no wing size to link to life span.
- D) male sizes smaller than female in all four months → accurate, but it compares the sexes rather than warmer and cooler months.