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) |
|---|---|---|---|---|
| October | 67 | 44 | 1.98 | 2.29 |
| May | 73 | 50 | 1.98 | 2.27 |
| July | 87 | 62 | 2.02 | 2.31 |
| September | 80 | 54 | 1.98 | 2.27 |
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. subobscura. Drosophila body size (for which wing centroid size serves as a proxy measure) correlates with reproductive fitness. 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 warmer months should tend to have greater reproductive fitness, 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 reproductive fitness, and the assertion is that flies collected in warmer months should be fitter. In the table July is the warmest month (average high 87) and May is cooler (average high 73).
Answer: B) the average female wing centroid size was larger in July than in May.
Why? Female wing centroid size is 2.31 mm in warm July against 2.27 mm in cooler May. Larger bodies in the warmer month is precisely the size-and-fitness pattern the assertion predicts.
Traps:
- A) 2.31 mm is the female July value; the male average in July is 2.02 mm, so the choice pulls from the wrong column.
- C) September's average low is indeed higher than May's, but the choice reports temperature alone and never mentions body size, so it cannot illustrate a fitness claim.
- D) Females do outsize males in all four months, but that compares the sexes rather than warm months with cool ones.