Question

A researcher carried out an experiment to study how daylength and temperature influence diapause in a moth species. He placed larvae in one of four treatment conditions for 2 weeks, with 30 larvae in each condition. The treatments involved two temperatures (18°C or 27°C) and two lighting conditions (12h:12h Light:Dark (LD) or complete darkness (DD)). At the end of the experiment, he counted the number of larvae that had entered diapause and those that had not. The data are shown below.

Condition	Larvae in diapause	Larvae NOT in diapause
Treatment 1 (27°C, 12:12 LD)	2	28
Treatment 2 (18°C, 12:12 LD)	7	23
Treatment 3 (27°C, DD)	12	18
Treatment 4 (18°C, DD)	29	1

Which one or more of the following conclusions can he reasonably make from these findings?

• A. Diapause is independent of abiotic conditions
• B. Only temperature influences diapause
• C. Only daylength influences diapause
• D. Both temperature and daylength influence diapause

Hint:

Compare the diapause rate while holding one variable fixed and changing the other, do this for both temperature and daylength, before deciding what the data support.

Answer 1

The Correct Option is D

Step 1: Convert the counts to percentages entering diapause.
Each treatment has 30 larvae. The fraction that entered diapause is
\[ \text{Treatment 1 (27°C, LD)}:\ \frac{2}{30}\approx6.7\% \] \[ \text{Treatment 2 (18°C, LD)}:\ \frac{7}{30}\approx23.3\% \] \[ \text{Treatment 3 (27°C, DD)}:\ \frac{12}{30}=40\% \] \[ \text{Treatment 4 (18°C, DD)}:\ \frac{29}{30}\approx96.7\% \]

Step 2: Test the effect of temperature, holding light fixed.
Compare Treatment 1 with Treatment 2, both under LD light. Cooling from 27°C to 18°C raises diapause from about 6.7% to about 23.3%. Now compare Treatment 3 with Treatment 4, both in DD. Cooling from 27°C to 18°C raises diapause from 40% to about 96.7%. In both light conditions, the colder temperature clearly gives more diapause, so temperature does influence diapause.

Step 3: Test the effect of daylength, holding temperature fixed.
Compare Treatment 1 with Treatment 3, both at 27°C. Switching from LD light to full darkness raises diapause from about 6.7% to 40%. Now compare Treatment 2 with Treatment 4, both at 18°C. Switching from LD to DD raises diapause from about 23.3% to about 96.7%. In both temperatures, removing light clearly increases diapause, so daylength also influences diapause.

Step 4: Rule out the other options.
Diapause cannot be independent of abiotic conditions, since the rate swings from about 7% up to about 97% across the four treatments, so option (A) is wrong. Diapause is not driven by temperature alone, since light also changed the rate at both temperatures, so option (B) is wrong. It is not driven by daylength alone either, since temperature also changed the rate under both light regimes, so option (C) is wrong.

Step 5: Final conclusion.
Since a colder temperature and a shorter or absent daylength each independently raise the proportion of larvae entering diapause, and the two effects even appear to add up in Treatment 4, the researcher can conclude that both factors influence diapause.
\[ \boxed{\text{(D) Both temperature and daylength influence diapause}} \]