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

This question hands us a small 2 by 2 experiment, two temperatures crossed with two light regimes, and asks what the resulting diapause counts actually support. The cleanest way to read a factorial table like this is to change one factor at a time while holding the other one still.

1. Diapause is independent of abiotic conditions: the diapause rate moves from about 7% in the warmest, lightest treatment up to about 97% in the coldest, darkest one. That is a huge swing, so diapause clearly depends on the conditions. This option fails immediately.
2. Only temperature influences diapause: hold the light fixed at LD and just change temperature: 7% at 27°C rises to 23% at 18°C. That alone supports temperature mattering. But now hold temperature fixed at 27°C and just change light, from LD to DD: 7% jumps to 40%. Light is clearly doing something too, so only temperature cannot be right.
3. Only daylength influences diapause: by the same logic, holding temperature fixed at 18°C and switching from LD to DD takes the rate from 23% to 97%, so daylength matters. But holding light fixed at DD and switching temperature from 27°C to 18°C takes 40% to 97%, so temperature matters too. Only daylength is also wrong.
4. Both temperature and daylength influence diapause: every one of the four possible one-factor comparisons above showed a real jump in the diapause rate. Cooling raises diapause at both light levels, and losing light raises diapause at both temperatures. Both factors are doing real work, and the coldest, darkest treatment gives by far the highest diapause rate of all.

Working through the four comparisons rules out independence and rules out either factor acting alone, leaving both factors as active influences on diapause.

Let's summarize:

• Compare treatments in pairs that change only one factor at a time to isolate its effect.
• Both the temperature comparisons and the light comparisons show a clear shift in diapause rate.

The correct option is (D), both temperature and daylength influence diapause.