Question

A research group studied the timing of Arctic ground squirrel emergence from hibernation. They collected data over a 25-year period and found that female and male ground squirrels differed in how variable their emergence times were. Across years, no matter what the above-ground temperatures were, male ground squirrels emerged in the same week in April. Females usually emerged during the same week as the males if it coincided with snowmelt, but in colder years, they re-entered hibernation and emerged later after snowmelt. Which one or more of the following statements is/are possible proximate cause(s) for this phenological pattern?

• A. Males build up testosterone before emergence, which inhibits them from re-entering hibernation
• B. Early emergence helps males increase their reproductive success by gaining early access to females
• C. Hibernating females respond to both hormonal levels and environmental cues
• D. Female fecundity is negatively affected by colder temperatures

Hint:

A proximate cause is the immediate physiological or environmental mechanism behind a behaviour, not the evolutionary reason the behaviour was favoured over generations.

Answer 1

The Correct Option is A, C, D

Step 1: Separate proximate cause from ultimate cause.
Behavioural ecologists split the explanation for any behaviour into two kinds of cause. A proximate cause is the immediate mechanism that triggers the behaviour right now, such as a hormone level, a body clock, or an environmental cue like temperature or snowmelt. An ultimate cause is the evolutionary reason the behaviour exists at all, framed in terms of fitness and reproductive success gained over generations.

Step 2: Read the pattern given in the question.
Male squirrels emerge in the same week every April no matter what the temperature is. Females usually emerge with the males when snowmelt lines up with that week, but in cold years they go back into hibernation and come out only after the snow actually melts.

Step 3: Check option (A).
A rise in testosterone before emergence is a hormonal, physiological trigger acting inside the male's body right now. It directly explains why the males never go back into hibernation once they start emerging, so this is a proximate cause. Option (A) is correct.

Step 4: Check option (B).
Saying that early emergence raises a male's reproductive success by giving him early access to females explains why emerging early was favoured by natural selection over many generations. That is an ultimate, evolutionary explanation, not a proximate one, so option (B) does not answer the question asked. Option (B) is excluded.

Step 5: Check option (C).
Females sometimes emerge with the males and sometimes delay depending on snowmelt. This means their hibernation state is controlled by an internal hormonal signal together with an external cue, snowmelt. Both are immediate triggers acting on the animal, so this is a proximate cause. Option (C) is correct.

Step 6: Check option (D).
Colder temperatures acting on a female's body can directly lower her fecundity, her physiological readiness to reproduce. This physiological effect of temperature is exactly why females delay emergence in cold years, so it counts as a proximate, mechanistic cause. Option (D) is correct.

Step 7: Final answer.
The possible proximate causes are the hormonal trigger in males, the combined hormonal and environmental control in females, and the direct effect of cold on female fecundity.
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