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

This question is built around a classic idea in behavioural biology: every behaviour can be explained at two levels. The proximate level asks what triggers the behaviour right now, things like hormones, nerve signals, or a cue from the surroundings. The ultimate level asks why that behaviour was favoured by evolution in the first place. The question only wants proximate causes, so any answer built purely around raising fitness or reproductive success over time should be set aside.

1. Males build up testosterone before emergence, which inhibits them from re-entering hibernation: this is a hormone acting inside the animal's body at the time of emergence. It is a direct, mechanistic trigger, so it counts as a proximate cause.
2. Early emergence helps males increase their reproductive success by gaining early access to females: this talks about a fitness pay-off across generations, which is the definition of an ultimate cause. It does not answer what triggers the behaviour today, so it is left out.
3. Hibernating females respond to both hormonal levels and environmental cues: the question already tells us females track snowmelt and adjust their emergence, so an internal hormone state working together with an outside cue is exactly the mechanism in play. This is a proximate cause.
4. Female fecundity is negatively affected by colder temperatures: cold acting directly on a female's reproductive physiology is a mechanistic, right-now effect, and it explains her delayed emergence in cold years. This is also a proximate cause.

So the statements that describe a proximate cause are the testosterone effect in males, the combined hormonal and environmental control in females, and the direct effect of cold on fecundity.

Let's summarize:

• Proximate causes are immediate triggers like hormones and environmental cues; ultimate causes are evolutionary, fitness based explanations.
• Only the statement about gaining early access to mates describes an ultimate cause here, so it is excluded.

The correct options are (A), (C), and (D).