What causes female mice to become pseudopregnant?

• A. Injection of PMSG
• B. Change in the light/dark cycle
• C. The presence of high levels of pheromones
• D. Copulation with dud males

Answer: (D)

Pseudopregnancy in female mice is triggered by the act of mating itself. The physical stimulation during copulation sends neural signals that cause a surge in luteinizing hormone, leading to the formation of the corpus luteum and sustained progesterone production. This hormonal state mimics early pregnancy even if fertilization doesn’t occur. Because the trigger is the coital stimulus, copulation with a male who cannot fertilize (a dud or vasectomized male) still induces pseudopregnancy.

The other options don’t produce this pregnancy-like hormonal state: injecting a hormone to stimulate ovulation can alter the cycle but doesn’t create a pseudopregnant state; changes in light cycles or pheromone exposure influence cycle timing but don’t by themselves trigger the luteal progesterone-dominant state characteristic of pseudopregnancy.