If a pregnant rodent is exposed to the scent of an unfamiliar male, she will often spontaneously abort. This is known as the Bruce Effect
, after researcher Hilda Bruce who discovered the phenomenon while working at London's National Institute for Medical Research (NIMR) in the 1950s.
It's thought that the female rodent does this in order to make herself ready for mating with the new male — because the new male would probably kill the children of the other father once they were born, so why bother carrying them to term. The trick doesn't work with the scent of a castrated male.
The history of the NIMR (pdf - page 208
) offers some interesting details about Bruce's research. The Parkes mentioned was Alan Parkes, her boss:
The Bruce Effect implied that every male mouse smells different to every other male mouse, at least to female mice, and that he produces a spectrum of odours that vary slightly between individuals of the same strain and differ markedly between individuals of different strains. With lateral thinking on how to prove their theory, Bruce and Parkes turned to Boake, a world famous perfumery.
Knowing how skilful perfumers must be in distinguishing between thousands of different odours, they persuaded some Boake representatives to visit NIMR for the purpose of smelling the mice. They invited them to sniff at pieces of cloth that had each been exposed to different cages of various mouse strains. The perfumers had no difficulty in distinguishing the different strains as all had a unique aroma; they even commented that four of the strains were quite similar – all of which had been bred from one original colony at Hampstead. They also noted that the CBA mouse strain, which was fairly new to NIMR, had a wonderful and pleasantly musky smell that could be of commercial interest in perfume manufacture!