by Sylvain Comeau
The mating behaviour of the common rat shows remarkable similarities to the species homo sapiens, says James Pfaus of the Centre for Studies in Behavioural Neurobiology (CSBN).
In a lecture at the D.B. Clarke Theatre last term, Professor Pfaus said that the CSBN research team has replicated human patterns of behaviour in rats, suggesting that learning and conditioning play a central role in reproduction in all mammals.
Pfaus's research has shown that sexual stimulation is far more than just an incentive for copulation. It is, in fact, necessary for pregnancy and for the survival of offspring.
"We found that female rats need vaginal stimulation in order to get pregnant. That could explain why pregnancy rates in human females from artificial insemination are so low. That's a concern, when it costs thousands of dollars per attempt."
In males, sexual stimulation protects the offspring from infanticide, a tactic used by males of some species to compete successfully for the privilege of passing on genes.
"When males receive penile stimulation prior to ejaculation, they don't attack any infant put in their cage for 21 days afterwards. This is probably because they can't be sure whether it is their infant, since they received sexual stimulation associated with mating." Pfaus believes that some human parallels can be seen in statistics on child abuse, which show that stepchildren are more likely than biological children to be abused.
Like humans, rats can also be choosy about their mates. In one experiment, a male rat was given a choice of two females, only one of which was wearing "perfume" -- an almond scent.
"The male copulated with both, but only ejaculated in the one with the almond scent. The implication is that you choose who to have children with, but you copulate with whoever is in front of you -- such as someone you meet at a convention."
Speaking of copulation not intended for procreation, a study on the effects of alcohol on mating behaviour yielded interesting results. The animals became less choosy.
"We had conditioned some males to stay away from certain females, but they overcame that inhibition when under the influence." But males do quickly learn to steer clear of females who show hostility in response to overtures.
"They will back off from fighting females -- who act like they want to fight when the males make advances -- and they refuse to go back to those females. They will not waste time and energy on non-receptive females. Good studs learn to respect the word no."
Pfaus's lecture was part of a day-long presentation of CSBN research presented in the J.W. McConnell Building in November.