While female birds are known to choose their mates based on fancy feathers, a new study suggests that female mammals are more likely to follow their noses to the right mate.
Cambridge zoologist Tim Clutton-Brock and Harvard researcher Katherine McAuliffe point out that it is generally thought that mate choice plays a smaller role in mammals than in birds because vivid examples of female preferences—such as the ornate tails of peacocks that emerged because peahens prefer to mate with males that have showy plumage—are harder to find in mammals.
However, they say, female mating preferences are likely to be just as important in mammals, though they may not be as obvious to human observers.
The researchers point out that it generally becomes difficult to study mammalian mate choice because dominant males among them often chase away others for access to female partners, which makes it hard to tell whether females are choosing to mate with certain males or are merely mating with them by default.
"The most convincing evidence for female mate choice in mammals comes from studies of captive mammals …carried out under controlled conditions where the effects of male competition can be excluded," Clutton-Brock and McAuliffe write.
According to them, lab studies of olfactory signalling may provide the best evidence for female mate choice in mammals.
Given that many mammal species are sexually active at night, the authors say that they may be less inclined than birds to base preferences on visual cues.
They believe that females of many mammalian species may be more likely to choose males using olfactory cues.
Referring to past studies, the authors say that female mammals commonly investigate scent marks left by males, and prefer to mate with those who scent mark more frequently.
Clutton-Brock and McAuliffe also say that recent sutides have shown that mammalian females use scent to pick out genetically dissimilar males, which makes sense considering that parents with dissimilar genes in a certain part of the genome tend to produce healthier offspring.
They say that male mammals advertise their genotype through scent, and females pick up the signal and preferentially mate with dissimilar males.
According to them, this ability to sniff out a good genetic match has been found in mice and humans.
Some studies on rodents have even shown that females dislike odours of males who are infected with parasites, and may avoid mating with them.
The authors say that choosing a parasite-free mate may be beneficial to offspring because resistance to parasites is often a genetic trait.
Though the study of olfactory mating cues is still in its infancy, Clutton-Brock and McAuliffe believe that this line of research will continue to reveal much about mammalian mate choice.
"(I)t is possible that in some mammals, males produce olfactory signals that match the elaboration and complexity of the peacock''s tail … or the sedge warbler''s song …," they write.
Their review of evidence for female mate choice has been published in The Quarterly Review of Biology.