Mate-choice copying, or non-independent mate choice, occurs when a female of an animal species copies another fellow female's mate choice. In other words, non-independent mate-choice is when a female's sexual preferences get socially inclined toward those of their fellow females. This behavior is speculated to be one of the driving forces of sexual selection and the evolution of male traits. It is also hypothesized that mate-choice copying can induce speciation due to the selective pressure for certain, preferred male qualities. Moreover, mate-choice copying is one form of social learning in which animals behave differently depending on what they observe in their surrounding environment. In other words, the animals tend to process the social stimuli they receive by observing the behavior of their conspecifics and execute a similar behavior to what they observed. Mate choice copying has been found in a wide variety of different species, including (but not limited to): invertebrates, like the common fruit fly (Drosophila melanogaster); fish, such as guppies (Poecilia reticulata) and ocellated wrasse; birds, like the black grouse; and mammals, such as the Norway rat (Rattus norvegicus) and humans. Most studies have focused on females, but male mate copying has been also found in sailfin mollies (Poecilia latipinna) and humans.
Mechanism
Visual copying
Mate-choice copying requires a highly developed form of social recognition by which the observer (i.e. copier) female recognizes the demonstrator (i.e. chooser) female when mating with a target male and later recognizes the target male to mate with it. Though it might seem simple, observer females actually do not copy the choice of any haphazard, demonstrator female; instead, they copy based on their perception of the demonstrator female's quality. In guppies (Poecilia reticulata) for instance, females are more likely to copy the mate choice of a larger sized fish than to copy the mate choice of a fish of the same or a smaller size. Besides immediate copying based on visual cues, it has been hypothesized that observer females tend to - later on - choose other males with the same qualities as that of the target male the demonstrator mated with. However, it is not known whether this generalization of preference holds true or the observer's inability to discriminate the target male from other similar-looking males accounts for the behavior. Interestingly, in some instances, an observer female tend to copy a demonstrator's female choice only in the same geographical region (i.e. location) it has observed the demonstrator sexually interact with a target male; if the observer female is presented with the same target male in a different location, there is a less likelihood that the observer would execute the same mate choice.
Olfactory copying
In some cases, a direct, visual observation of the sexual interaction between the demonstrator and the target is not necessary; female rodents, for instance, use olfactory stimuli as a reference to whether the target male has been chosen by other females or not. A female rodent may choose to mate with a target male if there is a smell of other females associated with this male’s urine, as an indication that it has been mated with by other fellow females.