Mate choice

If you are interested in the diversity of life, you can not ignore the plethora of striking behaviors and morphologies that have been the handiwork of sexual selection. The peacock’s tail is one emblematic result, but a compendium would also include: the songs of birds, frogs, and crickets, the brilliant colors of fishes and corals, the complex odors of moths and mustelids, and the differences between the human sexes that have led many to embrace the suggestion that men are from Mars and women are from Venus. That is what sexual selection does. How does it do it? Sexual selection occurs when some individuals in the population have more offspring because they are better at getting mates. This often happens because one sex selects mates from a pool in which members of the opposite sex vary in their attractiveness, a process known as ‘mate choice’. Mate choice can be exercised by both sexes, but it is usually the female’s domain and her influence on males is apparent as they evolve elaborate traits that make them more attractive. Despite some recent cries to the contrary, sexual selection does occur and there is overwhelming evidence for the efficacy of mate choice. Many studies, for example, have manipulated male traits experimentally and demonstrated that this treatment influences the male’s probability of being chosen as a mate in a manner predicted by patterns of male variation and mating success in nature (Figure 1). Knowing that mate choice occurs, however, does not mean we understand the rules that govern it, and uncovering these rules is a formidable challenge. ‘Choice’ is a behavioral outcome that results from females using internal rules to assess males, Primer but our assumptions about the basic properties of those rules have rarely been tested. Also, the well-controlled experiments that are necessary to document choice are often characterized by experimental controls that insulate the study subjects from problems they would encounter in the wild. For example, in the laboratory, stimuli are often presented to females continuously and are often binary. Both of these conditions could reduce the importance of memory and attention, which are critical when choosing among a larger number of simultaneously signaling animals. Internal factors of the female — such as her reproductive state — are usually standardized, and external factors — such as noise and predation risk — are usually minimized. Yet, these factors are known to skew mating decisions. In addition, when females apply a preference function to the task of assessing males, several factors can introduce error to the process, such that the female assigns preference values incorrectly and makes the ‘wrong choice’. Furthermore, not all females are the same, and variation among female preferences adds another level of complexity to understanding mate choice rules. Here, we review some of the factors that influence how the female’s inherent preferences are translated into mate choice. We sort these points into three categories: uncertainty about basic properties of the preference function, factors that introduce variability to these preferences and factors that influence the ability to accurately assess potential mates.