Measuring mate preferences: Absolute and comparative evaluation of potential partners

Quantifying the direction and strength of mate preference is essential to improve our understanding of sexual selection. Experimental designs, however, often do not consider how individuals evaluate and compare the available options, which may affect the results significantly. Preferences are often assumed to be absolute, with individuals assigning a fixed, absolute value to a cue or potential partner they encounter. However, individuals may instead also compare the available options, in which case the social context plays an essential role in the preference for each potential partner. Here we investigated the importance of considering the choosers’ evaluation process in mate preference tests. Using a mate preference study on wild great tit, Parus major, heterozygosity, breast stripe size and yellowness as a case study, we tested whether individuals use absolute or comparative mate preferences. We analysed how the perceived average attractiveness and the variation in attractiveness of the group of potential mates affected the measured preference functions. We found that the average attractiveness of the stimulus groups affected the total time individuals spent visiting all stimulus birds, and that the variation in attractiveness within groups affected the measured preference slopes. This indicates that the social context will affect the measured responses to stimulus groups, and that great tits may use both absolute and comparative evaluation. Considering how a study species encounters and evaluates potential mates and how the social environment may affect preferences is essential when choosing an appropriate experimental design to obtain reliable measurements of mate preferences. We therefore strongly advise future studies to consider not only the absolute stimulus trait values, but also the context in which they are presented. The ability to quantify preferences accurately will increase our understanding of mate preferences, mate choice and ultimately sexual selection.