The aim of this review is to consider variation in mating preferences
among females. We
define mating preferences as the sensory and behavioural properties that
influence the
propensity of individuals to mate with certain phenotypes. Two properties
of mating
preferences can be distinguished: (1) ‘preference functions’
–
the order with which an
individual ranks prospective mates and (2) ‘choosiness’ –
the effort an individual is prepared
to invest in mate assessment. Patterns of mate choices can be altered
by changing the costs of
choosiness without altering the preference function. We discuss why
it is important to study
variation in female mating behaviour and identify five main areas of
interest: Variation in
mating preferences and costs of choosiness could (1) influence the
rate and direction of
evolution by sexual selection, (2) provide information about the
evolutionary history of female
preferences, (3) help explain inter-specific differences in the
evolution of secondary sexual
characteristics, (4) provide information about the level of benefits
gained from mate choice, (5)
provide information about the underlying mechanisms of mate choice.
Variation in mate
choice could be due to variability in preference functions, degree of
choosiness, or both, and
may arise due to genetic differences, developmental trajectories or
proximate environmental
factors. We review the evidence for genetic variation from genetic
studies of heritability and
also from data on the repeatability of mate-choice decisions (which
can provide information
about the upper limits to heritability). There can be problems in
interpreting patterns of
mate choice in terms of variation in mating preferences and we
illustrate two main points.
First, some factors can lead to mate choice patterns that mimic heritable
variation in
preferences and secondly other factors may obscure heritable preferences.
These factors are
divided into three overlapping classes, environmental, social and the
effect of the female
phenotype. The environmental factors discussed include predation risk
and the costs of
sampling; the social factors discussed include the effect of male–male
interactions as well as
female competition. We review the literature which presents data on how
females sample
males and discuss the number of cues females use. We conclude that
sexual-selection studies
have paid far less attention to variation among females than to
variation among males, and that
there is still much to learn about how females choose males and why
different females make
different choices. We suggest a number of possible lines for future research.