S
exual selectioninvolves two components: male-
male competition (intrasexual selection) and female
choice of mates (epigamic selection; Darwin 1871).
However, studies of sexual selection have historically fo-
cused on males (e.g., aggression and dominance). The pre-
vailing paradigm assumed that males were “eager” to mate
whereas females were “comparatively passive,” only mat-
ing as much as necessary to achieve fertilization of ova.
In reality, females often do more than just accept the win-
ner of male-male contests or accept the most attractive or
least objectionable opposite-sex conspecific from a number
of candidates (Hrdy 1981, 1986; Andersson 1994; Lifjeld
et al. 1994). An alternative to the assumption of female pas-
sivity is that females may actively solicit copulations with
preferred males, seek copulations with more than one male,
and employ a variety of behavioral strategies to attract the
attention of preferred sexual partners (cf. Rosenqvist and
Berglund 1992; Birkhead and Møller 1993). Thus female
mate choice warrants more attention than it received in the
earlier days of animal behavior studies (Cronin 1991).
If females are active participants in sexual interactions,
differences in quality among potential mates may favor fe-
male selectivity (Trivers 1972). Numerous hypotheses have
been proposed to explain mate choice by females. Females
may choose partners based on heritable aspects of mat-
ing success and viability or on nongenetic benefits, such as
a high-quality territory or parental care (Andersson 1994).
As a result of female selectivity, males have evolved certain
sexual traits or signals, which serve as indicators of male
quality.
Previous studies have also ignored or deemphasized the
potential for female control over processes occurring within
their own bodies after mating. Interest in mechanisms reg-
ulating reproduction has provided new information on fe-
male reproductive anatomy and physiology, and suggests
that there is potential for postcopulatory choice by females
(i.e., cryptic female choice). Because fertilization is inter-
nal, female rodents may have partial or complete control
over whether a particular male will sire some or all of their
offspring.
After mating, females must successfully rear offspring,
which involves providing sufficient nutrition for pre- and
post-natal growth, warmth and protection from potentially
infanticidal conspecifics or predators. In many rodent spe-
cies, females will only breed if they have a home range that
excludes competitors (Bujalska 1973; Boonstra and Rodd
1983). In most of these species, females actively defend their
territories. Territorial defense has been suggested to prevent
infanticide (Sherman 1980a, 1981b; Wolff 1993b; Wolff
and Peterson 1998), or provide exclusive use of limited re-
sources (Ostfeld 1985, 1990; Ims 1987a). In some species,
females may disperse and bequeath the natal territory to
their offspring (Harris and Murie 1984; Price and Boutin
1993).
Although many female rodents can successfully rear off-
spring by themselves, in other species females nest with
males or live in extended family or kin groups (FitzGerald
and Madison 1983; Getz et al. 1993; Burland et al. 2004;
Ebensperger et al. 2004). In these groups, conspecifics par-
ticipate in care of offspring born to the breeding female