maintain high-quality territories (Wolff, R. J., 1985; Rich
and Hurst 1998). Dominant males may also be better able
to protect females from sexual harassment and protect their
offspring from being killed by conspecific males (Agrell et al.
1998). Thus, cohabiting and mating with a dominant male
may result in a direct benefit to the female through increased
survival of her offspring.
Although female montane voles do not show a preference
for males with high dominance rank compared to males
with low dominance rank, at least in the laboratory (Sha-
piro and Dewsbury 1986), the results from the majority of
lab studies on rodents consistently show that females prefer
to socialize with and mate with dominant males (table 4.1).
Also, in the field, yellow-toothed cavies (Galea musteloides)
preferred larger males (Hohoff et al. 2003). If body size is
positively correlated with dominance, these studies indicate
that the social preference for dominant males by females
observed in many lab studies may also be occurring in na-
ture as well.
Spatial ability
Females may prefer males with good spatial ability to those
with poor spatial ability because females that mate with
males that have better spatial ability are likely to gain indi-
rect fitness benefits for their male offspring. Because spa-
tial ability is heritable (Upchurch and Wehner 1988, 1989;
Okasanen et al. 1999), the male offspring of sires with good
spatial ability may be better able to locate mates and would
be favored by female choice. These indirect benefits might
be particularly important during periods of low population
density, when mates become more difficult to locate. Spa-
tial ability is also likely to be important for females (and
consequently all their offspring), for locating and returning
to nests.
Genetic compatibility
Most good genes hypotheses assume that all females in a
population benefit from mating with the same males. How-
ever, breeding studies indicate that the degree of related-
ness between males and females can affect female reproduc-
tive success (Bateson 1983; Ralls et al. 1986). Thus some
opposite-sex conspecifics would be better mates than oth-
ers. Molecular evidence reinforces the hypothesis that the
best mate varies among females within a population (Zeh
and Zeh 1996). The genetic compatibility hypothesis dif-
fers from good genes hypotheses in that the fitness conse-
quences of mating depend on the “fit” between the female’s
and male’s genes, as opposed to just being a function of
the male’s genetic quality (Zeh and Zeh 1996). The good
genes hypotheses predict that all females that mate with
the same male achieve the same reproductive consequences,
but the genetic compatibility hypotheses predict that fe-
male reproductive success depends on the mate. Three ways
in which genetic compatibility could be important are dis-
cussed below.Inbreeding
Detrimental effects of incest have been demonstrated in a
number of mammals (Wainwright 1980; Ralls et al. 1986).
When paired with a closely related male, females may
not mate (McGuire and Getz 1981), produce fewer litters
(Krackow and Matuschak 1991), and have smaller litters at
weaning (Barnard and Fitzsimons 1988; Keane 1990b) or
smaller pups at weaning (Keane 1990b). Outbreeding also
has costs, including breakup of coadapted gene complexes,
loss of rare genes, and loss or suppression of genes required
for adaptation to a local habitat (Bateson 1983). Females
may also avoid mating with an unfamiliar individual be-
cause it might be very different genetically.
Females showed social preferences for nonsiblings as
compared to siblings in only 3 of 9 studies (table 4.1). Al-
though Keane (1990b) demonstrated female preferences for
cousins as compared to siblings in captive white-footed mice
(Peromyscus leucopus), this preference has not been found
in laboratory or wild house mice (Barnard and Fitzsimons
1988; Krackow and Matuschak 1991). In most studies,
cousins have not been included in the stimulus set, so we
know very little about preference or lack of preference for
individuals of intermediate degrees of relatedness.Intragenomic conflict and self-promoting elements
One of the major factors involved in genetic incompatibil-
ity between mates is segregation distorters, which act to
increase their proportional representation in gametes, that
is, the ability to transmit themselves at the expense of the
wild type homolog from heterozygous males (Silver 1993).
The t-locus in house mice is one example of a well-studied
segregation disorder (Lenington 1991; Silver 1993; and see
Carroll and Potts, chap. 5, this volume). About 25% of
wild house mice are heterozygous for the t-haplotype (i.e.,
/t) (Lenington, Franks, and Williams 1988). Most t-
haplotypes carry recessive lethal factors, which result in the
death of embryos homozygous for the t-allele prior to birth.
In addition, there are also semilethal haplotypes in wild
populations (Lenington, Egid, and Williams 1988). Females
heterozygous at the t-locus preferentially mate with homo-
zygous wild-type males and thus avoid producing inviable
t/toffspring (table 4.1; see also Carroll and Potts, chap. 5,
this volume).Immunologically based compatibility
The highly polymorphic major histocompatibility complex
(MHC) genes control immunological recognition of self /Reproductive Strategies in Female Rodents 47