in the laboratory). While some observations may represent
an artifact of laboratory conditions, studies of wild and
laboratory rats in large outdoor enclosures (fig. 32.3) show
that females, which are typically in estrus for only one night,
both solicit /recruit and flee from neighboring males in a
series of mating chases. In high-density environments fe-
males can be followed assiduously by a string of up to
15 males whenever they move outside their burrows (Cal-
houn 1962a; Robitaille and Bovet 1976; Berdoy 1994 for
wild rats; see Berdoy et al. 1995 and also film footage in
Berdoy 2002 for lab rats). Chases are punctuated by mating
in a type of scramble competition (following lordosis by the
female) and /or disappearance of the female inside a burrow
until her next sortie. As mating reduces the probability of
infanticide by the male (Brown 1986; Wolff and Macdonald
2004) the female may benefit from such multiple matings.
By encouraging male-male competition, mating chases may
help the female to assess male fitness independently of male
dominance and exert mate choice by controlling mating op-
portunities (e.g., delaying lordosis or escaping into a bur-
row). Since males have little time to interact with each other
during the pursuit (as they would lose a mating opportu-
nity), even the most dominant males cannot prevent other
males from attempting to participate in mating chases. Thus
although dominant males are more likely to mate than
lower subordinates (confirmed by paternity data; Berdoy,
Stanley, Macdonald, unpublished data for wild rats, see also
Berdoy et al. 1995), they cannot always monopolize access
to the female, particularly as colony size increases (fig. 32.5).
Although anecdotal evidence suggests that wild male rats
can also exert mate choice in some situations (Berdoy, un-
published data), to our knowledge this has not been for-
mally investigated.
Mate choice in feral house mice involves some degree of
selection between partners of the opposite sex that share
overlapping areas of the home range. DNA-based paren-
tal assignments for house mice living in outdoor enclosures
(fig. 32.6) suggest mate selectivity exhibited by members of
both sexes (Robinson 2000; see also Rolland et al. 2004).
A number of factors are associated with mate choice in
wild house mice studied in the laboratory, including odors
(Mainardi, Marson, and Pasquali, 1965; Drickamer et al.
2001), odors associated with the T locus genotypes (Lening-
ton and Egid 1985; Lenington et al. 1988; Egid and Brown
1989; Lenington and Heisler 1991), odors associated with
presence or absence of parasites (Kavaliers and Colwell
1995b), early learning experiences (Mainardi, Marson, and
Pasquali, 1965, Mainardi, Scudo, and Barbieri, 1965), so-Comparative Social Organization and Life History of Rattusand Mus 387Table 32.1 Comparative social systems, behavior, and life-history traits for Musand Rattus
Rattus norvegicus Mus domesticusNo. of species in genus 51–57 37
Distribution Worldwide except in polar regions Worldwide except in polar regions
Common names Common, barn, brown, gray Norway, water, Common house mouse, domestic house mouse
wharf, sewer
Weight (as adults)
Males 250 –500g 17–23g
Females 250 –300g 15 –21g
Food intake (per day) 5 –10g /100g body weight 15g /100g body weight
Heart rate (beat /min) 250 – 450 310 – 840
Size of genome 2.75 Gb 2.6 Gb (Human2.9)
Genes and pseudogenes for olfactory reception c. 2,070 c. 1,510
Sexual maturity 65 –110 days 55 – 80 days
Estrous cycle 4 –5 days if not mated 4 –5 days if not mated
Vaginal plug Yes Yes
Post-partum estrus Yes Yes
Gestation 20 –23 days 19 –21 days
Litter size 6 –10 in wild (variable), up to 20 in laboratory 2 –7, up to 15 in laboratory
Lifespan About 12 –18 months in the wild (3 – 4 years in Up to 18 months in the wild (1.5 –3 years in
laboratory) laboratory)
Mating system Flexible: from polygynous to polygynandrous Flexible: generally polygynous, but also promiscuous
Spatial dispersion pattern Overlapping home ranges (feral) to group Home ranges (feral); territories (commensal)
territories (commensal)
Reaction to novelty Neophobic Neophillic
Use of urinary cues Moderate (limited data?) Extensive
Dispersal Male biased Both sexes
Involvement in spread of disease Extensive Limited data
NOTE: The values of many of the reproductive parameters strongly depend upon environmental factors such as densities and ambient conditions. Gbbillion base pairs.