T

he first behavioral and physiological re-
sponses of rodents to chemosignals were the preg-
nancy blocking effect for recently inseminated fe-
male mice by strange males (Bruce effect; Bruce 1959; Bruce
and Parrott 1960), and the tendency for grouped females to
remain anestrus (Lee-Boot effect; Andervont 1944; Lee and
Boot 1955, 1956), followed by estrous synchrony when the
females were exposed to a male (Whitten effect 1958, 1959;
Marsden and Bronson 1964). A decade later, Vandenbergh
(1967, 1969) first reported the acceleration of puberty in
laboratory house mice brought about by the presence of a
male or male urine. During the past thirty years, a great
deal of additional information has appeared in the litera-
ture pertaining to chemosignals that influence the timing
of puberty and reproduction in rodents. The house mouse
(Mus musculus) has been the principle subject for these
studies, though information has also been recorded for deer
mice (Peromyscus;Teague and Bradley 1978; Lombardi
and Whitsett 1980), voles (Microtus;Hasler and Nalbanov
1974; Storey and Snow 1990), and gerbils (Meriones;
Ågren 1981). Virtually all of these effects on reproduction
involve urinary chemosignals. Thus except as noted, when
I refer to chemosignals, I am writing about those in urine. I
also should note that where some people might choose the
word pheromoneas a label for these signals, I prefer the less
specific term chemosignal.
These urinary compounds act as primers — that is, they
generally operate via neuroendocrine mechanisms leading to
physiological changes (Macdonald and Brown 1985). This
means that we are dealing with substances in rodent urine
that alter the physiology of any recipients, often accompa-

nied by changes in behavior. Because the most extensive

work to date has been done on house mice, deer mice, and

voles, I have limited my approach here to those taxa.

My review of the urinary chemosignals that accelerate

or delay estrus and puberty in female rodents has several

purposes, which lead to the sections that follow. First, I

will summarize information on the three major categories

of urinary chemosignals accelerating or suppressing ro-

dent reproduction. This summary is, of necessity, brief, as

there are full reviews available and because my main fo-

cus is on rodent societies, not the chemistry or hormonal

mechanisms that underlie these effects (table 9.1 summa-

rizes these effects). The second section covers what is

known about these chemosignal effects under field condi-

tions. Then, I examine the issues surrounding differences

between laboratory-tested phenomena and their possible

occurrence in natural settings. The penultimate section cov-

ers what is known about the ecological and evolutionary

perspectives regarding these reproductive chemosignals. Fi-

nally, I attempt to synthesize the current state of this field

in terms of these investigations with suggestions on pos-

sible future paths of experimentation.

Rodent Chemosignals and Reproduction

Acceleration effects

Chemosignals have primarily two positive effects on repro-

duction. One involves accelerating the onset of puberty in

females via stimulation from male presence or male urine,

Chapter 9Acceleration and Delay

of Reproduction in Rodents

Lee C. Drickamer