Sexual Motivation 49Figure 2.4 A male and female blue gourami.the association of a single female with multiple males. These
polygamous strategies are common in species that distrib-
ute the burden of parental care unequally. These mating
strategies often influence sexual motivation. Monogamous
animals very often display biparental care of offspring, and
sexual learning does not typically influence male competition
in these species. Accordingly, sexual motivation in monoga-
mous species is relatively similar across sexes. In contrast,
species that display intense male competition typically adopt
polygamy, and sexual learning and motivation vary greatly
across sex (Domjan & Hollis, 1988).
Cues That Signal Reproductive Opportunity
Many species display cues that connote reproductive avail-
ability. These cues frequently are shaped by the genotype of
the animal. For example, in rodent species olfaction is the
primary sensory modality; rodents smell much better than
they see. Accordingly, olfactory cues such as pheromones
often signal a sexual opportunity in rodent species (Pfaff &
Pfaffman, 1969). In contrast, birds see better than they smell,
and visual cues ordinarily provide mating signals (Domjan &
Hall, 1986). Females of species that undergo estrus often dis-
play overt cues that signal reproductive availability. For ex-
ample, in primate species, such as the chimpanzee, females
display swelling of the vaginal lips during estrus, and this cue
signals reproductive availability (Mook, 1987).
Sign Stimuli
In some species the appearance of a member of the oppo-
site gender is the dominant cue for a mating opportunity.
However, often the essential cue can be reduced to an ele-
ment or component of the mating partner. These components,
called sign stimuli (Tinbergen, 1951), are sufficient to elicit
sexual behaviors. For example, male chickens attempt to
copulate with models of the torso of female conspecifics
(Carbaugh, Schein, & Hale, 1962), and male quails attempt to
mate with models including a female quail’s head and neck
(Domjan, Lyons, North, & Bruell, 1986). Thus, mere compo-
nents of a whole animal are sufficient cues to elicit reproduc-
tive behavior.
Learned Cues
Learning certainly contributes to the recognition of repro-
ductive opportunity. For instance, male blue gourami fish
(Trichogaster trichopterus) normally display aggressive
territorial behavior. These fish compete with other males for
nest sites, and they attack intruders because the control of
territory confers reproductive advantage. This aggressive
tendency is so pronounced that males often spoil mating
opportunities by mistakenly attacking female gouramis.
However, male gouramis can learn to anticipate the approach
of a female gourami when a cue reliably precedes her ap-
pearance during conditioning sessions (Hollis, Cadieux,
& Colbert, 1989; Hollis et al., 1997). As a result of such
Pavlovian conditioning, the cue acts as a CS that signals the
appearance of the female. Males trained with this contin-
gency both display less aggression toward females and
spawn more offspring (Hollis et al., 1997; Figure 2.3). Thus,
learning contributes to the recognition of a reproductive op-
portunity. Moreover, it contributes to evolutionary fitness by
increasing fecundity. This result by Hollis et al. stands as the
single most direct and unequivocal evidence that Pavlovian
conditioning, indeed any form of learning, has a direct influ-
ence on evolutionary success (Figure 2.4).
Learning also contributes to the mating success of male
Japanese quails (Coturnix japonica). For instance, neutral
cues previously paired with a sexual encounter elicit CRs,025050075010001250MEAN NUMBER OF FRYFigure 2.3 The mean number of offspring
hatched in the Pavlovian-paired (black bar) and
unpaired (hatched bar) groups. Fry were
counted six days after spawning (adapted from
Hollis et al., 1997).