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Chapter 6: Diversity of Hormone-Behavior Relations in Reproductive Behavior
– red-sided garter snakes and parthenogenetic whiptail lizards
Chapter 7: Hormonal Influences on Courtship Behaviors
– weakly electric fish, clawed frogs, and songbirds
Chapter 8: Hormone-Behavior Relations in the Regulation of Parental Behavior
– rat (as a model system)--species comparisons
– ring dove
Chapter 9: Hormones and Aggressive Behavior
– rat and other rodents (as a model system)--species comparisons
Chapter 10: Neuroendocrinology of the Stress Response
– effects of acute and chronic stress--metabolism, cardiovascular regulation,
digestion, growth, reproduction, immune system, analgesia, learning and memory
Chp 6: Diversity of Hormone-Behavior Relations
variations in reproductive strategies:
– different modes of reproduction
– different reproductive patterns: associated versus dissociated
1) function of sex behavior, 2) distinction between natural selection and sexual
selection, and 3) nature of constraints on reproduction
– additional issues of mate compatability, alternative life-history strategies
– different cues may activate and/or coordinate sex behavior in different species:
chemical signals, environmental signals, social stimuli
red-sided garter snake--example of a dissociated reproductive pattern
parthenogenetic whiptail lizard--example of an associated reproductive pattern
– steroid-mediated activation of female-like and male-like pseudosexual behavior
Different Modes of Reproduction
placement of testes and ovaries:
– gonochoristic: separate male and female individuals; males have testes and
produce sperm, females have ovaries and produce eggs
– hermaphroditic: individuals have both ovaries and testes
– parthenogenetic: all individuals have ovaries
development of fetus:
– viviparity: young develop within the body and are born live; there is an exchange
of nutrients and waste products between mother and fetus
– oviparity: refers to the laying of eggs, from just a few eggs to thousands of eggs;
eggs may have a protective shell covering; young develop apart from the mother
– internal
– external
Reproductive Patterns
Two distinct associated reproductive patterns:
associated reproductive pattern
– mating behavior occurs when gonadal activity takes place
– gonadal activity: development of eggs and sperm and increased sex steroid
hormone secretion
– Ex: rats, hamsters, primates, whiptail lizards
dissociated reproductive pattern
– mating behavior and gonadal activity occur at different times
– Ex: red-sided garter snake
Why do such differences exist in reproductive strategies?
What is the function of sex behavior?
reproduction can be viewed as the single most important element in an
individual’s life--it is the means by which we pass on our genes to future
sex behavior tends to be highly ritualized, stereotyped and characteristic of a
species; as a consequence, sex behavior can be viewed as either synergizing
or isolating reproductive activities
– reproductive synergism: sex behavior evolved to coordinate hormonal, gonadal,
and behavioral events (Ex. estrogen and progesterone in coupling behavioral
estrus with ovulation in the female rat)
– reproductive isolation: sex behavior evolved to prevent interbreeding or to
maintain species boundaries (mating usually does occur within a species)
Why do such differences exist in reproductive strategies?
Role of evolutionary forces:
evolutionary forces can interact often in opposing ways to lead to the
development of specific traits--such as behaviors shown during courtship or
other features like the coloration of males
two primary forces driving the evolution of various traits:
– natural selection: development of traits that are adaptational responses to changes
in the environment; animals that “survive” possess traits that are adaptive to their
– sexual selection: development of traits that arise from interactions among
individuals that compete for mating opportunities
Why do such differences exist in reproductive strategies?
Ex. Development of feathers that cover a bird--”plumage”
how does natural selection and sexual selection affect development of a bird’s
natural selection
sexual selection
bird would be harder
to see and less likely
to be killed by predation
female birds often choose
to mate with males the
have a showier plumage
“adaptive to be drab”
“drab may be lonely”
Why do such differences exist in reproductive strategies?
Reproductive constraints:
environmental constraints:
– environmental conditions that influence when reproductive activity occurs-availability of food, nesting materials, or predation
– events are often “signaled” by changes in day length (photoperiod), but they can
also occur in response to changes in temperature or moisture (rain)
– represents the phenomenon of “seasonal breeding”
developmental and physiological constraints:
– reproductive processes are time-dependent events; for example, development of
mature sperm in most species takes at least 6 weeks; similar time constraint also
exists in females with development of eggs (length of the ovarian cycle)
– during a given season, there may not be enough time for gametes (sperm and eggs)
to mature, adults to mate and for the young to develop before adverse
environmental conditions occur
Why do such differences exist in reproductive strategies?
Reproductive constraints:
(developmental and physiological constraints)
– scenario #1: in some species, sex behavior occurs immediately following a
period of hibernation; because cold temperatures inhibit the production of gametes
and gonadal steroids, sperm are produced during the summer, and are stored
during the winter and available for mating in the spring following hibernation (ex.,
red-sided garter snake)
– scenario #2: in other species, see phenomenon of embryonic diapause-implantation of the embryo is delayed; in this scenario, gametes have matured,
mating has taken place and an egg has been fertilized, but implantation of the
embryo and development of the embryo in utero has been delayed; embryonic
diapause can last for as little as one week to as long as several years; at the end of
diapause, the embryo implants and normal development resumes (ex., some
species of bears, kangaroos)
Why do such differences exist in reproductive strategies?
Reproductive constraints:
evolutionary constraints:
– concept #1: evolutionary history, or phylogeny, of a species can predispose the
evolution of certain “traits” but not others
– closely related species that live in different environments can have similar modes
of reproduction
– concept #2: different species that face similar environmental demands may
develop similarities in certain “traits” (phenomenon of natural selection)
– distantly related species living in a similar environment can develop similar modes
of reproduction
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--importance of mate compatibility
in some species, choosing a mate can affect reproductive success
– Ex. female canvasback duck
selects own
will lay eggs
“reproductive success”
randomly paired
with male
will not lay eggs
“reproductive failure”
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--alternative life-history strategies
definition: individuals within a given population can adopt different
morphologies, physiologies and behaviors
Ex. bluegill sunfish: (3 types of males)
– territorial male: large colorful male that defends territories and solicits females to
release eggs so that he can fertilize the eggs
– sneaker males: small males that “sneak” matings; when the large territorial male
is preoccuied, a sneaker male can rush in and release sperm to fertilize eggs
– female mimics: large drab males that look like females; these female mimics hang
around a territorial male that is courting a female; when the female releases her
eggs, the female mimic can rush in and relese sperm to fertilize eggs
– alternative life-history strategies are heritable: sneakers grow up into female
mimics, while territorial males produce young that are large and brightly colored
– androgen concentrations vary: territorial males > sneaker or female-mimics
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--cues that activate/coordinate behavior
previously we considered the following relationship:
– increases in gonadal steroids (and gamete production)-->increases in the display of
sex behavior (associated reproductive pattern)
however, other “cues” or factors may be important in “activating” or
“coordinating” the display of sex behavior
– chemical signals
– environmental signals
– social stimuli (social systems)
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--cues that activate/coordinate behavior
Chemical signals:
hormones: providing “internal communication” within an individual
pheromones: providing “external communication between individuals
– this distinction is becoming “blurred”: 1) hormones can act as pheromones (Ex.
goldfish), and 2) hormones do stimulate the production of pheromones
female pheromones can stimulate male sex behavior
male pheromones can also stimulate sex behavior in females:
– Ex. male pig: he will breathe into a female pig’s face (air current will carry a male
pheromone--”sex attractant” to female); if female is receptive, then the sex attractant will
cause her to stand immobile, arching her back in lordosis and allowing the boar to mount
– profitable science--companies manufacture an aerosol preparation containing androgen
metabolites called “Boar Mate” used to immobilize sows for artificial insemination
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--cues that activate/coordinate behavior
Environmental signals:
Ex. Desert-dwelling zebra finch
– considered an “opportunistic breeder”--engages in mating behavior when the opportunity
presents itself (right time=rain fall)
– desert-dwelling zebra finch lives in deserts of western Australia, in which rain occurs only
once in a 3-year period
– throughout each year, the male and female zebra finches possess high levels of gonadal
steroids and mature gametes
– however, mating occurs only when rain falls-- 10 minutes after the start of rain, mating
takes place, within 4 hours nests are built, within one week eggs are laid
– rain is the cue activating mating behavior; gonadal steroids (androgens, estrogen,
progesterone) play a permissive role by preparing the individual for reproduction once
rain has fallen
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--cues that activate/coordinate behavior
Social stimuli:
the social system of a number of species of birds are associated with different
endocrine profiles and different male-female and male-young interactions
– monogamous species: one male bird pairs with one female
– polygamous species: one male pairs with two or more females
– levels of parental care: to what extent does the male help in raising the young?
– levels of aggression: degree of male-male interaction (low--moderate--high)
– levels of testosterone: low--high, transient--prolonged
Why do such differences exist in reproductive strategies?
Diversity in hormone-behavior relations--cues that activate/coordinate behavior
Social stimuli:
basic relationships--focusing on the male:
– polygamous species--high degree of male-male interactions--low degree of parental care-high levels of testosterone that are prolonged
– monogamous species--low degree of male-male interactions--high degree of parental
care--low levels of testosterone that are transient
key point: different social systems are associated with different degrees of behavior
(male-male interactions and male-young interactions) and with different patterns of
testosterone secretion
Associated and Dissociated Reproductive Patterns
Dissociated reproductive pattern: Ex. red-sided garter snake
courtship and copulatory behaviors are not dependent on a rise in gonadal steroids,
nor on the presence of high levels of gonadal steroids
– sex behavior and gonadal activity are dissociated
– gonadal steroids are thought to “prime” the nervous system to respond to other cues that
activate mating behavior
Associated reproductive pattern: Ex. parthenogenetic whiptail lizard
increases in estrogen (occur with follicular development) activate the display of
female-like pseudosexual behavior and stimulate ovulation
subsequent increases in progesterone activate the display of male-like pseudosexual
– sex behavior and gonadal activity are associated
– gonadal steroids are thought to “activate” the nervous system to activate behavior
Dissociated Reproductive Pattern
Red-sided garter snake:
found in northern US and Canada
hibernate 9 months out of the year, emerging from hibernation late Spring
males emerge ‘en masse’, while the females emerge singly
as each female emerges from hibernation, a group of males will surround the female
forming a “mating ball”
female secretes an attractant pheromone on her skin that stimulates “chin-rubbing” from
– chin rubbing is the male’s courtship response and involves the male moving up and down
the back of the female rapidly and repeatedly with his chin while flicking his tongue on
the female’s back (contacts pheromone)
– eventually one male in the “mating ball” will copulate with the female--the male will
align himself along the female and will intromit a hemipenis into the female’s cloaca
Dissociated Reproductive Pattern
Red-sided garter snake:
– note: male lizards and snakes have 2 penises; when they mate they use only one, hence
the term--hemipenis
– note: cloaca is a Latin term for “sewer”; it refers to the fact that all vertebrates but
mammals have a single urogenital opening once mating takes place, the female becomes
once mating has occurred, the female becomes unreceptive and leaves the area; she
will gestate and the young will be born at the end of the summer
males will engage in sex behavior for about 3-4 weeks following emergence from
following courtship and copulation, both males and females will shift their
behavioral responses exclusively to feeding
Dissociated Reproductive Pattern
How does the behavior of male and female garter snakes reflect changes in
development of the gonads and secretion of gonadal steroids?
– at emergence from hibernation, the level of gonadal steroids are low, the size of gonads
are small, and the formation of mature gametes is low (true for males and females)
– at emergence, both males and females readily show sex behavior
– thus, sex behavior can occur independent of a rise or high levels of gonadal steroids; even
more striking evidence--(males) you can remove the pituitary, testes, and adrenal glands
in the fall before hibernation, the male snakes still show normal sex behavior in spring
– in males, sperm used to impregnate females was produced previous summer; during the
summer, there is an increase in androgen levels and production of mature sperm--events
that occur during the feeding cycle; sperm are then stored through winter months and used
for mating in the spring
– in females, mating stimulates a neuroendocrine reflex that will stimulate ovarian growth
and ovulation (6 weeks later); sperm received at the time of mating will fertilize the eggs;
these events also occur during the feeding cycle
Dissociated Reproductive Pattern
Red-sided garter snake:
If gonadal steroids are not important for activating sex behavior, what stimuli are?
– critical stimulus for stimulating male courtship and mating: period of low-temperature
dormancy followed by increasing temperatures
– critical stimulus for terminating male courtship and mating: a shift from mating to
What role do gonadal steroids play in reproductive processes of this species?
– gonadal steroids are not important in activating sex behavior in males or females
– gonadal steroids are important in spermatogenesis (males) and ovulation (females)
– gonadal steroids also play an important role in “priming” the nervous system to respond
to cues that will activate sex behavior--increases in gonadal steroids must occur at some
point during the year (usually occurs during summer with feeding)
– if you castrate the male and follow his behavior for several years, you will see a steady
decline in his courtship behavior; administration of testosterone can reverse effect
– exact mechanism? unclear
Associated Reproductive Pattern
Whiptail Lizards:
gonochoristic species--C. inornatus
– male and female members
– males show male-typical sex behavior, while females show female-typical sex behaviors
– [Figure 6.12] male-typical sex behavior: male will approach and investigate the female,
and if she is receptive, he will mount her; this often involves the male gripping a portion
of the skin on her back or next; the male will begin to maneuver his tail beneath the
female’s tail, attempting to appose their cloacal regions; this involves shifting his jaw grip
from the female’s nect to her pelvic region--posture called the “doughnut”; during mating,
the male will insert one of two hemipenes into the female’s cloaca and maintain that
posture for 5 to 10 minutes, after which the male dismounts and then leaves
parthenogenetic species--C. uniparens
– consists entirely of females
– parthenogenetic females show both male-like pseudosexual behavior and female-like
pseudosexual behavior
Associated Reproductive Pattern
Parthenogenetic Whiptail Lizards:
the whiptail lizards are seasonal breeders
– 3-4 ovarian cycles per season, each lasting approximately 3-4 weeks
– as follicles develop, there is a rise in estrogen that has 2 effects: 1) to activate femalelike pseudosexual behavior--female will be receptive to mounting from other females, and
2) peak of estrogen is associated with ovulation
– the rise in estrogen is followed by rise in progesterone which has the opposite behavioral
effect--to activate male-like pseudosexual behavior--female mounts other receptive
females and engages in male-like behaviors (like the doughnut); this occurs even though
the parthenogen has no hemipenis and intromission does not take place
– after ovulation, the ova (typically 1-3 eggs) will pass into the oviduct where shell
deposition occurs; shelled eggs are usually laid 7 to 10 days after ovulation
Associated Reproductive Pattern
Parthenogenetic Whiptail Lizards:
What role do gonadal steroids play in reproductive processes of this species?
– gonadal steroids are important in activating pseudosexual behavior
– estrogen activates female-like pseudosexual behavior, in addition to stimulating ovulation
– progesterone activates male-like pseudosexual behavior
– ovariectomy leads to a loss of female-like and male-like pseudosexual behaviors, and the
administration of estrogen restores activation of female-like pseudosexual behavior, while
the administration of progesterone restores activation of male-like pseudosexual behavior
Why should these parthenogens engage in pseudosexual behavior?
– the behavior is not necessary for reproduction as these individuals reproduce by
parthenogenesis (“virgin birth”)--eggs are not fertilized by sperm
– pseudosexual behavior increases reproductive success--parthenogens are more likely to
lay eggs and will lay more clutches if they engage in this behavior
Associated Reproductive Pattern
Parthenogenetic Whiptail Lizards:
Conservation of neural structures mediating male and female sex behavior:
Gonochoristic species:
– MPOA is larger in males than females-->importance of MPOA for male sex behavior
– VMH is larger in females than males-->importance of VMH for female sex behavior
Parthenogenetic species:
– the brain of the parthenogens looks like the brains of females in the gonochoristic species:
small MPOA and a large VMH--somewhat surprising finding!
– in ovariectomized females, estrogen implants into the VMH can activate sexual
– in ovariectomized females, progesterone implants into the MPOA can activate mounting
– in the parthenogen, the MPOA is not masculinized in size but in function and can respond
to the progesterone surge to activate male-like pseudosexual behavior