Intro. to Behavioral Endocrinology, Third Edition

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Chapter 3 Sex Differences in Behavior Sex
Determination and Differentiation
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Stereotypes based on trends.
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• Sexual differentiation the developmental
  process leading to becoming a male or a female
• Hormones and environmental experiences guide the
  development of physiological, morphological, and
  behavioral characteristics that are displayed
  later in life.
• Sex Determination and Sex Differentiation
• Chromosomal sex (fertilization)
• Gonadal sex (ovaries or testes)
• Gametic sex (which type of gametes are produced)
• Hormonal sex (estrogen to androgen ratio)
• Morphological sex (differences in body type)
• Behavioral sex (male-typical vs female-typical)
• Specifically in humans
• Gender identity (sex or gender a person feels
  themselves to be)
• Sexual orientation (preference for a sex partner)
• Legal sex (governmentally determined)

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3.3 Levels of sex determination
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ULTIMATE CAUSES OF SEX DIFFERENCES Parthenogenesi
s asexual reproduction in vertebrates they
will be female Polygamous having multiple
mating partners Sexual Selection a subset of
Natural Selection where selection pressures are
based upon the competition for obtaining mating
partners. PROXIMATE CAUSES OF SEX
DIFFERENCES Organizational / activational
hypothesis behavioral sex differences result
from a) differential exposure to hormones that
act early in development to shape the brain and
nervous system guiding these behaviors, and b)
differential exposure to sex steroid hormones
later in life (puberty through adulthood)
activate the neural circuits shaped in (a)
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3.4 Gonadal development of the human embryo
All mammals start out being BIPOTENTIAL they
can develop into either the male or female
sex. The germinal ridge will be able to develop
into either primordial gonad once acted upon by
proteins produced in the body.
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Anlagen a term relating to the dual primordial
tissues relevant to the development of secondary
sexual characteristics. Mullerian duct system
female accessory structures Wollfian duct system
male accessory structures
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3.5 The Müllerian and Wolffian duct systems
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Female accessory sex structures are the default
pattern in mammals. But, due to the anglen
effect (presence) of both systems intitally, in
rare circumstances, both systems can develop in a
single individual This leads to potential
hermaphroditism (now sometimes called
intersexism) is a group of conditions where there
is a discrepancy between the external genitals
and the internal genitals (the testes and
ovaries) or there are present both sexes in the
same individual.
Hermaphroditic Lamb
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Female development is the default, but male
development requires testosterone and MIH
(Mullerian inhibitory hormone). The
testosterone will activate growth of the Wolffian
duct mophology. The MIH will cause regression of
the Mullerian duct morphology.
There are two pathways that occur simultaneously
to guide sexual differentiation. These are
referred to as 1. The masculinization
demasculinization continuum masculinization
induces male traits while demasculinization is
the removal of the potential for male
traits. 2. The feminization defeminization
continuum - feminization induces female traits
and defeminization is the removal of the
potential for female traits.
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3.6 Normal development of the accessory sex
organs
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3.7 Embryonic development of human external
genitalia
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3.8 Normal development of the external genitalia
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3.9 Sexual differentiation in humans
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Aromatase Inhibitors - a class of drugs used
in the treatment of breast cancer and ovarian
cancer in postmenopausal women. Some cancers
require estrogen to grow. Aromatase is an enzyme
that synthesizes estrogen. Aromatase inhibitors
block the synthesis of estrogen. This lowers the
estrogen level, and slows the growth of estrogen
sensitive cancers. There are naturally occurring
aromatase inhibitors in the body.
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Rat Developmental Time Line
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Study of the Pharmacological Agent ATD
Receives Exposure to ATD (an aromatase enzyme
inhibitor)
Pregnant Female Rat
Pups are born having been exposed to the ATD (the
aromatase enzyme inhibitor) developmentally
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Reproductive Behaviors
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3.15 Development of female copulatory behavior
requires active hormonal secretion
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3.16 Ovary and oviduct of a chicken
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3.18 Three types of male tree lizards
Territorial males Sedentary, non-territorial
males Nomadic non-territorial males -
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3.19 Temperature-dependent sex determination in
reptiles
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3.20 Aggression in adult female geckos
In this graph, you need to note The high
temperature range is a low-female population. The
low temperature is an all-female population.
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3.22 Freemartins
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Freemartins - an infertile female mammal which
has masculinized behavior and non-functioning
ovaries. Genetically and externally the animal
is female, but it is sterilized in the womb by
hormones from a male twin, becoming an infertile
partial intersex. Freemartinism is the normal
outcome of mixed-sex twins in all cattle species
that have been studied, and it also occurs
occasionally in other mammals including sheep,
goats and pigs. It is possible this may arise in
dizygotic mixed sex twins in humans as well,
although examples are limited
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3.23 LH profiles of female and male rats
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3.26 Experimental protocol
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3.27 Testosterone is a prohormone
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3.28 Rat pups gestating in utero
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3.29 Rough-and-tumble play behavior is
demasculinized in males by stress in utero
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3.24 Positive feedback and the control of
ovulation
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3.25 The surge and pulse centers of the
hypothalamus