Animal Reproduction

1
Animal Reproduction

• Nancy G. Morris
• Volunteer State Community College
• Campbell, Chapter 46

2
Animal Reproduction

• Asexual reproduction is the creation of new
  individuals whose genes all come from one parent
  without the fusion of egg and sperm.
• Sexual Reproduction is the creation of offspring
  by the fusion of haploid gametes to form a zygote
  (fertilized egg), which is diploid.

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Animal Reproduction

• Sexual Reproduction is the creation of offspring
  by the fusion of haploid gametes to form a zygote
  (fertilized egg), which is diploid.
• Gametes are formed by meiosis.
• Female gamete egg or ovum
• relatively large nonmotile
• Male gamete spermatozoon
• generally, a small motile cell

4
Diversity in asexual reproduction

• Fission
• Budding
• Gemmules
• Fragmentation
• Regeneration

5
Advantages of asexual reproduction

• Animals in isolation will not die out
• Rapid ideal for colonizing a a habitat quickly
• Most advantageous in stable, favorable
  environments because it perpetuates successful
  genotypes precisely

6
Control of Reproductive Cycles

• Hormones
• Environmental cues
• (temperature, rainfall, day length)
• Lunar cycles

7
Variation in reproductive patterns

• Parthenogenesis
• Daphnia, aphids, rotifers, social insects,
  whiptail lizards
• Hermaphroditism
• Tapeworms, earthworms, sessile, burrowing animals

8
Variation in reproductive patterns

• Sequential hermaphroditism
• individual reverses its sex during its lifetime
• either protogynous female first
• or protandrous male first
• Reef fishes called wrasse p.915

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Mechanisms of Sexual Reproduction

• Fertilization union of egg and sperm
• External fertilization eggs shed by the female
  fertilized by the male
• Internal fertilization requires cooperative
  behavior

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External Fertilization

• Requires environment where zygotes can develop
  without heat or stress
• Many amphibians fishes use specific mating
  behaviors resulting in one male fertilizing the
  eggs of one female

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External Fertilization

• Courtship behavior is a trigger for release of
  gametes. There are two effects
• 1) the probability of successful fertilization is
  increased
• 2) the choice of mates may be somewhat selective.

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Phermones

• Chemical signals produced by one organism that
  influence the behavior of another organism of the
  same species
• Small, volatile or water-soluble molecules
• Active in very small amounts (like hormones)
• Many function to attract mates
• PowerfulSome insects can detect a mile away
• Gypsy moth attracts in concentration as low as 1
  molecule in 107 molecules of other gases in the
  air

13
Survival

• All species produce more offspring than survive
  to reproduce.
• Species with internal fertilization produce fewer
  zygotes but provide more parental protection than
  species with external fertilization.
• Species with external fertilization usually
  produce enormous numbers of zygotes, but the
  number that survive and develop further is small.

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Survival

• Amniotic eggs have calcium protein shells which
  resist water loss physical damage.
• Eggs of amphibians fishes have only a
  gelatinous coat.
• Marsupials retain the embryos rather than
  secreting a shells around them.
• Placental mammals develop entirely within the
  uterus, nourished by the mothers blood supply.

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Evolution of complex reproductive
systems

• Most complex reproductive system in the animal
  kingdom is in the parasitic flatworms
  (Platyhelminthes). Figure 46.6
• The least complex system is found in the
  polychaete worms (Annelida).
• In some species, the female possesses a
  spermatheca, a sac in which sperm are stored for
  a year or more.
• In many nonmammaliam vertebrates, excretory,
  digestive, and reproductive products are
  eliminated through a cloaca.

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Figure 46.6Reproductive anatomy of a
parasitic worm.
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Human Male Reproductive System

• external genitalia
• Scrotum
• Penis
• internal genitalia
• Gonads testes
• Accessory glands
• Associated ducts

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Male Reproductive Anatomy
Figure 46.8
19
Male Reproductive Anatomy
Figure 46.8
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Male Reproductive Process

• Testes develop in abdomen descend into the
  scrotum just before birth.
• Sperm cannot develop at normal body temperature.
• Placing the testes outside the abdominal cavity
  in the scrotum, reduces the temperature by 20 C.

21
Male Reproductive Process

• Penis serves as the copulatory organ
• Ejaculatory duct joins the urethra and opens at
  tip of the penis.
• Movement of semen through the urethra results in
  the sperm being deposited directly in the female
  system (internal fertilization).

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Figure 42.8 Parts

• Testes are comprised of highly coiled tubes
  surrounded by layers of connective tissue.
• Seminiferous tubules- the tubes where the sperm
  form.
• Interstitial cells are scattered between the
  tubules produce testosterone androgens.
• Sperm pass from the seminiferous tubules to the
  epididymis.

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Figure 42.8 Parts

• Epididymis contains coiled tubes where sperm are
  stored mature- gain motility
• Sperm are forced through the vas deferens to the
  ejaculatory duct.
• Ejaculatory duct forms by the joining of two vas
  deferens ducts and the duct from the seminal
  vesicles. It opens into the urethra.
• Penis is composed of 3 cylinders of spongy
  erectile tissue that fill with blood during
  erection.

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3 sets of Accessory Glands

• These glands add their secretions to the semen
• SEMINAL VESICLES
• PROSTATE GLAND
• BULBOUREHRAL GLAND

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3 sets of Accessory Glands

• SEMINAL VESICLES- secrete fluid containing
• 1) mucus
• 2) amino acids
• causes semen to coagulate after deposited in
  female
• 3) fructose
• energy
• 4) prostaglandins
• stimulate uterine contractions to help move semen
  to the uterus

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3 sets of Accessory Glands

• PROSTATE GLAND secretes a thin, milky alkaline
  fluid containing enzymes to balance acidity in
  vagina.
• BULBOUREHRAL GLAND secretes viscous fluid
  before sperm ejaculation which may neutralize any
  acid urine remaining in urethra.

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Female Human Reproductive Anatomy

• More complicated than male
• Structures not only for production of gametes,
  but also to house the embryo and fetus.
• INTERNAL
• Gonads Ovaries associated ducts
• EXTERNAL
• Clitoris two sets of labia that surround it
  and the vaginal opening

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Female Human Reproductive Anatomy

• Ovaries located in the abdominal cavity
• Each ovary contains many follicles (one egg cell
  surrounded by follicle cells, which nourish and
  protect the developing egg.)
• All EGGS are formed prior to birth!
• Follicle cells produce estrogens.
• Starting at puberty and continuing until
  menopause, one follicle matures and releases its
  egg cell during each menstrual cycle.

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Female Human Reproductive Anatomy

• During ovulation, the egg is expelled from the
  follicle. The follicular tissue becomes the
  corpus luteum, which secretes progesterone
  (maintains uterine lining) and additional
  estrogen.
• If the egg is not fertilized, the corpus luteum
  degenerates.
• The egg is release into the abdominal cavity
  near the opening of the oviduct.
• Cilia lining the oviduct draw the egg in and
  convey it to the uterus.

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Female Human Reproductive Anatomy

• The uterus (or womb) is a thick muscular organ 7
  cm long and 5 cm wide.
• The inner uterine lining, the endometrium, is
  richly supplied with blood vessels.

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Female Human Reproductive Anatomy

• The remaining reproductive structures are
• Cervix neck of the uterus opening into the
  vagina
• Vagina thin walled chamber the repository for
  semen during copulation forms the birth canal.
• The hymen, a vascularized membrane, usually
  covers the vaginal opening from birth until
  ruptured by vigorous physical activity or sexual
  intercourse.

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Female Human Reproductive Anatomy

• Labia minora -slender skin folds bordering the
  vestibule
• Labia majora a pair of thick, fatty ridges
  enclosing protecting the labia minora
• Clitoris bulb of erectile tissue covered by a
  prepuce (small hood of skin)

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Female Reproductive Anatomy
Figure 46.9
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Female Reproductive Anatomy
Figure 46.9
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Human Sexual Response

• Although variable, human sexual behavior is based
  in a common physiological pattern, the sexual
  response cycle.
• Physiological reactions which predominate in both
  sexes can be divided into two types
• 1) Vasocongestion increased blood flow through
  the arteries of that tissue
• 2) Myotonia both smooth skeletal muscles may
  show sustained or rhythmic contractions

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Human Sexual Response

• There are four phases in the sexual response
  cycle in human males females

• 1) Excitement
• 2) Plateau
• 3) Orgasm
• 4) Resolution

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Human Sexual Response

• Excitement
  the penis vagina are prepared for coitus
  (sexual intercourse)
• 1) Vasocongestion of the penis clitoris
  enlargement of testes, labia, breasts
• 2) Vaginal lubrication myotonia occur

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Human Sexual Response

• Plateau
  breathing heart rates increase from
  stimulation of the autonomic nervous system
• 1) vagina depresses to receive the sperm
• 2) the outer third becomes vasocongested, the
  inner third slightly expands the uterus elevates

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Human Sexual Response
Orgasm
is characterized by rhythmic, involuntary
contractions in the reproductive systems of both
sexes

• Male
• Emission forcing the semen into the urethra due
  to contraction of the glands ducts of the
  reproductive system
• Ejaculation - expels the semen due to contraction
  of the urethra
• Female
• Contraction of the uterus outer vagina

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Human Sexual Response

• Resolution
  reverses responses of earlier phases
  completes the cycle
• 1) Vasocongested organs return to normalcy
• 2) Muscles relax

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Spermatogenesis

• Spermatogenesis production of mature sperm
  cells in the adult male (Figure 42.12)
• Continuous process in adult males 250- 400
  million sperm cells per ejaculate
• Occurs in the seminiferous tubules
• Begins with differentiation of germ cells (2N)
  into spermatogonia (2N) in the embryonic testes
• Maturation of spermatogonia begins at puberty
  and continues until death

42
Spermatogenesis

• Primary spermatocytes undergo meiosis I to
  produce two haploid secondary spermatocytes
• Each secondary spermatocyte undergoes meiosis II
  to form two spermatids
• Result is 4 haploid spermatids through meiotic
  division
• Each spermatid becomes attached to a Sertoli
  cell from which it receives nutrients
• All four spermatids differentiate into mature
  spermatozoa

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Figure 46.12Spermatogenesis
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Figure 46.12Spermatogenesis
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Spermatozoon

• Thick head contains the haploid nucleus
• Acrosome at tip contains enzymes to aid in egg
  penetration
• Many mitochondria are present behind the head to
  provide ATP for flagellum movement

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Figure 46.11 Structure of a Sperm Cell
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Oogenesis

• Oogenesis is the development of ova (mature
  unfertilized eggs) Figure 42.13
• Begins at puberty and ends at menopause
• Begins in embryo -- germ cell undergoes mitotic
  divisions to produce a diploid oogonium.
• By birth, oogonia exist as primary oocytes, thus
  ALL potential ova at present at the time of
  birth!

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Oogenesis

• Between birth puberty, primary oocytes enlarge
  their surrounding follicles grow.
• They replicate their DNA and enter prophase I
  remain there until activated by hormones one
  per month beginning at puberty.
• After puberty, during each ovarian cycle, FSH
  stimulates a follicle to enlarge the primary
  oocyte inside completes meiosis I.
• The result is a haploid secondary oocyte and
  the first polar body.

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Oogenesis

• Meiosis then stops again
• LH triggers ovulation the secondary oocyte is
  released from the follicle.
• If a sperm cell penetrates the secondary
  oocytes membrane, meiosis II will occur and the
  second polar body will separate form the ovum.
• This completes oogenesis.

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Figure 46.13 OOGENESIS
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Figure 46.13 OOGENESIS
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Important Differences

• 1) In spermatogenesis, all four products of
  meiosis become spermatozoa, whereas
• 1) In oogenesis, unequal cytokinesis occurring in
  meiosis I II results in most of the cytoplasm
  being distributed to a single daughter cell which
  will form the ovum. The other cells (polar
  bodies) will degenerate.

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Important Differences

• 2) Spermatogenesis is a continuous process
  throughout reproductive life of the male, whereas
• 2) in oogenesis, all potential ova are present
  as primary oocytes in the ovaries at the time of
  the females birth.

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Important Differences

• 3) Spermatogenesis occurs continuously, whereas
• 3) in oogenesis, long resting periods occur
  between the formation of the initial steps and
  final production of the ovum

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Mammalian female cycles

• Estrous cycles occur in non-primate mammals.
• Ovulation occurs after the endometrium thickens
  is vascularized
• If pregnancy does not occur, the endometrium is
  reabsorbed by the uterus.
• Involves pronounced behavioral changes
  seasonal climate changes effect the estrous
  cycle more than the menstrual cycle.
• ESTRUS is the period of sexual activity
  surrounding ovulation is the only time most
  mammals will copulate. The length frequency
  varies widely among species.

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Mammalian female cycles

• Menstrual cycles occur in humans and many other
  primates.
• Ovulation occurs after the endometrium thickens
  is vascularized
• If pregnancy does not occur, the endometrium is
  shed form the uterus through the cervix the
  uterus.
• The term menstrual cycle refers to changes that
  occur in the uterus during the reproductive
  cycle. (Figure 46.15)
• In humans, cycle is on average 28 days.

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Figure 46.15Reproductive Cycle of
the human female