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

3. 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

9. 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

10. 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

11. 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.

12. 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
Powerful:Some 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.

14. 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 mother’s blood supply.

15. 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.

16. Figure 46.6 Reproductive anatomy of a parasitic worm.

17. Human Male Reproductive System
external genitalia
Scrotum
Penis
internal genitalia
Gonads – testes
Accessory glands
Associated ducts

18. Male Reproductive Anatomy
Figure 46.8

19. Male Reproductive Anatomy
Figure 46.8

20. 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).

22. Figure “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.

23. Figure “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.

24. 3 sets of Accessory Glands
These glands add their secretions to the semen:
SEMINAL VESICLES
PROSTATE GLAND
BULBOUREHRAL GLAND

25. 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

26. 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.

27. 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

28. 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.

29. 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.

30. 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.

31. 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.

32. 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)

33. Female Reproductive Anatomy
Figure 46.9

34. Female Reproductive Anatomy
Figure 46.9

35. 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

36. Human Sexual Response
There are four phases in the sexual response cycle in human males & females:
1) Excitement
2) Plateau
3) Orgasm
4) Resolution

37. 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

38. 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

39. 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

40. Human Sexual Response
Resolution reverses responses of earlier phases & completes the cycle
1) Vasocongested organs return to normalcy
2) Muscles relax

41. Spermatogenesis
Spermatogenesis – production of mature sperm cells in the adult male (Figure 42.12)
Continuous process in adult males; 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

43. Figure 46.12 Spermatogenesis

44. Figure 46.12 Spermatogenesis

45. 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

46. Figure 46.11 Structure of a Sperm Cell

47. 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!

48. 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.

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

50. Figure OOGENESIS

51. Figure OOGENESIS

52. 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.

53. 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 female’s birth.

54. 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

55. 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.

56. 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.

57. Figure 46.15 Reproductive Cycle of the human female