ANIMAL REPRODUCTION Chapter 46

1. ANIMAL REPRODUCTIONChapter 46 Asexual- mitotic Sexual- both mitotic and meiotic divisions Increases genetic variability due to combination of genes from two parents Have variety of phenotypes

2. Asexual reproduction: - invertebrates- fission, budding (colonies) - sea stars, sponges, annelids- fragmentation and regeneration Advantages: -enables isolated animals to reproduce - enables creating lots of offspring in short time - in favorable environments perpetuates successful genotypes precisely

3. Reproductive cycle: - periodic nature allows animals to conserve resources and reproduce when environment is favorable and more energy is available. - controlled by hormones and environment PARTHENOGENESIS: - fresh water crustacean- Daphnia- produce eggs of two types. Haploid adults produce eggs without meiosis - bees, wasps, ants- males (drones) are produced parthenogenetically - among vertebrates, several genera of fishes, amphibians and lizards reproduce by a complex parthenogenesis- doubling of chromosomes after meiosis. Ex. whiptail lizards - no males, one female mimics a male.

4. Hermaphroditism: earth worm - produce double the number of offspring Sequential hermaphroditism: individual reserves its sex during its life time Ex: Caribbean blue head wrasse (reef fishes)- female- first species- largest female becomes male Oysters- male- first species

5. Fertilization: - depends on mechanisms that help sperm meet eggs of the same species. - external- requires moist habitat- prevents gametes from drying, allow sperm to swim to eggs. Timing is crucial to ensure mature sperm encounter ripe egg. - temperature or day length cause a whole population to release gametes at once. - Chemical signals from one individual releasing gametes trigger gamete release in others. - individuals may exhibit specific mating behaviors leading to fertilization of eggs one female by one male – courtship – which allows mate selection and increases probability of successful fertilization – by triggering release of both sperm and eggs.

6. Internal- adaptation to terrestrial life - enables sperm to reach an egg when environment is dry - requires cooperative behavior which leads to copulation - requires sophisticated reproductive systems including copulatory organs and receptacles.

7. Pheromones: - chemical signals released by one organism that influence the physiology and/ or behavior of other individuals of the same species. - they are small volatile or water soluble molecules active in small amounts - function as mate attractants

8. Ensuring the survival of offspring: - produce more offspring than can survive to reproduce - internal fertilization produce fewer zygotes – greater protection of the embryos and parental care of the young. - protection- tough egg shells, development of embryo within the reproductive tract of the mother, parental care of the eggs and offspring - embryo develop within the egg - embryo remain within reproductive tract of the female - marsupials - eutherians (placental) - embryos develop entirely within the uterus

9. Gamete production and delivery: - Gonads are organs that produce gametes in most organisms - polychaete worms (annelids) has simplest system, have separate sexes but no distinct gonads- gametes develop from undifferentiated cells lining the coelom - mature gametes are released from the wall into the coelome - mature gametes shed through excretory openings or swelling mass of eggs may split the body open, killing the parent

10. complex reproductive system include - sets of accessory tubes and glands that carry, nourish, and protect the gametes and developing embryos - Parasitic flatworms- hermaphrodites- most complex in animal kingdom - most insects have separate sexes with complex reproductive systems - in male- sperm develop in a pair of testes and are conveyed along a coiled duct to two seminal vesicles where they are stored. - During mating sperm are ejaculated into female system

11. - In female eggs develop in pair of ovaries, conveyed through ducts into vagina, fertilization occurs - in many species female system includes spermatheca, a sac in which sperm may be stored for a year or more. - in many nonmammalian vertebrates, digestive, excretory and reproductive systems have a common opening – cloaca CONCEPT 46.3 - for SDL

12. Concept 46.4 In humans and other mammals, a complex interplay of hormones regulates gametogenesis - Spermatogenesis- a continuous prolific process - each ejaculation of human male contains 100 to 650 million sperm cells - spermatogenesis occurs in the seminiferous tubules of the testes. - primordial germ cells of embryonic testes differentiate into spermatogonia(2n) – spermatocytes (n) – spermatids (n) – sperm cells (P. No. 975)

13. Oogenesis differs from spermatogenesis in three major ways. - during meiotic division of oogenesis, cytokinesis is unequal- only one cell- secondary oocyte develop into egg; in spermatogenesis all four cells of meiosis develop into sperms - cells from which sperms develop, continue to divide by mitosis throughout males life, which is not the case in human female - Oogenesis has long resting periods, sperms are produced from precursor cells in an uninterrupted sequence

14. The Reproductive Cycles of Females: - secretion of hormones and reproductive events are cyclic in female - males produce sperms continuously Menstrual versus Estrous Cycles: - menstrual (uterine cycle) - in humans and certain other primates - ovulation occurs after endometrium thicken and develop a rich blood supply - in menstrual- endometrium is shed- menstruation

15. Estrous cycle: - endometrium is reabsorbed by uterus and no extensive bleeding - more pronounced behavioral changes - stronger effect of season and climate - most mammals copulate only during period surrounding ovulation- this period of sexual activity- estrus- is the only time the condition of vagina permits mating - estrus= heat Duration of menstrous cycle - human 28 days; estrous- rat 5 days; bears and dogs one cycle per year; elephants several

16. The Human Female Reproductive Cycle: - it’s an integrated cycle involving two organs, uterus and ovaries- controlled by hormones. - gonadotropin- releasing hormone (GnRH)- hypothalamus; FSH and LH- anterior pituitory - concentration of FSH and LH in blood control production of 2 steroid hormones– estrogen and progesterone - ovarian cycle of hormones control uterine cycle of endometrial growth and loss.

17. The Ovarian Cycle: - cycle begins with release of GnRH - stimulates pituitory to release small amount of FSH and LH - they stimulate follicle growth - cells of growing follicles start to make estrogen - several follicle grow, but only one matures others disintegrate - high level of estrogen stimulates secretion of FSH and LH particularly LH- positive feedback - LH induces final maturation of follicles - maturing follicle develops an internal fluid- filled cavity and grows big - follicle and adjacent wall of the ovary rupture releasing secondary oocyte

18. - following ovulation, during luteal phase, LH stimulates the transformation of follicular tissue to form corpus luteum, a glandular structure - corpus luteum secretes progesterone and estrogen - as these concentration increases, produce negative feed back on hypothalamus and pituitary, inhibiting secretion of FSH and LH. - near the end of luteal phase, corpus luteum disintegrates, causing decline in estrogen and progesterone level releasing their inhibitory action on hypothalamus and pituitary- stimulates growth of new follicles, initiating next ovarian cycle.

19. The Uterine( menstrual ) cycle: - hormones secreted by the ovaries estrogen and progestrone have major effect on uterus. - high amount of estrogen secreted by follicles signals endometrium to thicken. - follicular phase of ovarian cycle is coordinated with proliferative phase of uterine cycle. - after ovulation estrogen and progesteron secreted by corpus luteum stimulate continued development and maintenance of endometrium, arteries and endometrial glands. - glands secrete a nutrient fluid that sustain an early embryo. - luteal phase of ovarian cycle is coordinated with secretory phase of uterine cycle.

20. - rapid drop of ovarian hormones when corpus luteum disintegrates results in menstruation- the menstrual flow phase of uterine cycle and beginning of new cycle. - estrogen induces deposition of fat in the breasts and hips, increases water retention, affects calcium metabolism, stimulates breast development and influences female sexual behavior.

21. Menopause: after about 450 cycles, between ages of 46 to 56. ovaries lose their responsiveness to gonadotropins, decline in estrogen production in ovaries

22. Hormonal Control of the Male Reproductive System: - principle sex hormones are androgens- testosterone, steroid hormones produced by the Leydig cells of testes, interstitial cells located near the seminiferous tubules. - primary and secondary characteristics of the male. - primary sex characters are associated with reproductive system, development of vasa differentia and other ducts, external reproductive structures and sperm production - androgens determine behavior in mammals - hormones from anterior pituitary and hypothalamus control androgen secretion and sperm production

23. Pregnancy or gestation - correlates with body size - human-266 days; rodents- 21 days; dogs- 60 days; cows- 270 days; elephants- more than 600 days Conception, Embryonic development, and Birth: -fertilization in oviduct, after 24hrs zygote begins cleavage, after 3-4 days zygote reaches uterus as a ball of cells, after a week- blastocyst - a sphere of cells containing a cavity which implants into the endometrium.

24. - embryo secretes hormones that signal its presence and control mothers reproductive system – human chorionic gonadotropin (HCG)- act like pituitary LH to maintain secretion of progesterone and estrogen by corpus luteum – through first few months of pregnancy - absence of this decline maternal LH due to inhibitory action of pituitary, results in menstruation and loss of embryo.

25. First Trimester: - human gestation – 3 trimesters about 3 months each - First trimester: most radical change both in mother and embryo - endometrium responds to implantation by growing over the blastocyst - differentiation of embryo’s body structures now begins - first 2-4 weeks of development, embryo obtains nutrients from the endometrium, outer layer of blastocyst- trophoblast, grows out and mingles with endometrium, helping to form placenta; umbilical cord

26. - first trimester is the main period of organogenesis - heart begins beating by the 4th week - by the end of 8th week, all major structures of the adult are present in rudimentary form. Now embryo is called fetus. - high level of progesterone in mother initiate changes in her reproductive system; increased mucus in the cervix that forms a protective plug, growth of maternal part of placenta, enlargement of uterus, cessation of ovulation and menstrual cycling, breasts enlarge and are tender.

27. Second Trimester: - fetus grows about 30cm and is very active - mother feel the movement - placenta takes over the production of progesterone Third Trimester: -fetus grows to 3-4 kg in weight and 50 cm length - fetus fills the available space within the embryonic membrane - mothers abdominal organs compress; a complex of local regulators (prostaglandins) and estrogen and Oxytocin induces and regulates labor - parturition; lactation (postnatal care)

28. Parturition is brought about by a series of strong rhythmic uterine contractions. Process of labor has three stages. First- opening up and thinning of cervix Second- expulsion or delivery of baby Third- delivery of placenta. Lactation: prolactin stimulates milk production oxytocin release milk from mammary gland.

29. Contraception – deliberate prevention of pregnancy. Prevent release of mature egg and sperms from the gonads, prevent fertilization, prevent implantation. Modern reproductive Technology – genetic and other congenital disorders. Amniocentesis and chorionic villus sampling – invasive techniques. Ultrasound imaging – noninvasive technique.

30. Solutions for infertility: Assisted Reproductive Technology (ART) In vitro fertilization (IVF) Zygote Intrafallopian Transfer (ZIFT) Gamete Intrafallopian Transfer (GIFT)