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Ch. 46 Animal Reproduction

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Ch. 46 Animal Reproduction Ch. 46 Animal Reproduction 1 Essential Questions: How do animals achieve reproductive success? What diverse mechanisms do animals use to reproduce? 2 Two types of reproduction: 1. Asexual­ no fusion of egg and sperm are involved to make offspring sea anemones budding 3 fission ­ Separation of parent organism into two individuals of equal size budding ­ new individuals forming and then splitting off from other ones gemmules­ in sponges, several types of cells come together in sponge and a protective coat surrounds them fragmentation ­body breaks into pieces and creates new adults, associated with regeneration ex. sponges, cnidarians, tunicates, Linckia sea stars 4 some organisms can do either sexual or asexual depending on conditions ex. Daphnia­female can produce two eggs depending on environment one can be fertilized, one develops by parthenogenesis ­egg can develop without being fertilized (adult would be haploid ­ no meiosis to make gamete) ­asexual under favorable conditions, sexual under unfavorable ­In bees, males (drones) are produced this way male females are produced from fertilized egg queen sterile female worker 5 parthenogenic lizards ­no males in species, all female but can behave as males during breeding season ­eggs undergo doubling in chromosomes from meiosis without fertilization both are females, one on top is behaving as a male every two/three weeks ­ switch sex roles ­related to ovulation 6 male and female behaviors are related to ovulation and hormone levels Ovulation ­ the release of mature eggs 7 2. Sexual reproduction­where gametes (ovum or spermatozoon) fuse to form a zygote (fertilized egg) sperm = motile ovum = nonmotile function ­ increase genetic variability Utethesia ornatrix red beetles 8 Why do animals have reproductive cycles? a. conserve resources and reproduce when have lots of energy b. reproduce when conditions are favorable for offspring survival ­controlled by hormones and environmental factors (temperature, rainfall, length of daylight, lunar cycles) Hermaphroditism­individual with both male and female reproductive organs can fertilize themselves or a mate ex. earthworms 9 sequential hermaphroditism (sex reversal)­ individual reverses its sex during its lifetime protogynous = female first protandrous = male first Wrasses ­ live in harems, if male dies, largest female becomes male, produces sperm instead of eggs Oysters are protoandrous ­ females are larger and lay more eggs 10 What are the mechanisms of sexual reproduction? Fertilization ­ union of egg and sperm external fertilization­eggs and sperm come together in the external environment ­Produce huge numbers of zygotes, but small number survive ­must have moist habitats ­depends on timing 11 ­can have courtship behaviors, trigger release of eggs ex. fish, amphibians ­once one organism has released eggs, may trigger other organisms to also release their eggs *need moist environment ­ why? ­pheromones­chemical signals that influence behavior of others mate attractants ­minute amount is very powerful ex. gypsy moth 12 internal fertilization­ sperm deposited in female reproductive tract where fertilization occurs ­requires specific reproductive structures (copulatory organs and receptacles) ­places for storage and transport of eggs ­usually reproduce fewer offspring, have a better tendency to survive ­greater parental care ­resistant eggshells ­can retain embryo in body for development ­pouch, uterus 13 Parental care giant water bug protects offspring by gluing them to the back of the male he keeps them moist 14 Reproductive systems can be complex or simple parasitic flatworm hermaphrodites complex simple­ polycheate worms: separate sexes but no gonads eggs and sperm develop from undifferentiated cells lining the coelom 15 Honeybee reproductive structures spermatheca­ sac that can store sperm for up to a year cloaca­common opening for digestive, excretory and reproductive systems in nonmammalian vertebrates 16 Human Male reproductive system 17 external organs = a. scrotum ­ holds testes at lower body temp. b. penis­copulatory organ internal organs = a. testes ­ contain seminiferous tubules (sperm form here) ­Leydig cells produce testosterone and androgens b. epididymus­where sperm passes from seminiferous tubules, where sperm mature (20 days)­become motile c. vas deferens­ tube from epididymus during ejaculation where sperm travel 18 d. ejaculatory duct ­ tube from vas deferens to urethra e. urethra­ tube to external body, carries both semen and urine (not at same time) f. glands that add substances along the way 1. seminal vesicles­provide thick, yellow, basic fluid for sperm (60% of semen volume) 2. prostate gland ­ largest semen secreting gland;thin, milky ­contains anticoagulant enzymes and citrate (sperm nutrient) ­problem in men over 40 ­ gets enlarged and cuts off flow of urine, can be cancerous ­test with digital rectal exam 19 3. bulbourethral gland­ pair of glands below prostate ­secretes clear fluid that neutralizes any acid in urethra before semen comes through ­does contain some sperm (bad for withdrawal method of birth control) ­ejaculated semen = 2­5ml of semen (1 tablespoon) 1ml =50­130 million sperm ­prostaglandins in semen thin­ mucus of cervix and help contract uterus ­semen initially coagulates (uterine contractions help it move) and then anticoagulant breaks it apart so sperm can swim 20 penis­made of erectile tissue, fills with blood during erection some animals (walruses, raccoons, rodents) have a baculum­bone inside the penis impotence­inability to maintain an erection causes: alcohol, drugs, emotional problems treatments: penile implants, Viagra(relaxes smooth muscles of blood vessels so blood can enter) glans penis ­ tip of penis prepuce­ foreskin, removed during circumcision 21 anterior view 22 Female Reproductive System 23 external organs a. clitoris­ made of erectile tissue b. labia ­ folds of skin surrounding clitoris and vagina labia minora­slender skin folds labia majora­thick, fatty skin folds, around labia minora internal organs­ a. ovaries­ in abdominal cavity, attached to uterus by mesenteries ­contains follicles (egg cell surrounded by layers of follicle cells, protect and nourish egg) ­woman born with 400,000 follicles, only a few hundred released during life ­produces estrogens­ female sex hormones 24 ovulation­process of egg being expelled from ovary remaining follicle tissue becomes corpus luteum in ovary ­corpus luteum secretes estrogens and progesterone (maintains uterine lining during pregnancy) ­if egg not fertilized, corpus luteum disintegrates b. oviduct­ fallopian tube, has fimbrae that pull egg into oviduct, where fertilization occurs c. uterus­ womb, muscular, where embryo matures endometrium ­ lining of uterus d. cervix­end of uterus that opens into the vagina e. vagina­ birth canal, thin walled tube, receives penis during intercourse f. hymen­membrane that partially covers the vagina 25 Internal organs 26 ovary follicle 27 Ovulation 28 g. mammary glands­present in males and females ­usually only function in women ­low level of estrogen in men prevent breasts form developing 29 How are sperm and eggs made? Spermatogenesis = process of making sperm ­occurs in seminiferous tubules 30 seminiferous tubules sperm 31 sperm structure 32 oogenesis­process of making eggs (ova) FSH ­ follicle stimulating hormone­ stimulates a follicle to grow, makes primary oocyte to complete meiosis I and start meiosis II ­penetration of egg by sperm cell triggers completion of meiosis II 33 oogenesis in ovary 34 How are hormones involved? In male­ ­androgens (testosterone ­ most important) responsible for primary (development of ducts, external anatomy, sperm production) and secondary sex characteristics (deepening of voice, facial/axillary/pubic hair, thickening of muscles) ­sex drive, aggressiveness ­controlled by hypothalamus and anterior pituitary 35 Hormonal control of testes LH­ stimulates FSH ­ acts on Leydig cells to seminiferous make tubules to androgens, increase stimulate sperm spermatogenesis production 36 In females­ two cycles in female mammals a. menstrual cycle­ in humans and primates humans ­ about 28 days b. estrous cycle ­ other mammals (called heat) these mammals only copulate around time of ovulation ­both have ovulation after endometrium thickens ­if no egg fertilized ­in menstruation ­ uterine lining sheds (menstruation) ­in estrous ­ endometrium is reabsorbed by uterus 37 How does the menstrual cycle work? day 1 = first day of menstruation (menstrual flow phase) ­ usually lasts a few days ~ day 5 endometrium begins to regenerate and thicken (1­2 weeks) (proliferative phase) day 14 ­ ovulation day 14­28 ­endometrium continues to thicken, and develops glycogen producing glands (secretory phase) if no egg implants, cycle starts over 38 What about the ovarian cycle? parallels the menstrual cycle follicular stage ­ several follicles start to mature egg enlarges in follicle and coat of follicle thickens (only one continues to grow) ­ends with ovulation ­follicle and ovary wall rupture­releases secondary oocyte ­corpus luteum secretes female hormones during luteal phase cycle starts again with new follicles forming 39 What roles do hormones play in these cycles? Five hormones: a. GnRH­ gonadotropin­releasing hormone ­released by hypothalamus ­regulates FSH and LH release from pituitary ­triggered by follicular phase of ovarian cycle b. FSH ­ follicle stimulating hormone ­stimulates follicle growth ­secreted by anterior pituitary ­gonadotropin c. LH ­ luteinizing hormone ­after ovulation
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