Chapter 46 Animal Reproduction
“Individuals are transient. A population transcends finite life spans only by reproduction” Biology, Seventh Edition Neil Campbell and Jane Reece
The diverse reproductive mechanisms in the animal kingdom
•Asexual reproduction new individuals whose genes all come from one parent -without the fusion of egg and sperm. •Sexual reproduction the creation of offspring by the fusion of haploid gametes to form a zygote (fertilized egg) -diploid. -Ovum: female gamete - usually large and nonmotile. -Spermatozoon: male gamete - usually s mall and motile. sexual reproduction may enhance the reproducti ve success
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Mechanisms of Asexual Reproduction z Fission the separation of a parent into two or more individuals of approximately equal size
襟疣海葵 (Anthopleura elegantissima).
Mechanisms of Asexual Reproduction zBudding New individuals arise from outgrowths of existing ones. -Certain tunicat es (被囊動物) and cnidarians -The offspring may either detach or remain joined
水螅 (hydra)
Polyp Stony Corals
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Mechanisms of Asexual Reproduction zFragmentati on and regeneration -The breaking of the body into several pieces, some or all of which develop into complete adults.
Advantages of Asexual Reproduction -Enables animals living in isolation -Creat e numerous offspring in a short amount of time Would be the most advantageous in stable, favorable environments
Some animals alternate the reproduction between asexual and sexual modes.
aphids
rotifer
Daphnia (crustacean)
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Parthenogenesis 單性 (孤雌) 生殖
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• Parthenogenesis the process by which an unfertilized egg develops into haploid adult. • Parthenogenesis plays a role in the social organization of species of bees and ants. ÆMale honeybees are haploid and female honeybees are diploid. • Several genera of fishes, am phibians, and lizards produce by a com plex form of parthenogenesis that produces diploid zygotes.
The complex form of parthenogenesis Some vertebrates use parthenogenesis to produces diploid zygotes eg: several genera of fishes, amphibians, and lizards
-By doubling of chromosomes after meiosis
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eg: about 15 species of whiptail lizards (genus Cnemidophorus ) reproduce exclusively by parthenogenesis. - !There are no males in these species!
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Ovary size
Figure 46. 3 Sexual behavior in parthenogenetic lizards
Hormones
Ovulation Estrogen
Ovulation Progesterone
May evol ve from species havi ng two sexes
Time Behavior
Æstill require certain sexual stimuli for maximu m reproductive success
Female- Malelike like
Female- Malelike like
Î Y chromosome disappe are d
The End of Men? As Y Chromosome Shrinks, End of Men Pondered
http://www.npr.org/templates/story /story.php?story Id=4225769
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Hermaphroditism 雌雄同體 Each individual has both male and female reproductive systems eg. Sessile, burro wing穴居 animals or parasites (derived from Hermes and Aphrodite, a Greek god and goddess).
Hermaphroditus and Salmacis www.imagesonline.bl.uk/britishlibrary/
Hermaphroditism 雌雄同體 zAlthough some hermaphrodites fertilize themselves, most mate with a member of the same species.
Advantages: zMore adaptable to the environments zEach hermaphroditic mating can result in t wice as many offspring as from a male–female mat ing
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Hermaphroditism 雌雄同體 z Sequential hermaphroditism an individual reverses its sex during its lifetime. • Female–first species: eg: Caribbean bluehead wrasse The largest (usually the oldest) individuals change from female to male
•Male–first species: eg: sedentary animals, such as oysters
The mechanisms of fertilization The union of sperm and egg zExternal fertilization: Eggs are released by the female into a wet environment, where they are fertilized by the male.
zInternal fertilization: Sperm are deposited in the female reproductive tract, and fertilization occurs within the tract.
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The mechanisms of fertilization zExternal fertilization: •A moist habitat -prevent gametes fro m drying out -allow the sperm to swim to the eggs. •Ti ming and environmental cues ensure that mature sperm encounter ripe eggs eg. Specific mat ing (courtship) behaviors Temperature or day length
Eggs
•Produce enormous numbers of zygotes -Ensuring the survival of offspring
The mechanisms of fertilization zInternal fertilization: An adaptation to terrestrial life that enables sperm to reach an egg when the environment is dry
•Advantages • Produces fewer zygotes -energy saving • Greater protection of the embryos
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Parental care of offspring
giant water bug eg: tough eggshells, embryo develops within the reproductive tract… -parental care of the young
Parental care of offspring –may occur in some external-fertilized animals
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Complex reproductive systems have evolved in many animal phyla zAnimals must have systems that produce gametes • The simplest systems: systems polychaete (多剛毛的) worms (phylum Annelida), ~ 15000 species The eggs and sperm develop fro m undifferentiated cells lin ing the body wall (coelo m).
z The most complex reproductive systems Contain many sets of accessory tubes and glands that carry, nourish, and protect the gametes and the developing embryos -eg. parasitic flatwo rms (hermaphrodites) （生殖孔）Genital pore Male organs: 4
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Seminal vesicle
Sperm duct (vas deferens)
(Digestive tract) Female organs: 3 Uterus Yolk gland Yolk duct 2 Oviduct 1 Ovar y
2 Vas efferens 1 Testis
Seminal receptacle
(excretory pore)
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Insect reproductive anatomy 1 Ovar y Accessory gland 4 Ejaculatory duct 1 Testis
2 Vas deferens
2 Oviduct Spermatheca受精囊 3 Vagina
5 Penis
3 Seminal vesicle (a) Male honeybee. Sperm form in the testes, pass through the sperm duct ( vas deferens), and are stored in the seminal vesicle. The male ejaculates sperm along with flui d from the accessory glands. (Males of some species of insects and other arthropods have appendages called claspers that grasp the female during copulation.)
Accessory gland (b) Female honeybee. Eggs develop i n the ovaries and then pass through the oviducts and into the vagina. A pair of accessory glands (onl y one is shown) add protective secretions to the eggs in the vagina. After mating, sperm are stored in the spermathec a, a s ac connected to the vagina by a short duct.
Vertebrate reproductive systems zDifferences between vertebrate reproductive systems •The cloaca 泄殖腔 Existed in many non-mammalian vertebrates The digestive, excretory, and reproductive systems have a common opening to the outside Probably present in the ancestors of all vertebrates.
•Mammals have separate opening for the digestive, excretory and reproductive systems
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Vertebrate reproductive systems zDifferences between vertebrate reproductive systems •The uterus Existed in most vertebrates - Most vertebrates is divided into two chambers except: mammals that produce only a few young birds snakes
•The copul atory organs in male Many nonmammalian vertebrates do not have a well–developed penis and simp ly turn the cloaca inside out to ejaculate
Human reproductive organs (female) Contain the epithelium with cilia Ovaries
Oviduct
Follicles Uterus
Uterine wall Endometrium Corpus luteum
Cervix
Vagina
•A wo man is born with about 400,000 follicles. •Only several hundred of wh ich will release eggs during a female’s reproductive years.
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Reproductive anatomy of the human female Uterus Oviduct
(Urinary bladder) (Pubic bone)
Ovar y
(Rectum) Cervix Vagina
Urethra Shaft Prepuce Clitoris Glans
Bartholin’s gland
Labia minora
Vaginal opening
Labia majora
Clitoris: consists of erectile tissue; richly supplied with nerve endings Bartholin’s glands 巴氏腺 : secrete mucus into the vestibule
Reproductive anatomy of the human male
seminiferous tubules Seminal vesicle (behind bladder)
(Urinary bladder)
Prostate gland Urethra Scrotum Glans penis
Bulbourethral 尿道球腺 gland Erectile tissue of penis Vas deferens Epididymis Testis
Testis: consist of seminiferous tubules Epid idy mis: p laces for sperm storage and maturation; ~6m tube length Bulbourethral g land: secrete mucus that neutralizes any acidic urine in the urethra
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Reproductive anatomy of the human male
(Urinary bladder)
Seminal vesicle (Rectum)
(Pubic bone) Erectile tissue of penis
Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland
Urethra Vas deferens Epididymis Testis Scrotum
Glans penis Prepuce
Penis: composed of three cylinders of spongy erectile tissue勃起組織 derived fro m modified veins and capillaries. Rodents, raccoons, walruses, whales, and several other mammals also possess a baculum (陰莖骨)
Reproductive anatomy of the human male
(Urinary bladder)
Seminal vesicle (Rectum)
(Pubic bone) Erectile tissue of penis
Vas deferens Ejaculatory duct Prostate gland Bulbourethral gland
Urethra Vas deferens Epididymis Testis Scrotum
Glans penis Prepuce
•Production of normal sperm cannot occur at the body temperatures of most mammals, except some animals with lower body temperature Scrotum: about 2°C below that in the abdominal cavity •Rodents can drawn back the testes in non-breeding seasons
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Gametogenesis zbased on meiosis, but details differ in females and males.
Oogenesis • the development of mature ova (egg cells) Spermatogenesis •the production of mature sperm cells
Oogenesis
Ovary-specific stem cells
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Spermatogenesis
Testis-specific stem cells
•Each ejaculation of a human male contains 100 to 650 million sperm cells,
Oogenesis and Spermatogenesis differ in three major ways Unequal cytokinesis
1. In the meiotic divisions of oogenesis, cytokinesis is unequal Æ polar bodies are excluded and degenerated In spermatogenesis, all four products of meiosis develop into mature sperm Ability of mitosis 2. Female: Oogonia stop mitosis in female emb ryonic stage Male: Spermatogonia continue to divide by mitosis throughout the male’s life Resting in the cell cycle 3. Oogenesis has long “resting” periods Spermatogenesis produces mature sperm in an uninterrupted sequence
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Sperm structure: • Head Haploid nucleus. Acrosome頂體 - Contains enzymes that help penetrate to the egg. •
Mi ddle piece mitochondria, provide ATP
•
Tail
Flagellum
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Acromosomal reaction
Zona pellucida
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Hormone regulations regulat ions of mammalian reproducti reproductive ve cycle zThe Reproducti ve Cycles of Females - Menstrual Versus Estrous Cycles menstrual cycles: Hu mans and certain other primates estrous cycles 動情周期 : other mammals -(estrus: fro m the Latin oestrus, frenzy, passion)
•In common •The lin ing of the uterus start to thicken with a rich blood supply - preparing for the possible imp lantation of an embryo. •Ovulation occurs
•Difference 1: the fate of the uterine lining if not pregnant Menstrual cycles: the endometriu m is shed from the uterus in a bleeding called menstruati on. Estrous cycles: the endometriu m is reabs orbed by the uterus, and no extensive bleeding occurs. •Difference 2: behavioral changes pronounced behavioral changes during estrous cycles than during menstrual cycles Sex reception Estrous cycles: animals copulate only during the period surrounding ovulation Menstrual cycles: receptive to sexual activity throughout their menstrual cycle •Difference 3: effects of season and cli mate stronger effects of season and climate on estrous cycles.
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The female reproductive cycle z An integrated cycle involving two organs, the ovaries and the uterus. Ovarian cycle : the cyclic events that occur in the ovaries Menstrual cycle : refers specifically to the changes in the uterus (uterine cycle); controlled by the ovarian cycle
zBoth control by tropic hormone systems secreted from the brain Hypothalamus
Pituitary
Ovary
gonadotropin–releasing hormone (GnRH)
Gonadotropins (FSH, LH)
Uterus
estrogen progesterone Ovarian cycle
Menstrual cycle
Figure 46.13 The reproductive cycle of the human female GnRH FS H LH Es trogen Progesterone
(a) Control by hypothalamus Hypothalamus 1 GnRH Anterior pituitary
Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen Inhibited by low levels of estrogen
FSH LH 2 (b) Pituitary gonadotropins 6 in blood
triggering the shooting up of FSH and LH LH levels by acting on the FSH hypothalamus FSH and LH stimulate LH surge triggers 3 The low levels of to increase ti s follicle to grow ovulation estrogen inhibit (c) Ovarian cycle 7 8 output of GnRH. secretion of the pituitary hormones, keeping the levels of FSH and LH Corpus Degenerating Growing follicle Mature low. luteum corpus luteum As relatively the levels of follicle Ovulation Luteal phase progesterone and Follicular phase Progesterone and estrogen rise, the Estrogen secreted 4 estrogen secreted combination of these by growing follicle in by corpus luteum hormones exerts increasing amounts Peak causes (d) Ovarian hormones negative feedback on 5 LH surge in blood the hypothalamus 10 and pituitary, Progesterone 9 Estrogen inhibiting the secretion Progesterone and estroEstrogen level of LH and FSH. gen promote thickening very low of endometrium (e) Uterine (menstrual) cycle Endometrium
Menstrual flow phaseProliferative phase 0 5 14 15 10 Days
Three phases
Secretory phase 20 25
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Menopause (更年期 (更年期)) of female zHappen after about 450 cycles (usually ~ ages 46 and 54) zReasons: •The ovaries lose their responsiveness to gonadotropins from the pituitary (FSH and LH) •Results from a decline in estrogen production by the ovary. zUnusual phenomenon in vertebrates In most species, females as well as males retain their reproductive capacity throughout life. •Exp lanation using evolutionary views: increased elder wo man’s fitness allo wed her to provide better care for her children
Hormonal Control of the Male Reproductive System z Controlled by andorgens (mainly testosterone) z Andorgens are secreted by the Leydig cells (mainly) z Functions of andorgens •Primary sex characteristics: •Development of the vasa deferentia and other ducts • Development of the external reproductive structures
•Sperm production.
•Secondary sex characteristics: Deep voice Muscle growth Sexual behaviors, eg: aggressiveness; singing in birds and frogs
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Hormonal control of the testes Stimuli from other areas in the brain Hypothalamus
GnRH from the hypothalamus regulates FSH and LH release from the anterior pituitar y.
Anterior pituitary Negative feedback
FSH acts on the Sertoli cells of the seminiferous tubules, promoting spermatogenesis.
LH stimulates the Leydig cells to make testosterone, which in turn stimulates sperm produc tion.
Leydig cells make testosterone Sertoli cells
Spermatogenesis
Primary and secondar y sex characteristics Testis
Conce ption, Pregnancy, Embryonic Development, and Birth zConcepti on (Fertilizat ion of an egg by a sperm)Î Impl antation 3 Cleavage (cell division) begins in the oviduct as the embr yo is moved toward the uterus (24 hs) by peristalsis and the movements of cilia.
(3nd-4th days)
Ovar y
2 Fertilization occurs. A sperm enters the ooc yte; meiosis of the oocyte finishes; and the nuclei of the ovum and sperm fuse, producing a zygote.
4 Cleavage continues. By the ti me the embryo reaches the uterus, it is a ball of cells. It floats in the uterus for several days, nourished by endometrial secretions. It becomes a blastocyst.
(7th days)
囊胚
5 The blastoc yst implants in the endometrium about 7 days after conception.
Uterus
1 Ovulation releases a secondar y oocyte, which enters the oviduct.
Endometrium
(a) From ovulation to implantation Endometrium
Inner cell mass
Cavity
Blastocyst
Trophoblast
(b) Implantation of blastocyst
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Formation of the zygote and early postfertilization events Conception (Fertilization of an egg by a sperm, stage 2) 3 Cleavage (cell division) begins in the oviduct as the embr yo is moved toward the uterus by peristalsis and the movements of cilia.
4 Cleavage continues. By the ti me the embryo reaches the uterus, it is a ball of cells. It floats in the uterus for several days, nourished by endometrial secretions. It becomes a blastoc yst.
Ovar y
2 Fertilization occurs. A sperm enters the ooc yte; meiosis of the oocyte finishes; and the nuclei of the ovum and sperm fuse, producing a zygote.
5 The blastoc yst implants in the endometrium about 7 days after conception.
Uterus
1 Ovulation releases a secondar y oocyte, which enters the oviduct. (a) From ovulation to implantation Endometrium
Endometrium
Inner cell mass
Cavity
Trophoblast
Blastocyst
(b) Implantation of blastocyst
Figure 46.13 The reproductive cycle of the human female (a) Control by hypothalamus Hypothalamus 1 GnRH Anterior pituitary
Inhibited by combination of estrogen and progesterone Stimulated by high levels of estrogen Inhibited by low levels of estrogen
FSH LH 2 (b) Pituitary gonadotropins 6 in blood
LH FSH 3 FSH and LH stimulate LH surge triggers follicle to grow ovulation (c) Ovarian cycle 7 8 Corpus Degenerating Growing follicle Mature luteum corpus luteum follicle Ovulation Luteal phase Follicular phase Progesterone and Estrogen secreted 4 estrogen secreted by growing follicle in by corpus luteum increasing amounts Peak causes (d) Ovarian hormones 5 LH surge in blood Estrogen
Progesterone
Estrogen level very low (e) Uterine (menstrual) cycle
hCG
Endometrium
Menstrual flow phaseProliferative phase 0 5 14 15 10 Days
Three phases
As the levels of progesterone and estrogen rise, the combination of these hormones exerts negative feedback on the hypothalamus 10 and pituitary, 9 inhibiting the secretion Progesterone and estroof LH and FSH. gen promote thickening of endometrium
Secretory phase 20 25
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hCG LH
zhuman chorionic gonadotropin ( HCG) •HCG acts like LH to maintain secretion of progesterone and estrogens by the corpus luteum through the first few months of pregnancy. •Levels of HCG in the maternal blood are so high that some is excreted in the urine, where it can be detected in pregnancy tests.
zPregnancy (gestation): the condition of carrying one or more embryos in the uterus •The average days of pregnancy Hu man (266 days; 38 weeks); Rodents (21 days); Dogs (~60 days); Cows (~270 days); Elephants (> 600 days)
•Human pregnancy can be conveniently divided into three trimesters
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z First Trimester of pregnancy (size ~5cm) 1. Formation of the placenta during the first 2 to 4 weeks Outer layer of the blastocyst, called the trophobl ast, grows out and mixes with the endometriu m
z Placenta function: Diffusion of material between maternal and embryonic circulat ions eg. nutrients, respiratory gases, metabolic wastes zPlacenta size: Can weigh close to 1 kg in the late pregnancy
Fetus blood directions Maternal arteries
Maternal veins
Placenta
Maternal portion of placenta Umbilical cord Chorionic villus containing fetal capillaries Maternal blood pools Uterus
Fetal portion of placenta (chorion)
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Fetal arteriole Fetal venule Umbilical cord
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1 4
Umbilical arteries Umbilical vein
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z First Trimester of pregnancy (size ~5cm) z 2. mai n period of org anogenesis, The fourth week: The heart begins beating, but can’t be detected until the end of the first trimester. End of the first trimester: All the other major organs are present Most sensitive to such threats as radiation and drugs
(a) 5 weeks. Limb buds, eyes, the heart, the liver, and rudiments of all other organs have started to develop in the embryo, which is only about 1 cm long.
z Second Trimester of pregnancy (size ~30cm) •The early part of the second trimester: feel movements •The placenta completely takes over the production of progesterone •The uterus grows enough and become obvious.
(b) 14 weeks. Growth and development of the offspring, now called a fetus, continue during the second trimester. T his fetus is about 6 cm long.
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z Third Trimester of pregnancy (size ~50cm; 33 -4 kg) Fetus activity decrease as the space limitation Mother’s abdominal organs become compressed Î frequent urination, digestive blockages, and strain in the back muscles.
(c) 20 weeks. By the end of the second trimester (at 24 weeks), the fetus grows to about 30 cm in length.
Mechanism of labor 陣痛分娩 z Hormone regulated (not fully understood)
from ovaries
Oxytocin from fetus and mother's posterior pituitary
Induces oxytocin receptors on uterus Stimulates uterus to contract
Positive feedbac k
Estrogen
Stimulates placenta to make Prostaglandins
Stimulate more contractions of uterus
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Modern Reproductive Technology zPurposes diagnose many genetic diseases and other congenital disorders zInvasi ve techni ques Amniocentesis (羊膜穿剌術) and chorionic villus (絨毛膜) samp ling
Modern Reproductive Technology z Noninvasi ve procedures ultrasound imaging to detect fetal condition
zHormone therapy and in vitro fertilization Purposes: help with a number of infert ility problems. assisted reproducti ve technol ogy (ART). surgically remov ing eggs Æ Fertilizing Æ returning to body • in vitro fertilization (IVF) •ZIFT (zygote intrafallopian transfer) •GIFT (gamete intrafallopian transfer)
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