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Animal Reproduction

Cellula e Cellula Biological Benefits of Asex • Cells divide to reproduce I. Asexual Reproduction 1. Eliminate problem to locate, court, & offspring from single parent retain suitable mate. (daughter cells have identical DNA as parent cell) 2. Much greater population growth rate.

II. Sexual Reproduction offspring Budding Hydra 3. Avoid “cost of meiosis”: from union of egg and – genetic representation in later generations (combine some DNA from both isn't reduced by half each time parent cells 4. Preserve gene pool adapted to local → genetically varied offspring ) conditions.

Sperm cells and

Asexual Reproduction: Asexual Reproduction: Fission / Budding Clonal Fragmentation • Divide in two • Adult breaks apart; pieces form new adults – protozoans, polyps, flatworms – Gemmules of sponges – Fissiparity in echinoderms

Asexual Reproduction: Parthenogenesis Parthenogenesis • Derived parthenogenesis & • Eggs develop w/o fertilization pseudocopulation – some rotifers, , crustaceans, , & lizards. in whiptail lizards • Obligatory – Whiptails • Facultative – Snakes – Aphids

Whiptails — Cnemidophorus uniparens

Heyer 1 Animal Reproduction

Sex = Meiosis + Syngamy Sexual Reproduction Produces Genetic Variation

• Variation arises from

I. Independent chromosome assortment in meiosis II. Crossing-over between homologous chromosomes in meiosis III. Random process of fertilization

Meiosis: Syngamy: 2n ! 1n 1n ! 2n Diploid ! haploid Haploid ! diploid

The Evolutionary Enigma of Sexual Reproduction Biological Benefits of Sex • Sexual reproduction produces fewer reproductive offspring than asexual reproduction, a so-called reproductive handicap 1. Reinforcement of social structure 2. Variability in face of changing environment. Asexual reproduction Sexual reproduction Generation 1 – why buy four lottery tickets w/ the same number Female Female on them? Relative benefits: Support from organisms both Generation 2 asexual in constant & sexual in changing Male environments Generation 3 – aphids have wingless female clones & winged male & female dispersers – ciliates conjugate if environment is deteriorating Generation 4

Figure 23.16

Monoecious sex: both sexes in one individual (Hermaphroditic) Dioecious: separate sexes • Advantageous if limited mobility and sperm dispersal and/or low population density – Guarantee that any member of your species encountered is the “right” sex • Gametic sex determination • Self fertilization still provides some genetic variation – Heterogenic male determination (XY male; XX female) • Or prevent self-fertilization by – Heterogenic female determination (ZW female; ZZ male) § copulation – Haplotypic male determination (XO male; XX female) sponges, flatworms, snails, earthworms § producing sperm or eggs at different times • Environmental determination – Temperature – Intrauterine position

Simultaneous sperm exchange

Heyer 2 Animal Reproduction

External Fertilization External Fertilization — Broadcast Spawning

• Esp. sessile marine inverts • Only in water – - larval mortality is very high. — gametes must be moist. • Release in response to: • Gamete release is – smell of other gametes synchronized. – environmental cues • Palolo Worm – Broadcast spawning • Make buoyant to – Courtship spawning concentrate at surface

External Fertilization Internal Fertilization — Courtship Spawning • Terrestrial forms need internal fertilization so gametes don't dry out • In fish & some marine inverts • Decreases energy spent on sperm production • Ensure large amounts of your sperm are on target • Behaviors stimulate gamete release • Allow females to store concentrated sperm • Produce fewer eggs but add in parental care – it’s a balance of investment strategy • Spermatophores are sperm packages – spiders, frogs • Adpressed Cloacas – birds lack intromittive organs

Copulatory Organs Copulatory organs of sharks &

• Legs – squids & spiders • Claspers – sharks & rays • Penises – insects – turtles, crocodiles – lizards, snakes w/ hemipenes – marsupials w/ bifurcated penis – eutherian mammals w/ penis & bacculum. • Vertebrate copulatory organs. (a) Clasper of dogfish (Squalus). • Glans penis of (b) opossum, (c) ram, (d) bull, (e) short-tailed shrew, (f) man, (g) Echidna.

Heyer 3 Animal Reproduction

Hemipenes Copulatory Organs

Python hemipenes Critical alignment copulang cornsnakes

Damselfly penises

Estrogens & Ovulation Ovulation triggered by a sharp rise in estrogens Oviparity: Egg Laying • Yolk w/ protein & fats Insert fig. 20.35 – Energetically very expensive! • Protective Coating – jelly-like substance in aquatic forms – earthworm's cocoon – horny egg case of some sharks Estrogen rise and female reproductive behavior (Estrus) – calcareous or leathery shell • Proceptive behavior: “flirting” — advertising sexual state of birds & reptiles • Receptive behavior: “in heat” – attentive to male courting • Conceptive behavior: accepting copulation

Ovoviviparity: Retain Eggs Internally Continued Parental Investment • Nest guarding • Brooding • “Mobile nest” • Resource allocation Dogfish shark “candle” from – Less energy spent on • Keeping eggs warmer female’s egg production speeds development. – Use energy insuring development of fewer – Cold climate reptiles offspring retain eggs rather than – Often, females spend laying them. energy on egg production – Males do the parental care

“Candle” opened to show small embryos with large yolk

Heyer 4 Animal Reproduction

Viviparity: Maternal Nourishment Viviparity: Maternal Nourishment • Maternal Nourishment • Maternal Nourishment – Spreads maternal energy demand over longer time period – Spreads maternal energy demand over longer time period – Allows embryo to grow beyond original egg size – Allows embryo to grow beyond original egg size • Placenta connects embryo to mother for nutrition & • Aplacental viviparity: intra-uterine feeding. gas exchange. – “Uterine milk” – rays – Placental mammals – Oophagy (& adelphophagy!) – mackerel sharks – Reptiles (rattlesnakes Gill filaments for & sea snakes) absorbing uterine – Fish (sharks, guppies, milk in river stingray pup. (Later, will drink surf perch) by bucchal pumping.)

Swollen bellies of oophagous porbeagle shark pups

Delayed Fertilization & Aphids — a little bit of everything! Delayed Implantation 1. .Asexual (parthenogenic) viviparity – And “telescoping generations” (born pregnant!) 2. Seasonally alternating with a dioecious generation having: Sexual oviparity

3–9 mo. Delayed implantation

7 mo. Delayed Fertilization

• How the reproductive cycles of four mammals native to Britain are related to the winter. – Figure 1.2 Reproductive cycles of (a) hedgehog, (b) red deer, (c) badger and (d) noctule bat, in relation to the winter. • Parthenogenic live birth (all females) – M=mating; F=fertilization of the egg(s); G=gestation; B=birth. • And the baby being born already has a baby!

Aphids — a little bit of everything! Photoperiod & Seasonal Sex

• Aphid yearly cycles

• Figure 1.1 Critical photoperiodic responses in two species: transition from sexual to asexual reproduction in the vetch aphid (Megoura viciae) and testicular development in the white- crowned sparrow (Zonotrichia leucophrys).

Heyer 5 Animal Reproduction

Human Reproduction Feedback Control of the Anterior Pituitary Reproductive Anatomy Sex hormones & gametogenesis: q Gonads — make gametes 1. Hypothalamus secretes releasing Ø Female: — make ova homone (GnRH) to stimulate Ant. Ø Male: testes — make sperm Pituitary.

q Sexual Accessories — ducts 2. Ant. Pituitary secretes gonadotropins (LH & FSH) to Ø Female: oviducts [fallopian tubes] stimulate gonads to: / uterus / 1. Grow & mature Ø Male: epididymus / vas deferens 2. Secrete sex steroids q Genitalia — external 3. Make gametes Ø Female: / minora 3. Sex steroids from gonads feedback / to inhibit pituitary from secreting Ø Male: penis / scrotum more gonadotropin.

q Secondary sexual characteristics Ø Female: enlarged breasts & mammaries / broad pelvis / ↑cutaneous fat Ø Male: ↑muscle & skeletal mass / beard

Spermatogenesis Spermatogenesis 7 weeks

• From seminiferous tubules, sperm pass to epididymis – Mature for another 3 weeks – Become motile – Non-ejaculated sperm reabsorbed Fig. 46.12

Ovulation & Menstrual Cycles Ovarian Cycle

• At 5 mo. gestation, ovaries contain 6-7 million oogonia. • of sex cells Insert fig. 20.30 arrested in meiotic [sexual] division (primary ). • Most degenerate: – 2 million primary at birth. – 400,000 primary oocytes at puberty. • 400 oocytes ovulated during the reproductive years.

Heyer 6 Animal Reproducon

Ovarian follicle development 1 Primordial follicle 1. The primordial follicle consists of a primary oocyte Oocyte Granulosa cells 2 surrounded by a single layer of squamous granulosa Oocyte Primary follicles cells. 3 Granulosa cells Zona pellucida 2. A primordial follicle becomes a primary follicle as the granulosa cells become enlarged and cuboidal. Zona 4 Secondary follicle pellucida Fluid-filled vesicles Granulosa cells 3. The primary follicle enlarges. Granulosa cells form more than one layer of cells. The zona pellucida forms around the oocyte. 5 Mature (graafian) follicle Oocyte Zona pellucida 4. A secondary follicle forms when fluid-filled Cumulus mass vesicles (spaces) develop among the granulosa Antrum cells and a well-developed theca becomes Theca interna Theca externa apparent around the granulosa cells. Granulosa cells 5. A mature follicle forms when the fluid-filled being converted to cells vesicles form a single antrum. When a follicle Oocyte becomes fully mature, it is enlarged to its Zona 6 Ovulation maximum size, a large antrum is present, and pellucidaCells of (oocyte released) the the oocyte is located in the cumulus mass. corona radiata 6. During ovulation the oocyte is released from the Corpus luteum follicle, along with some surrounding granulosa cells 7 Corpus luteum forms of the cumulus mass called the corona radiata.

7. Following ovulation, the granulosa cells divide rapidly and enlarge to form the corpus luteum. Corpus luteum 8. When the corpus luteum degenerates, it forms

the . 8 Corpus albicans

Cycle of Ovulation and Menstruation

Insert fig. 20.35

Heyer Animal Reproduction

Ovarian Cycle drives the Uterine Cycle Menstrual Cycle

Follicular Phase Luteal Phase

Estrous Cycles • Cycle: weeks-months Menstrual vs. Estrous Cycles • Estrus: hours-days “ • Anestrus: extended • Human – menstrual ( monthly) ~28 days periods of no cycles – Day 1 = first day of menses – Menses → follicular phase → luteal phase → menses • Non-human – estrous cycle – Length varies by species – Less endometrial thickening – reabsorbed instead of shed • No menses – Day 1 = first day of estrus • (proceptive/receptive/conceptive behaviors) – Estrus → luteal phase → follicular phase → estrus

Stages of early human development Fertilization Cleavages Sperm Egg Polar Zona pellucida (first cleavage completed about 30 hours after fertilization) nucleus nucleus bodies • Ejaculation 300 million Stem cells sperm, 100 reach (uterine) . – occurs. • Fertilization occurs in First cleavage Day 1 Day 2 Day 3 Day 4 the uterine tubes. Day 0 division 2-cell stage 4-cell stage Early Late morula Insert 20.39 Pronucleus formation • of sperm begins contains , an enzyme that digests Stem cells (pluripotent) a channel through zona Fertilization pellucida. occurs about 12-24 hours – Sperm fuses with ovum after ovulation

. Day 6-7 after fertilization implantation

Ovulation Uterus

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Heyer 8 Animal Reproduction

Early development Implantation • 6th day after fertilization, blastocyst attaches to uterine wall. • cells Insert fig. 20.45 produce enzymes that allow blastocyst to burrow into endometrium.

hCG (Human Chorionic Gonadotropin)

Fig. 21.12 bottom • Trophoblast () cells secrete hCG: “Embryo” – Produces effects similar to ↑ LH. —————— – Signals corpus luteum not to degenerate. ↓“Fetus” – Prevents immunological Insert fig. 20.46 rejection of implanting embryo. – Has thyroid-stimulating • All organs formed ability. • Body movements start • Basis of test. • Once placenta forms and produces sex steroids, corpus luteum no longer needed.

Formation of the Placenta Amnion

Maternal and fetal blood are • Envelop the embryo and brought very close, but do umbilical cord. not mix. • Amniotic fluid initially is isotonic, but as fetus Placental Functions: develops; concentration – Gas exchange changes by urine and sloughed cells of the fetus, – Nutrient exchange placenta, and amniotic sac. – Waste exchange – Immune rejection protection – Synthesizes hormones & enzymes

Heyer 9 Animal Reproduction

Other Placental Hormones Other Placental Hormones Sex steroids — replace role of corpus luteum Sex steroids — replace role of corpus luteum 1. Progesterone • Progesterone + Estrogens 2. Estrogens — from fetal-placental unit • Enlargement of mother’s uterus and – Placenta uses androgens from fetal adrenal endometrial growth, but inhibit contractions. cortex as precursors for estriol. • Growth of mammary glands & ducts, but inhibit prolactin secretion (milk production). • Suppresses LH and FSH (stop ovulating).

Chromosomal Sex and Development of Embryonic Gonads Parturition X • Estrogen in late pregnancy: – Stimulates production of oxytocin & Insert fig. 20.4 prostaglandin receptors in . – Produces gap junctions between myometrium cells in uterus. • Factors responsible for initiation of labor are incompletely understood.

Development of Accessory Sex Development of Genitalia Organs and Genitalia

• Presence or absence of testes determines the accessory sex organs and external genitalia. Insert fig. 20.5 • Male accessory organs derived from wolffian ducts. – Sertoli cells secrete MIF (müllerian inhibition factor). • Female accessory organs derived from mullerian ducts.

Heyer 10