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Cellula E Cellula Biological Benefits of Asex • Cells Divide to Reproduce I

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Cellula E Cellula Biological Benefits of Asex • Cells Divide to Reproduce I 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 sperm – 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 egg cell 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, fish, crustaceans, insects, & 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 & mammals • 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 Insect 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 uterus 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: ovaries — 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 / vagina 1. Grow & mature Ø Male: epididymus / vas deferens 2. Secrete sex steroids q Genitalia — external 3. Make gametes Ø Female: clitoris / labia minora 3. Sex steroids from gonads feedback / labia majora 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. • Oogenesis of sex cells Insert fig. 20.30 arrested in meiotic [sexual] division (primary oocyte). • Most degenerate: – 2 million primary oocytes 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 Theca interna form more than one layer of cells. The zona Theca externa 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
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