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69 Cards in this Set
- Front
- Back
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Fragmentation and Regeneration
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body breaks up into parts, each regrows the missing bits(some annelid worms, sea stars)
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Parthenogenesis
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eggs develop into new individuals without being fertilised(aphids)
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Asexual Reproduction is RARE in vertebrates
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a form of asexual reproduction(parthenogenesis) occurs in some fish,amphibians and lizards
-most reproduce sexually(humans) |
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Do all species need female and male individuals to reproduce?
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for species with SEXUAL REPRODUCTIOn- Yes
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Gametes
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special cells for reproduction
Male Gamete:spermatozoon(sperm),relatively small,usually motile, 50 micromters in length Female Gamete: egg cell,relatively large,non-motile, 120 Micrometers in diameter |
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Gonads produce the gametes by MEIOSIS
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A special type of cell division that reduces chromosome number by half
Female Gonad: Ovary Male Gonad: Testis |
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Gametes are HAPLOID
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They contain only HALF the number of chromosomes found in other parts of the body
Fusion of the egg and sperm forms a ZYGOTE: a diploid cell that becomes an embryo |
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Seuxal Reproduction produces VARIATION
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Offspring are NOT IDENTICAL to their parents(nor usually to their siblings)
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Are sexually reproducing individuals always either male or female?
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NO
Hermaphroditism:each individual has both female and male reproductive systems |
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What is the difference between Simultaneous Hermaphrodites and Sequential Hermaphrodites?
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Simultaneous Hermaphrodites are both sexes at the SAME time(e.g earthworms)
Sequential Hermaphrodites are both sexes at DIFFERENT times(e.g coral reef fish) |
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Carribean blue-headed wrasse: A SEQUENTIAL HERMAPHRODITE
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-are all born females
-females are smaller,orange -oldest, largest females become male -males are blue,larger |
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Do all species produce offspring that look like minature versions of the adult?
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NO
Oviparity:egg laying -amphibian eggs MUST be kept moist to prevent dessication eggs may hatch into a LARVA: a free living sexually immature form distinct in appearance from the adult |
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Reproduction
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The creation of NEW individuals from EXISTING ones
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Do all species need female and male individuals to reproduce?
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For species with asexual reproduction-NO
Asexual Reproduction common in invertebrates |
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Invertebrate examples of asexual reproduction
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Budding(Phylum Cnidaria)
Fission(Phylum Cnidaria) Fragmentation and Regeneration(Phylum Annelida) Parthenogenesis(Phylum Arthropoda) |
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Budding
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buds pinch off from parent hydra(Hydra)
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Fission
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parent splits equally into two(sea anemone)
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Amniotes
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the reptiles,birds and mammals
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Amniotic egg
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Extraembryonic membranes bring benefits(e.g amnion encloses fluid that bathes embryo)
Shell in oviparous amniotes -reulsting in CLEIDOIC egg: more waterproof |
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Oviparity in amniotes
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Birds: all lay eggs-hard,calcereous,inflexible
Reptiles: some lay eggs-sometimes hard; leathery and flexible Mammals: only a few lay eggs |
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Do all species produce offspring that look like minature versions of adults?
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Some do
Viviparity:(live birth) -has evolved from oviparity on many occasions -e.g NZ geckos are all vivparous but their relatives overseas are not |
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Only some mammals are vivparious
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Placental mammals are marsupials-YES
Monotremes(Closest relatives)-NO |
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Do all spcies look after their offspring?
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No, but some do(parental care)
e.g Archeys frog,Leiopelma archeyi: - an endangered speices(Waikato,Coromandel) -male broods eggs and carries larvae on his back |
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Do all species reproduce year-round?
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No, most show SEASONAL reproduction
e.g sheep(lambs born in spring) -related to environmental variations in temperature,photoperiod,food supply Humans are unsual(more or less continuous reproduction) |
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What are hormones?
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Berthold in 1849
-removed and transplanted testes(male gonads) in cockerels -concluded that testes contained a NON-NEURAL factor necessary for male characteristics -TESTOSTERONE,T(not synthesised and named until 1935) |
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Humans:>55 hormones known
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-Testosterone(T)
-Estradiol(E2) -Progesterone(P) -Leteninising hormone(LH) Follicle-stimulating hormone(FSH) Gonadotropin-releasing hormone(GnRH) (These discoveries have led to the science of Endocrinology) |
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Hormones are chemical signals that:
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-Travel in the blood
-Affect particular body tissues(those having target cells) -Their effects can be STIMULATORY or inhibitory -Some hormones are ANTAGONISTIC to each other -They are extremely low concentrations |
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Hormone-producing cells
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Two types:
-Endocrine glands-e.g LH and T -Neurosecretory cells-e.g GnRH |
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Hormones compared with nerves and local regulators
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Nerve cells-neurotransmitters
-faster -shorter duration -more accurately localised Other local regulators(Paracrine regulators) -affect nearby target cells, e.g growth factors(GFs) -autocrine regulators-act on the same cell type that produced them |
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Norris(1997)
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"Everything an animal does is either initiated,modulated or blocked by chemical regulators."
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Chemical groups of hormones
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Steroid hormones
-Lipid molecules made from CHOLESTEROL -e.g Testosterone,Estradiol |
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Chemical groups of hormones(2)
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Hormones made from amino acids
-Peptides,proteins,amines -e,g GnRH-small peptide(10 amino acids) -LH- a glycoprotein(carbohydrate+protein,>200 amino acids) |
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Hormone-receptor interactions
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An important step is interaction of the hormone molecule with a RECEPTOR protein
- only some(target cells) have the receptor for the hormone -peptide hormones located in CELL MEMBRANE -Steroid hormones located mostly inside the CELL(inside cytoplasm or nucleus) |
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Hormones in action
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Hormones can help regulate growth and metamorphisis
-e.g transformation of a larval insect into an adult |
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Growth hormone(GH) in vertebrates
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-Stimulates growth of bone and cartilage, and synthesis of protein
-Effect is partly indirect:GH stimulates liver to release insulin-like growth factos(IGFS) into blood stream Childhood excess-gigantism Adulthood excess-agromegaly(abnormal growth of hands) Childhood defeciency-short stature,dwarfism |
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Hormones and song in spring-breeding birds
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Increased day length
-reproductive organs(testes and sperm ducts) of male enlarge -make and transport sperm -make and release testosterone(stimulates many aspects of reproduction) |
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The HPG axis- the hypothalamus,anterior pituitary gland and gonads form a linked pathway
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H: the hypothalamus secretes relasing inhibiting hormones(from neurosecretory cells) that affect the anterior pituitary gland
P: the pituitary gland releases gonadotropins G:the gonads respond by making gametes and steroid hormones |
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Hypothalamus releases GnRH
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Gonadotropin-releasing hormone(GnRH) is released into portal blood vessels to reach the anterior pituitary gland
-recent research also reveals gonadotropin inhibiting hormone and other controls |
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Pituitary gland releases gonatropins
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-FSH and LH are the gonadotropins in mammals
-Anterior pituitary gland also releases at least six other hormones |
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Testes-the male gonads
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Paired: 2 testes(='testicles' in humans)
Abdominal in most vertebrates, scrotal in some mammals) Part of the genitalia(organs of generation) -Includes scrotum and penis(external genitalia) and testes,sperm ducts and sex accessory glands(internal genitalia) |
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Testes make sperm and hormones
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Spermatogenesis
Sterioidgenesis -cells between the tubules make androgens -the main androgen is testosterone |
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What does testosterone(T) do?
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In embryo
-stimulates genitalia and brain to develop in male direction In adult(from puberty) -enlarges genitalia -maintain sperm ducts and sex accessory glands -support spermatogenesis -stimulates male typical behaviours(sexual activity) -stimulates bone growth and muscle bulk -helps stimulate other features of sexual dimorphism |
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Ovaries-the female gonads
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Paired: 2 ovaries(in some species,only one is active)
Abdominal Part of the genitalia(organs of generation) -includes egg ducts(oviducts) and sex accessory glands(interal genitalia), and the vulva(including pubic mound,vaginal lips and clitoris,=external genitalia) |
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Ovaries make egg cells and hormones
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Oeegenesis
-production of ova-mature unfertilised egg cells Steroidogenesis -growing follicles make estradiol(E2, and estrogen) -Mature follicles and corpora lutea make progesteron |
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Oogenesis vs spermatogenesis
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Similarties:
-meiosis produces HAPLOID GAMETES -Whether, from pubery,meiosis occurs CONTINUOUSLY or CYCLICALLY -whether CYTOPLASM DIVISION during meiosis is equal -Whether meiosis ceases before death (net result: females produce FAR fewer mature gametes than males do.. important implications of reproductive behavior) |
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Human Menstural Cycle
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Ovarian and uterine activity fluctuate monthly
Menstrual cycle -seen in humans and other primates -involves discharge of sloughed lining of uterus(blood+other tissue) through the vagina at menstruation -the cycle is coordinated by hormones |
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Summary of menstrual cycle
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Before ovulation-uterus is prepared for an embryo
-estradiol form gorwing follicles-> uterus to thicken -Follicular phase(ovarian cycle) is co-ordinated with proliferative phase(uterine cycle) |
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Summary of menstrual cycle(2)
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After ovulation-uterus is maintained for an embryo
-Estradiol and progesterone from CL-> endometrium maintained and further developed -Luteal phase(ovarian cycle) is co-ordinated with secretory phase(menstural cycle) |
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What are endocrine-disrupting chemicals?
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Foreign substances from the ENVIRONMENT absorbed by the body that alter the normal function of the endocrine system
e.g they mimic or alter the action of natural hormones in the body |
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EDCS
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Effects may involve blocking or activating the cellular RECEPTOR for the endogenous hormone(thus influencing gene transcription)
-Molecular structure can be quite different from the endogenous form -May be retained for many years in animal tissues -May remain in the environment for many years even when use is discontinued |
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Particular concern:unintended examples arising from human activity arising from human activity
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Chlorinated organic compounds(e.g pesticides, polychlorinated bipehnols- in electrical insulation)
Alkylphenols in plastics and detergents -Natural and synthetic estrogens in sewage treatment waste -Hydrocarbons from fuel |
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Warnings: known effects of DES
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Diethylstillbestrol:synthetic estrogen
Daughters:increased risk -abnormal tissue in reproductive tract -problems with pregnancy -rare form of vaginal cancer Sons:increased risk -undescended testes -reduced sperm counts -testicular cancer |
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Lessons from the DES experience
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Subsequent animal studies,with experiemental controls, proved that DES could induce these effects
Confirmed greater vulnerability of embryos than adults, and potential for long term effects |
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Declining semen quality in men
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Carlsen et al.(1992)
-declining sperm counts -declining semen volume |
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Declining semen quality in men?Possible mechanim
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Early exposure to EEs->decreased FSH->decreased sertoli cell mitosis->decreased sperm production
Associated with increased incidence of: -abnormalities of penis -undescended testes -testicular cancer collectively,testicular dysgenesis syndrome |
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Other concerns in humans
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-Declining age of puberty
-Incrased incidence of breast cancer |
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Do EDCs have a role to play?
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Possible additional sources
-phytoestrogenns in soy -Phthalates in plastics,including toys -Estrogens in cosmetics and skin care products |
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Alligators: The lake Apopka sotry
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A lake in Florida,USA
Chemical spill(pesticides) in 1980 Subsequent low hatching rates Abnormalities of genitalia in young alligators -small penis in males -abnormal oogenesis and spermatogenesis -differences in blood level of sex steroid hormones compared with alligators from other lakes |
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EDCs
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Effects may be:
-Transgenerational -Greatest on embryos(the fragile fetus) -Delayed(not noticed until maturity) -Permanent -Additive or synergistic Effects may include the immune system and neural performance as well as reproductive function |
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Where to from here?
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-Be aware that new compounds are likely to have risks as well as benefits
-be aware that many years may pass before we know the full risks -New compounds should be tested for endocrine-disrupting effects -Testing should investigate transgeneration effects |
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Evolutionary significance of tuatara
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The only living genus of rhynchocephalian reptiles
-the sister group of squamates(lizards and snakes) |
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How does it compare with another 'nocturnal' NZ reptile?
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Tuatara,Sphenodon punctatus
Common gecko, Woodworthia maculata -Both are active at night |
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Activity times and temp in tuatara
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-Primarliy noctural, but also basks
-Activity(voluntary emergence) with body temperatures(Tb) of 5-30C -Most noctural acitivity Tbs- 10-20C |
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Activity times common in geckos
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-Still survives on mainland
-Primarily nocturnal -Occasional discreet basking -But actively thermoregulates under warm surfaces by day |
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Activity temp in common geckos
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-Activity Tbs between 5-33C
-Most nocturnal activity Tbs-10-20C |
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Conlucsions about temperature
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-Activity temperatures in tuatara are not unsual compared with geckos in similarly cool,NZ environments
-Common geckos also active at night with similarly low Tb and have similarly low critical thermal minimum(CTMin) -Primarliy nocturnal species(tuatara,common gecko) can reach daytime Tb similar to basking skinks |
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Incubation time in tuatara
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-Oviparous
-Eggs laid in spring -Hatch 11-16 months later -Incubation time is temperature-dependent |
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Pregnancy in common geckos
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-Viviparous
-Pregnancy begins in spring -Birth occurs 4-14 months later, warm sites:4 moth pregnancy, cool site-14 month pregnancy -Gestation time is temperature dependant |
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Conclusions about development time
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-tuatara not unique:some populations of common geckos also have extended embyronic development
-embryos nearly or fully developed by autumn -wait until spring for hatching(tuatara) or birth(gecko) -A strategy for avoiding birth as winter approaches Low activity temp and long development times in tuatara cannot be aswsumed to be ancestral features -more likely an adpatation to cool NZ environments |
