Ch 47: Animal Reproduction

Reproduction

goal of all animals, in order to increase fitness

Asexual reproduction

based on mitosis, offspring genetically identical to siblings and parents, three parts:

1. Budding: offspring forms on parent, breaks off, grows more (hydra)

2. Fission: Parent splits apart (anemones)

3. Parthenogenesis: female offspring come from unfertilized eggs (some lizards)

Sexual reproduction

based on meiosis, produce genetically different offspring

Spermatogenesis

formation of sperm in testes 1:4

1. Spermatogonium undergoes mitosis and differentiation to primary spermatocyte

2. Undergoes meiosis to two secondary spermatocytes

3. Undergoes meiosis to four spermatids, matures to sperm cells

Oogenesis

formation of egg in ovaries 1:1

1. Oogonium undergoes mitosis and differentiation to primary oocyte

2. Undergoes meiosis to seconary oocyte and polar body

3. Undergoes meiosis to ootid and three polar bodies (disintegrate)

4. Ootid become egg cell (uneven distribution of cytoplasm, energetically costly)

Mature sperm cell

• head and neck: DNA and mitochondria stored

• tail: long tail for swimming

• Really small compared to egg

External fertilization

Eggs fertilized outside of body, large number of genetes need to be produced, timing by environmental cues/by individual

Internal fertilization

Male deposit sperm directly into female reproductive tract or spermtophore released female picks up and places in tract

2nd male advantage

Competition among two or more males, second male has advantage (places more sperm in female)

Oviparous

egg bearing, embryo develops in egg in external environment, sometimes parental care (birds, fish don’t)

Viviparous

live bearing, develop in mother, direct connection between fetus and mother, live birth, nutrients from mother (mammals)

Ovoviviparous

develop in mother but receive nutrients from yolks, live birth

Male external anatomy

shape of penis or scrotum gives advantage

• beetle penis: genital spines anchor in female, longer = more offspring

• duck penis: corkscrew in one direction (vagina in other), length = more offspring

Spermatogenesis and Sperm Storage

testosterone released spermatogenesis occurs sperm produced in testes, sperm is stored in epididymis

Production of Accessory Fluids

As sperm moves through tube fluids (released by glands) provide energy and easier movement, fluids + sperm = semen

three glands: seminal vessicle, prostate gland, bulbourethral gland

Transport and delivery

Vas defrens: muscular tube transports sperm and fluids, joins with urethra

urethra: reproductive and urinary function, semen deposited for ejaculation

Female reproductive system: maturation of bird egg

1. Egg matures

2. Oviduct catches egg, fertilization occurs

3. Egg white, outer membrane and shell added

4. Egg is laid through vagina, out cloaca

1. Production and transport of eggs

2. Development of offspring

1. ovary: produce egg and estradiol releases egg to oviduct, oviduct: transport egg to uterus, fertilization occurs, uterus: implantation occurs, embryo develops

2. cervix: opening to uterus, vagina: birth canal and semen deposit site

Hormonal regulation

GnRH released from hypothalmus, targets anterior pituitary to release LH and FSH (spike at transition from youth to adult)

in males: target testis to produce testosterone, affect larynx

in females: target ovaries to produce estradiol, affect breasts

Ovarian cycle

Follicular phase

1. formation of primary oocytes within follicles

2. follicle growth/maturation

3. Ovulation: secondary oocyte released to oviduct

Luteal phase

1. Corpus luteum form from ruptured follicle

2. Degenerates and reabsorbs over time

Uterine cycle

1. Menstrual: uterine lining released, thickness decreases

2. Proliferative: uterine lining thickens

3. Secretory: blood vessels added to prepare uterus for implantation

How do the hormone cycles relate

• Estradiol low at beginning of follicular, increases, then drops in luteal

  • (low levels keep LH low through neg feedback at beginning, high levels keep LH high through pos feedback at end of follicular)

• Progesterone: low in follicular, high in luteal

  • (high levels cause low LH and FSH though neg feedback)

• LH remain constant, high spike causes ovulation

• FSH higher during follicular, spike at ovulation, low at luteal

  • (if corpus ludeum degenerates LH and FSH rise again)

Pregnancy in mammals

1. Monotreme: lay eggs, show parental care

2. Eutherian: mother carries offspring, young receive nutrients from placenta

3. Marsupial: no placenta, lacking connection, not very developed at birth, develop in pouch, nutrients from mom

Implantation

1. Ovulation: egg released to oviduct, day 0: fertilization, block other sperm from fertilizing egg

2. days 1-5: travels down oviduct day 6: becomes blastocyst (inner cell mass becomes fetus, trophoblast becomes placenta)

3. days 7-10: implantation in uterine wall, once implantation occurs hCG is released acts on corpus luteum to stop degeneration, detected in urine and indicates pregnancy

Human development

1. 1st trimester: differentiation of tissues, fluid filled sac to protect embryo, placenta starts to form

2. 2nd trimester: once placenta forms corpus ludeum is no longer needed

• 2nd and 3rd trimester all about development

Oxygen exchange

1. Countercurrent blood flow in placenta: maternal blood flows one way, fetal blood flows other way

2. Fetal hemoglobin has a higher affinity for oxygen, fetus always gains oxygen

Birth

1. Dilation of cervix: oxytocin increases and initiates uterine contractions

2. Expulsion: delivery of infant

3. Delivery of placenta