F3

• Animal reproduction takes many forms
• Sea slugs are both male and female, each one producing both eggs and sperm
• A population outlives its members only by reproduction, the generation of new individuals from existing ones
• Sexual reproduction


  The creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote
• Asexual reproduction


  The creation of offspring without the fusion of egg and sperm
• Budding


  New individuals arise from outgrowths of existing ones
• Fission


  Separation of a parent into two or more individuals of about the same size
• Fragmentation


  Breaking of the body into pieces, some or all of which develop into adults
• Parthenogenesis


  The development of a new individual from an unfertilized egg
• Parthenogenesis is mainly observed in invertebrates, but is observed rarely in some vertebrates
• Twofold cost of sexual reproduction

  Sexual females have half as many daughters as asexual females
• Despite the twofold cost, almost all eukaryotic species reproduce sexually
• Advantages of sexual reproduction

  • It may enhance reproductive success of parents when environmental factors change relatively rapidly
  • Asexual reproduction is expected to be most advantageous in stable, favorable environments
• Reproductive cycles


  Most animals exhibit reproductive cycles related to changing seasons
• Ovulation


  The release of mature eggs at the midpoint of a female cycle
• Climate change can decrease reproductive success because seasonal temperature is often an important cue in reproduction
• Hermaphroditism


  Each individual has male and female reproductive systems
• Some species exhibit male to female reversal, while others exhibit female to male reversal
• External fertilization


  Eggs shed by the female are fertilized by sperm in the external environment
• Internal fertilization


  Sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract
• Internal fertilization is typically associated with production of fewer gametes but the survival of a higher fraction of zygotes
• Internal fertilization is also often associated with mechanisms to provide protection of embryos and parental care of young
• The embryos of some terrestrial animals develop in eggs with calcium- and protein-containing shells and several internal membranes
• Some other animals retain the embryo, which develops inside the female
• In many animals, parental care helps ensure survival of offspring
• Gonads


  Organs that produce gametes
• Scrotum and penis


  The male's external reproductive organs
• The male's internal reproductive organs

  • Gonads: produce sperm and hormones
  • Accessory glands: secrete products needed for sperm movement
  • Ducts: carry sperm and glandular secretions
• Testes


  • Consist of highly coiled tubes surrounded by connective tissue
  • Sperm form in these seminiferous tubules
  • Leydig cells produce hormones and are scattered between the tubules
• Production of normal sperm cannot occur at the body temperatures of most mammals
• The testes of many mammals are held outside the abdominal cavity in the scrotum, where the temperature is lower than in the abdominal cavity
• Sperm movement


  1. From the seminiferous tubules of a testis, sperm pass into the coiled duct of the epididymis

  2. During ejaculation, sperm are propelled through the muscular vas deferens and the ejaculatory duct, and then exit the penis through the urethra
• Semen


  Composed of sperm plus secretions from three sets of accessory glands
• Accessory glands that contribute to semen

  • Seminal vesicles
  • Prostate gland
  • Bulbourethral glands
• Female external reproductive structures

  Clitoris and two sets of labia
• Female internal reproductive organs

  • Gonads
  • Ducts and chambers that carry gametes and house the embryo and fetus
• Ovaries


  • Lie in the abdominal cavity
  • Each ovary contains many follicles, which consist of a partially developed egg, called an oocyte, surrounded by support cells
• Egg movement


  1. The egg cell travels from the ovary to the uterus via an oviduct, or fallopian tube

  2. Cilia in the oviduct convey the egg to the uterus
• Uterus


  • Also called the womb
  • The uterus lining, the endometrium, has many blood vessels
  • The uterus narrows at the cervix, then opens into the vagina
• Vagina and vulva


  • The vagina is a muscular but elastic chamber that is the repository for sperm during copulation and serves as the birth canal
  • The vulva consists of the labia majora, labia minora, hymen, and clitoris