Reproduction

  • Asexual: does not involve the production of gametes (common in invertebrates)
  • Sexual: Involves the production of haploid gametes by meiosis (common in vertebrates, and many invertebrates use this in addition to asexual reproduction
  • Asexual Reproduction:
    • Budding: One individual is produced by another
    • Fission: Creature divides in half
    • Fragmentation: Creatures break up into parts
    • Parthenogenesis: Female produces unfertilized diploid eggs. Some organisms can switch between parthenogenesis and sexual reproduction. Occurs in some invertebrates, arthropods, lizards, snakes, and fish
    • Daphnia (water fleas) reproduce using parthenogenesis for most of the season where they produce many offspring in a short amount of time, at the end of the season they begin sexual reproduction and produce resting eggs
  • Sexual reproduction:
    • Dioecious: Male and female sex organs are found on sperate individuals
    • Monoecious (hermaphroditic): Male and female sex organs are found on the same individual. Most creatures will mate with another individual but some self fertilize
    • An organisms sex can be determined genetically or by environmental conditions
    • Turtles and crocodilians have temperature dependent sex determination, under normal conditions there is enough temperature variation in the nest to produce both males and females
    • Hermaphroditic animals may not have both male and female sex organs functional at the same time.
    • Sequential hermaphrodites may start out male and become female (protandry) or start out female and become male (protogyny), others can change back and forth
  • Fertilization:
    • In aquatic animals (both vertebrates and invertebrates) it is typically external
    • Internal fertilization requires some way of transferring the sperm from the male to the female
  • Vertebrates have different strategies for developing offspring
    • Oviparity: Eggs are laid and may or may not be incubated Ex. most bony fish, some amphibians, most reptiles, all birds, some mammals
    • Ovoviparity: Fertilized egg develops inside the mothers body but is nourished by the yolk, live births. Ex. some cartilaginous fish, reptiles and bony fish
    • Viviparity: Fertilized egg develops inside the mothers body and get all their nutrition from the mother through the placenta. Ex. Most cartilaginous fish, some amphibians and reptiles, most mammals
  • Fish and amphibian eggs have to be laid in a moist environment
  • Birds, reptiles, and mammals have amniotic eggs, which have three extraembryonic membranes: amnion, chorion, and allantois
  • Eggs that have a water proof shell can be laid on land
  • All birds and most reptiles lay eggs, and almost all birds incubate their eggs and care for their young
  • All mammals feed their young with milk
  • In mammals there are three types of reproduction:
    • Monotremes: Lay eggs and incubate them, the mammary glands lack nipples and the ducts open onto the skin, where it is then licked off of. Ex. duck pilled platypus and echidna
    • Marsupials: Babies are born underdeveloped after a short gestation, they make their way into the pouch and attach to the teat and finish their development. Ex. Kangaroos, wombats, opossums)
    • Placentals: Nourish unborn young through a placenta which is formed from an extraembryonic membrane and the lining of the uterus. The length of gestation varies based on the size of the animals and whether the baby is altricial or precocial