Chapter 43 Animal Reproduction
Reproduction • Produce copies of self • Continue survival of species • Ensure survival of personal genetics
Asexual Reproduction • Fragmentation • Sponges, some annelids, starfish • Organism breaks apart, pieces become new organisms
Asexual Reproduction • Budding • Hydras, cnidarians • Creates bud that breaks off and becomes new organism • Transverse fission • Some protists, planaria • Constricts, splits in half
Asexual Reproduction • Parthenogenesis • “virgin birth” • Eggs produced by mitosis, not meiosis • Egg not fertilized by male • Some insects and arthropods (bees, ants, water fleas) • Some reptiles (komodo dragons, geckos, whiptails) • Some fish, sharks • Same species can reproduce sexually as well
Sexual Reproduction • More “costly” to make and care for gametes • Potential mate needs to be found and possibly courted • Pheromone production • Time and energy in searching • May be time & injury risk when competing • Timing of gamete formation must synchronize between sexes • Neural & hormonal mechanisms in both parents • Overall more complex, more resources needed • So why do it?
Sexual Reproduction • Great genetic variation! • Humans • 22 pairs of homologous chromosomes (X & Y non-homologous) • 8,388,608 combinations of homologous chromosomes • 70,368,744,000,000 possible variations of offspring • Including crossing over in meiosis I, there are 4,951,760,200,000,000,000,000,000,000 possible variations! IN ANY SINGLE CHILD!!! • Many variations possible, some could enhance survival of organism
Sexual Reproduction • External fertilization • Sperm and egg unite outside of female • Must be in very wet environment • Sperm & eggs released into water • Marine invertebrates • Sperm deposited onto eggs • Many fish, amphibians • Internal fertilization • Sperm and egg unite within female
Male Reproductive Systems • Testes (internal or external) • Sperm • Motile, allows movement through fluid towards ova • Copulatory organs • For internal fertilization • Penis—mammals • Usually internal until copulation • Most contain bone (baculum/os penis)
Male Reproductive Systems • Copulatory organs (cont.) • Clasper • Chondricthyes • Inserted into female • Hemipenis (pl. hemipenes) • Snakes, lizards • Paired organs • Often barbed • Internal, everted into female during copulation
Male Reproductive Systems • Copulatory organs (cont.) • Cloaca • Pass sperm through direct cloacal contact • Most birds • Waterfowl have penis-like organ (phallus)
Female Reproductive Systems • Ovaries • Oviduct (Fallopian tube) • Uterus • Eggs/Ova
Female Reproductive Systems • Eggs • Protect & nourish growing embryo • Aquatic animals • Gelatinous, thin-walled eggs • Allow water to diffuse through egg wall • Fish, amphibians
Female Reproductive Systems • Eggs (cont.) • Land animals • Thick shell • Water impermeable (prevent dehydration) • Reptiles—leathery shell • Usually buried or laid underground to preserve warmth • Birds—hard shell • Requires incubation (warmth from parent)
Female Reproductive System • Eggs (cont.) • Amnion—fluid sac to cushion & prevent dehydration • Allantois—stores metabolic wastes • Yolk sac—food source for embryo
Sexual Reproduction • Hermaphrodite • Animal has male and female sex organs • Self-fertilization • Inseminates itself • Tapeworms • Cross-fertilization • Inseminate others • Slugs, snails, earthworms
Sexual Reproduction • Hermaphrodite (cont.) • Sequential hermaphrodites • Born as one sex, can change sex later in life • Mostly fish, some crustaceans • Clownfish harem • Large female, several males • Remove female, one male will become female • Wrasses • Largest fish always male • When male dies, female may turn into male
Sexual Reproduction • Oviparous • Egg laying • Little or no embryonic development within mother • Young hatch from eggs • Most insects, arachnids • Most fish, reptiles, amphibians • All birds, monotremes
Sexual Reproduction • Viviparous • Embryo develops within mother • No egg around embryo • Nourished by mother • Live birth • Most mammals • Rare in other animals, but exists
Sexual Reproduction • Ovoviviparous • Eggs develop within mother • Embryo nourished by yolk sac, not mother • Live birth • Some fish (guppies, mollies, swordtails) • Some sharks, reptiles, amphibians, invertebrates
Placenta • Most mammals • None in monotremes or marsupials • Feeds & nourishes fetus • Filters and eliminates wastes • Blood does not directly connect between mother & fetus • Produces progesterone to maintain pregnancy • Specific shape and attachments vary between species
