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 nonhomologous)
 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