2.2 Sexual Reproduction in 2.2 Sexual Reproduction in AnimalsAnimals

SpermSperm

(23)(23) zygote (46) zygote (46) embryo (46) embryo (46)

  EggEgg

(23) adult(23) adult

  

An embryo is a fertilized egg during early An embryo is a fertilized egg during early development.development.

   both male and female gametes must both male and female gametes must

arrive in the same place at the same arrive in the same place at the same time for fertilization.time for fertilization.

The zygote must receive adequate The zygote must receive adequate food, moisture, warmth, and protection food, moisture, warmth, and protection to develop.to develop.

Successful sexual reproduction requires:

Mating in the Animal KingdomMating in the Animal Kingdom

mating is timed for offspring to be born at mating is timed for offspring to be born at times with the best chance for survivaltimes with the best chance for survival elk, deer, etc. once a yearelk, deer, etc. once a year grunion mate at full or new moon.grunion mate at full or new moon. Honeybee’s mate once in a lifetimeHoneybee’s mate once in a lifetime Desert Toads only after a rainfall.Desert Toads only after a rainfall.

FertilizationFertilization In a warm, moist environment ONLY for In a warm, moist environment ONLY for

sperm to swim, and for fertilization to sperm to swim, and for fertilization to result.result.

May be INTERNAL or EXTERNAL.May be INTERNAL or EXTERNAL.

External FertilizationExternal Fertilization

Most Most water-dwellingwater-dwelling animals. animals. Non-moving animalsNon-moving animals - (ex. Anemones) - (ex. Anemones)

release large numbers of eggs and sperm into release large numbers of eggs and sperm into water. Eggs and sperm meet by chance. water. Eggs and sperm meet by chance. Zygotes form larvae which swim and feed Zygotes form larvae which swim and feed themselves.themselves.

Swimming animalsSwimming animals – (fish) Females lay eggs – (fish) Females lay eggs in suitable spot. Males release sperm onto the in suitable spot. Males release sperm onto the egg cluster. This is called spawning.egg cluster. This is called spawning.

Sockeye Salmon Video -- National GeographicSockeye Salmon Video -- National Geographic

Internal FertilizationInternal Fertilization

Animals on land (& aquatic mammals) Animals on land (& aquatic mammals) use this method.use this method.

Sperm is transferred directly to the Sperm is transferred directly to the female.female.

ReptilesReptiles

Male transfers sperm into female’s cloaca Male transfers sperm into female’s cloaca (where urinary, reproductive and digestive (where urinary, reproductive and digestive ducts lead).ducts lead).

Eggs have enough food to feed the Eggs have enough food to feed the embryo until hatching.embryo until hatching.

No care for young. No care for young.

Sperm entering the eggSperm entering the egg

BirdsBirds

Males and females have a cloaca.Males and females have a cloaca. Close body contact allows for sperm to Close body contact allows for sperm to

transfer.transfer. Parents shelter, protect, and feed the Parents shelter, protect, and feed the

young.young.

InsectsInsects

Internal fertilizationInternal fertilization Incomplete MetamorphosisIncomplete Metamorphosis

Eggs hatch into nymphs (no wings)Eggs hatch into nymphs (no wings) nymph sheds exoskeleton for growth nymph sheds exoskeleton for growth

(moulting)(moulting) nymph develops into winged adultnymph develops into winged adult

Complete metamorphosis   Complete metamorphosis   Offspring look completely differentOffspring look completely different Cacoon/crysallisCacoon/crysallis

Egg Egg larva larva caterpillar caterpillar

moth moth pupapupa or butterflyor butterfly (cocoon)(cocoon)

  

http://farm4.static.flickr.com/3235/2993342324_3066810afb.jpg

The cost of reproductionThe cost of reproduction

The male empid fly offers his larger The male empid fly offers his larger partner the gift of a smaller insect to avoid partner the gift of a smaller insect to avoid being eaten after mating.being eaten after mating.

The male praying mantis shows up empty The male praying mantis shows up empty handed and the larger female often eats handed and the larger female often eats the smaller male after mating (starting with the smaller male after mating (starting with the head).the head).

MammalsMammals

Internal fertilizationInternal fertilization embryo develops inside mother for embryo develops inside mother for

protection and nourishment (Placenta and protection and nourishment (Placenta and umbilical cord)umbilical cord)

mother produces milk and parents care for mother produces milk and parents care for young.young.

MarsupialsMarsupials

Kangaroos, Opossums give birth very Kangaroos, Opossums give birth very early in developmentearly in development

Young must crawl into pouch and attach to Young must crawl into pouch and attach to a nipple for food for several months while a nipple for food for several months while they develop.they develop.

HermaphroditesHermaphrodites

Have both male and female reproductive Have both male and female reproductive organs on each individual.organs on each individual.

Includes flatworms (planaria), and Includes flatworms (planaria), and earthworms.earthworms.

Each hermaphrodite injects sperm into the Each hermaphrodite injects sperm into the other’s reproductive pore.other’s reproductive pore.

AssignmentAssignment

HowStuffWorksHowStuffWorks Videos "Fertilization and Videos "Fertilization and

Sexual Reproduction: Part I"Sexual Reproduction: Part I" Questions on page 59 # 1 – 7Questions on page 59 # 1 – 7 Sexual Reproduction Handout (Manitoba Sexual Reproduction Handout (Manitoba

Fisheries)Fisheries) ““Fish Net” Scavenger Hunt – Group Fish Net” Scavenger Hunt – Group

Activity Activity

Page 59 1-7Page 59 1-7

1.1. The fundamental cycle that allows all The fundamental cycle that allows all animals to reproduce sexually is:animals to reproduce sexually is:

a)a) Meiosis produces gametesMeiosis produces gametes

b)b) Fertilization (male gamete combines with Fertilization (male gamete combines with female gamete)female gamete)

c)c) Zygote produced embryoZygote produced embryo

d)d) Embryo develops through mitosis into Embryo develops through mitosis into mature offspring – cycle repeatsmature offspring – cycle repeats

Sexual Reproduction QuestionsSexual Reproduction Questions

1.1. FertilizationFertilization External fertilization takes place outside the External fertilization takes place outside the

organisms bodyorganisms body Internal fertilization sperm are transported Internal fertilization sperm are transported

into the oviducts of the femaleinto the oviducts of the female

2.2. Amphibians and most fish use external Amphibians and most fish use external fertilizationfertilization

3.3. The disadvantages of The disadvantages of externalexternal fertilization are:fertilization are:

Only one parent to care for offspringOnly one parent to care for offspring Parent usually disappears – no care for Parent usually disappears – no care for

eggseggs Less genetic variability in organisms of Less genetic variability in organisms of

same speciessame species

4.4. Internal fertilization is necessary because Internal fertilization is necessary because there is no aquatic environment and there is no aquatic environment and fewer eggs are produced (therefore more fewer eggs are produced (therefore more parental care is provided)parental care is provided)

5.5. The purpose of the amniotic egg is to The purpose of the amniotic egg is to provide a “life raft” for water animalsprovide a “life raft” for water animals

6.6. The chicken’s egg white provides an The chicken’s egg white provides an artificial pond for the developing embryoartificial pond for the developing embryo

7.7. Amniotic egg must be fertilized internally Amniotic egg must be fertilized internally so that the sperm can enter the egg so that the sperm can enter the egg before the shell formsbefore the shell forms

8.8. A placental mammal is an animal that A placental mammal is an animal that keeps the embryo inside their bodies in a keeps the embryo inside their bodies in a specialized area called the womb/uterus.specialized area called the womb/uterus.

9.9. Care for young because they have fewer Care for young because they have fewer to ensure survival.to ensure survival.

10.10. All embryos develop in a “pond.” The All embryos develop in a “pond.” The embryo develops in a bag filled with embryo develops in a bag filled with amniotic fluid – this breaks just before amniotic fluid – this breaks just before birth.birth.