1. Infer Why might sexual reproduction, as opposed to asexual reproduction, produce a population better able to survive disease or environmental changes

2. Predict Why would you expect most species that employ external fertilization to reproduce in the water

3. Compare and Contrast What is the difference between a nymph and a pupa

CH 28 ANIMAL SYSTEMS II28.3 Reproduction

Asexual Reproduction

Many invertebrates and a few chordates Requires only one parent Can reproduce rapidly Lack genetic diversity.

Types of Asexual Reproduction

Divide in two Budding Parthenogenesis

Females lay eggs that develop without being fertilized by a male.

Sexual Reproduction

Involves meiosis, creates gametes Male and female gamete join to create zygote Genetic diversity Requires two individuals of different sexes Greater needs.

Most animal species that reproduce sexually have individuals that are either male or female Some species are hermaphrodites Some species switch sexes.

Reproductive Cycles

Some invertebrates have life cycles that alternate between sexual and asexual reproduction.

Blood flukes mature in the body of an infected person

Reproduce sexually and release embryos that pass out of the body in feces

Embryos develop into larvae and infect snails and reproduce asexually

Larvae infect people.

Jellyfish

Aurelia polyps produce medusas asexually by budding.

Medusas reproduce sexually by producing eggs and sperm that are released into the water.

After fertilization, the resulting zygote grows into a free-swimming larva.

Larva eventually attaches to a hard surface and develops into a polyp continuing the cycle.

Internal Fertilization

Eggs are fertilized inside the body of the egg-producing individual

Many aquatic and all terrestrial animals Sperm may taken in from surrounding water, be

gathered by the female, or deposited in side the female.

External Fertilization

Eggs are fertilized outside the body of the egg-producing individual

Aquatic invertebrate and vertebrates.

Development and Growth

After fertilization, the zygote divides through mitosis and differentiates

Development occurs under different circumstances in different species

Care and protection given to developing embryos also varies widely.

Animals may be oviparous, ovoviviparous, or viviparous.

Oviparous

Embryos develop in eggs outside the parents’ bodies

Most invertebrates, many fishes and amphibians, most reptiles, all birds, and a few mammals.

Ovoviviparous

Embryos develop within the mother’s body, but depend entirely on the yolk sac of their eggs

Young do not receive any additional nutrients from the mother

Guppies and some shark species.

Viviparous

Embryos obtain nutrients from the mother’s body during development

Most mammals and some insects, sharks, bony fishes, amphibians, and reptiles.

Viviparous

Young are nourished by secretions produced in the mother’s reproductive tract in insects, and in some sharks and amphibians.

Viviparous

Placenta Specialized organ that enables exchange of

respiratory gases, nutrients, and wastes between the mother and her developing young

In placental mammals.

Most newborn mammals and newly hatched birds and reptiles look a lot like miniature adults.

As invertebrates, nonvertebrate chordates, fishes, and amphibians develop, they undergo metamorphosis

Metamorphosis Developmental process that leads to dramatic

changes in shape and form.

Aquatic Invertebrates

Have a larval stage that looks nothing like an adult Swim or drift in open water before undergoing

metamorphosis and assuming their adult form May have multiple larval stages.

Terrestrial Invertebrates

Some undergo gradual or incomplete metamorphosis

Nymph Immature forms that resemble

adults Lack functional sexual organs and

some adult structures Molt several times and gradually

acquire adult structures.

Some undergo complete metamorphosis

Larvae look nothing like their parents, and they feed in different ways

Pupa Stage in which an insect larva

develops into an adult Controlled by amount of juvenile

hormone produced.

Care of Offspring

Species that provide intensive or long-term parental care give birth to fewer young than do species that offer no parental care

Type and amount of care varies greatly.

The Amniotic Egg

Provides a protected environment for an embryo to develop out of water

One of most important vertebrate adaptations to life on land

Reptiles, birds, and a few mammals.

Amnion Fluid-filled sac that surrounds

and cushions the developing embryo.

Chorion Regulates the transport of

oxygen from the surface of the egg to the embryo and the transport of carbon dioxide in the opposite direction.

Yolk sac Contains nutrient-rich food

supply for the embryo Allantois

Stores waste produced by the embryo

Later fuses with the chorion.

Mammal Adaptations

The three groups of mammals: Monotremes Marsupials Placentals

All nourish their young with mother’s milk.

Monotremes

Lay soft-shelled, amniotic eggs that are incubated outside her body

Young are nourished by milk produced by the mother.

Marsupials

Bear live young that usually complete their development in an external pouch

Young spend months attached to a nipple drinking milk and growing inside.

Placentals

Nourished through a placenta before they are born and by their mother’s milk after they are born

Born at a fairly advanced stage of development.