Infer Why might sexual reproduction, as opposed to asexual reproduction, produce a population better able to survive disease or environmental changes Predict Why would you expect most species that employ external fertilization to reproduce in the water Compare and Contrast What is the difference between a nymph and a pupa

Ch 28 Animal Systems II 28.3 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 In placental mammals. 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 Allantois Contains nutrient-rich food supply for the embryo 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.