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Animal Reproduction
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Reproductive Cycles and Patterns

Ovulation is the release of mature eggs at the midpoint of a female cycle.

Most animals exhibit reproductive cycles related to changing seasons.

Reproductive cycles are controlled by hormones and environmental cues.

Animals may reproduce asexually or sexually, or they may alternate these methods.

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Sexual reproduction is a special problem for organisms that seldom encounter a mate.

Sexual reproduction is a special problem for organisms that seldom encounter a mate.

One solution is hermaphroditism = each individual has BOTH male and female reproductive systems.

Some hermaphrodites can self-fertilize.

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Individuals of some species undergo sex reversals.

Individuals of some species undergo sex reversals.

Some species exhibit male to female reversal (for example, certain oysters), while others exhibit female to male reversal (for example, a coral reef fish).

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Fertilization depends on mechanisms that bring together sperm and eggs of the same species

Fertilization depends on mechanisms that bring together sperm and eggs of the same species

The mechanisms of fertilization, the union of egg and sperm, play an important part in sexual reproduction.

In external fertilization, eggs shed by the female are fertilized by sperm in the external environment.

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External fertilization

External fertilization

Eggs

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In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract.

In internal fertilization, sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract.

Internal fertilization requires behavioral interactions and compatible copulatory organs.

All fertilization requires critical timing, often mediated by environmental cues, pheromones, and/or courtship behavior.

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Ensuring the Survival of Offspring

Ensuring the Survival of Offspring

All species produce more offspring than the environment can handle, and the proportion that survives is quite small.

Species with external fertilization produce more gametes than species with internal fertilization.

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Species with internal fertilization provide greater protection of the embryos and more parental care.

Species with internal fertilization provide greater protection of the embryos and more parental care.

The embryos of some terrestrial animals develop in amniote eggs with protective layers.

Some other animals retain the embryo, which develops inside the female.

In many animals, parental care helps ensure survival of offspring.

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Parental care

Parental care

in an invertebrate

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