Sexual Reproduction Involves the union of reproductive cells (gametes) from two different parents, called fertilization and results in the formation of a zygote The union of the two gametes is called fertilization Offspring are genetically unique from either parent

Sexual reproduction: Pros Cons Genetic diversity among offspring Allows for evolution (ability to adapt) Higher survival rate Recombination can disrupt successful adaptations Huge amount of energy required to make gametes Requires more time Reliance on a mate

Hermaphroditism Most animals have distinct sexes (male or female) Hermaphroditism occurs when one individual has both male and female reproductive structures They usually still mate with other individuals but self-fertilization is possible during mating or in times of environmental stress that prevents finding a mate

Hermaphroditism Simultaneous Hermaphroditism An organism that has both male and female sexual organs at the same time For example, earthworms, land snails, and land slugs are simultaneous hermaphroditic species Most plant species are simultaneous hermaphrodites

Hermaphroditism Sequential Hermaphroditism Occurs when the individual is born as one sex, but then later changes into the opposite sex It is common in fish, jellyfish, snails, and slugs

Hermaphroditism Protandry describes sequential hermaphroditism in the case where an organism is born as a male then changes to female Example: Clownfish inhabit a sea anemone and consist of one large reproductive female, a smaller reproductive male, and several even smaller non-reproductive males If the female is removed, the reproductive male will change sex to become a female and the largest non-reproductive male will become reproductive

Hermaphroditism Protogyny sequential hermaphroditism in the case where an organism is born as a female and then later changes to male Example: Wrasses are born as either females or male form in the initial form, they look the same and are non-territorial Terminal Phase males are territorial and have bright colouration Both initial form males and females can become terminal males

External Development External development is taken to be the ancestral condition and where either unfertilized eggs or fertilized eggs are spawned No embryonic development takes place within the mother External Fertilization the female releases unfertilized eggs into the environment and the male then fertilizes them outside of her body

External Development Internal Fertilization The derived condition where the eggs of a female are fertilized within her body by the male inserting sperm The female then lays an egg that contains the zygote and a significant yolk to feed the developing embryo In many species, one of the parents or both will continue to feed the young after hatching from the egg