Animal Reproduction A. Russo-Neustadt CSULA

Asexual versus Sexual Reproduction

Asexual Reproduction Asexual Reproduction – reproduction that produces individuals who are genetically identical to the parents No sperm and egg fusion  Examples – budding in hydra, fragmentation & regeneration in sea stars, fission in Sea Anemones

Budding

Fission

Sea Star Fragmentation Linkia genus

Advantages of Asexual Reproduction Isolated/sessile species Time efficient Conservation of energy Like parent/Like offspring (instant adaptation)

Huge Disadvantage of Asexual Reproduction What if environmental conditions change – become unfavorable?

Sexual Reproduction reproduction that produces offspring who are genetically different from either parent (genetic variability) requires production of gametes that fuse to form a fertile egg - Example – humans, frogs, earthworms

Humans

Frogs

Earthworms-Hermaphrodites

Advantages to Sexual Reproduction Genetic variation Environmental Adaptation

Disadvantages to Sexual Reproduction Isolated/solitary/non-motile animals One potential solution for a few select animals is the evolution of Hermaphroditic characteristics (earthworm, tapeworm)

Sexual Reproduction Internal versus External Fertilization

External Fertilization used by aquatic animals

Internal Fertilization Used by some aquatic animals and all terrestrial animals Requires copulation – and specialized organs

Internal Fertilization Embryological development post-fertilization can be Oviparous Ovoviviparous Viviparous

Internal Fertilization oviparous – eggs laid and hatch outside the body (examples – birds, reptiles)

ovoviviparous – eggs develop inside of female’s body, but do not receive nourishment from her (example – some sharks) Interuterine Canabolism Sandtiger (embryophagy) Great White (oophagy) *others are viviparous and oviparous

Viviparous – embryos develop in female’s body and receive nourishment directly from her, often using a placenta (example – mammals)

What happens after animals are born or hatched?

Young that hatch or are born can be Precocial – highly developed and able to move about and feed themselves, “miniature adults” (example – reptiles)

Young that hatch or are born can be Altricial - immature and require considerable parental care to survive Note the energetic trade off between parental investment in lots of gametes versus significant parental care of young

Human Reproduction There are two basic types of reproductive system organs – Gonads = primary sex organs = essential sex organs; ovary and testis 1. Produce the gametes 2. Produce the sex hormones that – Regulate the reproductive process Regulate development and function of the other reproductive system organs

Types of reproduction system organs - continued Secondary sex organs = accessory sex organs; involved in - a. transport b. protection c. nourishment of the gametes, embryo or young

Human Reproductive Anatomy

The human male primary sex organ and associated organs Testes = primary sex organ; spermatogenesis occurs in seminiferous tubules, testosterone production occurs in cells of Leydig Site of final sperm maturation, takes several weeks Sperm transport – through inguinal canal to abdominal cavity out urethra, fluids added along the way

The human female primary sex organ and associated organs Ovary = primary sex organ; egg production and estrogen and progesterone production all occur within the follicles Oviduct = fallopian tube, site of fertilization of the egg, transport of egg from ovary to uterus uterus

Endocrine Control of Ovary and Testis Function Hormones control reproductive function