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

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 Fertilizationused 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 CanabolismSandtiger (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 testis1. 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 - continuedSecondary 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