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Animal Reproduction. Two Modes. Asexual – Invertebrates Fission Splitting into two Budding Splitting off parent Sponges produce gemmules Fragmentation Parent breaks into pieces Mature individuals are created through regeneration. Arm of a star fish create an adult. Sexual
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Two Modes • Asexual – Invertebrates • Fission • Splitting into two • Budding • Splitting off parent • Sponges produce gemmules • Fragmentation • Parent breaks into pieces • Mature individuals are created through regeneration. • Arm of a star fish create an adult. • Sexual • Involve a large non-motile cell • Ovum • Small Mobile Cell • Spermatazoan
Advantages and Disadvantages of Asexual Reproduction • Advantages • Enables the animal to reproduce in an isolated environment. • Many offspring can produced very quickly and thus colonize a new habitat rapidly • Ideal for stable environments • Disadvantages • No genetic variability in case the environment changes • One disease can kill the entire population
Reproductive Patterns Vary • Some animals will switch to sexual reproduction under environmental stress and reproduce asexually under favorable conditions. • Some animals only reproduce through parthenogenesis. • Adult develops from an unfertilized egg • Adults that develop in this manner are usually haploid • Whip tail lizards create a diploid zygote by doubling their chromosomes after meiosis • There are no males • Mating females switch roles and act male or female depending on the level of estrogen or progesterone in their bodies.
Sexual Reproduction is a Problem for Sessile, Burrowing or Parasitic animals. • Solution? • Hemaphroditism • Have both male and female reproductive organs. • Sequential Hemaphroditism • Species switch sexes during their lifetime. • Protogynous - female first • Protandrous - male first • Reef fish call wrasses switch from female to male based on size
Menstral CyclePreparing the Endometrium • There are three phases • Proliferative - endometrium thickens • Secretory – endometrium becomes vascular and creates glandular structures. • Menstral flow – endometrium is expelled.
Ovarian CyclePreparing the Egg • There are three phases • Follicular – several follicles begin to grow • Ovulation – one follicle matures and breaks out of the ovary • Luteal phase – remaining follicular tissue becomes glandular. • Secretes estrogen and progesterone to support the growing endometrim.
There are Five Hormones that Synchronize the ovarian and Menstral Cycles • GnRH, FSH, LH, Estrogen, and Progesterone • GnRH • Gonadotropin releasing hormone • Released by the hypothalamus • Causes the pituitary to releases FSH and LH • FSH • Follicle stimulating hormone • Respond to receptors on the follicle and encourage growth • Growing follicles secrete estrogen • Small amounts of estrogen inhibit the release of FSH and LH from the pituitary. • A steep rise in the release of estrogen from the follicle cause the opposite effect and stimulate the release of FSH and LH from the pituitary. • The follicle now respond to receptors for LH.
LH • Lutenizing Hormone • Cause the maturation of the follicle and it is released from the ovary • The follicular tissue left behind now becomes the corpus luteum which is glandular in function and secretes estrogen and progesterone. • Estrogen and Progesterone • An increase in the production of these hormones inhibit the hypothalamus and pituitary which inhibits the release of FSH and LH. • Progesterone supports the endometrium • Without LH the corpus luteum disintegrates • Without progesterone the endometrium disintegrates. • Blood vessels are choked off and the uterus undergoes spasms. • The endometrium is expelled • Without the corpus luteum the hypothalamus and pituitary can once again release FSH and LH and the follicular phases begins again.
