Animal Reproduction Chapter 46

YOU MUST KNOW Advantages of asexual vs. sexual reproduction Various reproductive strategies in response to energy availability Timing and coordination of reproduction may be triggered by environmental cues as well as pheromones

I. Asexual v. Sexual Reproduction Sexual reproduction – fusion of haploid gametes to form diploid zygote Asexual reproduction – creates clones 1. Fission – parent splits in two 2. Budding – new individuals form from outgrowths from parent 3. Fragmentation – individual breaks into pieces and each one regenerates new adult 4. Parthenogenesis – females produce eggs that develop without being fertilized Hydras, coral Cnidarians = jellyfish Starfish, sponges, cnidarians

II. Fertilization External fertilization – eggs shed by female and meet sperm outside the body (usually in water), produce large number of gametes

Internal fertilization – occurs inside the female, allows sperm to reach egg even in dry environments, fewer gametes produced

Reproductive readiness 1. Can be triggered by day length, resource availability, etc. so that male and female gametes are produced at the same time 2. Pheromones – chemicals that are produced by individuals that influence the behavior of others (sexual attractants, trigger reproductive readiness) 3. Global climate change – has resulted in some resources emerging earlier, before some species are ready causing them to miss their best reproductive window

III. Gametogenesis Spermatogenesis – production of sperm in the testes (from puberty on) Oogenesis – development of ova in the ovaries (begins in embryonic development, pauses at prophase I, each month during reproductive years one or a few eggs finish meiosis I and begin meiosis II, pause after prophase II unless egg is fertilized)

Spermatogenesis Oogenesis Millions of sperm/day from puberty throughout life 1 secondary oocyte/month between puberty and menopause 4 gametes from each germinal cell 1 gamete from each germinal cell (+ 3 polar bodies) Gametes are small with little cytoplasm and organelles Gamete is large with substantial cytoplasm, organelles, and nutrients Mitosis replaces germinal cells daily Mitosis only replaces germinal cells in early development Some cell growth before meiosis I Substantial cell growth before meiosis I Spermatids remain in seminiferous tubules until differentiation into spermatozoa occurs Differentiation begins in the ovary but finishes after fertilization Occurs in testes Occurs in ovaries

IV. Hormones & Reproduction GnRH – gonadotropin-releasing hormone – from hypothalamus, stimulates pituitary to release LH and FSH FSH - along with testosterone, stimulates meiosis of spermatogonia LH - stimulates Leydig cells in testes to produce testosterone

FSH & LH stimulate production of estrogen by the FSH & LH stimulate production of estrogen by the ovary, production of Graafian follicles, lead to ovulation and creation of corpus luteum Estrogen – increases vascularization of endometrium Progesterone – maintains thickened endometrium HCG – Human Chorionic Gonadotropin – secreted in early pregnancy to maintain thick endometrium, used for pregnancy tests