Animal Reproduction Chapter 46

Two Ways to do it… Asexual Reproduction Sexual Reproduction Creation of offspring without the fusion of egg and sperm Sexual Reproduction creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote

4 Types of Asexual Reproduction 1. Fission separation of a parent into 2 or more individuals of about the same size Common in invertebrates 2. Budding new individuals arise from outgrowths of existing ones

What type of reproduction? What type of reproduction? Figure 46.2 Asexual reproduction of a sea anemone (Anthopleura elegantissima)

4 Types of Asexual Reproduction (page 2) 3. Fragmentation breaking of the body into pieces, some or all of which develop into adults Fragmentation must be accompanied by regeneration, regrowth of lost body parts

4 Types of Asexual Reproduction (page 3) 4. Parthenogenesis It gets weird here, so stay with me the development of a new individual from an unfertilized egg There is a female (egg producer) & there is a male, but no fertilized egg The egg doubles its chromosomes during parthenogenesis = diploid (viable) organism

Why sex? Seriously? Humans & dolphins know why  Genetic recombination Accelerate adaptation to environmental forces Shed harmful genes more rapidly

Asexual reproduction Sexual reproduction Female Female Male Generation 1 Female Generation 2 Male Generation 3 Generation 4

Patterns of Reproduction 1. Ovulation Release of mature eggs Typically cyclical in nature Influenced or determined by hormonal cycles Associated with the release of chemicals (pheromones) indicating sexual receptivity (estrous cycle) Also influenced by environmental cues, e.g. day length, changing of seasons, etc.

Patterns of Reproduction (page 2) 2. Hermaphroditism each individual has male and female reproductive systems Individuals can self-fertilize or mate Some individuals are capable or switching genders depending on environmental conditions Effective reproductive strategy for solitary animals

Patterns of Reproduction (page 3) Who’s your daddy? 3. Sex Reversal Individuals can change gender during its lifetime Bluehead wrasse Reef fish If male dies, largest female becomes a male She (He) produces sperm now

Fertilization Fertilization - union of sperm & egg 2 Types of Fertilization External Fertilization Eggs shed by the female are fertilized by sperm in the external environment Large number of gamete production Internal Fertilization Sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract Adaptation to dry environments

Female Reproductive Physiology Female gonads (ovaries) lie inside the abdominal body cavity Each ovary contains many follicles, which consist of a partially developed egg, called an oocyte, surrounded by support cells Prior to birth each oocyte is arrested in Prophase I (meiosis I) Called primary oocyte

Puberty The primary oocyte stays in prophase I until puberty Beginning at puberty, 1 oocyte per cycle completes meiosis I & arrests at metaphase II Called secondary oocyte after metaphase II Due to FSH secretion, a follicle grows and an egg or oocyte continues its development Finally, following fertilization oocyte completes meiosis II

Spermatogenesis differs from oogenesis in which ways?

Differences Spermatogenesis Oogenesis Production 4 spermatids 1 egg Duration Continuous from puberty to death Discontinuous Begins before birth Stops Starts up after puberty Menopause Meiosis Continuous process, and completes at regular intervals 1. Eggs are arrested in Prophase I, prior to birth 2. Prophase I  Metaphase II, 3. Finish after fertilization

Female Cycles Primates have menstruation cycles Endometrial lining is shed from the uterus through the cervix & vagina 3 Phases of Menstrual Cycle 1. Menstrual Flow Phase Most of the endometrium is shed, menstrual bleeding occurs 2. Proliferative Phase Endometrium begins to regenerate & thicken 3. Secretory Phase Endometrium continues to thicken and if no embryo is implanted, proceeds to menstrual flow phase

Ovarian Cycle Controlled by hormones Parallels the menstrual cycle Note the important role of hormones throughout the cycle Note the parallels between the ovarian & menstrual cycle as well

GnRH – Gonadotropic releasing hormone Note: FSH stays relatively constant LH shoots up = ovulation

Estradiol – secreted by ovarian follicle -- Causes endometrial lining to thicken Progesterone – follicle rupturing causes spike in this hormone -- When it falls, so too the endometrial thickening